Automotive Race car suspension Class

[Ranger Mike]

corvette spindle and the wilwood spindle was about $220.00...not bad...
in my opinion..quit re-inventing the wheel and buy these...if you are scratch building you got enuff other details to worry about. ref- A-arm length...any time you can keep the camber build down to 1 degree per inch or less..is a good way to go..in this case less is better..

 

[autodoctor911]

I guess one important factor for choosing spindles that wasn't even discussed yet is steering arm placement. It will determine where the rack and pinion has to go.

 

[bigbolt52]

I am trying to correct a Mod-Lite dirt car, 1300 lb-14,000 rpm-1/4 to 3/8 mile dirt tracks. Looking for some ballpark numbers on where the roll center should be located, any help greatly appreciated.

 

[bigbolt52]

Here is some numbers.

 

[Ranger Mike]

Welcome Bigbolt
That is one light narrow car! Geometry looks pretty good. Roll center height is a little high in my opinion. Where is the rear RC?
what is % ft to rear and lft side weight?


I have never worked on a car like yours so all i can do is speculate what works on metric E-mods and the like on dirt.
In an ideal world 3.5 to 4 inch high front RC would be good and having it located 4 inch offset to the right side would provide more down force to load the rt ft tire.

Glad you got a good software program to analyze the camber build. You are well on the way to a checker.

 

[bigbolt52]

Thanks Ranger Mike it is basically a dirt Legend car, 74" wheelbase, a lot less restrictive rules class too. 57.8% rear 52.4 left and 52.8 cross, and a 1/2 wider wheel base on the right. Still confused on roll center moved to the left or right, the car seems to set and fall back down and tends to make my son feel like he needs to drive the turn harder to keep it set up.

 

[bigbolt52]

Back roll center.

 

[bigbolt52]

I think there is too much difference front to back on the roll center, and I am leveling out the lower control arms which is dropping it even more, and I want to raise the inner upper arm points too which should drop the RC even more to around 3".

 

[Ranger Mike]

Big bolt i will get back to you shortly on this.

I have been talking with Peter Walker at

http://www.walker-partnership.com/
on his unique suspension CC&AR. The question was posed to him...How is the front Roll Center calculated. He gave me permission to reply. Here it is.
"As the upper wishbones of the CC&AR system are free to float laterally, its roll centre is purely determined by the lower wishbones. It’s very easily missed but you will find it marked in the diagrams on the CC&AR page of our website."

Anyone who is interested in this system should post questions as Peter has agreed to share some info about this unique system but I have to channel it to him.
I must spend some time with the software to figure this out. My friend Conrad is thinking of going to this on his special built car project.

I have to prepare the formula car for race next week and am getting very busy so post will come later i am afraid.

 

[bigbolt52]

Thanks Ranger Mike, I wish our rules didn't say " No cant-a-lever or cant-a-lever type device will be permitted in or on any area of the race car". So I guess everyone that use a traditional shifter is illegal, lol. I better go order a cable shifter,lol and swich to a cable throttle, looking forward to your reply.

 

[Ranger Mike]

Ok, Big Bolt sent me private message and authorized me to share set up info so all you racers can follow along.

Bigbolt, please post the following info.
Left front spring, tire pressure you run, caster, camber and ride height. same on RT Ft.
on the rear I need ride height, spring rate and tire pressure, stagger unless you run open Toyota rear end.
I need toe out on the front. Whats is the wheel base on the left side and right side. Are your rule open on tires or do you run spec tires?Are you running camber cut tires?
are you using 3 link or 4 link rear set up?
Have you squared the rear end lately?

 

[bigbolt52]

Springs-LF 180, RF 180 (trying 200 this week0, LR 160 (trying 180 this week) RR 140 (trying 160 this week)

Air 6# Left 8# right

Caster L 4, R 6

Camber L -3.6, R 2.25

Ride Height Front 5" Rear 5.5"

Stagger in the rear is around 1.5" ( recently switched from 3"-big improvement)

Wheel base Left 73.5 Right 74 ( recently went to this from squared up, seemed to help but not sure if it was just a crutch, was having trouble keeping car down and this did help it from drifting up the track.

Toe out 3/16"

Tires Spec 40 duro American Racers, Hoosiers are too stiff. And the are grooved but not camber cut.

3 link as per rules with a 24" right bar and 19" left bar,

Panhard bar to the center, left side to the frame ( pondering switching to a J bar to move roll center over to the right)

 

[Ranger Mike]

all springs are on soft side.
car is about an inch too high on ride height.
springs -
try 185 LF ft., 200 RF., 165 LR , 145 RR
You are real close on LF and LR so do not change these
One legend racer here runs LF 185, RF 200, LR 165, RR 145
another runs LF 200, RF 225, LR 165, RR 145 so I am pretty confident on the above recommendations..

use pyrometer to get best tire pressure
no reason to go to J-bar yet. Is side bite a problem? Can not address side bite coming of the turn until we manage to enter the turn properly..

lower the rear roll center to help side bite, add down angle to increase it.
I would square up the rear end as you have introduced rear roll over steer.
go to at least 1/4 inch toe out. up to 3/4 inch toe out on 1/5 dirt track
on front roll center I am firm believer in offset roll center to plant the right front tire.
If possible try to get at least 3 inch offset to the right, 4 is better and you need this on dirt.

 

[bigbolt52]

Offset the front roll center towards the RF tire? And am I thinking correctly that the heavier sprung corner will get the most traction? Another piece of info, the front running cars, well most of them, run the LR coil over in front, and the RR behind the axle, that is how we are, not sure on the dirt Legends.

 

[bigbolt52]

It is also getting over on the right rear very hard, body clear down to the tire. Rear tire temps have been close together and the RF less than half the rears, and the LF is stone cold cause we usually are carrying it off the turn, I have to do some surgery up there to get it to lay down because it limits out on the Mono ball joints.

 

[bigbolt52]

Here is a video of our last race, our car got toe knocked out to 3/4" on the first lap. http://youtu.be/8kNNFME3F8k

 

[Ranger Mike]

offset the frt roll center toward the right side tire...yes..drop the roll center as well..i held off on this until you can tell me if the ride height can be lowered by an inch. we have the right side springs too soft. the car is pan caking the right side springs. This makes for a loose car going in. the tire temps are indicators and the right front should be the hottest tire on the car. detroit muscle cars had the left shock mounted in front of the axle and the right shock in back of the axle tube to stave off axle wrap under acceleration.

note in the video the driver is sawing the steering wheel in the turns. the rear end wants to come around..looooose...Bigbolt if you can not change the Roll Center in time...change the springs out and get tire temperatures right so you have similar temps across the tire face on the right front..and the other three. concentrate on this and worry about front to rear temps after you have close temps on inside, middle and outside of each tire. make good notes..

 

[bigbolt52]

I can do everything but get temp in the LF, geometry just won't let it hang low enough. and I can't lower the car or stuff will hit the ground.

 

[bigbolt52]

Roll center on the front is no problem and I can drop the panhard bar 1" in the rear.

 

[Ranger Mike]

Once you get stiffer rt ft spring it will throw some weight onto the left front tire

 

[bigbolt52]

I hope its enough to get some temp. I'll update after this weekend, I have the roll center down to 4" in the front and to the right 2", with a ride height of 4.75", I'm dropping the back down to 5" ride height and dropping the roll center over 1" in the rear also, with the spring changes recommended, thanks for your help.

 

[Ranger Mike]

Me too.. Got huge race next weekend
Oil cooler has leak
Transaxle layshaft pinion bearing is toast
Broke thrust washer
And replacement bearing has no flange face
Got to get on the lathe and tool up a spacer
And it's 88 degrees in the garage
Ya got to love racing

 

[autodoctor911]

If you ever need to go lower with the rear RC than possible with the Panhard or Watts can achieve there is also the Mumford Link:
The RC is the imaginary point where the two long links would intersect.

 

[bigbolt52]

Well it worked awesome on Friday night in hotlaps then got rained out, Saturday night car was junk, horrible. Took a huge swing on something I wanted to try for a long time and moved to both coilovers in front of the axle, wow! My son started coming through the pack like gang busters and then on a restart the leaders started playing brake check games, a car got turned sideways right in front of my son (15 yrs old) and bang, no more car. We are done with this class, unpredictable cars, and terrible drivers we have had enough, going into the late model class.
On a positive note the front end was awesome thanks to your help but now its a mangled mess, but my son is ok, I do appreciate the help.

Here is the accident https://www.youtube.com/watch?v=7Yb4uHdPM9E&list=UUsdXuwezocDERdqB0LdvvuQ

 

[Ranger Mike]

anytime you can walk away it is good..glad he is not hurt...that is the important thing..
thanks for the kind words...and good racing in the late model class

 

[mikey531]

We are racing a 2550 LB asphalt modified. What are the advantages and disadvantages of having the left rear spring in front of the rear end and the right rear spring behind the rear end? We also have a decel/acel push/pull bar on the center of the rear end. Approximately 600 lbs of torque from the engine.

 

[mikey531]

welcome...nice to meet a fellow racer..short answer is spring mount location can help a little bit on spring wrap under acceleration..torque link is to dial in hook up under acceleration as well..long answer is both questions are addresses in above post Race car suspension Class
by Ranger Mike

rm

Thanks I have read the posts and the big problem we have seems to be traction off the turns. The third link is supposed to increase bite off but they have tried it with staggered springs. Here is the info.
http://www.rightfootperformance.net/...4121065422.pdf
We have the accel set at 14 degrees down and the decel at 5 degrees up I think. I will have to double check the angles.

Thanks for the info above!

 

[mikey531]

The track is low banked 1/4 mile, we have been trying to get more bite off the corner by changing the angle on the accel bar. I think we are going to move the left rear spring behind the axle and try that. Unless anyone has another idea?

 

[Ranger Mike]

Usually a Loose Off condition is caused by too little Stagger. Another cause is too soft a right rear spring.
Typically 3rd links are used to tune the chassis. You have to have it handling properly before monkeying with the fine tune settings.
my main concern is the mounting location of the 3rd link. It should be mounted at the center of weight of the car. i.e. if car has 60 inch track width and 53% left side weight then
60 x .53= 31.8 inch and 3rd link should be mounted 31.8 inch to the left of the RIGHT TIRE CENTERLINE. Is it?

Next question is what springs are you running and how much stagger?
Is the 1/4 mile track tight radius or wide sweeping radius. Is track a paperclip or more of an oval?
any idea of shock absorber rates you are running?
what is % rear weight, left side and cross weight?
The good news is that it sounds like you have mastered the corner entry and now have Phase Three problems coming off. You are getting close.

Detroit muscle cars used to have the rear shocks mounted in back of the differential on the Rt Rear and in front of the diff. on the Lt rear to fend off axle wrap under acceleration.
In my opinion all coil overs and sliders should be mounted in back of the differential. This gives you the longest spring base (maximum distance between spring mounting points over the wheelbase to deal with sprung weight). Screwing around with one in back and one in front is asking for trouble. When you mount the left side spring in front of the diff. you have shortened up the left side distance by 5 or 6 inches. That adds up to 5% diff.

Mikey and bigbolt..not directed to you..just in general...
Rant to follow – Why in the heck do racers mess around with tricks and gimmicks to make a car handle when the car is not even close to the basic setup! Happens every time I'm in the pits...current trends, fads about super low tire pressures , trick locker rear ends..concealed sway bad loaders, tire soaking tricks..arrrrrr!

Square up the car. On a “ flat “ garage floor level up the race car frame. At your four bench marks make sure it is same distance from the floor. Take out the frt spring and disconnect the ARB (sway bar). ALL A-Arm /control arm frame mount points had better be parallel to the floor. if not..fix them. (may not be possible if you run metric frame but make sure the left and right side are mirror image of each other. The ARB should be parallel to the floor. Move to the rear end. Make sure it has not been bent. check it for rear steer. Square it up. Make sure the mount points are the same and make sure it moves parallel thru bump and rebound. Put 5 degree down in the 3rd link and put it back together.
rear end. Get the left side, rear and cross weight right. get the caster camber, toe and bump steer correct. get the spring rates in the ball park. Stagger should be close to what everyone else is running. ( if you want to win make sure the roll center is where it should be on the front and rear). Take it to tune and test and use a pyrometer. don’t forget the cardboard box!

 

[mikey531]

RM with the spring in front of the rear axle the distance between the front mounting point and the rear mounting point shortened the spring base about 16 to 18 inches. You said 5 to 6 inches would be 5%. 5% of what?

Thanks
mike