Squeezer

Over the weekend at an Auto-x there was a very mild but wide curve to the left, but it was enough to make the car lean a little with stock suspension. The curve was gentle enough I could accelerate through it, hit 9k rpm and shift to 2nd and still have more room to accelerate before I had to break for a tight box. When I shifted from 1st at 9k into 2nd, the tires would bark (i'm running kumho escta 712's) and the back end would pull towards the right. is this normal? when I shift from 1st at 9k rpm to 2nd while going straight, the tires don't back and the car doesn't jerk, so why does it do this in a curve? is it because of intertia, LSD, and tranny trying to sync the synchros and engine revs? i don't remember other cars barking theit tires when they shifted in this curve.

glagola1

Wow, where to begin... I'll try to sum it up but you should go buy a book called "Secrets of Solo Racing: Expert Techniques for Autocross and Time Trials" and read it.

Anyway, when you are cornering you are putting more duty on the tires. They don't like to be upset while they are at the limits of traction. When you are accelerating the weight is shifted to the rear of the car so the rear wheels have more traction. When you "lift" off the accelerator, you are lessening the traction because the weight of the car is shifting more to the middle. When you slam the clutch back and the gas down, you are asking the tires to do more than they can handle so they slip for a moment. Once they grip all is fine.

You don't notice this while going in a straight line because the tires aren't being asked to prevent the car from sliding sideways. They are only doing one job so the available traction is greater.

Trust me, you should get that book and enter every event you can.

GamecockS2K

If this turn was any tighter or if you were pushing any harder you probably would've spun shifting in a turn like that! Not usually a big deal on an autocross course and definitely a good place to learn; however, just a note, you generally don't want to lift (take your foot off the gas) in a hard turn. That shifts the weight of the car from the rear to the front, causing the rear to 'get light' and not want to stay in place, which in turn (excuse the pun) causes you to see the part of the course you just came through!

No biggie, as like I said, autocross is definitely the place to do this stuff. The best way to learn is to get seat time and talk to experienced drivers! Keep going out there and having fun, just be careful on the street because a quick little mistake like this could cost $!

Squeezer

so should I have stayed in 1st and not shifted and kept it at redline, or been in 2nd before the curve started even though i'd be below 6k rpms but may have ended up at over 6k rpms when i need to start breaking for the tight box, or kept my foot on the gas while shifting instead of letting off the gas?

glagola1

I think you did the right thing by shifting. If the turn wasn't severe enough to cause a spinout during the shift then it's correct to shift, especially if you're at redline.

There is no tricky way like keeping the foot on the gas to perform this shift without disturbing the car. you did the right thing. Don't worry about it.

Now if you were hauling ass thru a sweeper in second gear at redline and you shifted to third anywhere around the apex, you may spin out. That's something to watch out for on those diminshing radius highway on ramps.

jzr

A few things to maybe try:
Shortshifting to 2nd gear in straight section preceeding corner. Overall acceleration through might be lower but at least it's not broken up with a shift.

If the sweeper doesn't take 100% of the tire's grip, try staying in first, cornering a little harder than needed, then straighten the wheel to shift, then resume cornering.

Shift very slowly and smoothly. Just remember those back tires can only do so much at one time, and shocking them with a hard shift in the middle of a hard corner is asking for trouble.

Your foot should ALWAYS come off the gas when you shift.

jguerdat

And just let the clutch out a bit less abruptly. You don't have to bang the gears...

Sideways

[QUOTE]Originally posted by jguerdat
And just let the clutch out a bit less abruptly.