Mech33

I see, you think simply because the weight is shifted forward typically on turn-in (with some trail braking)?

orthojoe

I don't know, to be honest. I'm guessing you don't want them to sit around for more than a year, and these tires are approaching being one year old. No idea if I'm way off base or not.

My mpsc2 order was placed 10/7, so let's see what happens!

MileHigh911

Historically, I have always been informed (by tire shops) that tires have a shelf life of 4 years. But I assume this is for traditional all season rubber and the like. I do know that sticky rubber's effectiveness is affected by heat cycles, as the rubber slowly changes with each heat cycle. My guess would be there is nothing wrong with sticky tires up to 2 years from mfr date, as long as they havent been heat cycled out, nor faced extreme cold temps (remember the cracking Corvette MPSC2 tire debacle). I would bet a call to Michelein would give us the info. 1 year seems a bit short.

MileHigh911

In looking at the website, they say the MPSC2 have a 6 year mfr defect warranty. They don't mention usable track shelf life. I did find it interesting to see they used the N2 race slick rubber in the outer tread (they don't specifically say how much is the outer tread), and a rigid elastomer compound in the inner tread.

I think this is why everyone struggles with even tire wear. The tire was designed similar to the Pilot Supersport, and if you track it, there will never be even tire wear, by design. Anyone that has tracked super sports knows this outer wear issue too. I think this is also why some GT3 owners report being just as fast with the OEM camber settings. Adding more negative camber may just have you driving on the "less sticky" rubber, trying to get it to wear at the same rate as the N2 racing slick compound. I also think this is why everyone reports heat cycling out these tires. Michelein has designed a tire to take to the track, but be safe when wet, and allow the driver to make it home when his race compound is worn off. I think what everyone should be shooting for is even front-to-back outer shoulder wear, and change the tires together at the same time.

Manifold

This is what I've been saying and thinking for a while, though I've been reluctant to replace the rears at the same time as the fronts, since the rears 'look' ok even when they're clearly heat-cycled out. Maybe I need to just bite the bullet and stop being so cheap.

I still don't understand why the front tread wears faster than the rears, though I speculate that it has something to do with the RWS, e-diff, PTV, etc. With the 991 turning in better than the 997, somehow the car seems to be finding a way to work the fronts harder and improve the turn-in, despite still being rear-engined. I suppose the sway bars could be played with to even out the wear of the front and rear tires, but that may throw off the balance of the car, which seems pretty good to me if some trailbraking is used where appropriate. There's something going on here that I just don't understand.

I think all of this also explains the variation in optimal hot pressures people are seeing. With less camber, you need more pressure (~32 to 35 psi) to 'push out' the middle of the tread and even out the wear of the outer sticky tread, whereas a lower pressure would wear the outer edge prematurely. With higher camber, higher pressure may put the wear too close the center of the tread and not fully use the outer sticky tread, hence people using hot pressures closer to 30 psi.

The other point to consider is handling. TPC Racing has a lot of experience with this car, and told me that simply increasing camber by itself (even to ~2.0 degrees) can throw off roll centers and have a net adverse effect. That gets into suspension geometry issues which are mostly over my head, but I can certainly say that the handling of the car feels significantly better to me with the factory 1.5 cambers and alignment, rather than 2.0 cambers, on both road and track. Turn-in and load transfer during turn-in feel better, and the car also feels more planted through the corners. TPC Racing also told me that the 991 GT3 is much better set up for the track from the factory than the previous generations, so less can and should be done to optimize it for pure track use. Being able to develop the car with a dual-use, dual-compound tire may have something to do with that.

Supporting the above thinking, the Owners Manual (p. 233) gives info on chassis setup, and recommends the standard sway bar settings on the track. And the Driving on the Race Circuit Manual (p. 5) states that the factory settings are 'suitable' for both road and track, providing 'a balanced compromise between high maximum lateral acceleration and excellent controllability, including on the race circuit', and also notes that the car is 'very sensitive to small changes in the chassis setup'.

If we had a tire like the NT01 with the same rubber across the tire width, a different setup (with more camber) may make sense.

MileHigh911

Agree!!!! They need to make a Sport Cup3, with the N2 race slick rubber all the way across, a 100 treadwear rating, then all will be fine in this unknown suspension set up world.

Manifold

That would be awesome. Tweak alignment and/or pressure in that sucker and hold on for dear life!

orthojoe

You guys make good points.
I wonder how the dunlops are made? Single compound all the way across? Maybe I'll end up loving the dunlops with my setup!?

MileHigh911

Appears to be single race derived compound all the way across Joe! And in the description, it does not claim wet driving prowess. I would guess you may be correct, in that you will see normal wear across with these.

Did you see the uneven wear with the Trofeos??

orthojoe

Interesting!
TrofeoR wore fairly evenly, but oddly enough, the rear tires wear out much quicker than the front with those tires.....

DeerHunter

Maybe I'm mis-remembering, but isn't the design upgrade to the Cup 2 (vs. the original Pilot Sport Cup) that they put a harder compound on the shoulders so that they don't wear disproportionately to the rest of the tire?

Manifold

Outer part of tread is soft and sticky and when I come off the track.

Another point to consider is camber change under loading. The way the PASM works on the 991 GT3, the car really doesn't roll much (by comparison, Cayman R rolls vastly more, despite feeling fairly firm on the road). Maybe less roll means less camber change, which means less static camber needed?

http://www.hotrod.com/how-to/wheels-...tire-traction/

Macca

Some really great thinking hear from manifold and mile high. I've been having a few off line conversations with Manifold and I agree there is definitely something going on with this tyre. I love the tyre but have reverted to stock geo and seen no real change in tyre life and the car feels real good.

Joe. Once you are done with the dunlops ID be prepared (and a few others in sure would too) to PayPal you a contribution to cover 2x ego change to get you to factory on a new set of mpsc2 then back again (if you did not like) for a run at your favourite track to see if you are any slower or the tyre wear more detrimental...it would be a worth while experiment....

orthojoe

Oh man, I don't know if I can stomach screwing around with the car anymore now that I love how it feels. I think Ben and Chris will kill me if I screw with the car again since all 3 of us love the setup. If the dunlops end up being markedly better than the mpsc2, then your theory about the tires could be right. I might consider it, but only if the dunlops are significantly better.

Manifold

I hope to be proven wrong, but I'm predicting that the Dunlops will last only a fraction as long as the Sport Cup 2. When I tried them on the Cayman and 997, they degraded quickly when pushed hard, and I vowed never to try them again.