Learn Me: How to cure FC RX7 understeer

Okay specs are:

Tokiko blues stock springs 1/8" toe out front AND rear 2.8 deg camber front 1.5 deg camber rear

old worn bushings everywhere.

Stock front and rear swaybars

The car is VERY pushy! We started the practice day at Monticello motor club with no rear sway, 1/8" rear toe IN. We quickly put the stock rear sway back on. it helped. We also made the rear toe out. It helped. Finally, we got some old circle track spring rubbers and modified them to fit the rear springs. This also helped.

Why is the car still pushy? I hear the hot setup is toe IN at the rear and no rear swaybar. We are soo far off of that right now.

We run this car in Lemons and Chumpcar. all solutions must be cheap / free.

What I was thinking was to fix some of the rear bushings with stock new bushings. I was also tempted to get some ST rear springs (120# rate vs stock of 80#).

What say you O gurus of the RX7?

Thanks!

Rob R.

Also, has anybody rebuilt an rx7 or Miata trans before? Any links on info / how to?

What kind of tires do you have and what pressures are you running?

In reply to wvumtnbkr: While I don't have the same setup as you even when the car had standard suspension it never understeered that much. Could this be a tire problem?

Crap. That would be important info.

Star Specs (Z1) 205 50 15 stock wheels.

38 hot front 37 hot rear.

Where is it pushing? Corner entrances? Steady state? Corner exit?

Steady state. It turns in "okay" then it just kinda gives up. Corner exit sucks as well. Power on or off does not matter. Obviously if you slow down, the front will grab a little better.

Rob R.

Tire temps?

My guess would be a lot of roll up front. Any pics of it pushing steady state? Lemons solution would be: Remove front bar, weld a piece of angle iron to it, reinstall.

Just guessing though.

Stiffening the front to reduce understeer? That doesn't sound right. I would suggest try removing / disconnecting the front bar and see what that does.

Have you considered the possibility the FC's rear steer is part of the issue? Or have you disabled that? I believe it works by causing toe in in the rear, that would certainly cause a push.

Thanks guys!

No idea on Tire temps. I would like to not stiffen the front.

The rear steer could definitly be an issue. I have the eliminator bushings. I will do that as well.

Thanks!

aircooled wrote: Stiffening the front to reduce understeer? That doesn't sound right.

Depends whats causing the understeer. Lots of cars get understeer from excessive body roll. A huge front bar will mitigate that and keep the rear tires planted. It may also provide enough roll stiffness to run no rear bar to keep the drive wheels planted (like the OP mentioned other cars are doing).

Its pretty common to see autocross cars with monster front bars in stock-class, which would be pretty similar to the restrictions from the OP. Wouldn't surprise me to see a similar setup on a track car.

If trying to do fix this with just sway bars, the front needs to be bigger.....if it was tail happy as hell you'd want to remove the front bar.

Conversely, possibly evening your tire psi's out could solve your problem. You could have too much grip with the rear end.

My thinking was stiffer rear bar takes grip away from the rear and "adds it" to the front. Stiff front bar would do the opposite.

Am I wrong on this?

Thanks,

Rob R.

Different levels of mechanical grip will make an FC understeer like crazy. I had 205 on the front and 225 on the rear with a 2 way locker. That thing would understeer all the time. As soon as I evened out the tires to 205 all around things became much more manageable.

In reply to wvumtnbkr:

Depends on the chassis.....most FR layouts use the front bar for oversteer, then a smaller rear to somewhat control it. Most fwd setups need a bigger rear bar to help get rid of understeer.

On that note, does your car have a rear sway bar?

We had it off to start the day. That was bad. It pushed very much badly.

When we hooked it back up, it was better.

wvumtnbkr wrote: My thinking was stiffer rear bar takes grip away from the rear and "adds it" to the front. Stiff front bar would do the opposite. Am I wrong on this? Thanks, Rob R.

That's basically true on a well-balanced theoretically ideal car (due to changing weight transfer rates front vs. rear), but in practice it's a lot more complicated and you can get seemingly "backwards" effects like this.

wvumtnbkr wrote: We had it off to start the day. That was bad. It pushed very much badly. When we hooked it back up, it was better.

The front bar? If putting the front back on made it better, you need to stiffen the front bar more.

GameboyRMH wrote: That's basically true on a well-balanced theoretically ideal car...

Some would say, that describes an FC very well. As stock, they are very close to 50/50 weight distribution. Generally, rear roll stiffness will add to mid-corner oversteer. As noted, things get complicated.

No expert, but maybe the heavy front bar oversteer cure is most effective on front heavy cars?

yamaha wrote:

wvumtnbkr wrote: We had it off to start the day. That was bad. It pushed very much badly. When we hooked it back up, it was better.

The front bar? If putting the front back on made it better, you need to stiffen the front bar more.

No, the rear bar. I was refering to your post asking if the car had a rear bar.

Thanks!

Rob R.

Report back when you eliminate the rear steer. That needs to be eliminated before tinkering with anything else.

Yeah the rear toe system does introduce some poor handling in racing situations.

Which differential?

aircooled wrote: No expert, but maybe the heavy front bar oversteer cure is most effective on front heavy cars?

Its not black and white - bars are just one piece of a system. Bars can tune balance, but they can also add a E36 M3 ton of roll-control to a car with soft (stock) springs. A lot of FR autocross cars running huge front bars are not what I would call front heavy: E36 M3, S2000, Miata, RX8, 944, etc.

Its an easy test. Get a spare stock front bar (which has to be cheap) and get some 1/8" thick 0.75" x 0.75" angle iron, weld it onto the straight section of the bar, install, drive.

From an ES 944:

I thought I knew a lot about suspension dynamics before I joined this forum. Embarrassing as it may be, I'll admit I've never tuned a suspension on a car that had performance tires.

All of my tarmac experience (with the exception of 1 autocross event where I ran nearly corded hand me down RA1's) has been with my Scoob (No RSB) on 640 treadwear, all-seasons sized 195/75-14. I was on a flugelbinder budget and the car was stock so I ran in H-stock. The actual pressures varied but I usually ran 45+ psi in the fronts and about 30 psi in the rears. These tires had tall, soft sidewalls so my strategy was to prevent rollover with the fronts and allow it to happen to the rears. It actually worked quite well. Some fellow cone-heads told me I had it backwards so I tried over-inflating the rears but I found it less predictable and too "skatey" feeling.

I eventually got tired of the lack of negative camber up front so I bought some smaller diameter grade 8 bolts and dialed in just under 3 degrees, then set the toe slightly out. Then I snagged a set of used RS struts and some Legacy coils from the junkyard. I cut the coils (dumb, I know) and went back to dodging cones...still on the same soft-sidewall, hockey puck tread tires. It "handled" quite well but the overall level of grip was much better than stock but still rather low compared to those who ran Azenis or Ecstas.

Anyway, have you put some shoe polish on the shoulders and checked to see if the tire is rolling under or if you're using the whole tread? That's what lead to my inflation strategy.

Or, do you have a pyrometer?