Aku700

Just to give some background info, had the car now 5 months, 2015 MT GTS, driven it about 4500 miles now and i just replaced my P0's 500 miles ago for the new PS4S, supposedly for better performance, traction and noise . I am having performance issues, but maybe its not and I am just pushing the tires beyond what they can do and I need to perhaps upgrade to Sport Cup 2's or other, so need help from you guru's out there. When i drive the canyons or anywhere i can, I punch it, i drive it pretty hard, when i go freeway on-ramps, i floor it, when freeway is empty(waze good, no V1 going off), i push it, but the rear is shuddering, meaning the PSM is kicking in to stop the rear wheels loosing traction. For fellow GTS'rs, when you drive your car this hard, should the tires shudder/psm kicking in? Starting tire pressure is at 31/35, after warm up, they get to about 37/38 fronts, 39/41 rears and when i come out of corners and punch it in 2nd, they shudder. When i come to stop or lower speeds and come out on 1st, they shudder, when driving corners at decent clip, i kinda feel the rears are just kinda slipping, i just feel the tires arent holding overall, so is this normal? do I just need Cup 2's? I dont recall having this issue on the P0's, but honestly dont recall if i drove it this hard when I first got the car, so perhaps i just started driving it harded due to more experience behind the GTS? The P0's started shuttering when tread was down to 3mm, dealer said compound is harder when its down to 3mm, hence why i need new tires so they dont shudder anymore.

and if I do go Cup2's, what the deal with them, i hear they are very noisy and just not good for regular roads. I drive the car pretty damn hard about 10-15% of the time. I also heard the Cup2's arent a "certified tire" for the GTS, which I dont get, its certified for GT3, but not a slower GTS? My dealer said if i switch to the Cup2's, the tires might shudder more, really? What am I missing here??

I got into Porsche becuase i friend got me hooked, he bought new GT3 and we ripped through the canyons a few and i got hooked, I had to get a 911, but i never recal his tires doing this, and he drove it pretty hard.

thoughts?

Porsche_nuts

Were you wheels road force balanced?

Aku700

Yes. I had to have the rears replaced becuase the 1st set was cuasing a vibration throughout the car, but after 3 days in the shop, they replaced the tires, road balanced, aligned, etc, so they did everything a porsche dealership should have done.

Highyo

dont have this experience at all

Aku700

so you have same tires and when you punch it to the max, the tires dont shudder/skip/slip or other?

Highyo

yes i have the same tires and when i go very fast i dont get shuddering, skipping, understeering, or other. think you probably have to get them balanced

Aku700

And what happens when tires are cold and you punch it at light, going around corner onto say freeway on ramp, you get shudder then? or the tires just stick?

chuck911

What exactly are we talking about here? Because "shudder" even with years instructing PCA track, autocross, and Driver Skills, "shudder" is a new one for me. Judder, when the steering wheel vibrates back and forth under braking, that one I know. Tires however, there's always a little variety thrown in by type of pavement, temp, etc, but in general they all go through the same progression. Under moderate cornering the tread bends or squirms. Corner harder and the squirm starts to make a scrubbing sound or vibration. Corner harder still and they squeal. Tire squeal by the way indicates maximum traction. Pushed even harder to the point the tire is sliding or drifting it howls. Watch any Chris Harris video, its pretty clear the rear end or even the whole car can be made to slide and drift if pushed hard enough. If you're doing this and the tires are howling, that is perfectly normal. If you're doing this and the car is hopping around that is suspension, not tires.

That's about it. Only other thing I can add, 41 psi, that is getting to the area where the tires are clearly overinflated from a maximum traction point of view. Load carrying capacity, different story. But you want to corner hard, you want to be below 40. Rears at about 38 max hot, fronts 33 or so hot, will work much better for you.

Aku700

ya, this is an odd one, the porsche service rep called it that, shuddering. he said the psm is kicking in becuase the tires have reached maximum grip, so it holds the tire, then releases, holds, releases, etc, so its like the right rear tire is kinda chattering, its hard to explain. so, no squeling, howling or other, would prefer that. I live in Thousand Oaks, CA area, so very good roads, temps in the 60's to 90's last 7 days.

cas1337

I don't have this experience at all. My PSS are nearly at the wear bars and the sidewalls and shredded. Even then, I have trouble breaking the rear lose with PSM on and dry weather. The rear either walks out completely or stays put, no shudder.

golfnutintib

normal gts's won't do that

look at your rear diff, wheel balance

cup 2's don't ride harder than 4s... they just give you more dry grip at the expense of wet grip and longevity

WCE

If this occurs under hard acceleration, not cornering, it's perfectly normal depending on road surface traction.

Chris C.

No error lights?

Drop pressures for sure, too high for performance driving.

LavaGTS

Try PSM sport or PSM off.. Drive like a man.

Jon D