This topic is always a good one (almost up there with what oil to use) but I thought I'd share my experience.

The PO ran summer Pilot sports so when it came time for renewal I followed, twice. Then I tried PS2s and ran out of rubber faster.

Then I thought I probably never push the car hard enough on the street to fully appreciate the tyres and was always nervous in the spring and fall where it may snow up here so I went to Pilot Sport All Season.

The All Seasons have worked very well but still had the same harsh ride as the previous rubber with the eibach/bilstien suspension.

Fast forward to last week and I'm looking closely at the rears thinking that I may be lucky to last the season I thought I'd play with the pressures. Lowered fronts and rears to 30psi and wow................what a diff.

Softer ride and great grip up to and beyond 200kph.............I'm sticking with these pressures for now for now.

 

Hmmm....interesting. I may try. It makes sense from thestandpoint that a lower tire pressure will result in more heat, and therefore additional stickiness?

 

..........and the ride difference

I should add that the first sets of PS rubber were run at factory spec...........the PS2s were run at GTS spec.

 

Best to measure pressures across the tire tread immediately after a spirited run. If center is hotter, lower the pressure a couple of psi and try again. My Dunlop Direzzas like 30 psi.

 

That's the way to get the right pressures

 

I run my PS-2's at 36-38 all the way around. I should adjust the camber a little more negative, after obsering that the PS-2's seem to like a bit more negative camber for initial turn-in and to avoid some of tthe outside-rib scrub under brisk driving. Then I could drop the front pressure a bit. The car rides and handles very well in the low 30's, but with factory settings on camber, the temps and wear say it's not enough pressure.

Note that the above observations were made while using Mobil-1, not Amsoil.

 

I think the Amsoil would help with your fetzer valve sticking though. That would surely give better tire performance.

 

I drive more aggressive than most, sounds like Malcolm does too. But I have monitered my tire wear a great deal and I find I get better tire life and wear on average with around 32 psi. This gives me equal wear across the surface. This does vary slightly with different brands though. High perf tires like the ps2 like lower pressures and higher temps. If they are run cold the entire time they don't last as long.

 

Thank you for this post! I assume Porsche has performed these tests for the stock setup already. For those running stock wheels and newer generate of tires, will the stock pressures take this into consideration or does it make sense to remeasure temperatures with every new tire?

I can say without question that the handling of the GT is far better at stock pressures. The higher pressures stiffen the tire enough to improve response and road feel without being harsh.

 

Are you running 17" wheels ? With stock 36psi front/rear now reduced to 30psi ?

 

Which pressures do you recommend for front/rear for 17" wheels?
For spirited street driving that is.
Width is 225F // 245R.

EDIT:
I guess, OP recommends 30psi all round?

 

Whats the best tool for measuring tire temps across the tread?

 

I use the 10% rule.

Proper tire pressure (hot) should only be about 10% greater than the cold pressure. If it is more, then cold pressure is too low. (This is something I learned racing motorbikes..)

However, another 10% rule is 10% below max pressure for max fuel economy / highway driving.

Personally I usually run 10$ below max and adjust downward until I get within the 10% hot/cold pressure ranges. This usually leaves me right around 38psi front / 40Psi rear cold for typical 225/50-16 tires

YMMV

 

I have a very vintage direct contact pyrometer that's served me well. Fast-forward to modern tech, and the IR temp gun reads quite close to and a lot faster than the old tool. Just shoot from close in, maybe an inch or two. --Record your readings!!!--

The 'correct' pressure varies with the way you are driving. A 70MPH straight-line run on a smooth road, wth just you and a half-tank of fuel, will be different from two up touring with luggage and clubs, through the sweeping mountian roads on the way to your getaway destination. Of course track days take different pressures too. Make sure the readings you take consider all the conditions the car will see, unless you adjust for different uses.

Get a GOOD repeatable tire pressure gauge. Accuracy is important but repeatability is more important. Use that same gauge all the time, especially if you are logging and tracking wear profiles vs. pressure, as some of us do. The mechanical dial gauge I use has 0-50 PSI displayed on a 270º scale. I bought a nice little digital gauge for K after she had a low-press warning a few years ago. Turned out to be the spare with low press... So when she got another warning she drove it home low since she didn't remember how to use the fancy gauge. So keep it simple, repeatable. The best gauge is the one you use regularly.

 

no, you dont want your tires anywhere near 40psi cold, UNLESS you want best fuel economy. I always tell the story of the NSX boys (about 5 of them) that were at our track day and they ALL were spinning out all over the track. when I interviewed one of the guys, who seemed to be the ring leader, ( wiping up dust from all over his car from an off road spin) I asked what pressures they were running. they replied that they were at 40psi cold. I told him to take temps afterward, but I would bet them to be in the 45psi range , min. he then told me that ALL of the guys were running the same pressure (would explain the similar performance of the group ) anyway, I suggested 30psi cold. his jaw almost dropped on the ground. anyway, without too much coaxing, they alll dropped the pressure to 30psi and were all very happy with the handlng. 34-36psi on most all street tires is a good range to be at hot. not too many tires I know about, will be happy on the track at 40psi hot and neither will you.

Oh yeah, the rest of the day, not one NSX ever spun and made a big dust cloud again!