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I want to change the OEM stock tires on my 2009 Porsche 997.2 C4S.
They came with 235/35/19 on the fronts; and, 295/30/19 rears.

My plan is to change the only rear tires to 325/30/19 for a meatier look.

Now I'm hearing that if I change the tire diameters it may damage the differential, since it is an all-wheel-drive car. (??)

I've seen upgraded factory wheels on C4S's and they had 305 rear tires in the back coming right from the factory.

If this is true, would increasing the fronts to a 245, in conjunction with the 325 rears help?

Am I getting the straight skinny here, or is this just a bunch of hoo-ey?

Thanks

 

I have been told that if you remain with 1% of the OEM tires diameter you should be okay. I would check with a good dealer or Suncoast Porsche for more info.

 

George, the 325 should work according to this guide, but it recommends a 12 - 13 inch wheel. I run a 315/30/18 on a 11" wheel for the track without problems.

 

True, but your sig says you have a 2-wheel drive car. I was told it may cause problems with the 4S all wheel drive system.

 

George, a C4S will come with 305-30-19 on the rear and a C2s will if you order the Carrera Sport wheels 11.5x19....so yes with out a doubt you can use this size on the rear as it is a stock size for Porsche. The 305's will fit just fine on a 11x19 wheel.

However you will not gain any noticabl performance on the street but going from a 295 to 305 but the 305 might look at little wider...it will be hard to tell though.

 

Correct !

 

I wasn't referring to tire height, I was commenting on the wheel width. Personally I would stay with the OEM tire size, as Mike said the 325 won't give you any performance improvements.

I would also find out why your car came with a set of 295's 305's are OEM sizing on a C4S, did they swap them with a C2S?

 

Sorry, my bad.
The stock rears are 305's....... but I still want to go to 325's in the rear. So you're saying that will work????

 

Like I said in my initial response to your initial post, less than a 1 percent disparity from OEM. I realize that C4s come with 305mm rears having owned two of them. Regardless your reference point should be from a 305 baseline. Because it is AWD, I would validate any proposed changes with your Porsche dealer or as I said above; Suncoast Porsche and/or Wheel Enhancement.

Even if you get the answer that you're looking for from an internet forum be certain to validate that info as any issues could take many miles to uncover.

I had the same concerns with my dd 335Xi coupe, made the swap and kept the disparity within 1 percent. I have had no issues in 12,000 miles.

 

According to the site that spits out the comparison chart, 3 % is the mark for concern, but I agree that checking with the dealer is a great suggestion.

 

In theory the tires should fit and work, but the C4 concerns you have are legitimate. On a C2, no question...C4 check with the dealer, preferably a tech not the service advisor.

 

3%; good to know!

 

I put 20" HRE P40's with PS2's on my 08 C4S the 325/25/20 the rears are only 0.1" difference in radius vs the 305/30 19's - or 0.7% slow on the speedo.

The fronts are 245/30/20 and are only 0.2" diff (larger) on radius and 1.2% on the speedo.

Check out:
http://www.miata.net/garage/tirecalc.html



There should be no issues.

 

997's also have a differential heat sensor that the 996 cars didnt have. if the height difference is too much, you will get a light.

 

Same here. Running 245/30/20 front & 325/25/20 rear on my 06 C4S.