2fcknfst

I will go to a 265/325 setup on factory 20s after the first set of P4s' are done.

That will be an almost perfectly matched set - if memory serves, it will be within 1/10th of an inch radially for P4S'.

pfbz

I am much more familiar with F/R diameter issues on the 996 Turbo which uses a completely different AWD technology, a viscous coupler that is sensitive to correct F/R diameter ratios. Too big of a difference and you'll cook your diff. Additionally, in order to correctly bias the diff you want the fronts slightly taller than the rears.

With the 991 electronic center diff, I'm not sure how big of a difference you can run without ill effect. You also have the issue of having to find a tire that has both the fronts and rears available, not just pick an arbitrary size... For example, to run 255/35-18 & 325/30-18, tire rack has only one tire available in both those sizes, the Proxes R888R, which is even more of a track tire than the Cup 2s and not a tire you'd really want on a street car.

The F/R diameter increase is 2.6% instead of 1.5%. OK? I don't know...

Proxes R888R in 255/35 325/30

Steven31371

the variance in roll rates are within the tolerances built into the car

***CORRECTION***

fronts 255/35/20
rears 315/30/20

not the 325 rear as the role rate variance is about 2.5% between the Toyo R888R 325 to 255 rear to front...the cars are supposed to be able to handle about a 3.0 % role rate variance but that’s too close for comfort for me.

and the 315 lighter and only 0.5 inches less wide

the roll rate variance between the 315 rears and 255 fronts is 1.6%, which is about what the stock PZero roll rate variances are.

as an aside...Sambo who knows his shot strongly recommended the new Toyo R888R over the Cup 2’s

the newly designed R888R is much quieter than the old R888...and gets up to good operating temps easier in spirited street driving...Sambo says that even cold the R888R are much grippier than the Cup 2’s.

so I’m going with lighter wheels, and slightly (but not much narrower tires, with a much stickier R compound.

but I’m also able to make that decision because I live where it almost never sees temps below 50 degrees Fahrenheit even in the winter, and it doesn’t rain much...otherwise I’d still use these R888R but only as my summer tire.

for what it’s worth on the organal post question...the Cup 2’s in those wider fitments than the stock PZero put down the power and handle WAY better than the PZero’s that came on the car.

Paliknight

Anyone know if I can go to the MPS4S 265/325 on stock everything WITHOUT any modifications? 991.2 TTS. Factory Centerlocks.

Where do you guys buy and install them?

2fcknfst

These sizes will go on when new ones are need, on the stock rims and lowered.

Steven31371

in those tires you have to use:

265/35/20 fronts
315/30/20 rears

the 325 width rears only come in a 25 side profile which makes the rolling diameter too far off of the front rolling diameters.

use the 315/30/20 and 265/35/20 in the PS4S and you’ll be fine...

Paliknight

Thank you very much for the response. Do you know if the dealership would carry and install these or do you guys go somewhere specific? I cant install these myself.

Steven31371

the 325/255 R888R combo will probably be fine...but to be extra safe I’m buying the 315/255 combo in the R888R

Steven31371

i usually order my tires from Tirerack, but only because they heat cycle them for me, which is important for R compound tires...then I have a local shop that mounts and balances them for me.

they know me and the car there...so I have Tirerack deliver them tires directly to the shop, when they get in the shop calls me

pfbz

If you are not comfortable with minor mods, possibility of a rub at full lock, etc. stick with the OE sizes and dealer installation...

As a FYI, my local dealer just quoted me for stock size MSPS4 at $1,800 installed, not bad considering that TireRack is $1,500 for the tires alone... About $150 more than having my local mobil tire installer do the job with a tire rack purchase.

2fcknfst

I was pretty sure that Randy was running that size on his turbo and was lowered and did not experience any running, perhaps save for a bit on the track.

It also looked the part with lowered suspension.

Pb Pedis

That sounds like a bargain to me! I just paid $2100 for those same tires/OE sizes installed with an alignment. And that was the lower of two quotes I got from two different Porsche dealers! Gotta love the S. Florida penalty tax.

Makavelim3

Guys,

• Can you run 265/325 on OEM wheels ? Yes, circumference will increases from 2135 mm to 2179 mm (2.1%) is a bit high however people are running them no problem.
• The front 265 tires will not be optimally stretched on a 9 inch wheel, hence your aren't fully taking advantage of the wider tires. So a 255 well stretched tire on a 9 inch wheel could have a better tire patch vs. 265 squeezed tire. You need an after market 9.5 wheels upfront to accommodate for the 265 wheels. Thats why the 991 GT3rs has 9.5 wheels up fronts.
• My recommendation is stick to OEM sizing or upgrade/upsize to 255/315 R888R tires.

2fcknfst

OK...

In a P4S, you can fit, on the factory rims the following:

265/30/20 - front, 325/25/20, rear.

The diameter of 265 on a 9.5' rim will be 26.3"

The diameter of the 325 on a 11.5" rim will be 26.4"

By using a 9 inch rim on the front and an 11" on the rear, our OEM, the above noted set should almost be perfectly matched on our OEM rims, by that I mean less than 1/10 inch difference front to rear.

Steven31371

that last bit is inaccurate

stock sizes have greater then a 1/10 of an inch variance front to back...