Steady State Understeer and Stiffer Rear Springs
 

Hey all,

After researching causes and solutions, I feel my best bet is to change my spring rates. Currently on Tein SS's, I have 8/6 F/R. We could go into a book, I know, on solutions but don't really want to do that in this thread. Let's just focus on springs.

Question: Is it best to increase the rear spring rate or lower the front spring rate? My initial thinking is to go to 8/7.

Ben

I'm surprised you have steady state understeer with those spring rates.

Some more info would be helpfull:

Is this on an FD?
What are the tire sizes?
What sway bars are on the car?

Being that this is an LT1 conversion, and the bias is now 52/48 may have something to do with it.

Lets see if this helps:

FC
Camber set for good tire temps at track (-3/-1.5)
245 front / 255 rear
1-1/8 bar up front/bar delete in the rear

What kind of wheel rates are you getting with those springs?(it looks like you may have your corner weight info) My first thing to try would be to soften the front bar if you can. The rear springs would be the next on the list if your ride rates won't get too far out of whack.

Since my RX7 experience is with a rotary powered FD, I can't offer specifics, but here's some general thoughts.

It sounds like you have done some good work in alignment tuning, getting good tire temps! Way ahead of many.
What's easiest to do for you?
Adding a rear sway bar should help.

You are correct in that either softer front or stiffer rear springs will help understeer. As for which to do in your case, hmmm... How's the overall stiffness of the car? Too stiff leads to compliance problems over bumpy sections of track, and you don't want the springs stiffer than your shocks can deal with. Is it more for track use (leans one to stiffer rear) or street (comfort says softer front).

Ahh, the endless suspension tuning game goes on!

Sorry no corner weights. I am not familiar with my options on bars and assume that a stock bar would be too soft. I guess because I don't have an ajustable front bar, the back springs seemed easiest.

I tried the rear bar delete technique and my times went down mainly because I am able to power out of corners earlier and the rear stay planted with over 400 ft-lb of torque.

It has been stated that you adjust the area that is giving you problems. understeer, adjust the front. So from my point of view, I don't want to soften the front but stiffen the back. This is counter to good racer logic and wanted to hear from others on this.

Appreciate it,
Ben

I suggest. Stock swap bars. No more than -2.0 camber on the front. and possibly 245's or 255's all the way around.

Easiest at this point would be to try adding stock rear bar and see how that goes.

Or, I'll be the first in the thread to mention driving style... A steady state understeer may not be a bad thing with an LT1, you have enough power to bring the rearend out at will. A slight oversteer is just a right foot away!

HE has no rear swaybar because he was tyring to get grip out of it?

I have heard of evos using tein springs and getting some fugly undesteer. Stock springs are way better than tein for evos.

It has been indicated on this board to try it with an FC and in my case, it did work to keep the rear planted when exiting the corner. Times went down because I was able to apply more power sooner. It was indicated that it has something to do with the rear suspension dynamics of an FC.

I can agree with you to a point on having V8 torque available will counteract the understeer. However, the issue that I feel I have is a feeling of the car "maybe" even pushing on exit and full throttle. Hard to explain with my limited experience racing. However, the understeer is very apparent at steady state (corner apex).

I would agree going with 255's all around probably would come close to solving the problem but right now that is not a cheap option as I would need new rims. Only 8" up front.

Irentat. I had the same problem on my last event.
MY conclusion came down to getting a 9" rim up front with 255 or 245. I also run a 255 on the rear.

I know how u feel. U hit the gas. The chassi sits on the rear wheels and pushes the front with nasty understeer.

Toe settings?

Toe settings shouldn't make a huge difference in steady state cornering. It mainly effects: tire wear, high speed stability, and corner entry. You could always try some toe out and see if it helps, but I would check your tire temps and see if you need more camber.

Disagree. It can explain corner entry (as you said), steady state and corner exit understeer (or oversteer), too. And don't forget part of toe is getting the thrust angle correct. And we haven't even talked about the affects of rake, yet.

Too much toe-out turns you in to a snow plow, with enough power you'd never notice going straight, but you'd really notice it fighting you through the corner.

I agree with jgrewe, though, that the most common cause of apex and corner exit understeer is driving style... with a V8 in the car hitting the gas at the apex should result in some nice oversteer, and not further understeer, though, unless you really over-cooked it, or there's a set up issue. But chasing this with rear spring seems like the wrong approach since the rear sounds great right now, it's planted. It's front grip that's the issue...

Exactly.......

Let's talk front toe out.

Before these tires, I had toe 0 with 225/255 F/R. With that setup, I had lots of understeer in steady state but could swing the back around with the V8 torque on exit.

Referencing this discussion and continued understeer issues, I went with 245/255 with some toe out...approximately 5/16". I did not realize that my toe out could cause pushing (again newbie to road racing).

Based on the new advice, I will change to 0 toe to determine if this makes a difference before I go with springs.

Ben

5/16" !? Damn, that's *a lot* of toe-out. I wouldn't even run 5/16" toe-in in the back to keep oversteer under control.

Try somewhere between 1/32" toe-in and 1/16" toe-out in the front. 1/4" toe-out *might* work on an autocross. Try somewhere between 0 and 3/16" toe-in on the back.

Keep in mind that I'm just coming back to my FC, but those numbers are where I'm going to play to start with. Maybe somebody else can pipe up a bit.

Also, you could raise the rear a bit, or drop the front a bit, to get more front bite. Rake can play a huge role in this stuff. Have you done a corner weight?

Are the struts/shocks adjustable?

If the problem truely is steady state shocks are out of the equation.

It sounds like alignment will be a step in the right direction before changing parts.

Yes. This is why I specifically indicate steady state understeer as compared to transitional understeer. Transitional I have been able to compensate for easily with my adjustable Tein's.