hlee1169

Just want to share my experience with the rear tire wear with PDCC. Having owned 997.1 and .2 C2S, I knew that the rear tires tend to wear out quickly, and the inner edge went bold first. I read that PDCC, by striving to keep the tire in maximum contact patch, would reduce uneven tire wear as a side benefit. So 13000 miles later, I decided to check if this is true.

I put about 3000 miles on the stock Pirelli before switching to Michelin PSS. I've done two track days at Thunderhill on the Pirelli, and about 13 track days on the PSS, plus regular street driving. Also note that I was pushing the PSS harder since I was getting more comfortable in pushing the car on the track. 13 track days were about half at Thunderhill, and half at Laguna Seca.

Pirelli PZero


Michelin PSS


As you can see, the tire wear seems even across the tread, and the PSS is just awesome in sustaining the wear on track. I wonder if they will heat cycle out first before wear down to bold. I guess we will find out in a year.

Cogito_Ergo_Zoom

Wow. This would seem to be a pretty impressive case for both PDCC and the PSS.

One DE + 11,000 mi on my non-PDCC S and my Zeroes are wasted. New rubber going on this week.

Does anyone know the static weight distribution for the 991? (Assuming an S Coupe)

chuck911

Were those tires really used on a track? Really? Because they sure don't look like it to me!

Hammer911

I'm only 2000 miles in on my car (with PDCC), so too early to tell. I do know that I blew through rear tires in 7 or 8,000 miles on my 997. I'd be thrilled if the PDCC makes as much difference as your example above!

ww007

Awesome! That's what Sascha Glaeser unofficially told me about the PDCC too and it's nice to see that it's true!

I guess this means that over time, the PDCC will actually pay for itself by reducing the number of times the tires need to be replaced. I wonder when the break-even point is...

Cogito_Ergo_Zoom

Not only was he saying they were used on the track, but they were used on the track 13 times!

I have no reason to doubt what he is saying is true, so in that case I'm really regretting not getting PDCC and that I'm stuck with the Zeroes for another cycle!

exponential

Weight distribution
Porsche 997 C2 : 38% front , 62% rear
Porsche 997 C4 : 40% front , 60% rear
Porsche Cayman : 45% front , 55% rear

The 991 engine moved ~7cm forward (in relation to the rear axle),

the weight distribution of the 991 C2 is now 42% front / 58% rear.

Cogito_Ergo_Zoom

Thanks, I couldn't find that anywhere but assuming that's a correct (most likely) dry weight figure, that would seem to match up with the OEM tire section widths because these are usually proportional to the static weight distribution f/r. The "total" contact patch section width (each side) is 245+295=540, so that would give it a 45% front / 55% rear distribution in terms of tire contact patch.

Let's think about this analytically:

First compare it to the 997: Given that the wheelbase of the car is longer (100mm) and the front track is also wider (F: 54mm!!!, R: almost identical), there is less longitudinal and lateral load transfer happening from tire to tire. The 991 is also 88 lbs. lighter. It's also slightly lower (4.57mm) and makes extensive use of aluminum in the roof, doors, and hood which means it has a substantially lower cg (center of gravity) vs. the 997. All of this adds up to a car that, just by the redesign of its basic proportions and use of lighter materials, is going much less harder on its tires than the car it replaced before the effects of PDCC are even factored in.

PDCC seems to cut down on body roll substantially, which means theoretically you are minimizing situations where you are "overloading" the tire contact patch at the limits of adhesion due to excessive load transfer. This implies, all other things equal, the car will be sliding around less at the limits of tire adhesion in comparison with a non-PDCC equipped car. Everyone knows that sliding around a lot isn't very good for extending a tire's useful life. By how much? Who knows.

I'd also note that the PSS's have a UTQG rating of 300 vs. 220 for the OEM Zeroes, which implies a longer wear life in comparison. I've seen plenty of anecdotal evidence on Rennlist to support this, too.

So looking at all these things combined, it makes sense that his PDCC equipped 991 running on what are purportedly grippier, more progressive, longer wearing tires would be showing substantially less wear at the rears.

Still I'm shocked at the condition of those tires after 13 track days...that's pretty amazing.

Attilars

I got corner weights on my 991S coupe a few weeks ago. With a full take of fuel and 175lbs in the driver seat rear weight Distribution was 60.1%.

John's 991

I have worn out my stock Pirelli's and are waiting for the MPSS to arrive, hopefully before the summer. I have also done several track days at Laguna, Thunder Hill and Sonoma Raceway (aka Sears Point) and while I don't have PDCC, all four of the tires have worn quite evenly, just as yours have.

In the past on an E36 M3, I would wear out the outside edge, even with 2-3 degrees of negative camber, so the 911 is a major improvement over that. The engineers at Porsche have figured out something, for sure. In addition to improved tire wear, the grip on street tires is amazing.

hlee1169

Well, I am not a particular fast driver, just starting DE in Sept last year. My best lap at Thunderhill is 2:15 without bypass, and 1:49 at Laguna Seca. Time was measured with PCA's time trial, so they are fairly accurate. Beside switching to a lighter and smaller 19" OZ track wheels and the PSS, no other mods. Convertible too.

The Michelin PSS are really something, although they do get greasy if the tire pressure went above 40psi, and they also seems to lose grip beyond a 20-min session at a hot climate location, like Thunderhill in summer where the ambient temperature is around mid-90's. However, they were phenomenal in the rain, I drove it once in the pouring rain at Thunderhill, it was pouring so hard I had to put the wiper in fast mode, but I was still passing everybody. Nice tires for DE beginners.

MayorAdamWest

What widths on the 19's, and what size tires?

hlee1169

8.5X19 front, 11X19 rear, OZ Superforgiata.

245/40/19 front, 295/35/19 rear, they should match the circumference of the stock front tires 245/35/20 and rear tires 295/30/20.

I saved about 7lbs on each front corner, and 12lbs on each rear corner, and I could feel the difference too, compared to the OEM 20". The car just flows over bad road surface and yet remains stable, love the suspension on the 991.

CarManDSL

Finally getting first track day next week with 991S with PDCC, SPASM, Sport Chrono.

At DE, what tire pressures were you happy with using stock Pirelli's?
How much did the pressure change after a session?

MayorAdamWest

I did a lot of playing around, and I found 30/33 cold felt pretty good. Outside temp was mid to upper 80's.