Race car suspension Class

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Mikey..on super late model if you swap coil over mount it would change 5%. on your car it is even more dramatic. Keep them both on the rear of diff. for max spread
 
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We ran the car last night and it was much better. Last weeks feature was canceled so they gave us a 50 lap race and we couldn't buy tires and I messed up and bought a tire that I guess was old as it was 10 to 15 points higher that the others after we had it mounted and practiced, so we were stuck with that tire. We put it on the right rear but were still able to get the car good and it responded to changes we made at the track. So we are going to leave the spring behind and work on getting it to come out better. It goes in good and turns in the middle but just couldn't get it to bite coming off. The car was just bit tight after practice so we left it alone for the feature. We are all done for this year but would like to try something more to get faster. We can still practice for awhile. Any suggestions? You said on a late model it would change 5% I don't know what would change the 5% ? Thanks again for your help.
 
Usually loose off the turn is due to Stagger. Since I do not know the stagger you have tried I am flying blind here. The other cause is too soft a right rear spring. From what you said, you bolted on a right rear tire that was 15 points harder than a new one...right? Since racing is all about tires..this could add to loose condition off the turn. Especially on asphalt.
One last time on the 5% thing. On a late model car swapping a coil over to the front on one side would reduce the mount point to mount point distance by 5%. I do not like this as you have less ability to manage the sprung weight by 5% versus keeping the distance at maximum possible.
A lot of racing is managing weight transfer with the tools available.In this case it is maximum lever you have to control it. When you mount coil over in front of the differential you set up a trapezoid. Now you no longer have square set up. If anything you have softened up the left rear spring by shortening the lever over which it acts.
Of more concern is the location of the top mount points. The rear coil overs should be mounted at or below the Center of Gravity. Ideally below the CG. This will help traction under acceleration. Now if the rear coil overs are mounted higher than the CG, when you accelerate you lose leverage. The G force vector acting on the CG is the same BUT leverage has been reduced and weight that COULD HAVE been dumped to the rear springs has been reduced.

Besides that it is a band aid. The real problem is stagger or a soft right rear spring or other basic problem.
 
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We may have found another problem. We checked the rear end with our toe gauge, we scribed a line and then front to rear it is toed out a strong 1/8" and top to bottom a strong 1/8" is this enough to affect handling?
 
A bent differential can cause all kinds of frustrating handling problems. I assume you used a good tire wheel set to measure? here is a good link to assist. http://www.circletrack.com/techarticles/rear_end_alignment_measurement_tech/

the center line generated by the rear wheel should be parallel with the vehicle center line or you are inducing an understeer/oversteer condition. The other huge problem is bearing failure and leaking seal. How did it get bent? usually the driver does it by whacking the wall. So for reliability sake fix it.
 
Hi ranger mike...i am writing too u from Ireland.we run a 700kg space frame car on a flat quater mile oval with Hoosier h12 tyres..we have a arm suspension on the front and 3 link on the rear with a panhard rod.just wondering about front roll centre and should it travel towards the wall or the infield when in dive and roll or should it travel very little...many thanks Damien
 
welcome Damien,
The Roll Center is that point where the suspension linkages act on during cornering, acceleration, braking...any type of weight transfer. The more consistent you can make it , the better. So as little migration as possible is what I try to maintain. We have to realize that the height and location will move in the real world. A minimum movement (especially during the first inch of dive) is desired. If you can keep it with in a 1 inch location from ride height over total dive you will have a good set up. Our formula car drops about 1 inch in dive but laterally is stable. I assume that you are turning right when racing so offset it to the left to help load the left front tire.
 
Yes we are turning right but for the last ten years our cars would have started with the roll centre 3 inches to the wall and it would slide across towards the in field which I'm starting to think now was the wrong way as we have a push rite in the middle of the Corner that no one can solve.. What would ur thoughts be on this if u don't mind thanks
 
phase two handling is when all the initial nose diving has taken place and you need to hook up the rear tires. If the stagger is not enough the car will push. Increase stagger.
The Front Roll center has done its job and the left front tire was properly loaded. The weight coming forward has been kicked back. But if the left front spring is too stiff or the left rear spring is too soft the tires will not hook up. Before swapping out the springs try raising the rear roll center to help the car turn.
 
Is there a desirable relationship between king pin inclination and caster on a circuit race car. I am racing a transam type car with 310mm wide front slicks. I seem to be getting a lot of RF inside tyre wear at tracks that have mainly right hand turns and still some outside tyre wear despite having static -4 degrees camber. I am also thinking front instant center may be too long?
 
Welcome Philthy and thanks for the great question- 4 degrees neg static camber sound like a lot. Our purpose built left hand turn cars only run 3.5 ° negative camber on High bank tracks, eve less on flat tracks. Perfect tire temperatures reflect perfect static amber settings. Can you check tire temps after just exiting a turn at the race course?
Typically, on our left hand turn cars , if you have 3 to 3.5° camber , you want the outside tire temp to be 10 to 15 ° cooler on the right front tire.
Don’t try to get the tire temp even across the tire as this will mean a push condition (under steer as the tire will have too much positive camber and no make contact with the track for max adhesion. Don’t forget, with huge static camber if you have a lot of straights and few turns the inside of the tire will be in constant contact and the outside of the tire will be loafing along not carrying any substantial load.

a few other things to check-
Bump steer- you may be adding a lot of toe in / toe out if you do not know what it is. I keep bump steer under 0.030” per inch
Camber curve over 3 inch suspension travel – on a flat track you want 4.25° negative camber over 3 inch of bump travel as a starting point.Caster should be even so the car will steer neutral.
King pin inclination and scrub radius - please read post #325 on page 17 of this same post.
What is you Ackermann? see post #636
 
Ranger Mike said:
Welcome Philthy and thanks for the great question- 4 degrees neg static camber sound like a lot. Our purpose built left hand turn cars only run 3.5 ° negative camber on High bank tracks, eve less on flat tracks. Perfect tire temperatures reflect perfect static amber settings. Can you check tire temps after just exiting a turn at the race course?
Typically, on our left hand turn cars , if you have 3 to 3.5° camber , you want the outside tire temp to be 10 to 15 ° cooler on the right front tire.
Don’t try to get the tire temp even across the tire as this will mean a push condition (under steer as the tire will have too much positive camber and no make contact with the track for max adhesion. Don’t forget, with huge static camber if you have a lot of straights and few turns the inside of the tire will be in constant contact and the outside of the tire will be loafing along not carrying any substantial load.

a few other things to check-
Bump steer- you may be adding a lot of toe in / toe out if you do not know what it is. I keep bump steer under 0.030” per inch
Camber curve over 3 inch suspension travel – on a flat track you want 4.25° negative camber over 3 inch of bump travel as a starting point.


Caster should be even so the car will steer neutral.
King pin inclination and scrub radius - please read post #325 on page 17 of this same post.
What is you Ackermann? see post #636

Bump steer is good. Unfortunately virtually no ackerman (nearly 8 times wheel base) due to front steer with brake rotor in the way.
I will read post 325, thanks.
The camber gain is less than your suggestion and I think this is the root of the problem. That is an easy fix with changing the top control arm angle on either the chassis or the upright, or both.
 
Philthy said:
Bump steer is good. Unfortunately virtually no ackerman (nearly 8 times wheel base) due to front steer with brake rotor in the way.
I will read post 325, thanks.
The camber gain is less than your suggestion and I think this is the root of the problem. That is an easy fix with changing the top control arm angle on either the chassis or the upright, or both.
Akermann will help it turn and lack of it will definitely impact on tire wear. lack of camber build will also contribute..good job on identifying he problems..
 
Camber build and toe in vs toe out
I just returned from a race weekend at the local sports car course. Had an old friend racing a corvette. He had 10 inch tires on the front. The left front was really wearing from the inside edge to the middle and the portion from center to outside was like new. Looked like a bad camber build situation. No way would I try to correct this at the track unless I had a lot of time. You have to measure the spindle at ride height, take out the spring and shock, chart the camber over 3 inch suspension travel and see what gain you have. You can do this without the computer software but the program helps.

One question arose regarding toe in vs. toe out. On round track where you are turning left only, you can get by running toe-out as this will assist the outside tire to follow the different radius. Add to this the fact that most round track cars run caster split ( like 3.5 degree rt ft caster and 1.5 lft ft caster) the normal risk of running toe out being too darty is minimized.
On road course you run toe into take advantage of the self correcting effect and is more dynamically stable if you hit bump or get a gust of wind.
 
A lot of racers in the very restricted stock class ask me what the hot set up is for a particular class. My answer is – How high is the sky?
Racers are running Chevelle spindles, Impala spindles, C10 truck spindles Mopar ball joints , the combination of possibilities are all over the place.
When you are limited on components that you can use the options a re limited. Compromise is the rule. When the rules restrict you I am a firm believer in using the suspension software to find out where the roll center is. Next find out where it goes in roll and dive. Next figure out what camber curve you have. Find out what bump steer you have.
You will go insane trying to do this without the software. Just swapping in the “ hot set up components “ and not knowing why is a sure fire path to last place.
Example- A Chevy Camaro has a stock roll center about 1/2 inch above the track. That’s why they called it the “ hugger” when introduced in 1967. One hot setup is to RAISE the roll center to improve the camber build. Don’t forget..racing is all about tire contact patch.
Why is the front roll center located to the left of center line? Two answers. 1. You may have so much aero down force that you need to unload some down force on the right front tire at turn entry. The other reason is because of the mix of components you have installed, the roll center will migrate to the right of center line location on roll and dive.
A lot of the time you will need a lot of left front static camber since you can not use custom A-Arms and change mount locations due to the rules.
Racers use Mopar ball joints do move the ball joint up in the bottom A-arm to give a little more travel before the lower a-arm hits the frame.
In a restricted class, most of this work is accomplished by changing the angle (mounting location) and length of the upper a-arms (and a taller spindle). It would also be good to have the inner lower control arm pivot level with the pivot point on the lower ball joint. Don’t be afraid to use the software and run some different scenarios with spindles and upper a-arm locations.

You might get close by running a Camaro spindle on the right and the taller truck one on the left. If your ride height has the lower control arms level (pivot to pivot level) this might get you in the ballpark with roll centers without moving the upper a-arm mounts. But we can prove it on the software. Using a taller truck spindle on the LF and an Camaro spindle the RF you might get the roll center in a favorable location for dirt, but you would have to prove the results on the software. Again you are mixing and matching and when you have a non symmetrical situation things get real squirrelly unless you got the software.
You might also have to lengthen the LF upper a-arm a little which could be against the rules but who measures A-arms anyway??
 
Great read,i have included a pic of a front end that we run for 1/4 scale,after reading everything I see 2major problems
1) the front a arms are parallel and does not allow adjustment of role center
2) when we put positive camber in left front,it puts left front king pin angle at a positive killing the scrub radius
 

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Thank you ranger Mike and all involved for this post,this is the stuff that you can figure out over time,but at the same time the kind of info and experience that people take to the grave with them.
Thanks in advance
Bret
 
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Ha...good one..Bret...there is a song that says " the good, they die Young.." so I'll be around for quite a while!
 
Ha, I like it,any info or suggestions on this suspension Mike would greatly be appreciated?
 
I planned on drafting the front and rear suspensions out on the drawing board, what computer software would you recommend to do some work on this type off car?
 
Is my thinking correct on the king pin angle and those a arms being parallel?
 
Mike I love that phrase you always use about getting the neighbor hood fat kid,makes me laugh to tears.
One thing I find puzzling is we end up with allot of reverse wedge and have allot of trouble getting over 50%left side weight,the best I can figure is because of the spring rates we have to run to try to band aid the front geometry. Any thoughts you would have would help me out greatly, hopefully too know I'm headed inn the right direction.
Thank in advance
Bret
 
i got no clue...never messed wit h the 1/4 stuff...until you get software everything is just a guess..
i mean the typical data to make any decision is toe in or toe out? how much ackermann? what caster what camber build, any weight placement should be with driver, engine body on and fuel topped off...all the car is race day set up...get the soft ware and measure out everything before making any changes,,,,bench mark before changing things
 
Okay thank you,what package of software from pref trends duo you recommend,i know of this company cause we use this software on our 1/4scale engine dyno.
 
Hi, I have a couple of questions please:
What do you think about raising the centre of gravity to promote more forward bite via balast placed above the rear axle? This is for a New Zealand Super Saloon which is closest to a US dirt late model in design. Runs on a flat slick 1/4 mile track with tight turns.
Also, why do Late Models run such a large scrub radius on the right front?
Thanks, John Lovelady NZ
 
welcome John
rear Cg..weight shift is about the only way to change things at rear of the car if you run leaf springs. aside from lowering blocks options are limited. ref the scrub radius..there are posts on this..i am on the road and don't have notes..usually we run offset wheels and spacers on the right side to try to shift weight to left side so you will have more scrub due to this. personally id would shoot for proper left side weight and worry about wheel feel and wheel feed back to driver less..
 
Thanks Mike. I would like to give you a little more information on the car. The front suspension is very close to a late model set up - 3 1/8 front roll centre slightly to the right. We use the same front tyres as a late model, shocks are open. We use the new Bilstein with any valving options (which we have). The engines are 434 maximum iron block aluminium heads, around 720 ft lbs torque. (Klein Engine). However the rear is a lot different to late models. We use a sprint car rear end with an open tube axle with 104 inch right rear tyre, left rear range from 94 to 100 inch. Rear suspension layout can vary. We use typical sprint car layout with torsions and plenty of adjustment at the front of the rear radius rods. This car can also run 4 bar link with j-bar on right or left hand side of the car. When we built the car our goal was to keep as much weight between the wheel base as possible and as light as possible. In doing so, we now need to add over 300lbs of ballast to bring it to minimum weight for our rules. We originally built a weight box which sat between the driver and the driveshaft and had close to 180lbs in it. We had various other weights on top and bottom rails in the rear, both left and right hand side to bring the car up to weight. Its rear percentage was only 51.5% with left rear weight 55.5%. The car from the start has lacked forward and side bite. As we started to move more weight up, side bite has increased but forward bite still remains a problem. I began to think that the car became too stable and was not moving around and transferring weight so last week we moved some weight behind the rear axle and about 18 inches above the centre line of the rear axle height. The car is better but now I am wondering whether we are transferring too much weight onto the right rear and leaving not enough weight on the left hand wheel to get the car going forward in the middle of the turn. We already run heavier torsion on the left hand side with the split of about 25 - 30 lbs spring rate at the birdcage. Would appreciate your thoughts on weight distribution - high or low - inside of wheel base or outside of wheel base. Thank you :)
 
Sounds like you have a good start to a winning car. I would put the weight at polar moment. Moving lead around is not the best option. F1 spends millions just to save a few pounds of weight at driver height just so they can place lead as low as possible... You have the most tune able suspension you can run on that car given restrictions. I would study how to dial in the 4 link and solve your traction problem because if you are not able to hook up the car with the 4 link...well... I would concentrate on this area. correct me if I am wrong but from your posts you have phase one problems handled and are into phase two exit and phase three.