I've been using a few psi below that for the street (32/33 cold) per Powerhound's recommendation and it's been working great even in cold temps (40s F / 5-10C). Here's the thread: https://rennlist.com/forums/996-gt2-...l#post12541030

I've got no experience with the car at track/autocross yet but I'm expecting big things

 

Thanks, I saw that post. I will give it a try and report back. Cheers!

 

I was just going to ask that question...this is what I run on the track (hot) but also now doing the same pressures on the street (cold). I think Porsche recommends 32/36 for the street on our cars? Have tried this and even at "just legal" street speeds the rear end wants to let go when accelerating out of a corner.

 

My door card has 32f/39r which I think would be dicey on the street with these tires. I can only suspect that those numbers work with the OEM N-spec tires of last decade...

 

Regardless of tire (track NT-01, street Sumis) I'm using much smaller r-f psi diffs (1-2psi tops), if any at all. Car drives much better (more neutral) that way. I don't think I've ever even experienced a 6gt3 with a 7psi r-f diff. It was probably suggested as a way to minimize potential liability by introducing plenty under-steer. Most shops who know GT3s recommend that you keep the f/r pressures close to equal at the track.

 

Agree with your logic 100% but the Porsche recommended split would introduce more oversteer (less grip in the rear) which is why it's so odd to me. Thus the rear tires must be "special" to require such high pressure - that's my only hypothesis at this point...

 

Higher rear pressure REDUCES oversteer.

 

I think we agree more grip on rear tire reduces oversteer...

A lower tire pressure increases size of contact patch and higher pressure reduces the size of contact patch. A larger contact patch will have more grip... thus lower pressure = more grip -> less oversteer.

This obviously has a lower bound as a flat tire doesn't have the structure to support the vehicle but generally this applies.

 

My tech says I need to change tires every 90 days. BWAHahahahahahhaha (I crack myself up - this refers to another post where I advise that I was advised I need to do an oil change every 90 days)

 

What you say makes sense but I've delegated the answer to the experts and they have all said that higher rear pressure REDUCES oversteer, which also overlaps with the practice of almost all car makers to recommend higher rear pressures for that exact reason (to reduce liability by reducing oversteer). I posted a link in my previous message. Here's another one saying the same thing:

http://www.tirerack.com/tires/tirete....jsp?techid=58

Google is your friend.

 

I hear you... and I trust tirerack more than your first post... but that's just not right. Now I have to go read my eng books

Check out what google gives when I search "tire pressure vs grip": https://www.facebook.com/notes/ultra...0134442380550/

 

The issue is obviously a complex one. I think it's a confluence of two main (countering) factors: (1) your contact patch argument and (2) spring rate, with the second one typically seen as prevailing.

Here's a RL discussion about it:
https://rennlist.com/forums/racing-a...ndersteer.html

You made me look into this myself instead of accepting the experts' wisdom at face value, so thanks for that.

EDIT: In the end, it's probably best to follow the money. Porsche wouldn't be recommending street f/r pressures of 32/39 (and BMW rates of 30/38) if it INCREASED their liabilities through increased oversteer. It's a well known fact that OEM street pressures on all cars are set for understeer and none of them has f > r recommended pressures.

 

You're looking at the subject very narrowly. There are a lot more components that factor into a cars handling than tire pressure (and spring rate).

It's unfair to attribute a cars characteristics to either one of those two things.

 

Wrong...

 

We're talking 'all other things being equal/unchanged', of course.