2004 996 Carrera Cab 56K miles. I have owned this car for about a year and LOVE the way it drives, handles, everything about it....except rear tire wear. Pirelli that came on it on the rear blew. Replaced with the only tires I could find in Eastern Texas on a Sunday afternoon, 275/35R18 Firestone Firehawks. Good tires. I had no complaints except I only got 5000 miles out of them. Replaced with the same size Michelin Pilot SPT AS 3+ 95Y in January of this year. I mixed with 224/40R18 BF Goodrich G-Force C2 A/S. I know this is not recommended but thank the good Lord that I had tread on the front tires to keep me on the road in the rain on the highway. The Michelins have gotten 5000 miles since installed in January! I should have paid more attention to the tire pressure that was added during installation as all 4 tires had 32 lbs added. I checked depth across the back tires and they have worn to 2/32nds on the outsides but still have 4/32nds on the insides. All else constant, is this the behavior I would see with low tire pressure? Could the slightly different tire size from stock in the back cause excessive wear? The car has not been wrecked, per the dealer and I see no evidence to say that it has been. Thanks in advance for your help.

 

275/35/18 is definitely far from OEM spec. What rear rim size to you have on the rears? 18x10?

 

Thank you for the reply. I am not sure what the 10 represents but have 18 inch rims. Porsche recommends 285\30R18 on the rear but the only tires I could find on a Sunday afternoon after a blowout was 275\35R18. I wouldn't think the difference would cause additional wear but it could be part of my problem. Any thoughts?

 

On the Mk2 narrow body cars, the OEM rear wheels are 18x10 ET65 - tire recommendations 285/30ZR/18

If they're wide body wheels, then more than likely they're 18x11 ET63 and the normal tire recommendation is 295/30/18 . Some people put wide body wheels on NB cars, which can be a problem if offsets are far off.

IMHO, the tires should work in spite of the slight difference in size, but it really depends on the wheels. Can you take a up close picture? Do you know the width and offset?

 

I was speaking about the rear wheel width. This may explain the wear issue.

 

Have you had an alignment? Wear on outside might be an excessive toe issue. For the record, I've been running 275/35-18s on my C2 Mk2 (10" rears) for three years without issue, other than rapid wear. Car came with BS in 185/30-18 and were toast in less than 5000 miles (warn opposite of yours, mine wore out on inside edges). Had an alignment with mildest street spec possible, and got about 8000 miles on last two sets of Fallen FK453s (275/35-18). Now onto Michelin PSS, just installed, so we'll see how they work out.

For the record, the Mk 1 cars came on 10" rear wheels but spec'd 265 rears, so my thinking is 275 splits the difference.