Author Topic: TFA Racing Lakester "tweak" diary  (Read 98013 times)

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Offline superleggera

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Re: TFA Racing Lakester "tweak" diary
« Reply #75 on: September 18, 2014, 11:36:58 AM »
2. Re-determine our Cg-Cp relationship, basic vehicle info

Is your base data measured using your heaviest driver in the seat (and fluids in tanks) or empty/dry?
- me: Mark - home: Dry Heat, AZ USA - build: motorcycle streamliner

Offline Glen

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Re: TFA Racing Lakester "tweak" diary
« Reply #76 on: September 18, 2014, 12:09:30 PM »
Can you slow the steering down?
Glen
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Offline RichFox

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Re: TFA Racing Lakester "tweak" diary
« Reply #77 on: September 18, 2014, 12:30:36 PM »
Maybe rethink that steering reverser a little. Those gears are over kill anyway.

Offline SPARKY

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Re: TFA Racing Lakester "tweak" diary
« Reply #78 on: September 18, 2014, 12:51:00 PM »
CASTOR the helps nothing-- it hurts --weight jacks the car when you "Steer"----my suggestion--read and study front  wheel drive drag cars ---I think Sum is right about the toe in---FWD drag cars start with toe out so that it pulls into alignment under power---talk to Bob Johnson your fellow class member! 

My opinion---You are already on to the biggest thing---DRIVE to the Chute---I would THEN ease off the throttle to ZERO thrust ---then shift into neutral for roll out---

your advantage going down the track under power will work against you when you are try to slow down your breaking and steering are nearly all on the same tires.  YMMV
Miss LIBERTY,  changing T.K.I.  to noise, dust, rust, BLUE HATS & hopefully not scrap!!

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller

We are going to explore the racing N words NITROUS & NITRO!

Offline DSR88

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Re: TFA Racing Lakester "tweak" diary
« Reply #79 on: September 18, 2014, 01:39:45 PM »
This has been my experience on the salt. The first time I drove Bonner Denton FWD AA/BFMS over 2000+ HP I went about 190 MPH @ the @ 2 1/4 the car was hunting all over could not understand how he ever drove this thing 300+
I cut the run short. I ask Bonner what the toe was and he said it was set 1/8 in. So trying to get in my head what all that HP was trying to do to them front tires I asked about setting the toe an 1/8 out he told me well your the one driving. The next pass the car drove so much better I felt like I was driving the car instead of it trying to drive me oh one that pass 2 1/4 speed was 240+MPH the car had never seen a speed that fast that early in the run. Now I know all car are different but front wheel drive the tires are trying to pull together just the opposite from rear wheel drive.
Remember this is what worked for me and something for you to think about.
Donnie Stringfellow

 

Offline Sumner

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Re: TFA Racing Lakester "tweak" diary
« Reply #80 on: September 18, 2014, 02:01:10 PM »
....FWD drag cars start with toe out so that it pulls into alignment under power---talk to Bob Johnson your fellow class member! ... Sparky

....So trying to get in my head what all that HP was trying to do to them front tires I asked about setting the toe an 1/8 out he told me well your the one driving. ..Donnie Stringfellow

I think Sparky and Donnie are onto it and I'd reversed my comments about amount of 'toe-in' to trying 'toe-out' first. 

In rear-wheel drive the front tires/wheels are being pushed so as all of the play gets pushed out at speed the toe-in goes to probably close to neutral. 

They are right that with the front wheels/tires pulling, starting with toe-out when the play in the front-end is pulled out the tires/wheels will become more neutral.  No matter how hard one tries there is going to be some play in the front end that will go one way or the other.

Possibly setup toe-in and toe-out and have marks so you can go to either fairly quickly on the salt.

Hopefully you re-post all of this next summer after running with what you finally did and the results.

Sum

Offline Rex Schimmer

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Re: TFA Racing Lakester "tweak" diary
« Reply #81 on: September 18, 2014, 02:07:46 PM »
I received a message from Tom Burkland regarding the alignment options on the TFA lakester and Tom mentioned that on a FWD car large amounts of caster maybe is not a good idea. Caster increases the trail of the suspension in side view, which means the tire, which is pushing forward, has a longer lever arm to try to disrupt the direction that it is pointed when deflected by an outside force, like a bump or a driver correction. As the caster is decreased the lever arm is shortened and the steering should become more stable but this also means that the steering mechanism should be very stiff i.e. minimum deflection related to applied load, so such things as the steering links from the steering box to the wheels should be large diameter and the steering arms should be stiff and the rod ends should probably be larger and probably should be in double shear on both ends and the mounting of the steering box itself should be very stiff.

Imagine a caster style wheel, like the kind on one end of your tool box, it  is allowed to pivot around a vertical axis which allows you to "steer" your box around the shop, this works pretty well because the caster wheel has lots of "trail" (the offset between the wheel axle and the vertical "steering" axis) and the force that the wheel applies to the vertical axis is behind the axis and is in the opposite direction of movement. So now imagine if you could now apply a drive torque to the wheel so it is trying to push forward on vertical axis, as soon as there is any misalignment of the wheel (now driving forward) with the centerline of vertical axis, the wheel will want to drive around the vertical axis, which means it is no longer pointed forward. This argument probably could mean that using zero or possible some  negative caster may be the most stable under power . This configuration could possibly have a stability problem at trailing or no throttle conditions because of the lack of positive caster. I think I would really consider a good steering dampener.

Regarding toe in or out for driven wheels it is probably very dependent on the scrub radius. If the scrub radius is positive (a line through the steering axis falls outside the center line of the tire patch) as drive force is applied the wheel wants to turn outward increasing toe out which would indicate that a static toe in alignment would be desirable. If the scrub radius was exactly on the center of the tire patch there should be no increase or decrease of toe due to the drive force, and obviously if the scrub radius is negative the drive force will cause a torque about the steering axis to increase toe in. All this being said I believe that any toe out on a driving wheel (front wheel drive or rear wheel drive) is not desirable and can cause direction instability, so my recommendation is to always align the wheels with toe in. The amount would be very dependent on the stiffness of the steering system to reduce deflection due to drive wheel torque inputs around the steering axis.

Rex  
Rex

Not much matters and the rest doesn't matter at all.

Offline Glen

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Re: TFA Racing Lakester "tweak" diary
« Reply #82 on: September 18, 2014, 02:10:44 PM »
Rex, good and wise words. :cheers:
Glen
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South West, Utah

Offline John Burk

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Re: TFA Racing Lakester "tweak" diary
« Reply #83 on: September 18, 2014, 04:05:58 PM »
I'm not convinced that caster causes a problem with front wheel drive . If the contact patch is directly inline with the kingpin axis (zero scrub) how does the distance between them change things ? When the wheels are turned adding caster makes the tires lean more but steering input during a run is very small . Ken Walkey said his FrWD streamliner handled well with 26* of caster . 

Offline SPARKY

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Re: TFA Racing Lakester "tweak" diary
« Reply #84 on: September 18, 2014, 05:03:59 PM »
operative word here is---ZERO  scrub radius

 I would try to figure out my tire growth and  either go with slightly negative scrub radius to allow for tire growth or build center point king pin frt axles 

do not discount torque deflection---study what the frt wheel drag guys have gone through in the last 20 years  there is a reason nearly all of the high HP fr wheel drive production cars have torsen-gleason
« Last Edit: September 18, 2014, 06:08:36 PM by SPARKY »
Miss LIBERTY,  changing T.K.I.  to noise, dust, rust, BLUE HATS & hopefully not scrap!!

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller

We are going to explore the racing N words NITROUS & NITRO!

Offline maj

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Re: TFA Racing Lakester "tweak" diary
« Reply #85 on: September 18, 2014, 05:51:42 PM »
Been a lot of yrs since i did wheel alignments but
hunting to me has usually been a toe in/toe out issue , excessive of either ,in this case i agree with Sparky , some tow out to compensate for "pulling the car along between the wheels  "


the other influence this yr is the salt condition, it was soft and possibly getting differing traction conditions from one side to the other  as you ran , i want to say it will feel light on one side or the other but its not quite the right description and will feel less regular than hunting from toe in

but all influences interact

Karl our busa was "hunting " too about 2-4 times a second ...., that i can do without 

Offline Sumner

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Re: TFA Racing Lakester "tweak" diary
« Reply #86 on: September 18, 2014, 07:50:20 PM »
Good info Rex, but I do have a question about the following....

...and obviously if the scrub radius is negative the drive force will cause a torque about the steering axis to increase toe in. ....Rex

Other than cars running A-arms and such which I don't know much about most cars with front axles like you find on roadsters, lakesters and streamliners (maybe) and maybe the case for this front wheel drive lakester have negative scrub (some a lot).  If that is the case and according to your comment above...

Quote
if the scrub radius is negative the drive force will cause a torque about the steering axis to increase toe in.

... the drive force will increase toe then wouldn't you want some 'toe-out' to begin with as the force would then help to straighten the wheels/tires out.  If you started with 'toe-in' then it would just become more.  Possibly I'm not interpreting what you are saying right??

Sum

Offline Rex Schimmer

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Re: TFA Racing Lakester "tweak" diary
« Reply #87 on: September 18, 2014, 08:27:12 PM »
Sum,
My thoughts are are when you step of the gas with a FWD car and if you happen to have front wheel brakes, which would be appropriate on a FWD car as most of the weight is (or should be) on the front wheels and toe out under braking is unstable. Now looking at the pics of the TFA car they do not appear to have front brakes so this may be a moot point with them. On a car that wants (needs) straight line stability I don't think I would ever recommend toe out. On road racing cars slight toe out can help turn in but they are usually not slowing from 200+mph.

John Burk, I would love to see the details on the Ken Walkey FWD streamliner. Specifically the amount of scrub radius and the configuration of the steering system.  26 degrees does sound like a ton but maybe the steering configuration was such that the turning loads that could be generated by caster were restrained and dampened by the steering system. FWD is something that we don't see often and some one that has an operational system would be great to talk to. BTW John how is your FWD streamliner coming????

Rex
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Offline John Burk

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Re: TFA Racing Lakester "tweak" diary
« Reply #88 on: September 18, 2014, 10:43:22 PM »
Charles Nearburg bought Ken Walkey's streamliner besides the Harold Nafziger's streamliner he races .
Health has slowed things on my FrWD streamliner but it should be at the salt next year . Thanks for asking Rex .

Offline entropy

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Re: TFA Racing Lakester "tweak" diary
« Reply #89 on: September 19, 2014, 06:08:08 AM »
Once again I am speaking out about something I know nothing about. But on your list i didn't see check front tires for roll out. On a rear drive car i found pressure equalization to be not important compared to diameter. Maybe it is important, I just didn't notice it. But diameter is for sure important, I think.

Rich, excellent point and one that i had given no thought to wrt handling, THANKS
we are careful with rollout as I zero in on the calibration of the front wheel mph log (hall effect)
we were specifically advised to match our front tire diameters, so i think we are OK, but thanks again.
karl