Landracing Forum
Tech Information => Technical Discussion => Topic started by: bbarn on October 23, 2009, 09:56:18 AM
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Greetings. Durring our runs on the salt at the WF, we noticed the tires on the rear of our lakester we were showing a cord on the diagonal of the tire (just one per tire). We checked around and got some good advice that this is common as it is the butt connection of the tire cap. I know the guy that told us about them was giving us good advice that the tires were still good. He showed us the same "issue" on his streamliner tires.
My question is, how do you know when a tire that has no tread to measure is in need of re-tirement (pun intended)? I don't think that Lincolns head on a penny is going to be of any use here.
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When it goes beyond concern and SCARES you to WITS END!!!!!!!!! :evil:
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When it goes beyond concern and SCARES you to WITS END!!!!!!!!! :evil:
Can you be a little more specific?
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I'm a scardy-cat on this stuff, so my thought is, if in doubt, change 'em out. There's enough to worry about to risk your neck on tires you question. Yeah, there seems to be a lot of old rubber on the salt, but in the end, you're the one riding on 'em.
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Rob, I cannot speak for the current (2007-up) Mickey's, but in 2005 I borrowed a earlier set of the same size which had several fifty cent size bare (cord showing) spots and several more diagonal cords showing.
I used the time tested method of cleaning out the cord areas and applying black RTV silicone to those areas.
I made one pass with my 4300# Studebaker with a 700 horsepower Early OLds engine in it.
When I stopped to pick up my timing slip the person handing the ticket asked me incredulously if I had just run 214 (I think) on those tires. I got out and looked at what appeared to be sofa cushions that had been attacked by a pit bull.
My suggestion to you is that you call M/T tires, ask thier advice, and use your best judgement.
A lot of people run these tires in a simillar condition, but I doubt that many of them would pay to buy those same tires.
The fact that none of the users own the tires, and the fact that you signed a multi-page disclaimer to rent those same tires, releasing the tire manufacturer and the tire leasor of any responsibility should have made you aware that its every man for himself when using a experimental tire ( as is printed in raised letters near the rim on the sidewall.
You have chosen to be a part of a pretty safe sport, but as you raise the speed, you raise the potential risk of failure of any and all parts of your race car...... the advice you need to follow is that of your own head and no one else's.............Bob
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We bought the car with those tires from Dave Haller.
I had noticed that we had cord showing on one of the tires. Dave only had one or two runs on the tire and I believe his as there were still casing nubs sticking up not far from the showing cord. He called Mickey Thomson and they said this was normal. It appears that there is a little overlap of the cords and since there is so little rubber cast onto the tire, this is where it will wear through first.
If cords showing on these tires are a problem, I don't know what we can do as we can't afford to put a new set on every two runs.
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Rob, I have had my tires inspected after each season- by some one I respect as one of the more knowledgeable LSR tire guys. I watch him CLOSELY, as well asks questions when he inspects my tires---whether it is the sidewall splits and crack of the GOODYEARS or the diagonals of the MTs---what he is looking for is cord seperation and breaks---
I run a PG or an AT and no TQ converted with a STOCK valve body--to keep from spinning my tires needlessly---you have a much larger issue wit tire spin than I do---my experience is you can hook up around 2500 lbs of TE on a good track ---some of the more succesful racers STAGE their power---as the mechanical advantage goes down the power goes up.
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Rob, unfortunatly, the M/T tires have very little rubber on them even when new. Keep in mind they are designed to go 600 mph so the tire mass has to be kept to a minimum. Also keep it in mind that what kills tires is spinning them. With that in mind, you need to find that delicate spot where that is held to a minimum (ala traction control).
The time proven method is to either add weight or downforce, or lift on the throttle when the tach speeds up (a tough thing to judge).
As Sparky mentioned, aero plays a large part, especially in your type of vehicle.
If it was my car, I would watch for signs of tire spin, which would probably show up as a very rough surface, and then try out adding more weight, although a external wing would be better.
I would also try to determine which end of the cord is lifting and mount the tires to reverse this if neccessary. M/T tires are not directional, however the Goodyear LSR Tires are.
If at all possible don't trailer the car on the race tires.
When you get home, drop the pressure to about thirty psi, clean them off and use a UV protectant spray like 303 aeromotive protectant (available at most parts stores near the tire cleaners). Put the tires in a cool dark spot and cover them up. They DO NOT like light, including flourescent lights.
Do not leave them ON THE CAR......... nothing good will happen.
Another option would be to run the 28 inch Mickeys, which are a lot cheaper, and are rated at 300. Seth Hammond and many others have gone over 300 using them. Bob
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I'm under the impression that Goodyear is going to enter the LSR market with a new 450mph tire. I'll bet it has a little more rubber on it and address all the prblems just spoke of. I've spoken to Dave Farwell, the Goodyear engineer in charge of this and the dragrace tires, and they won't come out with something unless its right.
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Boy oh boy, that would be good news to the 85% of us that need a larger or wider tire than the GoodYear 28's but don't need a 600 mph tire. Sign me up George!!!
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Bob, unfortunately I have heard they MAY be MUCH more expensive than there present tires.
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We were 80 psi in the tire at WF. Is that too much?
I know we spun the tires but not a whole lot until the last run but the cord was already showing by then.
Been keeping the tires in the temp and light controlled environment and certainly not transporting with them on.
We can probably get a few more licensing passes on these current tires then it will be time for a new pair.
C'mon Goodyear!
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Rob, do a search on this subject from back before MT made their current tire and you will find that Al Teague and others ran on some tires that many thought to be very scary. Your tires may have a lot of use left in them. Aren't they 6 ply? Run em down till there 4. Heh heh
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I'm still a FNG, but here's what I know:
On the M/T's, even when brand new, you can see where the cord will show first. There is only 1mm rubber on top of the cord to seal it. Or so I was I told when I asked M/T. Kinda wish they would have made the second cord red, so when you see red, you discard. This is the way some aircraft tires are. I run either the 26" or the 30" on the front only at 90psi with about 1700lb loading.
Dunlop Racing tires are 32" dia on 18's, and have lots of tread on the them. IMO, they are very tractible in the dirt. Krause Racing sells them. I run them on the rear only at 75psi. I've only run 197 on them, but at 2000lb loading per tire. I've been told they are good to 250mph.
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Bob, that is going to be my criteria---when I start seeing several cord seperation in the 2 cords I will relagate them to lower lisc runs.
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What 600 mph tires,are they available,how much???
Rob, unfortunatly, the M/T tires have very little rubber on them even when new. Keep in mind they are designed to go 600 mph so the tire mass has to be kept to a minimum. Also keep it in mind that what kills tires is spinning them. With that in mind, you need to find that delicate spot where that is held to a minimum (ala traction control).
The time proven method is to either add weight or downforce, or lift on the throttle when the tach speeds up (a tough thing to judge).
As Sparky mentioned, aero plays a large part, especially in your type of vehicle.
If it was my car, I would watch for signs of tire spin, which would probably show up as a very rough surface, and then try out adding more weight, although a external wing would be better.
I would also try to determine which end of the cord is lifting and mount the tires to reverse this if neccessary. M/T tires are not directional, however the Goodyear LSR Tires are.
If at all possible don't trailer the car on the race tires.
When you get home, drop the pressure to about thirty psi, clean them off and use a UV protectant spray like 303 aeromotive protectant (available at most parts stores near the tire cleaners). Put the tires in a cool dark spot and cover them up. They DO NOT like light, including flourescent lights.
Do not leave them ON THE CAR......... nothing good will happen.
Another option would be to run the 28 inch Mickeys, which are a lot cheaper, and are rated at 300. Seth Hammond and many others have gone over 300 using them. Bob
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Glen, in my hands is a copy of the flier from M/T tires that was sent to Landracing.com and posted by Jon Amo on Thursday, 29 March, 2007, advertizing the M/T 30" tire with a estimated speed rating of 590+.
Sorry if I cheated you out of ten miles an hour....................... Bob :-D
P.S. $760 per tire plus shipping........... seems like with shipping around sixteen hundred......... next?
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One more interesting thing, the flier says the tires are for sale yet the disclaimer/release you sign says basicly that you don't own squat, you are only leasing them and must return them on demand at any time to M/T.
I would bet the lawyers on both sides of the fence could make a ton of money on that deal...........
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If the cord showing is at the splice joint, probably nothing to worry about. Take a look at the attached flyer from MT. I have been running MT tires for years with no problems.
Roger L
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Roger---thanks for the refresher!!!!!!!!!!
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If the cord showing is at the splice joint, probably nothing to worry about. Take a look at the attached flyer from MT. I have been running MT tires for years with no problems.
Roger L
Thanks for the MT bullitin, that answers the question precisely.
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It appears we have a short supply of tires, and an oversupply of Lawyers. Tort reform will never happen as long as we keep supplying Congress with that excess. :cheers:
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Yesterday I call Mickey Thompson's tech line.
I and several others are running M/T ET Drag Radials,,, those tires are mention ( I believe) in SCTA and ECTA rule books and are tech'd to 200 or 225 MPH.
I asked the tech line at M/T about recommended tire pressures for paved/concrete for both the Mile and the 1.5 Mile tracks (Maxton and Loring) as well as the Salt Flats.. the Tech guy refused to give me any tire pressures and said the tires where not intended for long distance use, just short bursts of high speed DRAG RACING
Can anyone shed any light on this ? I just bought them and made 2 runs Sunday at Maxton. my plan is to use them on the Stude next year for Maxton and Loring and if OK even Bonneville ???
Charles
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Charles, the problem is with the construction on both the M/T drag tire and the Goodyear drag tire (which is identical to the LSR tire except for code #).
Neither tire has enough sidewall cords to handle the side stress of a spin, especially if the car is heavy.
Lots of people have made many runs on these or similar tires, but why run cheap tires on a expensive car? What's your tush worth?.....................Bob
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Here's what I can tell you about soft DOT Drag Radials (highway rated). In this case it was M&H.
I've run these for years at the drag strip with no problems on a heavy truck (up to 7000+ lb) and up to 130mph so far.
But, coming back from Colorado after a race, we had a blowout on our tow vehicle. As luck would have it, I forgot the spare. I took one of the M&H DR's and put it on the tow vehicle to get to the next town at 45mph. I did not make it 10 miles before it failed. Even though it was raining, the tire overheated and separated the tread from the belts, and blew. The tire was at over 40psi (recommended max).
With a light vehicle or short distances, it is probably not an issue. But I'd be scared to run heavy for sustained speeds.
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Here's what I can tell you about DOT Drag Radials (highway rated). In this case it was M&H.
I've run these for years at the drag strip with no problems on a heavy truck (up to 7000+ lb) and up to 130mph so far.
But, coming back from Colorado after a race, we had a blowout on our tow vehicle. As luck would have it, I forgot the spare. I took one of the M/T DR's and put it on the tow vehicle to get to the next town at 45mph. I did not make it 10 miles before it failed. Even though it was raining, the tire overheated and separated the tread from the belts, and blew. The tire was at over 40psi (recommended max).
With a light vehicle or short distances, it is probably not an issue. But I'd be scared to run heavy for sustained speeds.
What is the weight rating on those drag radials and how much weight with truck and trailer?
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IIRC, they are rated at about 2000lb. This is approx what the per wheel loading was on the tow truck at failure. This is not significantly different load than when we dragrace with them on the trucks. Front tires see about 1900lb, rears about 1500lb.
The following is dragrace/AutoX experience, not LSR (yes, certain DR's are excellent AutoX tires):
I've run several different brands of DR's or DOT bias-ply slicks on the street and track on about a dozen late-model vehicles.
Stories about quick failures are not unique, and even happens in lightweight cars like Corvettes. Some have reported failures during long-range sustained freeway driving or greatly accelerated wear (cord them in 100mi). Nitto DR's or BFG's are fine. But the really soft DR tires like M/T, Hoosier, or M&H don't seem to like long range.
I suggest if you dragrace with these kinds of tires, limit yourself to 20 miles drives to the track or change them at the track. Regardless of the DOT rating, they really aren't street tires. They are drag slicks with rain grooves (oh, they seriously suck in the rain even when new).
As far as LSR goes, I personally wouldn't run them on a long course especially with a lot of ballast, but that's just my personal opinion. Nitto's AOK since they are a much stiffer tires. BFG's are AOK as well.
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Gosh, I should have asked before I bought the M/T drag radials...
My 33 Vicky with me in it and ready to race weighs 2925 lbs with 52% on the back tires.
I ran them at Maxton and my only full pass was 151 MPH... Ran the mile and then coasted through long shutdown , I was never hard on the brakes. Track was cold.. no noticable wear.. but only made 2 runs,, the one I just mentioned and an aborted pedal fest slip sliding thru the mile.
So 1 mile is to much for these ? I do not drive this car on the street any more,
If I should only use these tires for Drag Racing,, what should I use for LSR ?
I was going to put them on the Stude,, but it will weigh 4000 lbs race ready and about same 52% rear weight ??
Charles
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Charles,
Glad you are asking this question. I have not bought tires yet and need to know about the choices too!
Geo
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GEO, I am drag racing this Friday night at Zmax dragway Charlotte, NC... So the purchase of the M/T's is not a total loss.
Guess I will need to re-think what tires for the Stude.
Charles
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Gosh, I should have asked before I bought the M/T drag radials...
My 33 Vicky with me in it and ready to race weighs 2925 lbs with 52% on the back tires.
I ran them at Maxton and my only full pass was 151 MPH... Ran the mile and then coasted through long shutdown , I was never hard on the brakes. Track was cold.. no noticable wear.. but only made 2 runs,, the one I just mentioned and an aborted pedal fest slip sliding thru the mile.
So 1 mile is to much for these ? I do not drive this car on the street any more,
If I should only use these tires for Drag Racing,, what should I use for LSR ?
I was going to put them on the Stude,, but it will weigh 4000 lbs race ready and about same 52% rear weight ??
Charles
Running 1.5 miles probably isn't a risk. The first sign is going to be a bulge in the tire. I do know that in 1/4mi racing I go about 2-3 mph faster on steel radials. Soft DR's are excellent for good 60' times and low ET's, but if it's a well prepped track (Vegas) I'll run stiffer tires. In a mile, sixty foot times aren't significant. Heck, if you cut a 2.5 sixty, your trap speeds in the quarter will be virtually identical to when you cut 1.6's. A violent launch really doesn't change MPH.
Toyo Proxies are a good daily driver drag tires with good trap speeds, and they are much cheaper than soft DR's. We've cut 1.6x sixty-foot times with them. We also ran them at Bonneville to 175. They are even good for sled-pulling on hard tracks.
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McRat, thanks for the info. I will look into other tires for LSR
Charles
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My Pontiac weighs 3985 and we been running 325/50 - 15 MT Drag radials with no problems. 49.7% rear weight.
They are a great tire but I wish they would last a little longer street driving.
http://www.youtube.com/watch?v=I3IuTIDnaV0
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Cajun, I think your 4,000 lb weight is a good starting point, but make sure you have a plan for a place to put another 1,000 to 1,500 lbs more if needed. Keep in mind you wan't it between the front and rear axles, as low as possible. Do not put weight in the trunk behind the rear axle unless you like spinning on the salt. I ran my Stude at 4300# with 650+ h.p., and now with about 850 to 900, I have about 5200 in it. I run about 48% on the front and it still wants to spin the tires after the first mile.
Also, in looking at your interior tin work, make sure that the drive shaft tunnel is removable for inspection if you are running a step pan. Keep up the good work...........Bob
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Bob,
No step pan, and yes the tunnel is removable, but will not be that easy once Fire system and such is in,
Is it required to be removed,, both drive shaft loops can be seen from under the car and no step pan. ??
I plan on a starting weight of 4000 to 4200 lbs total weight and 52% rear ? Bob what is best weight distribution?
Is 52/48 about right to start.
Using E motor... max hp 550 to rear wheels
Charles
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Charles, all sounds good for starters. The only time you will need to show the hoops would be going thru tech the first time at Bonneville. Thats when you recieve your chassis tag and log book. The tech guys may not be to hot to crawl under the car. Pictures would probably suffice, and a photo album could save a lot of hassles when teching the car.
The 48/52 front/rear bias is a pretty good spot to start with on the 53 Stude.
As far as the horsepower, build the car to run a blown hemi............. you won't be sorry. You never know when someone may give you one. Seriously, I like to plan ahead. If you need a SFI 15 suit, why not spend a little more and buy the 20? Remember all the rules are MINIMUMS. Why not run twice as much fire protection as required? The last thing you need in the event of fire is to have "allmost" enough extinguishant.
The same goes for chutes. Your class record may not mandate dual chutes, but the second one might save your bacon.
The last thing in todays sermon, don't show up with one set of wheels and tires. When you run over the chunk of pushrod from the guy in front of you, where the hell are you going to find a spare? OH, yeah, allways carry at least TWO spares for the trailer................... ( I know) Bob
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Bob what kind of rear suspension do you run?
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Bob, thanks for the pearls of wisdom and experience.
I have twin 6.5 lb firefox systems. The Chassis will handle all the HP I can beg borrow or steal. I am starting with my E motor. I have a C motor and will build a high winding 18 degree or SBII "D" motor late next year... So I will have a C, D and E motors.
Chutes ? never thought of two chutes for the speeds this car needs to run (and who knows if it ever will?) But I will look into provisions for two.
I will get a new suit ( I am on a mission to drop 35 lbs by March 1st. then size and order a new suit).
Thanks again...
Charles
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Charles, that isn't much for fire duty. For minimal dollars you can run a 10# co2 to the engine, and use both the others inside. I run that plus a 10# cold fire to the engine, and 3 5 lb. halons in the car. I also installed a exhaust fan in the car to pull smoke and salt out of the drivers area just in case.
Bviller, pretty much the same as yours, I bought lighter springs and havn't installed them nor changed my four link like you have yours, but I am going to this winter. ( thought I don't pay attention to your posts.......... ha!)
I also want to congradulate myself on making it to the eve of my 63rd birthday................ Sober...............tommorrow is All Saints Day which is why they call me Saint One Run............
I think I need a drink.
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......tommorrow is All Saints Day which is why they call me Saint One Run............
SOR... you forgot most of us close the bottom of the last letter and just call you SOB.... (not Saint One Bob.. :roll: )
By the way.... Happy Birthday.... yea hijacking another one
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He, he, Bob I was just wondering why you were still breaking loose at the mile? Great to hear you have suspension and we have quite a bit of weight on the rear axle or behind it without having any problems with it wanting to spin. Good luck going fast. :-D
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Are you guys saying that a 4 link rear is not a good idea ?
For the longer course and response time, I agree.. I will use the two 6.5 lb FireFox systems for driver protection and get a larger system ( 10 lb) for the engine bay. What is the best for engine bay coverage ?
Charles
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Charles, our four link works great! We may do some minor adjustment to it this year, we do run a soft set up. :-D
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Chaz,
Nope, I run and recomend a adjustable 4-link, coilovers, and (panhard bar or watts linkage, but NEVER a diagonal link). What BVLR and I are refering to is the instant center setting of the four bar.
I have always run mine in a neutral position with 400# coils, and he runs his for a much softer hit with "sissy" springs.
So now I Am going to try it his way, so if you see me bouncing like a buckboard down the salt, blame him.............................. (p.s.) I hope it works!!!
On the weight deal, weight behind the axle is fine as long as the nose of the car is going straight forward, but if you get it sideways the weight becomes a pendulum and it wants to keep going.......... not so bad with a tru-trac or posi, but nasty if you run a locked rear end. I can describe from experience what the panoramic view of the flats is. You can tell how many times you have spun by remembering how many times Floating Mountain goes bye..................................
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Bob, I too have a very adjustable 4 link and will be using a long panhard bar (to start). I have elected to start with 300# springs but will have 350# if need stiffer..
As to weight, I do plan on a 52% rear, 48% front and will have 4 provisions for adding weight low on the chassis.
If the pic comes out... at the purple arrows is where I can add weight.
(http://i261.photobucket.com/albums/ii43/cajunkid5690/chassisweightbox1.jpg)
Charles
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Bob, I too have a very adjustable 4 link and will be using a long panhard bar (to start). I have elected to start with 300# springs but will have 350# if need stiffer..
As to weight, I do plan on a 52% rear, 48% front and will have 4 provisions for adding weight low on the chassis.
If the pic comes out... at the purple arrows is where I can add weight.
(http://i261.photobucket.com/albums/ii43/cajunkid5690/chassisweightbox1.jpg)
Charles
The 222 camaro [bvillercr and my car] and Alston drag race chassis came with 88lb springs and Alston and Prochassis who built the car
didn't like us going to the 112lb. Of course spring rate depends on were the coil overs are mounted.
As to weight distribution,one has to think about Fast freddy,he has got to be over 65- 35% plus the added downforce of the wing.
JL222
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Okay, 88lb springs? How do you get enough preload on them? That sound like drag racing stuff to me. No that there's anything wrong with that (Sienfeld). I been trying to design around using road race stuff. I got so much preload in my 1200lbs springs just to get back up to ride height that I thought I was going to wear out my spanner wrench. I designed the car with 3 inches of travel and it sits one inch into travel when you take it off the jackstands. This goes for front and rear but I only have 550lb springs in the front.
I can imagine some day that we will use a wing that will generate another 1500 lbs and at that rate we will squat the car another .6" in the rear so we have to be careful. My design work though is mostly geared around Maxton and not the salt. I feel we need these rates at Maxton as the bumps are so harsh that if we used anything softer we will be bottoming on the concrete transitions.
As far as the 400lb springs, I don't feel you will get a buckboard effect as long as you have the proper dampening.
That being said, can we get back to the original topic on this thread and talk some more about tires. Does anybody know when the new 450 mph Goodyears are going to be available and what sizes they will be offered?
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Tires ? I just need to know what kind of tires I can use on the Stude for a max speed rating of 250mph,,
The shortest rear tire I can use would be 26" the tallest would be 28" to keep my ride height where I plan.
My goal is 220 to 225 mph. (as I think current record is 217.xxx)
Charles
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Robfrey, suspension is directly related to how your tires are affected. Too stiff and you will spin your tires right off, ask Fred. :-D
Bob I got severly sideways at El Mirage and had no pendulum effect, just the normal steering to correct the problem.
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Robfrey,
I would like to know your definition of "preload". I think of preload to be when you have the shock loaded and you have turned the adjustment collar past the point that achieves your desired ride height and the shock is fully extended such that any additional raising of the spring collar only compresses the spring and does not raise the car because the shock is fully extended. When this is done your suspension will need to be loaded until this preload is over come and then it will begin to deflect. If this is what you are doing then you definitely have a problem. This makes the suspension very stiff and skidish. As John said we do not know what your mounting system for the rear shocks is so we cannot determine the what the wheel rate is but I certainly agree with John that 1200 lb/inch springs certainly seem very high for a live rear end suspension. If you are truly "preloading" the suspension to be able to carry the aero loads from your wing then I would certainly suggest going to longer shocks and springs preferably softer. I assume that you probably have the standard 4 link rear locator suspension, are you running any anti squat or anti dive in the four bar set up? By this I mean are the bars parallel to each other, top and bottom in side view, or do the angle together with an imaginary point that their center lines intersect? This set up makes the rear end housing into a very stiff anti roll bar as the rear end is now rotating around the point of convervence of the 4 bars which will work for a bump that both wheels hit, but if only one hits the bump then the bars are trying to twist the rear end housing, just like a big anti roll bar. I am sure that your rear end is capable of some amount of deflection of one wheel but this is only due to the deflection of the bars, the heim joints and their mounting brackets. One way to still have some anti dive or anti squat is to only run one bar on one side of the rear end and two on the other, typically the single bar side is mounted to the horizontal center line of the axle on its side. If you think that you need an anti roll bar then I would suggest installing one that is designed specifically to act as an anti roll bar and this can provide your with the ability to statically transfer weight between the rear tires.
Rex
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Charles, not to sound like a smarty, but re: your tire search, try (and I don't know if your computer is set up the same) the little panel that, on my machine, is in the upper right corner with GOOGLE in it.
Then do a search for, for instance, GOODYEAR, MICKEY THOMPSON, and , maybe DUNLOP.
Let us know what YOU found regards your tire quest.
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Charles, My suspension is not topped out if that is what you are asking. When we sit the car down onto its wheels, the car sits into travel 1". I did need to preload the springs in order to keep the car from bottoming under its own weight.
Everyone keep saying we are way too stiff but the car used to run all the time with no suspension. I don't believe Fast Freddie's car has any suspension. To bounce on the suspension, it feels about right to me. I wanted to make it much softer but the the safety steward of the team said "no way". He has since left the team so he is no longer an issue
The bottom two bars of the four link are "X"ed to provide lateral location for the rearend (this is also the roll center) and also act like a giant sway bay. I am not concerned about one hitting a bump and the other not. I am concerned that if the car starts fish tailing that we will not get a lot of body roll.
Without data on the rear wing, I have absolutely no idea how much down force it will make at 350mph. I would like to develop at least 1500lbs. That will compress the rear suspension another .6
Remember, this suspension was designed to be able handle 300 mph at Maxton. Those concrete transitions are KILLER.
I don't really know if I have a problem or not at this stage. I was not in the car at 284mph to feel what was going on. I was able to break the tires loose on my licensing runs at lower speeds if I tried but I was running over 1000whp and I don't know what a really good traction car feels like to compare. How much traction can I expect. We can make over 1800whp and I can increase from 1000 to 1800 very gradually with a boost controller. We know the car goes 270mph with 1070whp with no issues. I know that we need a more efficient rear wing.
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robfrey,
Certainly sounds like you do not meet my criterial for "preload" of the suspension, which is very good, and it also sounds like your suspension actually does travel, also good. With the welding of the "X" across the lower bars you have made the rear suspension a single swing arm arrangement which will highly resist any type of one wheel bump or any roll of the chassis. Again since your suspension is "active" i.e. it does not need to over come any "preload" (my definition) I would certainly suggest that you use the old tye wrap on the shock rod to estimate the down force of your wing. This might not work at Maxon if the track is very bumpy, which most old air strips are, but at Bonneville you could probably assume that the maximum shock deflection was due to the down force of the wing. From this information you should pretty easily be able to come up with number for the amount of down force. Still think that 1200 # springs are pretty stout but you may not be able to go to something much lighter if you don't have some pretty long shocks. Any chance of a picture of your rear suspension??
Rex
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(http://i436.photobucket.com/albums/qq89/robfreyvogel/No93%20Lakester/progressvideo80709004.jpg)
(http://i436.photobucket.com/albums/qq89/robfreyvogel/No93%20Lakester/rearsusp.jpg)
You can see that even if we went with a longer shock, the rear will only come down so far as the brackets will hit under slung portion of the frame.
I could still go with a softer spring and just use the spanner wrenches to get the right preload. I always use big flat thrust bearings between the spring and the retaining nut. This will make it a bit easier.
Thanks for the compliments on the Pontiac.
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Rob,
When you jack up you car on the frame until the springs are unloaded and then set it back down how much do the springs compress? Obviously going to a lighter spring on the shock length you have could certainly lead to coil bind on the lighter spring, which is obviously the same as a solid suspension. This also needs to be taken into account with the potential aero load from your wing. Lots of intersting things to consider and it certainly looks like you have a very potent car, already looking forward to seeing you next year at Bonneville.
Rex
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Hi Rex,
The rear suspension sits into the travel 1.0 inch when we let the car down off the jack. We then have another 1 " of travel before contacting the bump stops. Thanks for the compliments but we sure have a lot to learn.
Rob
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I am currently building a 64 Dart to begin my journey into land speed racing. My current plan after I have observed as a spectator is to run the car first in the 130 MPH moving later to 150 MPH. What would be the recommended tires (15") to run at thoise speeds?
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Dart, H Rated Tires will get you by up to 150MPH. So if you are using 15 inch wheels you will have plenty of tire choices. If you plan on going any faster, I would try to start out with Z rated or better (I learned the hard way, bought H and had to upgrade to Z) Only problem with Z and higher rated tires is they do not have as many size choices in 15" ... if you need taller than 26".
Good Luck and Happy Thanksgiving
Charles
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Can we get some info on max loading of these tires? We are concerned about wing down force + vehicle weight exceeding the loading limits.
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Dart, H Rated Tires will get you by up to 150MPH. So if you are using 15 inch wheels you will have plenty of tire choices. If you plan on going any faster, I would try to start out with Z rated or better (I learned the hard way, bought H and had to upgrade to Z) Only problem with Z and higher rated tires is they do not have as many size choices in 15" ... if you need taller than 26".
Good Luck and Happy Thanksgiving
Charles
So, would drag radials work?
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none of the tire companies want to talt to you about running a drag tire even a mile let alone 5
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I am currently building a 64 Dart to begin my journey into land speed racing. My current plan after I have observed as a spectator is to run the car first in the 130 MPH moving later to 150 MPH. What would be the recommended tires (15") to run at thoise speeds?
Go to the U.S.F.R.A. site to check the rules.
130 club H minimum, 150 club V minimum, I would contact them about the drag radials.
Don
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Ref: Robfrey 4-bar suspension
While "X-ing" in the bottom two links of the suspension makes for a compact way to transfer the lateral and anti-roll loads, there is a reason that most 4-bar suspensions make use of a Panhard bar or Watt's linkage for lateral location of the axle, and a dedicated anti-roll linkage (if that is desired). From the photo posted earlier, it is apparent that the link pivots make use of Heim type joints. These ball joints are designed to carry only axial loads. By X-ing in the lower links, the large lateral location and anti-roll loads will be forced laterally onto the Heim joints, creating large bending stresses in the threaded shank of the joint. Large bending stresses located at stress concentrations (thread roots) are not a good idea. It would be good to re-think this method, or at least use ball joints that are suitable for carrying the lateral components of the loads.
Secondly, when in "anti-roll" mode, the only way that load is passed from one side of the X to the other is via torsion of the intersection at the center of the "X". From the CAD drawing it is apparent that this intersection is quite small in cross-section, and likely unable to effectively carry the load. It constitutes a largely ineffective and non-adjustable anti-roll function. A torsional failure at this point is merely a matter of time.
While pioneering "new methods" is to be encouraged, appreciation of the merits of the "tried-and-true" also has its place.
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Ref: Robfrey 4-bar suspension
While "X-ing" in the bottom two links of the suspension makes for a compact way to transfer the lateral and anti-roll loads, there is a reason that most 4-bar suspensions make use of a Panhard bar or Watt's linkage for lateral location of the axle, and a dedicated anti-roll linkage (if that is desired). From the photo posted earlier, it is apparent that the link pivots make use of Heim type joints. These ball joints are designed to carry only axial loads. By X-ing in the lower links, the large lateral location and anti-roll loads will be forced laterally onto the Heim joints, creating large bending stresses in the threaded shank of the joint. Large bending stresses located at stress concentrations (thread roots) are not a good idea. It would be good to re-think this method, or at least use ball joints that are suitable for carrying the lateral components of the loads.
Secondly, when in "anti-roll" mode, the only way that load is passed from one side of the X to the other is via torsion of the intersection at the center of the "X". From the CAD drawing it is apparent that this intersection is quite small in cross-section, and likely unable to effectively carry the load. It constitutes a largely ineffective and non-adjustable anti-roll function. A torsional failure at this point is merely a matter of time.
While pioneering "new methods" is to be encouraged, appreciation of the merits of the "tried-and-true" also has its place.
Interested Observer,
You need to observe closer but it might not show in the pics. The "X" is not the only way that the bottom bars are tied together. There is another 1.25" bar running across the front of the "X". It is quite rigid.
(http://i436.photobucket.com/albums/qq89/robfreyvogel/No93%20Lakester/rearsusp2.jpg)
We tried flexing it by jumping up and down with only one shock mounted and we probably could run it that way if we wanted to. It is that rigid.
Now for the side loading issue. One of the latest ways that many drag cars locate their rear axle is with a devise called a wish bone.
http://www.competitionengineering.com/catalog/CategoryDisplay.asp?CatCode=10049
I run one on my 63 8 sec Lemans for a couple of years now. It puts one rod end in the same kind of load as we put two. I have not heard of one failing so far. I did think of this when I designed the system and bought the highest quality joints just to on the safe side.
Of all the ideas we implemented on this car, I feel this was one of the best. I wouldn't hesitate to do this again. Car drives great. I tried zig zag real hard when we were pushing the car and I couldn't feel any body roll.
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Robfrey,
All I had to go on was the drawing that you submitted earlier in the topic which, if YOU will observe closer, does not have the cross piece at the front. While that addition will considerably stiffen the frame, it moves the area of concern to the bending strength of the X tubes just aft of their intersection, as well as the various weld joints in the frame which are undergoing tension/compression/bending/and torsional loads. The “new” configuration is an improvement, and if adequately executed will probably work, but is rife with concerns that other solutions eliminate. If you are happy with it, continued good luck.
My original and primary intent was to point out the mis-application of the rod ends. And again, while it may “work” as used here, it is not good practice, and is tantamount to asking for a failure. (The “wishbone” just gives me the willies.) Fortunately, drag racing and LSR are substantially one-dimensional activities in which lateral loads are minimal until one is in a heap of trouble, after which it is difficult to determine just what happened.
Regards,
Interested Observer
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Even if we got our car really sideways, I doubt we could ever generate enough side loads to hurt the joints. The pencil roll would probably happen long before.
Ultimately, I would of liked to use watts link but packaging on this car is a nightmare. It just wouldn't fit.
All in all, I thank you for your concern and because of this exchange, I will be keeping a closer eye on the lower front rod ends.
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Even if we got our car really sideways, I doubt we could ever generate enough side loads to hurt the joints.
Incorrect. In 2007 when we first built the Fairlane we only had a drag race style diagonal link (half of your x ). Spun at +/- 200 and found all 4 bar mounts and shock mounts bent. Have since added a watts(on a narrowed housing)
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interesting to read through this dialogue....
some well intended engineering principles.....and some "I doubt..."....
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Even if we got our car really sideways, I doubt we could ever generate enough side loads to hurt the joints.
Incorrect. In 2007 when we first built the Fairlane we only had a drag race style diagonal link (half of your x ). Spun at +/- 200 and found all 4 bar mounts and shock mounts bent. Have since added a watts(on a narrowed housing)
That single diagonal link is not nearly as strong what we got now. They always scared me. My favorite is the watts link link you have but impractical for quick change rear.
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wouldn't it work horizonaly, on top of the housing? :?
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I have used another variation on the WATTS link on my liner wannabe.
It is based on parts available from Streetrod Manufacturing in Castle Rock Co. which I have greatly modified and adapted to my application and packaging issues in both the front and rear. It works. Centers the axle and provides stable +-1.00" jounce and rebound that I allow. "That is in the shop" Proof will of course will be in the LSR pudding.
This design also puts the roll center considerably lower.
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I must be seeing something wrong. Wouldn't the X in you pic or a single diagonal put the same stress on the forward 4 bar mounts and rod ends? :?
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You need to observe closer but it might not show in the pics. The "X" is not the only way that the bottom bars are tied together. There is another 1.25" bar running across the front of the "X". It is quite rigid.
(http://i436.photobucket.com/albums/qq89/robfreyvogel/No93%20Lakester/rearsusp2.jpg)
Yes, the "X" is extremely rigid. Although if we go with only one diagonal instead of the "X", we can tune the alignment of the four link much easier. I have seen an "X" setup like this before and it took them MUCH longer to get the other linkage lengths set up to go straight at all speeds and torques than it would have with only one diagonal member on heim joints.
Yes, it has to be over-built. If set up properly all the bars are only in compression or tension and heim joints allow for precise tuning of all alignment angles; there are NO bending loads in a four-link. If there are, we missed something.
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wouldn't it work horizonaly, on top of the housing? :?
I think it would but would move the roll center much higher. Right now the roll center is the at the height of the bottom links. This desirable for how stiff our springs are. If springs were softer, it might be good to move the roll center higher.
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I like Thundersalts watts link... works good on most rear ends.. but on a Quick Change you can not do a rear mounted watts,,, if you mount it high you change the roll center,, so for QC rears you mount the watts in front ,,,they make a pinion housing mount for the QC... I will look for the pics (can't find right now) it is one cool set up,,, I was going to use it,,, but cost and fab time was more, so we decided to use the tried and true panhard bar for the Stud.
Charles
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Another idea would be to use a jacob's ladder from a sprint car. It works with quik changes.
http://www.spitzracing.com/index_files/Page724.htm
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Various observations and questions on the foregoing in more-or-less chronological order:
Thundersalt -- Nice to have empirical evidence that F=ma on the salt as well as on paper. Also nice solution.
Single diagonal vs. “X” vs. wishbone:
Both the single diagonal and wishbone would put the lateral location loads into one ball joint while the “X” could, possibly, with much precision and/or shimming, spread it over two. While under power, the forward tractive loads would tend to reduce the tensile side of the bending stress on the ball joint shank for single and X, but the wishbone would not benefit from carrying those loads. Under braking or trailing throttle this benefit becomes detrimental. Neither single diagonal nor wishbone act in anti-roll (except to the degree that they twist the axle and chassis, or deflect the bars longitudinally), while X is a fixed and probably high rate anti-roll device and consequently resists driveline torque. “X” largely precludes adjusting the static vertical load distribution on the tire contact patches via either the 4-bar links or springs. Depending on geometry used, single diagonal and wishbone, via the associated 4-bar linkages may have mild roll-steer effects. X would have minimal, since it is basically a trailing arm suspension with relative roll displacement limited by the stiffness of the lower X frame and springs.
Watt’s on top:
While such an arrangement would provide lateral location, with any vertical axle travel or chassis roll it is no longer a planar mechanism and would begin to impart small or moderate vertical loads into the system. Center pivot bearing would need thrust capability. High rear axle roll center.
Rick Byrnes “Watt’s” linkage:
This is an interesting arrangement, but the area of the two odd-shaped levers in the center is a bit of a mystery. Something in there must either have a sloppy fit, be riding in a slightly slotted out channel, have somewhat “compliant” pivot bearings, or be such that the vertical axle travel is quite restricted.
Also, the slight discontinuity at the chassis centerline in the horizontal tube to which the two links attach, is, or I assume, will be, welded as a single piece. Is this so?
Rick, for our edification, would you care to elaborate?
“Blue’s” reported set-up difficulties:
This seems odd, since with the X frame about the only thing that can be adjusted is the rear axle steer direction. It could be that moving the forward pivot points up or down to alternate locations, the side to side weight distribution was changed due to mis-matched pivot plate holes. Also, adjusting the upper links to different lengths would cause them to fight the lower X frame’s anti-roll resistance, probably resulting in erratic results.
Further to the statement “there are NO bending loads in a 4-link”: It is true that essentially no bending loads occur in a classic, unfettered, 4-bar linkage. However, when two of them are connected as in the X frame being discussed, the situation is entirely different. The roll resistance is provided primarily by the bending resistance of the cantilevered beam of the X members’ aft extension, and these vertical loads are carried as bending stress at the four ball joint shanks (due to the distance from the jam nut to the ball center). Lateral location loads are also seen as bending in the shanks, except that they are in the horizontal plane. These may be imposed on one forward joint and one rear joint, or somewhat shared between the two forward and two rear joints depending on the accuracy of the fitment and the stiffness of the bracketry.
_______________________________
Just for fun, the following simple finite element model of the linkage was made in an effort to illustrate and quantify the kinds of load and stress distributions that can occur in the arrangement. Estimating plausible dimensions from Rob’s sketch, the model is 24” wide, 23” long from ball centerline to centerline, lower X frame 6” off the ground and the upper links 8” above the lowers. The tubulars are 1.25 OD x .125” wall, and the 3/4 inch “Heim” joints are modeled as 5/8” diameter stubs extending 1.5” from the ends of the tubulars. The forward pivot points are at fixed locations in space, e.g., on the chassis. The rear pivots are located on an artificially modeled “axle” (which is deleted from the diagrams for clarity in viewing the linkage.) Each part of the model consists of a numbered “element” which can be used to correlate the tabulated stress results to the location of the element in the model. A laterally acting (left-to-right) load of 1000 pounds was applied at ground level below the rear pivots, simulating sliding sideways on the salt with enough friction coefficient to generate that load. No driving or braking loads were included.
The tabulated stress results are maximum VonMises stress occurring in an element, and can be compared to the material strength properties. This maximum stress reported for the element occurs somewhere in that element, but is not necessarily uniform throughout the element. In most cases the maximum occurs at one end of the element with lesser values elsewhere in it. As this is not a detailed model, it is not conservative in that the effects of geometrical non-uniformities and resulting “stress concentrations” at junctions between the elements are not taken into account--things could easily be worse than depicted at the tubular joints, although the Heim stubs are probably well represented except for thread root stress concentrations.
Two sets of stresses are given, the first with both of the X frame forward joints restrained from lateral movement, and the second where the left-side joint can slide sideways as it may wish, passing the load to the right side joint.
As can be seen, even with this fairly innocuous loading, significant stress can be generated, amounting to a considerable portion of the likely material strength.
VM max (psi) VM max (psi)
Element No. Both joints fixed Only Rt. side fixed
1 36,546 17,668
2 39,743 41,449
3 663 667
4 663 667
5 38,340 67,226
6 31,598 29,990
7 663 667
8 663 667
9 10,932 10,582
10 460 463
11 10,329 11,124
12 460 463
13 10,955 11,756
14 22,099 22,119
15 23,166 23,176
16 27,155 27,042
17 28,195 28,241
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The first test with a complex suspension would be to disconnect the springs and test the travel by hand .
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Interestingly, as many I'm sure are aware of, the above described suspension is used by probably 200 Super Comp dragsters around the country - some with a monoshock.
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Interestingly, as many I'm sure are aware of, the above described suspension is used by probably 200 Super Comp dragsters around the country - some with a monoshock.
Bottom line- If you were me, would you change what we have?
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photos speak loudly
The bearing fits snugly in slot. tests without springs indicate it works. How well we should know this summer.
The discontinuity in the support structure will end up bolted together with an outside slip fit tube. There should be no relative movement. All the parts are 4130. (and will be heat treated).
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"Interestingly, as many I'm sure are aware of, the above described suspension is used by probably 200 Super Comp dragsters around the country"
This morning my friend said his Super Comp dragster has the same X in the lower bars but said his rear suspension also has an anti-roll bar so the X is there just to center the rear . Anything that could put a side load on the rod ends is still risky .
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Walking across the street is also risky. I'm interested in knowing how risky?
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Millikan and Millikan's book "Race Car Vehicle Dynamics" although a bit pricey , IMHOP is the "Bible" of modern suspension literature.
Check the SAE website, probably even Amazon. SAE order No. R-146.
There are lots of succesfull straightaway cars whose suspension violates good engineering -including the sytem discussed. My comment above re: use in Super Comp cars was not a statement in defense, just a passing comment about its widespread use.
Saber es poder, knowledge is power! Research the literature and then make your own call!
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"Walking across the street is also risky. I'm interested in knowing how risky"
In suspensions , risky means look for an alternative . If the lower bars form an N and each of the 3 tubes tube has it's own rod ends and mounting points all the parts see only push and pull .
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"Walking across the street is also risky. I'm interested in knowing how risky"
In suspensions , risky means look for an alternative . If the lower bars form an N and each of the 3 tubes tube has it's own rod ends and mounting points all the parts see only push and pull .
Unless you get sideways.
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I would agree with Burk's "N" system's potential--since there are no other attachments to the links, loads can only be applied at the "frictionless" ball joints at the ends of each member, only axial loads would be active, and the ball joints would presumably be oriented in the axial direction. (I suspect Thundersalt may have misinterpreted the description.)
However, it would not provide anti-roll capability, so one would be back to the springs and possibly a dedicated A/R setup--which may not be a bad thing. Having the various functions separated and independently adjustable is much more versatile and user friendly.
Mr. Byrnes - Excellent depiction - Thanks
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Sorry, my bad.
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I think I'll just weld it solid and be done with it.
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This company from Australia has a pretty interesting software package for suspension design on a race cars. Even though I have not used it friends that have used it said its pretty good. Its about $270 and on the bottom of the page there is a link for a free evaluation download. http://www.bevenyoung.com.au/suswin.htm
This link shows the types of suspension it can model. http://www.bevenyoung.com.au/config.html I talked to the designer a few years ago and at that time he was willing to add models that weren’t listed on here. Tony
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If you ever happen to see one of the 80-90s Jack Roush Trans Am cars you will see an interesting mounting for a Watt link. Doing the normal mounting with the pivot link in a vertical plane make lowering the roll center difficult so Roush mounted the pivot link in the horizontal plane and connected it to the bottom of the diff housing. As the Roush cars won quite a few championships and the Daytona 24 Hours probably 6 or 7 times it probably works.
Rex
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Roush built our IMSA GTO car (only Thunderbird), which had that set up. I remember when I asked Bob Riley about why it was different than the previous cars we had, he said that it helped lower the roll center. I know that car handled like it was on rails and we finished the year within a heartbeat of the GTO championship. If I can find a picture of the setup I will add it later. Tony
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It is not uncommon to find a watts link horizontal and uner the diff on a live axle road race car.
What is not seen too often is a 3rd spring on the live axle that counters the normal springs for quicker transition.
In '05, one of the Rocket Sports cars won the SCCA RunOffs in GT1. This car had a top link that went through the car to just behind the shifter. It had a verticle adjustment to tune the IC/CoG while in motion.
John
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"In '05, one of the Rocket Sports cars won the SCCA RunOffs in GT1. This car had a top link that went through the car to just behind the shifter. It had a verticle adjustment to tune the IC/CoG while in motion"
John
Is that the single offset torque arm that lets driveshaft torque cancel the effect of axle torque you are referring to ?
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John,
yes, it was the top link from the rearend.
It had a slider assy with a jacking screw down the center.
John
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The more I think about it the more I still like my concept. As far as know, I'm the first to make the bottom arms also be the track locator and the anti roll bar. The simplicity of the design and compactness are it's biggest assets. I think the biggest problem is that I'm using adjustable spherical rod ends. I'm thinking on building billet ends with needle bearings that can be welded to the 4140 tubing. It only needs to move in one axis so there is really no reason to be using a spherical rod end. This would eliminate the problem of side loading the 5/8" minor diam. of the the threaded rod end.
When you think about it, it's really not that different than a quad's rear suspension. I have not heard of very many of them breaking.
You guys keep talking about lowering the roll center. Lower isn't always better. Front roll center. center of gravity, front and rear spring rates and many other factors go into that decision. In a road race situation, it's not about getting the car neutral handling as it is getting the car to have neutral handling no matter what the traction level (wet / dry /dirty, etc).
I chose a low roll center as my spring rates are way up there. Straight line stuff like what we do, I don't believe it to be super critical. Maybe on a roadster but not a long wheel base car like a lakester or streamliner
Interested bystander- I would like to see four times safety margin in my designs. I only see about a two times safety margin at it's worst point. Your design is not quite like mine. If I could ask you a favor, please move the front crossbar rearward about 2" onto the "X" itself and rerun the FEA. Might be better? Might be worse?
I still think the lakester will start the dreaded pencil roll long before we have any breakage problems but maybe I'm wrong. I've driven this car, the driver has no business ever getting this thing that sideways especially after we add the new body work and vertical stablilizer.
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Results of a rerun with the front cross member moved 2” aft are below, and as would be expected, there is very little difference from the original model. Note that there are now two new elements, 22 and 23 between the cross member and the center, and 14 and 15 are now short, going from the cross member to the forward pivots. Again, these results would not properly take into account the local geometrical stress concentrations at the tubular junctions. Also not forgetting that the pivot bearings at the axle have essentially the same loading problems as those at the front.
Also recalling that these results are from only a single load case that was perhaps reasonable, but chosen completely arbitrarily.
Fabbing out of 4140 would be even more ticklish than 4130, and should take cognizance of appropriate preheat and interpass temperatures, filler material, stress relief and/or post-weld heat treatment, then weld NDE inspection.
In lieu of needle bearings that would need some sort of thrust bearing as well, and may not especially like the salt with out being sealed and lubed, one might consider a plain spherical bearing, similar to the original rod ends but without being mounted on an extended shank. http://www.rbcbearings.com/sphericalplainbearings/index.htm (or similar).
BOTH FRONT JOINTS RESTRAINED
ELEM VMX (psi)
1 35159.
2 39766.
3 665
4 665
5 39729.
6 31575.
7 665
8 665
9 9514
10 462
11 8846
12 462
13 9679
14 13566.
15 13883.
16 28866.
17 29958.
22 24816.
23 23647.
MINIMUM VALUES
ELEM 10
VALUE 462.15
MAXIMUM VALUES
ELEM 2
VALUE 39766.
ONLY RIGHT SIDE JOINT RESTRAINED
ELEM VMX (psi)
1 17567.
2 52369.
3 669
4 669
5 67263.
6 20856.
7 669
8 669
9 9067
10 465
11 10524.
12 465
13 10197.
14 12717.
15 17528.
16 27944.
17 30404.
22 25192.
23 22923.
MINIMUM VALUES
ELEM 10
VALUE 465.08
MAXIMUM VALUES
ELEM 5
VALUE 67263.
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Interested Observer- Thank you very much! I do like that choice of bearing. its is very simple and should work well.
The lower number at point 5 is a little encouraging but I think I would still like to change it. Sorry about the confusion about the moly number and yes, it looks like I do want the 4130. I have used 4140 for other suspension parts like sway bars as they heat treat well.
Thanks for the input.
Rob
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Robfrey, don't confuse me, Interested BYSTANDER, with the above Interested Observer (even though I use that Nom de Plume on another semi-related board).
I.O's textbook calculations above are Very informative, but way beyond the grasp of more than 99% of the Landracing crew -even GLEN.
All this could be worded in laymens words and the numerical differences could be put in a form that indicates whether one would be A. Majorly in danger of a catastrophe, B. possibly in danger, or C. slightly, or . . .well it ain't the way Netwton and the phyics tecbooks woulda done it but it's aceeptable considering the narrow requirements of Landspeed racing. Something like that. More informative. Like Willie always trys to do.
And of course, since our pal Obama has finally gotten around to asking the Rebulicans "How'd you do things?" Maybe we could ask Interested Observer how he'd do it.
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Interested Observer,
I find your stress levels very interesting and after reviewing your numbers I can only believe that these are stresses that are generated at the welded joints of where the X member is welded to the fore and aft locator tubes. Is this what you are telling us?? If you looked at this structure as having pinned joints, i.e. unable to transmit bending moment in any axis (which would be the case if the X member were connected via rod ends) then the stresses in the tubes become nothing more than vector proportions of what the imposed side load is.
Please dilute our ignorance a little more on specifically where these high stresses occur on the structure its self.
Thanks,
Rex
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My original intent was to give Rob a cautionary “heads-up” on a situation that he may not have been particularly aware of or have thoroughly investigated, and that could possibly have significant consequences. To illustrate how quickly the stress in the Heim joint shank can rise when it is subjected to bending loads, the FEA model was done with roughly his geometry and a single, plausible, load case. It seems to have achieved that end.
Since the focus was on the shanks, the details of the rest of the structure were of secondary importance, although the results do give an indication of the stresses in the other members. Without writing a treatise on FEA or structural analysis, the following may help in understanding what was done and what these results indicate.
Using static force analysis and the theory of elasticity, classical engineering equations allow one to calculate the stresses and deflections of simple structures by hand. For instance: if one had a cantilever beam projecting from a wall with a weight hanging from the end, the nature of the loads at the wall end and the resulting stresses can be easily calculated. As is intuitive, at the top of the beam there would be tensile stress and at the bottom there would be compressive stress. If one grabbed the beam at the end and pulled away from the wall, the resulting stress would be uniform tensile stress across the beam cross-section. If the end of the beam was twisted about its axis, the stresses at the wall would be more complicated, but can be calculated. Each of these loads will create a stress component at any location in the cross-section and if all three loads were applied the net result would be the (vector) sum of their contributions at each location across the cross-section of the beam.
In the same way, the stress components at the mid-point of the beam could be calculated, or at any intermediate point along the length. The beam could be thought of as a series of short beams all connected end-to-end. If the calculations were done, the distribution of stress all along the length and across the the section of the beam would be known.
If we were to analyze the beam using FEA, we would do essentially the same thing. An FEA model is composed of “elements”, which “model” a section of beam, and in this case assume the beam is of uniform cross-section. The endpoints of the beam section are defined by “nodes” located in space. If we are not all that interested in the stress results along the length of the beam the model could consist of a node at the wall, another at the other end, and a single “element” in between. This model would use the appropriate equations to calculate the stresses in the same manner as would have been done manually above.
If we were interested in how the stresses varied along the length of the beam, we would have to create a model that consisted of a whole series of nodes with an element between each. The calculated results would then give the stresses at each end of each element along the length of the “beam”. This requires solving a lot of simultaneous equations which, fortunately, computers are reasonably adept at.
In general, the stress state at one end of an element may be different from that at the other end. In the simple single-element beam above with the weight and axial tension load, the stress at the outboard end would be the nominal tensile stress from the tensile load, but the end at the wall would be a combination of the tensile load stress as well as the bending stress caused by the outboard weight.
An FEA program calculates and stores the various components of stress at each location, generally tied to the direction in which they act within the element. This can often result in a lot of information that is difficult to interpret or relate to the ability of the material used to withstand the load. Fortunately, for steel and many other ductile materials, the stress components can be mathematically combined into a single net stress that can be compared directly to the strength of the material. One of these is the von Mises (or various other names) stress. If desired, FEA programs also will make this combination calculation and present that stress as a result for the element.
So, to bring this together as regards the suspension model, in the interests of simplicity, it was made of single element members, since the details of what was going on within the members was not of particular interest--just the magnitude of the greatest stresses of the particular member. Thus, the maximum von Mises stresses were tabulated for each element. For the Heim joint shanks, the maximum can intuitively be assigned to the end where the bending load is maximum, at its juncture with the link to which it is attached. (This is confirmed by looking at the more obscure results of the analysis.) To summarize, the tabulated results are an effective net stress that can be compared to the material strength for that member, given the arbitrary load situation analyzed, and in the absence of geometrical stress concentrations.
Stress concentrations ---
As described above, the elements used in the analysis assume uniform cross sections. If the size, shape, or configuration of the adjoining member is not a continuation of the one in question, a degree of stress concentration will occur due to a mis-match of the stiffnesses of the two elements. The model is, in effect, an idealization consisting of “perfect” connections between the members. At the welded joints of the tubulars, clearly the member cross-section is disrupted and stresses will be re-distributed depending on the nature of the loads and material configuration at that location. To answer Rex’s question, no, the tabulated stresses do not take into account the variations that will occur at the welded joints of the X frame. Those were not the goal of the exercise, although considerably more elaborate modelling of the junctions would give accurate indication of what is going on there. However, the given results for the members in conjunction with various stress concentration factors historically developed for similar joints would give a fair indication of what could be expected.
For the Heim joint shank, a smooth 5/8” diameter cylinder was assumed as an approximation of the root diameter of an assumed 3/4” OD thread, but due to the sharp root of the thread that reduction may not fully compensate.
The attached two plots may partially address the stress distribution question that Rex was sort of fishing for. The VM0 plot shows the stress magnitude on the top of the members, and so is largely driven by the bending loads in the vertical direction. As would be expected, the vertical bending induced in the trailing elements of the X by the “rolling” moment from the offset (lower) lateral load applied to the “axle” predominate. (That is, the X is being twisted by the axle.) This plot shows the stress magnitude by the offset from the normal element line, and the color code. It is basically the result at each end of the element, with the middle portion merely being interpolated from either end. Also notable is that the stress at the top of the element in the right side Heim is fairly nominal.
The second plot, VM90, shows the stresses in the horizontal plane, on the side of the elements, which are largely the result of the lateral load itself. As can be seen, the stress due to this is rather low in the X since its members are acting substantially by carrying longitudinal, not bending loads. Also note that the front right Heim is showing high stress at its base due to its carrying substantial bending loads.
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As regards Interested Bystander’s desire to more simply categorize the potential severity of the consequences--that is pretty much up to who is designing/building/driving the thing. And again, the stress situation discussed is for an approximation of a contingency situation. What one is willing to accept may be different if you are going to the moon or to Floating Mountain.
Rex’s discussion of all-pinned-joints sounds similar to the “N” braced version mentioned a number of posts back. Although, it would have to be an N, not an X. Any roll-axis motion would induce bending in the X (as in VM0 above.)
And if IO was going to do it, as alluded to earlier, he would opt to separate the functions for tunability and sanity, and eliminate bending wherever possible.
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I will need to reread this after a good night sleep. LOL! A couple of times.
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IO,
Thank you for providing the stress level graphics which so well illustrate the areas of maximum stress and are probaby most helpful in potentially designing a structure to carry the imposed loads. It is interesting that the maximum stresses are from the loading in which the X structure is trying to act as a anti roll bar, for which it is not well designed to do. I agree with you completely that each of the suspension loads should be addressed by an individual part to carry that specific load, i.e. an anti roll bar for the roll moment, a multi link to locate the axle longitudinally and some sort of watt link, panard rod etc to locate it laterally. The X member that Rob has selected does a number of these functions but as your numbers and illustrations show it maybe not be doing them very well and there may be some potential that they may extremely highly stressed under heavy loading.
Thanks again for "diluting my ignorance" on your analysis. Well done.
Rex
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What I have built here is just a slight variation of swing axle promod suspension that has been well tested over many years with as far as I know, has never been a failure.
The "N" has been known to fail on several occasions in the drag racing world. If the "N" design has never failed on the salt then I have even more confidence that I'm okay with what I have as there is less traction on the salt. I think I would like to change the rod ends but overall, I think it's good. It's very simple, compact and the bottom line is that it works.
My 92 Saturn's front sway bar was also fore / aft spindle locator. It was fine even with it's giant rubber biscuits at the attachment points. I believe Saturn stole that design from someone but I can't remember who.
The rear locating arms on my 2004 Saturn ion (delta chassis) are tied together with a brace to act as a swaybar also.
It's my opinion that it is okay for suspension parts to multitask especially when packaging is a very big concern.
We are just going straight here or least that's the goal.
I didn't design it to go road racing. If I was going road racing, I would want each of these components separate so that I could tune the handling by adjusting them individually.
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Ref: Rex's comments
One thing I neglected to point out explicitly is that the stress scales in the two most recent plots are not the same. "Red" in one plot is not the same as "red" in the other--one needs to look at the numbers associated with the color scale. (If the same scale is used, the high peak stresses of the shank tend to wash out the distribution of the lower stressed elements.)
Consequently, the highest stresses are not in the X, but in the Heim shank. These two plots illustrate the approximate locations and relationship of the stresses, but the actual magnitudes would be as tabulated in the earlier results.
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IO,
Could you run the "N" model for us? This is great stuff.
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An independent diagonal (N linkage) and a separate anti-roll bar would be safe and simple .
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I believe that an "N" type bottom bar setup puts all the lateral load on one rod end. Maybe I'm wrong? It is still loading the rod end in a way that it was not intended to take load therefore not really any better than what I have. Maybe IO can answer this for us with his FEA.
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I don't understand any of this. I bet I could after a week or two. But I do know that most landspeed cars get in trouble when they are not going straight. So counting on them to be straight all the time may not be wise. Drag cars get "straightened out" and contained by close guardrails. We don't have them. Is this too simplistic (from a roadster driver)?
Stan
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Rob.... Shouldn't the front heim-joints be solid joints? I know you have the bars Xed but will the heim-joints allow the rear end to move when pushed to the side?
JL222
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Rob,
wouldn't the "N" design give you different roll rate per side? R&L
John
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Rob.... Shouldn't the front heim-joints be solid joints? I know you have the bars Xed but will the heim-joints allow the rear end to move when pushed to the side?
JL222
I'm not sure what you mean but there is absolutely no side to side movement except maybe the slightest amount of slop in the rod ends but I can't feel it. The rectangle that is created here would have to go out of square for the rear to move from side to side.
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Rob,
wouldn't the "N" design give you different roll rate per side? R&L
John
The "N" designs that I have seen are not welded solid but have diagonal link with rod ends so everything can float a little.
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Rob,
yeah, that makes sense to me.
In all the work I have done in suspension design, it seems counter to create a suspended plane.
The "N" design would work allowing the suspension to roll without "uncontrolled rising rate of spring" component.
It would introduce less bump into the car when one wheel hits one.
Back to my hole, John
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Looking at the N layout I realize it has a fault . If one wheel tries to raise more than the other one bar travels in a vertival arc and the other three travel in a cone shaped path and everything sees high tension or compression .
A layout that would work is to have the lower bars like \ / with the rear rod ends close together under the rear and a separate anti-roll bar .
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With the model changed to an “N” configuration, the maximum stress results are tabulated below, with plots of element numbers and the end-to-end stresses of the top surface following.
The N diagonal was connected to the same point (node) as the endpoints of the bottom trailing arms as a matter of convenience. In real life they would be located separately but nearby. The results would not be much different. Since the N configuration does not supply anti-roll capability by itself, a rudimentary anti-roll bar and links were added. The arms and crossbar are (arbitrarily) of the same 1.25” dia, .125 wall tubing. (The unshown “axle” connects the aft ends of the upper links to the lower links.)
As can be seen, the links and shanks now have much lower stress levels and the higher stresses, due to bending in the arms, are in the anti-roll assembly, where they can be more easily managed. The diagonal, element 24, in this case is in compression (1384 lb/3782 psi) The diagonal shanks, 13 and 14, at 7598 psi are carrying the same load, and are much improved over the shank situation of the previous X solutions.
Regarding John Burk’s last comment--I agree that the four points (pivots) at the axle, for instance, will, in general, travel out-of-plane with uneven suspension travel side to side. However, given the limited travel likely to be allowed and the even more limited roll travel likely to be allowed, the mismatch may well be taken up by the slop in the system, elasticity in the system, or some designed-in elasticity.
ELEM VMX
1 2456.0
2 2456.0
3 666.86
4 666.86
5 661.48
6 661.48
7 661.31
8 661.31
9 1705.6
10 463.09
11 459.35
12 459.20
13 7598.5
14 7598.5
15 14353.
16 12423.
17 14351.
22 801.44
23 799.68
24 3782.2
MAXIMUM VALUES
ELEM 15 2
VALUE 14353. 2456.0
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Well the computer doesn't lie. I still think that we are missing a variable or two out of the equation but I will need to think on it some more. Looks like I need to get rid of the bar across the front and add a separate sway bar or re-manufacture the bottom bar assy to use a different bearing. maybe I don't even need a sway bar with my stiff coils. I really like the original concept though as it completely eliminates torque steer like a ladder bar car but puts the instant center out as far as I want. A ladder car's instant center is at the front pivot points. Eliminating the torque steer caused by chassis roll is so important on a high hp car with a narrow wheel track like a lakester because it will really change the on / off power steering bias.
Since I have such little real estate to work with I will probably re-manufacture the bottom assy.
It is sort of neat to know that the majority of the load is coming from the anti sway function. Thank IO.
I use computer sim for everything I can. Wonder how we ever got along without it.
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Looking at the N layout I realize it has a fault . If one wheel tries to raise more than the other one bar travels in a vertival arc and the other three travel in a cone shaped path and everything sees high tension or compression .
A layout that would work is to have the lower bars like \ / with the rear rod ends close together under the rear and a separate anti-roll bar .
I've seen this work well before on some road race applications.