Another First Auto-X & Tire pres questions

[Mrmaddbrad]

Heres a quick, super general guide to tire pressures:

1. Less PSI means more grip.

2. More PSI means less tire roll.

3. Play with them to learn what works.

4. When it comes to boxsters, count your blessings when the rear breaks away before the front at an autocross. It seems they all understeer like crazy.

NOTE:
You're tire pressures may be fine. However; playing with them helps to learn your car. Different weather and driving conditions will always make your car behave differently. As a SCCA national champion once told me "Even if your tire pressures are right, if you're not driving your car properly it may seem that they're wrong."

Best of luck,
~Brad

[jb92563]

Thanks for the tips.

I guess I need more grip in the rear so lowering the pressure a couple PSI may help that.

Since the fronts are sticking well, my turn ins are very sure footed with the help of brake to load the front tires, but the rear tends to come unstuck as the direction change completes so perhaps I need to get on the gas sooner as well to load up the rears to keep them stuck down.

I think I'll start a notebook to track what I did and whether it improved things or not.

I'll drop the rears 1 psi to 35psi for next time out.

Next I need "Harry's Lap Timer" so I can video and analyze what I did that day.


I was hoping to get a lot more feedback but perhaps the racers are on other forums?
Is there a busier Racing tips forum somewhere or do the racers share no secrets in general?
Just trying to learn and am looking for more info on tuning tires.

[san rensho]

Originally Posted by jb92563

Thanks for the tips.

I guess I need more grip in the rear so lowering the pressure a couple PSI may help that.

Since the fronts are sticking well, my turn ins are very sure footed with the help of brake to load the front tires, but the rear tends to come unstuck as the direction change completes so perhaps I need to get on the gas sooner as well to load up the rears to keep them stuck down.

I think I'll start a notebook to track what I did and whether it improved things or not.

I'll drop the rears 1 psi to 35psi for next time out.

Next I need "Harry's Lap Timer" so I can video and analyze what I did that day.


I was hoping to get a lot more feedback but perhaps the racers are on other forums?
Is there a busier Racing tips forum somewhere or do the racers share no secrets in general?
Just trying to learn and am looking for more info on tuning tires.

If you are on the brakes as you turn (trail braking) then that explains the rear coming out. Trail braking does that, which is one way to get around understeer.

[stephen wilson]

I've only done one autocross, but noticed that the quick transitions of slaloms make a normally understeering car oversteer. Sort of like the "scandinavian flick" in rally racing.

[jb92563]

Originally Posted by san rensho

If you are on the brakes as you turn (trail braking) then that explains the rear coming out. Trail braking does that, which is one way to get around understeer.

I brake before any turning takes place like we were taught in the PDS except where I end up coming in too hot every now and then and I definitely know my mistake at that point and the consequences of breaking in any part of the curve.

I mostly noticed my rear tires loosing grip a bit in a big sweeping curve while accelerating.
It was throttle steering through most of that part and the instructor felt the tires weren't "locking up" as well as they could.
To make matters worse the track was banked AWAY from the inside of the turn.

He mentioned adjusting pressure but did not say which way before he had to jump in his own car to grid for his laps.

[thstone]

Originally Posted by jb92563

... my turn ins are very sure footed with the help of brake to load the front tires, but the rear tends to come unstuck as the direction change completes so perhaps I need to get on the gas sooner as well to load up the rears to keep them stuck down.

Braking too hard and too late can be detrimental by putting too much weight on the front and causing the car to be unbalanced in the turn. As you note, turn in is great but then the rear slides around. We've all experienced this condition at one time or another.

Next time maybe try to keep the car more balanced by braking smoothly before turn entry and then getting back on the throttle smoothly as soon as possible (by end of turn entry or at the start of the middle of the turn) to keep the front and rear balanced. This technique will get weight back onto the rear tires as early as possible and also allow you to throttle steer through the middle and exit of the turn which will reduce steering wheel input, tire slip angle, and understeer which all serve to slow you down.

Last, remember not to pinch the turn entry and unwind the wheel as soon as possible on turn exit. The tendency of new track drivers is to try to overdrive the car which tends to result in a lot of understeer. Unwind the wheel and let that beast free!