Automotive Race car suspension Class

[Kozy]

There is 524lbs load transfer 'from the inside front tyre to the outside front tyre'. That 524lbs is always over the front axle though.

Similarly, there is 259lbs transfer from the inside rear to the outside rear, however again it stays over the rear axle and does not shift diagonally.

 

[Ranger Mike]

Thanks Kozy..my point is you need to counter this with the ARb and the spring..right? So would you not need a 262# ARB and an effective wheel rate of 262#? A 350# spring times the .765 motion rate is 267# ..right?

 

[Kozy]

You've lost me again I think. Where have you got the 262lb wheel rate/ARB from?

The load is dependent on the springs. If you swap those rates and put 700lbs/in at the rear and 200lbs/in at the front, instead of 524lbs across the front and 259lbs across the rear, you'd get 111lbs across the front and 697lbs across the rear.

In this scenario, you'd need to add a significant front ARB to even it up. The wheel rates from the springs would be 115lbs/in and 700lbs/in F/R, so you'd need something in the order of 685lbs/in contribution from the bar to equalise the load transfer.

This seems fairly typical of MR racecar setup, where the rearwards weight distribution requires stiff rear springs to set the ride frequencies correctly, and then use a large front ARB to set the load transfer distribution so that it does *NOT (Edited to add that) suffer dangerous oversteer.

The opposite is also true of performance FWD cars. The heavy nose requires stiffer ride springs in front to support, but this alone would cause a lot of understeer. Solution: Fit a big rear ARB to take a large portion of the load transfer across the back axle to neutralise understeer.

 

[smithdl4]

Kozy;
The bar rate includes the arm length. It is a tubular bar made by Speedway Engineering. Its 37 1/2 inch x 1 1/4 inch x 0.188 wall tubular bar in front using 12 inch arms. Rear is 37 1/2 inch x 1 1/4 x 0.095 wall
tubular bar using 10 inch arms. They measure using an Intercomp sway bar tester. That's as much as I can tell you about how it's rated.

Appreciate the clarification on the ARB rate when attached other that at the ball joint.

I believe Ranger Mike got the 262 value from his last statement in an earlier post to me (593 previous page) where he mentioned that the ARB should equal the springs or something on that order. Half of your 524 equals 262 for the ARB therefore the spring rate should be close to 262lbs supporting the total of 524. Using Ranger Mikes example then the 350 lb springs equate to 267 lbs rate when reduced by the MR. Total rate would be 529 lb to handle the 524 lb weight transfer. Am I on track Ranger Mike? Dave

 

[Ranger Mike]

ok break time.........
please let me reply upon reflection ,,,,,

 

[Ranger Mike]

Smith..,you are correct...you want the total ARB and front spring package to equal the maximum amount of weight coming forward AND amount of aero downforce you will be experiencing, If you have 524 pounds moving from the LF to the Right Front..you would want to split this so ARB handle 50% and RF spring 50%. 524 / 2 = 262 so a 350# spring with .765 MR= 267#
to my way of jaded cynical thinking I prefer my method of finding the total weight being slung around at 1.15Gs, figure out max amount coming forward. Then add in diagonal weight and the total amount is divided by 3...it will be close ..we still have not added in aero down force so if you are a little stiff...you should know it at tune and test day..THIS WORKS FOR ME..but not best correct number as Kozy can tell you..

 

[Kozy]

Mike have you tried entering some setups you are familiar with on my calculator and comparing the notes to what you get? I'd be interested to hear what you think of the figures.

 

[Ranger Mike]

kozy..will do!

 

[rick7343]

Interesting stuff!

How do you determine how far you want the suspension to dive or compress under the weight transfer ?

 

[Kozy]

Kozy;
The bar rate includes the arm length. It is a tubular bar made by Speedway Engineering. Its 37 1/2 inch x 1 1/4 inch x 0.188 wall tubular bar in front using 12 inch arms. Rear is 37 1/2 inch x 1 1/4 x 0.095 wall
tubular bar using 10 inch arms. They measure using an Intercomp sway bar tester. That's as much as I can tell you about how it's rated.

OK so I bunged those stats in with the rest of the setup.

It takes the roll angle from 2.3° with springs alone, down to 1.07°. FLLTD is 51.2% which assuming the weight distribution is 49% seems nicely balanced. Tyre stagger may affect this though.

Overall, it looks pretty stiff, but I have no idea what sort of roll angle is reasonable at 1.15G. These figures are assuming 0 roll center heights, above ground RCs will add some more roll stiffness.

 

[Kozy]

Interesting stuff!

How do you determine how far you want the suspension to dive or compress under the weight transfer ?

Is that at me or Mike?

From a design standpoint, if you've got camber curves for the suspension, you can figure out what sort of wheel displacements are going to keep the tyre in it's optimum range. That is getting pretty advanced though.

From a testing standpoint, you'd tune the camber with a tyre pyrometer. If you can get a nice temperature profile without maxing out the adjustment in the negative direction, then the car has enough roll stiffness. If at maximum negative camber you're still leaning on the outer edge hard, then you need more roll stiffness. Add roll stiffness then re-tune until you get where you want to be. Do not add more roll stiffness beyond this point though, you want as little as you can get away with really.

Longitudinal load transfer and pitch motion is a little more tricky to calculate as it requires knowledge of pitch center height. Roll center heights are hard enough to find! Again, pretty advanced stuff.

 

[Ranger Mike]

Kozy..I got to dig up my set up sheets and enter the data on your calculator and will be doing this ..this weekend..The track condition will dictate the suspension travel. The total CAMBER build also dictates the travel. it is all about tire contact.
In racing, we can assume a certain degree of ideal conditions, or at least more ideal than public roads. In a stock street car, even notoriously "bumpy" race courses feel glass smooth compared to most public roads. In these conditions, the purpose of the spring can be focused to maintain maximum and consistent contact of the tire with the relatively much smoother road surface. Under these conditions, very little wheel assembly travel is required. The spring can be optimized for smaller wheel travel conditions. For example, a CART or Formula 1 race car driven on smooth courses may only have 1/4 to 1/2" of total suspension travel! On our Formula Car I bump steer it on 2 inch bump and two inch dive. The linkage type and layout influences the camber build so a full blown Indy type suspension may have 1.05” spring compression on the LF in a right hand turn. The LF tire would build 1.3 degrees and the RF may have 1.3” droop and the RF tire goes to 3 degree camber.

On the stock car suspension and considering the pitiful condition of the tracks these days we need at least 3 inch travel +/-. You will not have this much travel required on the track but entering and exiting the race track to pit road , the scales and the access roads around the track is where you need the travel. Some tracks are literally 3 inches higher than the infield and all you need is to be forced off the track by a shunt or race hazard and you are in the ruff. The desired camber build is 4.25 degree negative camber in 3 inch of bump travel on right front. Left front should have .5 to .75 degree positive camber per inch of rebound travel. I bump steer over +/- 3 inch travel..keep it under .040” per inch.

 

[rick7343]

KOZY: is that calculator supposed to be interactive? When I download it, there is double typing and it won't let me change any numbers... Maybe my old browser?

Thanks!

 

[Kozy]

New link here:

http://blackartracing.zxq.net/Chassis/Load Transfer 2.php

The inputs in cyan should be editable yes. The results in green are not.

What browser are you using? I use Chrome/Firefox. It will not work on Internet Explorer.

It should look like this:

 

[rick7343]

That would explain it! thanx!

 

[Kozy]

Yes IE is a PITA to script for. Requires it's own subset of code or something like that (I am a total n00b at web development) which to be honest, I can't be bothered with.

I could do with a popup warning advising visitors to upgrade their browser though!

 

[Kozy]

Can't go back to edit previous posts, but the old link no longer works.

New one here. http://blackartracing.zxq.net/Chassis/LoadTransferDC2.php

 

[Ranger Mike]

I made a mistake

My previous post about using diagonal weight is WRONG.

Kozy
I plugged in the numbers on the latest version calculator. Your calc said total load transfer 801 lbs. I came up with 813 on my post on physics forum.
Your calc said 534 lbs. front end 271 rear..I came up with 521 lbs. front and 292 rear weight.
My previous post about using diagonal weight is WRONG.

I made a major mistake by not adding in t he ARB motion rate which is huge. If anyone wants to know specifics look on page 22 post 358 of this post. I apologize for this error. Disregard my calculation of diagonal weight transfer.
My other disconnect on this is the heavy amount of rear weight transfer but the effective spring rate that works is only 95 pounds.
We have between 271 and 292 pounds of weight coming from the left to the right side of the car. Then it hit me like a ton of bricks. Only 95 pounds was slinging through the roll centers the rest was straight lateral transfer through the rear axel center line to the outside tire contact patch. Duh!
I had to add up the UNSPRUNG weight and it proved out.
Kozy I think your calculator is a very good tool to use.

UNSPRUNG Weight
coil spring front 17# each
coil spring rear 11# eacj
Ford 9 inch floater rear end 133#
Quick change rear end 208#
brakes front and rear ( disc) 20#
Rear Trailing Arms 28# each
Spindle, hub, backing plate assbly 35# each

the following are 50% sprung and 50% unsprung
ARB ( sway bar) 15#
Tubular upper A-arm 5#
Shock absorber (damper) 4# but depends on mounting .
Could be 1 # sprung 3# unsprung if hung like stock production automotive.
If you reverse you have 3 # sprung 1# unsprung.

 

[Kozy]

Christ, that's a lotta unsprung weight!

 

[Ranger Mike]

yes..that was what was giving me fits, kozy. Coil overs take some of it out but 50 pound tire / wheels and that heavy differential add up quick. Your calculator was a very good deal and confirms my post on calculating the weight ( without diagonal figures).

 

[Ranger Mike]

All the chassis tuning in the world will not help when the car is 3 seconds slower than the number one car qualifying. A compression test told the story. Two out of four cylinders were down 15 % psi. If we had a V8 the impact would not be as dramatic but we were getting pulled two car lengths on the straights...No way can you win races when this happens. Now the decision is to race or not race the car at the final event. I do not like losing! But a day at the track beats a week at work, right??

 

[rick7343]

Just order 4 more cylinders and fix the others!

 

[Ranger Mike]

I did not go to the track the last race weekend of the year. We won both days...With the engine that had two cylinders 15% low...and we found a front ARB that was cracked. Now wonder the cr was off. The front ARB sway bar arm was giving way and after swapping in a new one..we were back to the old fast time. Lesson to remember. Check for cracks, have regular maintenance scheduled, and never assume anything. Or don't have the crew cheif at the track..i will have to test this theory next year!

 

[Kozy]

Good effort Mike! A crack in the ARB would stump even the best engineers I reckon!

I've written up an article with built in calculations based on my model of load transfer, to complement the calculator I wrote. First part of a multi-part set of articles anyway.

http://blackartdynamics.com/Chassis_Articles/Tyres_and_load_transfer.php

 

[radracr]

Hi Ranger Mike! I got to say, I good friend of mine referred me to this site and…..WOW!

My question: How best to determine shock compression / rebound values front and rear? We have determined that our Motion Ratio is 2.0 on the Front A-arms. The car is a mid-70s A-body.

Thanks again for the thread and incredible insight!

And, I recently purchased the Circle Track Analyzer 3.6. (Yes, my application is circle track.)

 

[Ranger Mike]

Thank you much Radracr..kind words always good to hear. I assume you are running Chevy Chevelle A body. what is the race ready weight?

 

[radracr]

Actually it's a 76 Cutlass - but it's the same - 112" wheel base.

Class rules are 3200# MIN - I'm at 3270.
Class rules are 56% MAX left side - I'm at 55.8
Class rules are 47.5%MAX rear - I'm at 44% - 45.5 with a full 22 gallon fuel cell and 3380#.

Left side is running 3" offset 8" wheels.
Right side is running 2" offset 8" wheels with 1" spacers @ RF. RR = 1/2" spacer.
I have not checked track width.

We were running LF = 14/4, RF = 12/4 but it seemed that once we took out the anti dive and went to an 800# RF, 700# LF springs, the RF shock could not keep up - the RF would smack the track surface going into the turns. We were previously at, with anti dive 900# RF, 800# LF

 

[Ranger Mike]

Sounds like you are real close. The left side wt. is perfect. it would be great to move 65# to the rear or take it off the car period. You are at the classic point of making the front end a tad too soft. Sounds like 850 optimum Rf spring. Maybe #750 on LF. We always ran 76 shocks on the front on the monte carlo. Can you run 3way adjustable shocks?

 

[radracr]

Stock shocks in stock location. We can run rebuidable - hence the 12/4 and 14/4 - but not adjustable. A lot of the racers in the other classes are running the same shocks I am but they are outboard. I'm sure that the motion ratio plays a role.

The current thought process is to leave the rebound alone but increase the compression to 8, 9, or 10? Is there any way to determine this upfront before forking out the cash on a new set?

Also, we plugged in some 'rough' numbers and it said that our RF natural spring frequency is 1.51, while the rears are 1.53 ish. The LF was 1.1. I thought the RF was to be 2.0? Currently, RC = +1.7, 7.0 to the right. The car, just like the software says, has always been a little too oversteer and therefore no bite off.

Thanks,

 

[Ranger Mike]

Move the Rc back to 3 inch offset to the right. You have too much leverage at 7 inch offset. This lifts the left side of the car. You may have too much rebound on the shocks up front. Present set up means the rf spring is pancaked, the shock is tying the rf down and probably same on lf shock.
On corner off acceleration there is not enough lift at lf front to transfer weight to RR tire to hook up off the turn so is loose off.

bumping up compression is not the answer..fix RC first. then change springs 50 # then tune with shocks
but..dial in camber build and bump steer too

 

[radracr]

Thanks, RM! The bumpsteer is not something I have messed with yet. Quite frankly, I'm not sure how to. With the rules - 'stock' - there's not a lot of wiggle room for me on this even though I hear that the A-bodies have good bumpsteer. To me, there's only so much that can be done with the steering - there are no aftermarket components that can correct the bumpsteer - at least with stock-appearing, tie rod ends and center link.

Or am I missing something?

 

[Ranger Mike]

You should at least learn how to measure what you have, even if you can not correct it. It builds toe in. If you are going to master a race car you better know all about caster camber, toe etc..

just saying..if nothing else you can rebuild it at the track to some know bench mark after a wreck.

 

[radracr]

Ranger Mike - Last year we measured and re-measured caster, camber and toe. (I also bought wheel scales and a caster/camber gage.) Tire temperatures were checked religiously. Up to this point my approach had always been to put some power into the car and drive the wheels off of it. That worked - to a point - we broke the track record right off the bat and won two races. But, as you know, that is never enough so that's why we kept pursuing speed - to that end we regressed and by 2/10ths.

Over the winter we have not focused at all on the motor but instead turned to this forum and the CTA software.

I've borrowed some 10" stands to put the car on. We'll be plotting out the car this weekend. When we ran the software in continuous mode the RC moved voilently to the left, and down. I'm going to start with the springs you suggested and set up the lower control arms 'level'. From there the goal will be to get the RC as you stated.

 

[Ranger Mike]

Excellent plan. I would check the rear end for rear steer as well. Takes a few hours to pull out the springs and measure wheel base thru bump but can see what is happening at the rear end while cornering. Once complete you have no worries on that end. Then back up front and try to get the RC offset correct and try to maintain it close to 3 inch thru cornering. At least the first 1 /2" if nothing else. Just remember it is a stock class and you are very limited by the rules. Not much to be done..but..little things matter and if you can have many little things working for you then you will have a better car than the rest.

 

[radracr]

RM - Whew…measuring, changing and re-measuring RC - what a process! But we have been able to get the RC to start out at 3.4" above ground, 2.8" Right. But, I have measured my CL based upon the frame center, and not tire patch. Since I'm running offsets and spacers the tires would cause the CL to shift 1.5" right. Thoughts?

What I have also noticed, by driving change with the software, is that there is a certain rate of change caused by two variables - dive and roll. By "Analyze Suspension" the software is telling me that I should expect 2.3" dive and 1.6* roll. Is there a particular equation I should be looking at?

Also, the software discusses 2 CPS for RF (LF = 0.85RF) and 1.6 CPS for the rear. Steve Smith's Advanced Race Car Dynamics suggests 2 CPS and 1.4 CPS. If I go 'by the book' my RF spring rate will increase to 1163#! This seems way above anything that I've talked to others about.

Right now, based upon my current set up my RF CPS = 1.8, all others = 1.6

If I follow the logic of 1* roll / 1" travel, the RC:

@ 1 = 2.5"H, 5.3"R
@ 2 = 1.7"H, 10.7"R
@ 3 = 0.7"H, 23.0"R

But, if I plug in the MAX dive/roll that the software suggests (2.3" / 1.60*):
RC = 1.5"H, 10.4"R

Finally, my anti dive is: RF = 8%, LF = 5%. This is very close to 'textbook' - 10%, 5%.

It may not look like it (by looking at the car) but we have made several changes. Interestingly enough, we are running the same BJs for the lowers and the same for the uppers. (I would have expected to stagger these.)

I really like the software.

 

[Ranger Mike]

Wow- good job racer! Gives the public an idea just what we do in the winter in a cold garage!
There is a lot to digest. When you use wheel spacers to move the vehicle center line to the right we are adding left side weight. I assume your roll center calculations are based on the final adjusted center line. We try to run as much left side weight as we can get away with. Even used to crank in the ARB (sway bar ) adjuster before rolling across the weight scales.

I am very impressed that you have taken the time to read up on your ideal setup from various source..Excellent.
To all racers a word of caution- I swear by using software programs like this one to measure out where the car is and base line it. BUT,,do not get over zealous and start gaming the race car set up. Two huge factors will ruin your ideal set up you have gamed out.
Reality and Aero. All the software in the world can not predict real world things like damper dynamics ( shock action), true spring action, ARB action, and the 32 some moments on a typical stock car. Shocks will heat up and permit more dive/roll during the race. You are burning off weight every lap ( as you eat gasoline). Tires go away from lap 1 on..just the reality of it.
Aero dynamic drag is a lot more problematic and can not be accounted for with this software.
I rely on the software as much as my pyrometer. It is a tool only and should be thought of that way.

On dive and roll, i think you have done a lot of work and should stop.
You have the RC exactly where it should be at static. All the software has indicated it will migrate to the right. I don't really care after 2 inch travel where it ends up as the the max weight transfer has already happened.

Until you can read the shock stops after a hot lap and know actual shock compression, everything else is a guess.

no way will a 1100# spring work.

Good job on anti dive. I think you have taken it as far as you can in the virtual world. Now back to checking rear steer and making sure we don't have suspension bind anywhere. Make sure you do thorough bolt check and get rid of any farm bolts and bolts under grade 8.
you got a real good jump on the competition this year.
rm

 

[radracr]

"I assume your roll center calculations are based on the final adjusted center line."

No. If I need to take this into consideration then my RC is 4.3" to the right. If I make any efforts to shift it further left, the RC really starts taking off to the left which will only make the car 'feel like' it has a very soft RF spring. (Which was the case last year.)

 

[radracr]

Also, to get the RF CPS to 1.8 I ended up with a 950# spring.
LF 850, RR 150, LR 200, all equal 1.6

When we tore the front suspension apart we immediately noticed issues with the lower control arm mounts - they weren't lined up. This took a bit of 'fabricating'. Afterwhich, we used 9/16" drill rod to make sure the pivot point was in line. We then used a digital angle finder to make sure that both sides were as close as possible - 0.5*. We also used a tape measure to make sure the heights were the same.

With all this, and since we are allowed to run tubular uppers, we contacted a respectable company to have uppers made with the specific caster offsets as well as the correct lengths to get the RC where it needs to be.

Like I said, what a process! Hopefully we'll have a play-day this weekend.

Now all I have to figure out are my shocks. (Right after I check the rear end.)

 

[Ranger Mike]

At this point I would not monkey with the Roll center location any more. It is migrating where it should. Concentrate on the tire contact patch and look at camber build your actual spindle set up. Use a bump steer gage so you know what it is doing in 2 to 3 inch dive..and on left front too. I would say you have gotten just about all you can out of the software..now it is real world time on new fabricated front end parts..Sounds like you found some major areas to improve!

 

[radracr]

As a reference, last years RC was 1.9H, 8.5L! The car acted like it had a 2-ton gorilla jumping up and down on a 5-foot torque wrench! It would roll on the Right side severely.

We're now in the process of measuring bump steer - front and rear. So far, interesting number on the front.

We're looking forward to the NEW car!…

Thanks, Ranger Mike! Booyah!

 

[Ranger Mike]

Bingo..no wonder the car was pushing going in and loose coming off the turn. If you have a front track width of 65 inch and the RC is located at 32.5 or centered then 50% of the weight would roll thru the center when cornering. With the RC located 8.5 inch to the left you had only 37% of the car weight rolling thru the center..not enough to stick the RF tire and not enough to transfer to the right rear on corner exit to hook up the rr tire. With a RC at 3 inch to the right of center you have 53% of the weight rotation thru the RC..much better and the recommended location..because you have enuff to plant the tire but not enough to start to lift the LF tire like the old sprint cars used to. I think you found the underlying problem. This is huge. If you had not taken the time to find this all your efforts would be to band aid the problem.
The other teams having the RC 8 inch to the left would be chasing their tail with cranking in rear steer to hook up the car, swapping out RF spring / shocks , preloading the ARB, cranking in cross weight, adding stagger, to find the best combination. This process will drive you CRAZY.
Good job! let me know bump steer and don’t forget to check akermann my other pet peeve.

 

[radracr]

The lower control arms were set at the same angle as ride height. The centerline of the car was established and then each rotor was set parallel. A bar was clamped against each rotor which represented the contact points of the face of the tire (when setting the toe by string method). The contact points were 21” apart. A plumb bob was then used to establish the toe. A ruler was laid on the floor and square to the car’s centerline. Each tie rod was adjusted until the bar was parallel.

The bump was then measured. Again, it proves why the car liked ¼” of Toe Out.

The Pitman Arm and Idler Arm seemed to be pointed in equal and opposite directions.

The RF is really strange – it’s OK through the first 1.25” of bump but then really starts to toe in!

The LF has a gentle curve which suggests that something needs to be changed.

 

[Ranger Mike]

not too bad,,you are allowed .030 to .040" toe per 1 inch bump..don't mess with it..not worth the effort. btw that is a classic case of the outer tie rod end to high or too low..see chart attached

 

[radracr]

What would you suggest setting the static toe-out to be? My thought is:

0.08" (LF @ 2") + 0.05" (RF @ 2") + 0.13" = 0.26"
The 0.13" would be to compensate for the steering linkage shrinkage during cornering. This would likely net a dynamic Toe-out of 0.05"?

Do I set this equally? Or as per the respective sides toe change? Meaning, LF = 0.16" toe out, RF = 0.10" Toe out.

 

[radracr]

Ok, Rear Bump. We set the gage on the LR and bumped the rear end up evenly 1". The front indicator moved -0.006" The rear indicator moved -0.008" - telling me that the wheelbase on the right side is getting shorter.

We did not check the RR.

 

[Ranger Mike]

If you can adjust the bump steer and Ackermann ..read thisI looked over my past post and on page 1 post 13 we discussed Bump Steer. I never did go into Toe and Ackermann in detail so maybe we should at this late point.
Toe-Out. If you have to ask what it is please leave this post. Toe in is for production cars with spongy rubber steering bushings. The theory is at speed the tire will move from toe into toe out condition. Race carts have metal bushings with no give so they are toed out at static alignment. If no toe out was dialed in the car would be floaty. You need d a degree of toe out to keep the tires from wondering on the track at speed.
When you go into a left hand turn both tires are turning about a common center. The inside or left ft. tire is closer to that center point and has to turn sharper. It is running a shorter radius. Rt.Fnt. is using longer radius. Both tires are pointing in different directions while in a turn because of this. Static Toe out is used to balance out this difference and make best compromise so that each tire follows the ideal path on its own radius. When the front wheel is not following the ideal radius it is pointing against the radius and scrubbing off horsepower. If you go with too much toe out you will be scrubbing the tires on the straightaway. Using only a tape measure to measure toe is a no-no because tape flex can add a lot of error on a 65 inch track width car. As little as 1/16 inch difference can mean a lot of headache.

Ackermann steering came about in horse drawn carriages in 1818. Rudy Ackermann wondered why the wheelwrights had to replace the metal hoops on the wood wheels so often. The wagons and carriages of the day actually scrubbed off the rims in a turn because of the above described different steering radius. So he came up with Ackermann.
Ackermann is used to keep the tires from slipping sideways when following the non-ideal radius in a turn. It works by having both front wheels to have their spindles arranged as radii of a circle with a common center point. This center point, when the steering wheel is pointed is straight is usually the middle of the rear axle. In a turn the intersecting point of the axes of the front wheels will fall on a line that is the center line of the rear axle which means that the inside front wheel is turned at a greater
The bottom line is that modern steering linkage is not a simple parallelogram, but by making the length of the center link shorter than that of the distance between each spindle axis the steering arms of the hubs appeared to "toe out". As the steering moved, the wheels turned according to Ackermann, with the inner wheel turning further.
Ackermann steering is actually dynamic toe-out. It only creates toe out in a turn which is what we want... Minimum toe out going down the straight. We need a large amount of toe out on a short track race car IN THE TURN. Not on the straights. Ackermann is gained as the turn the steering wheel more in the turn. We need Ackermann on the right and left wheel as we may need to counter steer to avoid spinning out.

 

[Ranger Mike]

How to measure Ackermann.
If you are into racing and ca n afford it buy some turn plates for $750.00 see photo. Or buy some wax paper and a cheap plastic protractor. Use a straight edge and mark a zero line on the garage floor on the RF and lf tires when the car steering is centered. Crank the RF to the left 18 degrees and mark a line on the floor. Use the straight edge to mark the line where the lf tire is pointing. This is the Ackermann you have in the car.
How much Ackermann?
The left has to steer 15 % more than the right front. A typical asphalt track car needs 3 to 4 degrees more Ackermann on the left front in 18 degrees for right front steering. You crank the wheel to the left and hopefully you get 21 to 22 degrees.
One way to gain Ackermann is with BUMP STEER. For short track asphalt cars we want zero bump on the left front. No bump at all in compression or dive and rebound. Right front we need 0.035 to .040 “bump. Don’t forget the right front is the steering tire. The deeper you go into the turn the more bump you have. As the right front bumps to toe out the more you can steer to the left without pushing.
Whatever you do...do not change one the length of one steering arm on one spindle. It will really mess up the whole steering parallelogram.

 

[Al Johnson]

This has been a long read but what a treat! Thanks to all involved for sharing so much knowledge, I came around interested in the physical aspect of stock car racing and I will now need months to digest all I have learned lol.

I'd like to ask some questions if you don't mind, as I'm curious to know some things in more detail. For example, I have seen some references to shock absorbers but no indications of the ~ damping ratio stock cars usually run (Or the max/min range). Also, are different SA mounted left and right, or is the need for assymetrical setup covered just by regulating them differently?

Cheers

 

[Ranger Mike]

welcome Al
I am out of country this week..drinking plenty of fine German beer

I can tell you every shock ( damper) application is track specific. Mount location and angel are pretty consistent but important thing is to mount them bind free with best geometry to make max use of the dampening regardless of direction. The ration compression vs rebound varies in application and track, banking, speed..example..it used to be common at Daytona to run shocks with 12 inch travel..

 

[Al Johnson]

Enjoy the german beer, I have swallowed enough of it to know it's one of the best ;-)

Thxs for the comment, I take it then that the teams generally just shop shock absorbers for their applications and trust the seller's choice, right?