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View Full Version : Setting up a 94 Celica GT for autox?? (I want neutral to oversteer)



cwatson
01-20-2011, 10:30 AM
I'm going to start getting into auto-x this year with the celi. My autox experience lies mostly with mid engine RWD high downforce formula cars (FSAE, 2+ g on higher speed corners). I ran the Celica once at a driver school and it was unpleasant to say the least. Simply pushed everywhere - braking, lift-off, and, obviously, on throttle.

I would like the following characteristics: neutral to very slight oversteer on constant speed, constant radius turns. Neutral to slight understeer on corner exit. Slight oversteer when lifting the throttle in ~2nd gear. Moderate oversteer on quick transitions (slaloms) and during heavy braking.

Car is stock. Ran on terrible tires, 205/70/r15 front and 205/60/r15 rear UTQG ~ 600. 205 or 195/50/r15s should help with the balance by getting the roll center to cg distances back in check but I imagine the understeer won't go away.

First thing is tires. I'm going to get a new set in a week or two because my sidewalls cracked on the fronts and the rears are gone. Probably going to go with 205/50/r15 Yokohama s.drives or similar because I will be using them on the street. I will get r-comps in the future if I feel like the car has potential to handle well. On that note, I will be doing or getting an alignment. Does anyone have recommended toe settings to improve turn in? Camber is tire dependent but what have you all had luck with? What camber adjustment options do I have?

Grip comes from the tires, but balance (and lateral g force) comes from controlling the steady state and transient lateral load transfer distribution (LLTD). To remain in SCCA G stock class, I am allowed to remove the front roll bar and change the shocks. Removing the front ARB will decrease the front roll stiffness and move the LLTD rearward, but is it enough to get a neutral balance in steady state?

As for shocks, I am considering the koni yellows because of cost, reputation, adjustability (Can't consider changing spring rates without adjustable dampers). While the single-adjustment shocks could help slalom performance, bump damping will be ruined without a corresponding spring rate change. Shocks will do nothing to help with steady-state cornering. Decoupling bump and roll damping would require 4 way adjustable shocks which I am not willing to pay for.

Do the konis for our cars have different perch settings? I could raise the rear and lower the front to (susp geometry allowing) decrease the front roll moment and increase the rear roll moment which would help more with balance.

To summarize:
Where in this sequence of modifications would I get a neutral balance?
1. Crap tires (205/70 fronts, 205/60 rear) to good UHP summer tires (205/50s)
2. Remove front ARB
3. Lower front and raise rear with adjustment range of koni sports (yellows)
........at this point the car is out of G stock and in to some street modified or prepared class.....
4. Add rear ARB
5. Spring rates
I should be able to have add enough rear stiffness by this point to lift the inside rear. Do our cars oversteer before they lift the inside rear at stock height or do I also need to lower the CG (to lower overall weight transfer and allow higher rear LLTD before lifting inside rear)?
6. Slam car
7. Give up and buy RWD car

I'm hoping some of you guys have experience with getting the proper balance and it would be great if you could tell me what it took for you to get there. Numbers are welcome...nobody happens to have mapped out the suspension? cg height, roll center heights, roll stiffness, wheel rates...anything helps.

Thanks in advance,
Chris

bloodMoney
01-20-2011, 06:53 PM
I had a nice long answer for you, but it got erased when the board logged me out....

So, the short answer is NO. None of the engineers here have mapped out the 6g suspension. I know that I after I pulled the front strut tower bar and put some good tires on mine, I was fine on the Dragon. You are going to have to be the first if you want this info. (feel free to share)

As I already have Eibach ProSports on the car, my next plans for my car is to get adjustable dampers or coilovers, a rear strut tower & ARB and maybe a trunk brace to really stiffen things up in back.

KoreanJoey
01-22-2011, 07:04 AM
As far as mapping the suspension... yeah... that doesn't really do anything to help your cause. Numbers are great but results are better. You can check the camber curve pretty easily but it's dynamic VS roll so it's still a play with it til it's right sort of game. It's a McStrut car so the camber curves blow, meaning you'll need some static camber and stiff springs in order to make any real handling with the car.

I think ditching the FSB is a bad idea since there is so much weight on there that it'll slow transitional response unless you go seriously high on the front spring rate (but that's also sacrificing overall grip).

Truthfully it's a FWD car... you want to autocross it, easy solution. Get the front to transition as you'd like with a soft a spring as you can go. Set the rear about 10-15% over the front (against weight balance; My 5th gen GT coupe was 63/37) and play with toe-out settings in order to achieve a level of oversteer that you can stand (I had the rear .25* neg). It helps to have a good LSD in order to bite in the front. Use a bit of lift oversteer or left-foot braking before the corner entry and use the throttle to induce understeer to balance out the car. It's the only real way to drive an FWD fast. If you're finding that you're having to countersteer too much start backing off the toe out (a little goes a long way). Be prepared to spin... if you don't, your car is probably slow or you're not trying hard enough.

cwatson
01-28-2011, 08:49 AM
Sorry for the late replay, I appreciate your responses.


As far as mapping the suspension... yeah... that doesn't really do anything to help your cause. Numbers are great but results are better. You can check the camber curve pretty easily but it's dynamic VS roll so it's still a play with it til it's right sort of game. It's a McStrut car so the camber curves blow, meaning you'll need some static camber and stiff springs in order to make any real handling with the car.

I think ditching the FSB is a bad idea since there is so much weight on there that it'll slow transitional response unless you go seriously high on the front spring rate (but that's also sacrificing overall grip).

Truthfully it's a FWD car... you want to autocross it, easy solution. Get the front to transition as you'd like with a soft a spring as you can go. Set the rear about 10-15% over the front (against weight balance; My 5th gen GT coupe was 63/37) and play with toe-out settings in order to achieve a level of oversteer that you can stand (I had the rear .25* neg). It helps to have a good LSD in order to bite in the front. Use a bit of lift oversteer or left-foot braking before the corner entry and use the throttle to induce understeer to balance out the car. It's the only real way to drive an FWD fast. If you're finding that you're having to countersteer too much start backing off the toe out (a little goes a long way). Be prepared to spin... if you don't, your car is probably slow or you're not trying hard enough.

I wish to stay in a G stock class because that is where I have a chance of being competitive. Springs, rear ARB, engine, trans/diff, and weight must remain stock. I don't think I am going to get dampers this season (too much $$). That leaves tires, alignment, front ARB, and driver mods.

I agree with your statement on trying to keep the front ARB. The car already rolls too much as is...wouldn't want to exacerbate any camber or bump steer problems.

Is changing the rear toe the correct way to get the car to oversteer? A change to the rear end that is independent of the front and results in oversteer may mean grip is reduced in the rear rather than increased in the front or transferred rear to front. Or is rear toe out decreasing the rear yaw moment without affecting the force towards the turn center? Grip needs to be maximized with alignment and pressures (with allowances for transient response) and LLTD is then modified to achieve the desired us/os characteristic. However, toe out should certainly help with transient response and the rear end has a pronounced phase lag (in yaw) behind the front in my car. I'll map this in planview (only need WB/Tracks, and long. CG. Will assume slip angles) to see what is happening with increased rear toe.

So, I picked up a set of slightly used Potenza RE01Rs in 195/50/15 that will go on the stock rims. Will be mounting the tires once the temps come up a bit (in MD). They are a bit worn on the outside but full tread on the inside and center. How much camber does the stock car need front and rear to keep even temperatures at ~1-1.1g steady state. If anyone knows the stock spring rates, I can probably get pretty close with some basic calcs. I will obviously need to modify the alignment after getting on track but would like to get it close so I can determine if I need to go up or down on the front ARB. I will probably build my own based on how the car handles with the new tires mounted. If I have to build a bar, I will map out the suspension while I'm at it FYIW.

There is some hope I think...A friend just loaned me a couple of all seasons (Khumo ASX) in 205/55/16 that I put on the rear. I put my no name (Shadow?), almost worn rears in 205/55/15 on the front and can get the car to really oversteer (the kind you have to recover) if I flick the wheel. 30/40 psi F/R.


Be prepared to spin... if you don't, your car is probably slow or you're not trying hard enough.

Sound advice. This is what I tell all the new guys driving the formula car.

edit: What is the range of camber adjustment for the stock bolts? Where can I get the 2 or 3 dot crash bolts?

KoreanJoey
01-28-2011, 10:28 PM
I believe there is a tsb available for smaller bolts. With the 3 dot crash bolts fitted to the 90 gts I can easily get to -2*. Lithia can get them for you. Sadly the Celica isn't going to be able to compete with the Genesis, even with it's size and weight the stock tires can fit some pretty meaty tires and it does have a substantial power increase over the Celica. Honestly I don't know how the 94-99 is in GS vs the 87-93 is in HS even though they're very, very close in specs.

*shrug*

Even going into ST you'd be against the Civics and the CRX which... isn't really fair.