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Discussion Starter #1
Wish I could have hung out w/ the cool people at summit, but I'm not that cool.

I've been runnig khumo mx in 205/40/17 and they seemed ok for a street tire. Up to speed in the heat and they just push like crazy. There is a long sweeper at nelson ledges where I'd have to keep stabbing the gas to get it back down to hit the apex. So they are done on Saturday, and Sunday morning I get some pilot sport cups mounted in 225/45/17. Head back to the track with same conditions as the day before. Now there is zero push and rear end felt real twitchy, so twitchy that I lost it oak tree (60-65 mph corner). I had also adjusted my hot pressure to 34F and 30R, so I should have plenty of grip.

So my thought is the khumo fronts would overheat and push, where the psc fronts would come up to just the perfect temp. I'm guessing I couldn't get enough heat into the rears.

Anyone else experience something like this?
 

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Addition of sticky tires can change the balance of the car as now you are exerting more force on the suspension. You may have been able to roll the rear end more, losing camber and therefore grip.

BTW, Oak Tree as in VIR? Were you running Viper Days with weekend?
 

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Discussion Starter #4
Addition of sticky tires can change the balance of the car as now you are exerting more force on the suspension. You may have been able to roll the rear end more, losing camber and therefore grip.

BTW, Oak Tree as in VIR? Were you running Viper Days with weekend?
Didn't think of that. Glad I hung onto my stock rear bar.

Bmw club at nelson ledges.

Depending on the weight of the car, 34 is pretty much what everyone runs.
 

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Discussion Starter #6
I need to see if I can more negative on the rear. Pretty sure I told the mechanic to set them full positive, but that was 2 years ago.

I mean it's not "really" bad, just different from what I'm used to.

I was thinking not enough heat in rear tire 'cause everyone tells me it's hard to get them hot enough and should only be used june-august.
 

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keep stabbing the gas to get it back down to hit the apex
Huh, I usually lift to bring the front in. Stabbing the gas, you are unloading the fronts, making it worse.
34/30 HOT? Isn't that low?
Yes. Yes, it is.
How about starting out at 36-38 and building up to around 40-45 hot.
If you are overshooting apex, lift the throttle and you get throttle off oversteer. Front bites and rear rotates.
 

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Discussion Starter #11
Just wanted to follow up on this in case anyone ever runs pilot sport cups.

A good starting cold pressure is 28 front, 26 rear. These tires provide the best grip when they are 34-35 hot. Confirmed this with the 911 guru's who run 26 front, 28 rear.

I bought used tires and don't know how many heat cycles were in them. After my 3rd event with these, for some reason the 1st session is very sketchy. Not sure if it's a psc thing, or a drive on the street thing, or a used tire thing.

Now for the 2nd session on, once they heat up, the tires are simply amazing. Good wear and excellent grip.

My spin at oak tree I think was a combination of the tires not up to temp and more speed into the corner followed by more trail braking over an undulation in the track.
 
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