Oversteer help

[ReQ]

Hello

I have an 84 Cutless Supreme circle track car, freshly built for a 1/4 mile 12 degree banked asphalt track, this is my first time dealing with a metric car of any kind on a racetrack, or a RWD for that matter, so it has a few set-up issues keeping me on my toes in a bad way

the car must weight 3400lbs 545 left side, unfortunately I do not know how much it currently weighs, the season has yet to start for this year and the car has never been races, only test laps thus far and i have no access to scales, I know this would be very valuable information, my question probably cannot be answered without it but maybe an educated guess could be given?

that question is basically, springs and shocks for the rear, it has new but factory shocks, and springs that are WAY too stiff, came from the front of an 89 4WD ford F150, cut down to about 8 3/4", must have a 6" ride height but its currently about 4 1/2" but they never seem to be too picky about ride height, tire size is 215/70-15 (required tire size is 70 or 75 series only) with 8" wheels

the problem I am pretty sure is simply spring rate and shocks that cant keep up, no pun intended, it has terrible over-steer and as soon as I lift off the gas, no matter how I do this to enter the turn, the back tried to pass the front and I fight it all the way through the turn, cannot even think about more than 1/4 throttle until the car has settled and is straight, watching a much more experienced driver manhandle my car around the track, I noticed some scarey things about the rear

entering the turn the right rear tire will actually JUMP off the ground, which seems strange to me, is this just an example of springs that are way too stiff and terrible shocks? or is there more to worry about here, the driver who took my car out for a few laps says he would buy a 225/250 and 275 spring, then swap them back and forth between the rear to see which way works best, also replace the shocks with adjustable racing shocks

not allowed to alter anything on the suspension, only replace shocks and springs with "factory-like" replacements, planning to replace all front/rear control arm bushings with solid and spherical where appropriate, has a roll-cage of course, so the frame/body is very stiff, leaving the suspension to do all the work, I am afraid it is having some binding issues in the rear

any tips or advice would be much appreciated, also if anyone needs more information feel free to ask away, I have plenty of other questions, this is just the only one I could not seem to find the answer too, in this particular context/set-up

 

[pontiacgp]

What springs are you running up front, on a track like that your right front should be 1100 and left front 800 along with a big bar that's at neutral at park. The right rear should be 250 and left 175. For camber I would try +4 on left and -4 on right, caster 1.5* on right and 3* on left so the car tracks left. For stagger I'd try 1/2- 3/4" up front and 2" in the back. Can you run a spool or do you have the gears welded? Also how are you running 4.5" ride height. With that height your lower will ride on the frame and that would be causing your rear to come unglued and at that point your probably headed for the wall.

I'm just giving you basically what we had in our metric when we ran it in a bull ring, you can try it and tweak it if you want but talk to the guys who race there. They'll be glad to help you out since the more competition the better the racing.

 

[ReQ]

Sorry, completely forgot to mention the rear is welded locked, we are allowed to run spools and limited slip, probably going to try experimenting with an LSD, everyone says they don't work with these cars on this track, but I don't know to believe them

the frame height at it's lowest point in front of the left rear, me+full gear and fuel with tire pressure set is around 4 1/2, it could very well be bottoming out on the frame and causing the problems, believe me it is quite a job keeping it off the wall at times, I actually have not checked to see if it is bottoming out, if you bounce on the rear bumper, its like the car is on jack stands :shock: so I will check that first thing tommorrow

the front springs are the original springs from a longer wheelbase metric frame, no idea what the frame came from, but we had no front springs at the time, cut them to around 12" and stuck them under it, we do have racing shocks on the front from a friend, no idea what they are however, just that they are "pro" brand, the sway-bar is also completely factory mounted, we are not allowed to alter the mounts unfortunately, is there any way around this "rule" ? also, we are only allowed 3 degrees of camber and no toe-adjustments(very stupid rule)

thanks a lot for the numbers you gave by the way, I have been racing at this track since I was 15 (26 now) but only in stock 4cylinder, mini-stocks and mod-mini, all FWD, so this metric stuff is greek to me

the class I am running is suppose to be for "beginners" in the V8 class, stepping stone to street-stocks, since our local street-stocks are basically sportsmens, an example of a legal car:

http://i.imgur.com/US42X.jpg <Camaro

huge divide between the completely stock "stepping stone" to the street-stock class, how do we go from no adjustment on our cars, to a full range? we need to learn somewhere

 

[pontiacgp]

I know the problems where you can't change much on the car. Changing mount locations has been tried in every different way and tracks are wise to it. See who has some springs to sell you cause you really need to get the rate up in the front. There is a hump on the rear of the lowers that you are probably not allowed to remove and that limits the travel on the suspension. Are you allowed to run a front hoop so there is some down tubes running from that to stiffen up the front frame?. Put a piece of tape or paint that hump and that will tell you if it's hitting on the frame. Are you allowed to run 14" wheels on the left so you can play with stagger

 

[rustyroger]

It doesn't make sense to me having a locked diff on a car going round a circular track, but I know nothing about racing a Gbody.
But I'm always happy to learn new stuff, any able to enlighten me on why it would help?.

Roger.

 

[pontiacgp]

you need stagger to have a locked diff or the car would be loose going around the corner. We have, depending on the nite, 1.5 to 2.75 rear stagger meaning the right side tire is taller than the left so turning left the tires ought to be turning the same. The front has less stagger as the tires rotate independent but if you don't have enough you'll have a push when braking for a corner. The car is not set up to go straight, it naturally turns left

 

[UMI Sales]

you need stagger to have a locked diff or the car would be loose going around the corner. We have, depending on the nite, 1.5 to 2.75 rear stagger meaning the right side tire is taller than the left so turning left the tires ought to be turning the same. The front has less stagger as the tires rotate independent but if you don't have enough you'll have a push when braking for a corner. The car is not set up to go straight, it naturally turns left

Oooh, this thread has awesomeness already.

ReQ, welcome to the oval track world. PontiacGP and I should be able to get you going.

Unknown spring rates unfortunately make it very difficult to diagnose what's going on.

Do you have weight jacks at all? Do you have any way to change ride height?

You can get a little bit of an idea of crossweight (wedge) by jacking the car up with a socket as a pivot point under the rear end. You probably want some wedge so you'd want the RR tire to come up an inch off the ground before the left one does (with a tank of fuel and you in the car).

Any tire coming off the ground is bad. We need to get that fixed.

Where are you racing? 2-bbl car? Big power?

Excited to help.

ramey

 

[UMI Sales]

I always kept a book of exactly what was on my car.

You should be able to get the numbers off the Pro Shocks. That'll help us tune. Keep in mind, shocks (or dampers in technical terms) are the fourth or fifth thing towards getting a car right. You can get up front on a standard racing shock without anything extravagant.

Slight toe out will help the car turn-in.

Corner entry loose is bad. We need to get that fixed.

ramey

 

[pontiacgp]

The only way I can see the right rear wheel coming off the ground when braking for the corner is the right lower CA is resting on the frame, the left front still has some suspension movement because the car is starting to turn left and the brakes is shifting enough weight to the front to raise the back. With the right lower CA sitting on the frame the weight is transferred to the left front leaving the car to pivoting on the right front and left rear allowing the right rear wheel to come off the ground with alot of the weight on the front left. Soon as the brakes are release the rear will snap on you when it's back on the ground but that right lower CA is still on the frame with the weight on it going around the corner so your car just starts heading to the fence...coming out of the corner if you try to stomp on it coming out of the corner the back end will probably try to swing out since the right lower CA is bouncing on the frame and it won't let the car settle until you're on the straight

 

[ReQ]

This has been a great deal of help already, you are spot on with the control arms bottoming out, the ride height was just too low, I am frankly surprised we were even able to get the car around the track at all, but this is a brand new car so its still in the very first stages of tune, thanks a lot for that tip about checking wedge with a jack and socket, could be very helpful for a rough estimate until we get it on some scales

we have a friend thats giving us a bunch of springs for the front/rear, I have no idea what the springs will be until we get them in the next day or so, going to get the ride height up enough so it will not bottom out front and rear, hopefully some stiffer springs up front and softer in the rear

no bars are allowed to touch the frame past the bellhousing bolts, however we did run bars from the main cage to that point on the frame, then bars from the front of the car to just about touching the downbars, were not sure if the techs would let that slide but they passed it, no weight jacks or any kind of adjusters of any sort are allowed

we are running the same tire stagger that everyone else seems to say they are running on the rear, all 4 tires must be the same except for the first number, can run 225/70 and 215/70s for example, but not 15s and 14s, or 75/70 for example

as for the powertrain setup, 40 over 350 basically all stock with 882 heads and a 450lift isky oval track cam, brand new factory q-jet, running a 3-speed saginaw factory clutch/PP pulling the track in first gear, 2.54 with a 2.73 ring/pinion, not very big on power for the setup works VERY well together for this track, if you can keep it collected through the turns it pulls extremely hard all the way

that is also part of the problem, very unforgiving throttle response with the loose condition of the car, it loves to go sideways


thanks for the warm welcome and help everybody!


PS, picture of my car if anyone is interested, note that the tires in the picture were only temporary, it has slightly smaller tires now, 225/75s pictures, currently running 215/70s

http://i.imgur.com/B1EEB.jpg