Fairly bad understeer, is this normal? Need help before auto-x meet!
 

Ok, I have an 88 TII with a few minor suspension mods done by the previous owner. It has Eibach lowering springs (a pretty minor lowering job), and tokiko (SP?) shocks, both about two years old, as well as a front STB. The tires are 225 Yokohamas all the way around, with the rears being slightly worn.

My question is this:

While playing around in the parking lot getting ready for the first autox this year, I noticed the car has a tendancy to "plow", AKA understeer. Is this normal? I was practicing at fairly low speeds, is it possible that the steering was turning too far or something? (I'm not sure how the steering works on a TII). Does the steering rate increase/decrease based on speed?

Any info (and tips) you guys could give me would be great, I am the only RX7 running this one and I'd like to at least make a good impression:D

Yeah, from what I've noticed, FC's tend to understeer. Especially at lower speeds. Try ridning the brakes into the turn to keep the weight more forward. That should help somewhat to keep the front gripping.

Tire pressures?

To compensate for the push, recommended tire pressures are around 36 to 38psi front, and 30 to 32psi rears.


-Ted

Try an alignment also.

Rob

Does it still have the DTSS bushings?

ted is right about the tire pressure - this is the easiest way to change the overall balance of the car. try out different combos and see what works best for you (front to back, left to right).

Also, it would be a good idea to put a dab of shoepolish on your tires so you can see how much the tire is rolling over.

You put two marks of shoe polish on your tire. Start just where the tread touchs the pavment and put a small strip towards to the sidewall. Make these marks opposite of of each other. This will help you nail a tire pressure for the day.

Also, if you are pushing. Slow down before the turn. In slow out fast.

James

I agree with the tire pressure comments. But take a look at rear camber. These cars tend to sag in the rear over time. And if you have lowering springs you may have too much camber in the back (relative to what you have in the front). Too much camber and/or incorrect toe in the back will cause understeer.

Rob

Cool, thanks for the replies guys! I'll see if I can't get this worked out before sunday.

I had the same understeer problem on my GXL running 205/50-16s on stock TII wheels and stock TII struts. I increased my neg camber in the front by repositioning the dots on the upper strut perches to the inside rear, loosening all the front mounting hardware slightly and retightening with a friend torquing the wheel toward neg camber. With no other changes, it now oversteers slightly with the throttle off and rides dead neutral under partial throttle. :D

That was actually really helpful, thanks!

Nice link. Thanks!

I have been troubling with this ever since I autox crossed my car, I'm assuming it has something to do with my Suspension tech springs I believe there 140 all the way around, which prolly makes it worse, I really wanna kick those damn Z06s asses!!!

when autocrossing my TII I found the best setup was with about 44PSI front and 36 PSI rear... The car tended to be a bit of a handful though so maybe even 38PSI rear wouldnt' be bad...

that's the most correct thing i've read in a long time.

stop trying so hard. i went to an auto-x one time and this guy with a 4th gen camaro had HUGE yoko AVS sports on 17's and was pushing all over the place. i told him to slow down and he took about 8 seconds off his times.

My '88 TII with stock suspension pushes like a bitch.

Like others mentioned...slow down before the turn and get that weight transferred to the front.

I have an autocross coming up on the 3rd and will again be fighting the understeer battle. Blah.

also, i don't suggest being on the brakes while turning, yes, you might be putting more weight up front but a lot of the cornering traction is being used up by braking traction. using all the tire for cornering will yield the best cornering speed.

This is a very advanced braking technique called "trail braking", and it does have its uses in autocross.


-Ted

well, i always thought trail braking was for higher speed stuff, never really thought it could be applied to autocross.

when watching autox events, i notice some guys turn way too much causing understeer. just try to keap the wheels from understeering by not turn so much, the brake idea sounds like it would work, or mabey just have a little fun and drift all the turns

Keeping wide angles helps alot. This means dont run up to a turn, then slam the wheel. That is asking alot from the car. You have to gradually tranfer the weight to approach the turn.

Mechanically, rear-steer (DTSS)eliminator bushings are supposed to make a massive difference in rear end predictability. The fact that they are cheap helps too. :D

just wonderin sry if this dosent belong in this thread. but where do u guys go to sign up for auto x. i juss recently bought a rx7 and am goin to start learnin how to drive and wut not juss wonderin how easy it is to get into auto x or whever about it is. i live in so ca

your quit right, depends on the corner, if its a decreasing radius corner, then you might want to trail break a little more, but if its a increasing radius corner, you might want to trail break less. but yeh like fstrnyou said, it works best at higer speed straight leading into a hard corner. but it seems best to lift off the gas, and apply light breaking, slow down enough, to make the turn at the best possible speed, if your on the breaks hard you tend to loose too much need speed.

Note: to give your car more understeer, stiffen up the back suspension (more then the front) and give the front breaks more bias. hope that helps you out.