Landracing Forum
Tech Information => Steering - Suspension - Rear End => Topic started by: restless1 on October 21, 2012, 01:41:08 PM
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Just wondering what guys run for caster angle on a belly tank?
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There are a ton of discussion on here. Spend some time digging around. (thats what I did/do) :cheers:
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yeah ive noticed, seems guys are all over the map with ideas. was kind of looking for a nice starting point. thinking of trying 15 deg.
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Circle track guys put caster in cars to "WEIGHTJACK" the cars off the corners--- is this what you want? Caster will change the bite of the rear tires side to side-- when you make steering corrections!!! There may :? be reason why most hesitate to STEER at B'ville
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I'll add a question . For lsr what are the disadvantages of too much caster ?
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I'll add a question . For lsr what are the disadvantages of too much caster ?
Bumpy return roads=lost thumb nails
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restless, I will tell this, I am new and building my lakester. I STILL do not know what I am doing for caster yet. Will soon, front end is going together shortly. Good luck :cheers:
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When we built the Bockscar we picked 37 degrees, basically what the rails were running. It went straight, quite a bit of pressure was required to steer at speed. Was that way for about 26 years... we broke an axle last year, decided to build a new one for this year. The new axle has about 14. Steering is definitely different... there is a lot less pressure required to steer. The flopper is gone, it backs down the trailer easier, and pushes by hand a little straighter... at 37, once the front started to flop, it went. I made a couple of passes before Pork Pie took the reins, I like it at 14 but I may add a reversed quickener to allow a little more wheel movement. It seemed to steer too easy. :-o Pork Pie had no trouble keeping it on the track, even with the cross wind that popped up during his last record run.
Pick a number... 0 to 37... all have been used, these days I would say 37 is too much... 10 -15 is where I would land. Just remember caster is not your only variable, pay close attention to scrub radius and bump steer
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Ours is 30deg. We ended up with that because the guy who'd built ours,Graham Robinson, built one for John Lynch's bellytank at 23 and he suggested we go to 30. It doesn't "flop" , runs really straight...unless the motor is shaking itself apart, the wheel alignment is right and so on.....
Stainless has the comparative view, 37 to 14 , everything else is subjective.
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Thanks for the help..Im thinking Ill try 15 deg. Ill be using model A spindles and hubs, whats the fix for correcting the scrub. Im looking into the 20:1 rack and pinion from Prowerks for the steering.
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Thanks for the help..Im thinking Ill try 15 deg. Ill be using model A spindles and hubs, whats the fix for correcting the scrub.
Wheel offset is the easiest way.
Pete
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You might have trouble with the 20:1 r&P from Pro Werks as I think I bought the last one several years ago for my lakester. Check with them.
Rex
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If building with a straight tube axle, you can make saddle clamp mounting with one cap slotted for a locater stud (with locking nut) in the tube. You'll be able to quick adjust your caster, within reason, to see what works. We wound up at 14 degrees on a 156" wheelbase mod-roadster. Worked fine up to our best speeds around 185.
We did aluminum hubs with close-in wheel flange to correct scrub and keep bearing load points happy. It will also give you some bearing choices if you make your own hubs.
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The Chassis shop has 20:1 r&p's
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Thanks for the tip..Ill give them a call........ and thanks to all the others for the ideas on the caster angle.
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I changed the axle in our lakester in 2010....we had been running 12degrees..... i had a discussion with"Fast" Freddy Dannenfelzer about what may be an optimum angle for a lakester.... he went into a bit of dragster history - informing me that, in years gone by, they had commonly run 45degrees of caster... he told me he was running 30degress.... I was not able to get to 30degrees as the dropped avle began "undropping".... I settled for 24degrees..... It works well, self steers and stays straight.... it is a bit of a "bearcat when steering it around in the pits or the shop as it wants to stay straight..... BTW, we have run, on more than one occasion, over 280mph with our car....
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All the info given here is assuming it's "Not" a front wheel drive, you didn't specify. FWD is a whole different deal.
Ackerman theory is often not addressed on cars being built & is very critical in our world. If you don't understand it, have a chat with your friend Google.
Sid.
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I think front wheel doesn't change the need for caster . Scrub needs to be zero which puts the thrust directly behind the steering axis . Ken Walkey had no problem with 26 deg .
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Sid;
"Ackerman theory is often not addressed on cars being built & is very critical in our world."
LSR ... running in a straight line???????????????????????????????????????
Regards, Neil Tucson, AZ
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Just noticed the subject has reared its head again.
Caster is load (weight distribution) sensitive also.
Ask a Porsche mechanic and then ask a mechanic who has worked on say an older rear wheel drive Lincoln, Imperial, etc. Big difference.
Day and night.
The perplexing one is the front end pic of the legendary Tom Beatty Lakester on this forum one of the last times caster came around . Looked darn near ZERO yet it's a rear engine belly tank that went straight -into the record book.
Proper Scrub and Toe(in) are as important IMHOP.
All three improperly applied can cause a car to seek.
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Really Neil, how often does a car make a pass without some steering input?
Sid.
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"Proper Scrub and Toe(in) are as important IMHOP.
All three improperly applied can cause a car to seek". :cheers: :cheers: :cheers:
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Really Neil, how often does a car make a pass without some steering input?
Sid.
Sid;
The only time Ackerman is important (if it really is) is turning around in the pits or trying to recover from a spin. Even then, who cares if one tire isn't quite tracking the other. A little scrub on the salt under those conditions ...BFD.
Steering inputs on the course are so small that Ackerman does not matter at all.
Regards, Neil Tucson, AZ
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Having spent most of my life doing race set ups on road racing, oval track and the odd drag race car I can honestly say that there is no one set of rules that apply to all cars for all events. Depending on the venue some factors work better for some cars than others. There are also some geometry and alignment items that are much more critical than others. A little common sense will get you close.
If anyone wants to go into things further for their particular car feel free to e-mail or PM me and we'll look at your individual situation.
Pete
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I love this forum. The knowledge (and thirst for knowledge) here is amazing.
I found this video helpful to better understand Scrub Radius-- http://www.youtube.com/watch?v=JAnIa5wcn4E
I also found this article really helpful: http://www.hrsprings.com/technical/scrub_radius
Gotta take a ride up to my chassis shop now and look this over--
Current plans for my Gas Coupe (RWD - Nissan 240sx Chassis)
Neutral Camber
Very slight Toe-in, maybe 1/16"
15-20 degrees of Caster
Zero to slightly negative Scrub Radius appears to be what I want in a RWD car right? Slight negative would cause the forces act to 'toe-in' the car at speed which should contribute to stability more-so than toe-out?
Am I grasping this concept properly? In general does it sound like the settings above are in the ballpark or at least within the bounds of sanity? ;)
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Found... those numbers seem pretty close to where our lakester is... the lakester is probably a little narrower than your GC but I would guess you will run fairly straight.
YMWV
:cheers:
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Thanks Stainless!
Looks like I've got about an inch of positive scrub radius currently, but we're not done setting it up yet, currently shortening the LCA's a bit and getting the caster where we want it. I think we can get it to neutral without too much trouble. I can have custom wheels made if needed as well. The little 4" wide wheels I'm running only come in zero offset off the shelf.
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Check with Marsh Racing Wheels I have picked up some with a special centers they can use
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So is it correct,
That if a rear wheel drive car has positive scrub, it should be set up with toe-in
and with negitive scrub it should be set up with toe-out.