I've searched around but can't find any definitive info. I know most guys with staggered 20x9F / 20x10R SportTechno wheel set-ups are running 275/40 up front and 315/35 in the back.

My question is, what sizes came from the factory with this wheel option? I assume the 275/40 fronts were standard, but were the backs 315 or 295? Anyone know?

 

275/40/zr20 all around

 

Really? What's the point of the wider rear wheel?

 

Not sure I changed to a 315. But I had 275 all around on mine when I bought mine. The only real difference is one is concave and the other is convex.

 

No cayennes were offered with a staggered setup. Symmetrical on all four corners. I wager the awd system would be slightly miffed by a larger contact patch in the back - but perhaps you can get away with it.

 

i've got 275/40/20 all around with 9's in front and 10's in back.

 

This is surprising. What was Porsche's thinking of offering a staggered wheel set-up, that totally negates the ability to rotate tires, AND use the same size tire all around?? Makes absolutely zero sense.

And the comments regarding upsetting the AWD system by running different tire sizes interesting. A valid concern indeed. However, the X5, GG SRT8, and 911 get away with it, among others. Anyone care to expound on this?

Thanks for the replies.

 

Do you have any pics you could share?

 

Actually, staggered 9's and 10's were standard on the '06 Turbo S. All wrapped in 275/40/20 tires. You could "upgrade" to the optional "Sport Design" wheel, which was 20x9, with no 10" option available. Porsche offered an accessory 17mm spacer kit to push out the rears on Cayennes for those owners who wanted a wider track in the rear when running 9" rims.

 

Contact patch doesn't matter for this situation; to keep AWD really happy, the front and rear overall tire diameters need to either be ideally identical, or within .5% of each other. It's probably possible to have a tad bit more front to rear diameter difference, but I've never read any authoritative specification on what the absolute maximum variation can be, so to keep the computers and mechanicals happy, I'd error on the lower margin of difference.

 

The picture I posted in the "Basalt Black" thread shows the factory staggered set-up, 9's and 10's, with 275/40/20 tires all around (N-spec Bridgestones)

 

Thanks for getting me up to speed. I assumed because tires were the same... Wheels were too.

 

What Spooltime said for the '06 CTTS. staggered wheel width with the 275's. Some do put the wider 315/35-20 tires on the back which are yes wider but they are almost the exact same diameter as the 275/40-20.
28.66" dia for the 275/40-20
28.68" dia for the 315/35-20
Almost a perfect match.

 

The primary issue to be concerned about using a 315/35/20 tire on the stock rear rim is the fact that it is not designed or intended to be used on a 10" wide rim. The minimum width rim for that size tire is 10.5". If you do mount that size, the sidewalls will be pinched in more that they were designed to be, resulting in potential handling and load bearing issues.

I wouldn't want to run a tire/rim mis-match like that on the track or haul a trailer with it, but for normal driving around, you can probably get away with it so long as you understand you will be creating a lot of additional understeer on the Pig due to the width of the tire versus the stock tire size.

 

Good point Spooltime. Width for 315/352-20 tires: Rim Width Range: 10.5 - 12.5 in.
I run the OEM wheels with stock tire size (all seasons) for Winter and run BBS RXII 10.5x21" wheels with 295/35-21 Tires (currently Michelin Latitude Sports). Love the Michelin's and they are coming down in price as are most all 21" tires (getting more applications) but Michelin's are still pricey, may go back to something else.