yardpro

ok.... so i autocrossed for the first time this past weekend.

i had much more understeer than i remember from my previous sporty driving..

I am replacing my tires (the inside of the ones are chewed up from misalignment)..

I am wondering what i can do suspension wise to help reduce the understeer.

I realize that tightening the loose nut behind the wheel is the best way to go faster, but i am looking for some other tips as well...

RKD in OKC

Where is the car understeering, ie. turn-in, mid corner as you apply gas, or corner exit?

First, Get the new tires you are planning to run and have the car aligned at the aggressive end of the stock specks. (most alignment places will not align outside of the stock specs.)

Then get a cheap one of the infrared temp guns. Check temps across the tread as soon as you can after a run. Set tire pressure so the temps are even across the tire. If middle is hotter less pressure, if edges are hotter, more pressure. Tires will gain a little pressure every lap. Higher temps on the outside (not edge) of tread shows it can use more negative camber. Higher temps on inside (again not the very edge) tread shows too much camber.

Once you find the best tire pressures at the stock alignment you can start messing with more aggressive alignment (if needed see temps above) and suspension.

The most import ant thing that will effect your times is mid-corner car balance. A good way to check this is to go out in a big empty parking lot and drive around in a circle the size of the average turn. Slowly accelerate keeping the steering input fixed. Take note which breaks loose first the front or the rear. Do it several times. Get comfortable maintaining your circle without steering input at the point the car breaks loose. Play with the throttle at this point. Give it gas see why happens, after you give it gas lift abruptly, see what happens. You will get a feel of not just whether the car is understeering, or oversteering, but how much. I try to do this first with the anti-sway bars disconnected (one side on each). This lets you know how well the springs and ride height are balanced. Adjusting the ride height can help here a little but not much. Any spring set you have should be fairly closely balanced.

Once happy with springs and ride height adjustments for good mid-corner balance. Connect up the sway bars and repeat the circle thing. Whichever end is loose, tighten up the other end. When balanced, note speed the car breaks loose and tighten both ends a little until you see the speed start to drop, then back them off a bit. You may run out of adjustment or not be able to adjust your sway bars. I have the DEVEK adjustable front bar and Ott Steroid drop links in the rear. Both are adjustable.

The last thing is to adjust the dampers or shock rebound. Springs are for compression, dampers control rate. For the Front rebound (if adjustable) do the circle thing again and punch it. If the front lifts and the car understeers firm up the rebound to keep it down. If the front doesn't feel like it is lifting and the rear tires spin to easily soften the front rebound. The rear rebound is a little more difficult to set. Brake hard into a corner and strait to turn in. If the rear does not get a little loose or you get understeer as you turn in soften the rear rebound. If the rear gets really loose under braking before you actually start turning in, firm up the rear rebound.

So the sway bars adjust mid-corner handling, the front rebound corner exit and the rear rebound corner entry.

Andre Hedrick

http://www.928motorsports.com/parts/...rame_brace.php

I have this on mine and I can now point the car, there is still minor low speed under steer, but once you hit the power, the over steer takes over and that is easier to feather, imho.

yardpro

thanks guys...

i will play around with the suggestions.

brutus

Most Autocross courses are too tight and too slow for a 928 to actually do well. The size and weight makes quick changes in direction a challenge. You will find out that to get the car to rotate you may need some power induced oversteer created by pushing down your right foot.
Also if you turn in too abruptly it upsets the balance trips the car and causes gross understeer with much squeeling of the front tires. Max out the negative camber dail in maximum caster and spend some time on tire pressure and temps.

yardpro

i agree that the 928 in not an ideal autocrosser...
i want to do a few of these before i do a DE.

thanks for the tips

Dave928S

RKD has given good step by step advice ... the key is to be methodical and work through things one at a time. Never alter more than one thing at a time, or you won't know what effect you're getting from individual changes. Making sure there are no defective parts, and setup to aggressive stock is a good starting point.

RKD in OKC

A really good setup for autocross will be loose at a DE. Setups have a range of corners and speeds they work well in. The tighter and slower speed corners more understeer, and bigger faster speed corners oversteer. Mostly sway bar adjustment. That's why I recommend when driving circles to setup the car to choose a radius that is the average corner of a typical course.

Speedtoys

Good DE's have total novice levels where the last thing you'll be doing is WOT runs down the track anywhere.

http://nasa-se.com/
http://nasa-se.com/hpde.php

brutus

I am not sure that autocross helps much with doing a D E because most DE is done in 15-20 minute sessions with other cars so just go on out to a DE get an instructor and listen and learn. Typical autocross you get a few minutes of runs, good DE you get many times that hour hour and a half per day . Plus no stupid drag racer launch to start the run and you get heat into the tires to make them work. The way to drive an autocross would shred the tires in a 15 minute D E session it is really that different.

yardpro

i raced motocross for over 20 years. I also raced hair scrambles. like DE and Autocross they required VERY different setups and riding styles..

I am starting out with the autocross because they are close, low cost, and they will get my feet wet.

Thanks for the advise. My next event will be in a month, so it will give me some time to work a few things out...

brutus

It is ALL good fun just get out and do it ! Be aware that new full tread depth tires are NOT going to like agressive D E driving it rips chunks off the edges off the tread blocks in about 15 minutes !

Speedtoys

Some tires..ya..but your first day, especially being as cautious as the OP would be, I wouldnt worry bout it.


I fear for people generally stepping into thier first DE at about 'group 3' speed, of four.


The worlds faster sprinter..started by crawling.

These are wise racing words to live by.

fbarnhill

STEVEN, any way I might be able to get in on the next one if Anne is ready to be alone for a day?

Just thought I would ask... I am an autocross virgin...

fbarnhill

Oh, one more thing, I managed to light the tires today leaving a right hand turn and it was just heaven to have that dear loving tire smoke in my nose again and that symphonic sound of our wonderful V8s. My car sounds unusual with the stock exhaust. I think I may even like it. It is somewhat quiet but kind of growls like a dog getting ready to eat your A&(*)%. I wish I could hear one with the xpipe and stock rear muffler to see if I am going to like the sound.