I've been talking with a Customer Commitment rep at Porsche North America about proper wheel sizes for the AWD C4S (I bought a snow tire setup from TireRack that is not identified in the car manual as being ok. TireRack swears its ok and that Porsche has approved the setup even though it's not in the manual.) I thought it would be interesting to see what Porsche had to say about this allegedly approved setup.

So I told the Customer Commitment rep at Porsche that I had these 18" snow wheels with certain specs. The next day, she called me back to say that the setup was not OK because my car was OEM with 19" wheels and the snows are 18" wheels. For that reason by itself, the setup will destroy my car. (Yes, she literally said that it would "break" my car.)

She wasn't just making that up either. She said that she went back to "headquarters" with my question and this is what they told her.

Does that many any sense at all?? If my car came from the factory with 19" wheels (as they all do), that I can't use 18" wheels in any circumstances?

Thanks.

 

I'm no engineer, but it doesn't make much sense to me. People do it all the time 19-20's, 19-18's. I would think as long as front and rears are within a few percent of each other in rpm's they should not hurt the drive train.

 

Perhaps its only the 4WD cars.

I know that they are more sensitive due to the differentials.

 

Why does Porsche equip the C4/C2 with 18" wheels?

I don't think it makes any sense, perhaps you should call "headquarters" aka PCNA, ask there customer service department, and get them to fax you there response for future reference.

 

Last time I checked, Porsche published that for snow tires for the 997 product, 18" is recommended. Anyone have that? I don't have a manual handy...

Here's something from Porsche - saying the 18" wheels and snow tires are for all 997 except the Turbo with PCCB. I would imagine if the C4S was included in the exclusions, so to speak, it would say that here on the official Porsche website.
http://www.porsche.com/usa/accessori...hideintro=true

 

I have the same brochure you have, it is at home some where. I would really double check with PCNA, after all, they carry the warranty, not the dealer.

 

Rubish......and my experience w/"Customer Commitment" people is the are good for reading paragraphs out of their manuals and that's about it.

For the last 15 years, the range I've run is 17s in the winter, 18s on the track and 19s for bling. My cars are all C4, C4s or Turbo.
Pay attention to the circumference (rolling diameter as some refer) and you are fine.

 

I don't buy ANY of that crap.

If the rims clear the brakes, and the tires clear the body/suspension, I don't believe it'll matter at all if the diameters front to rear exhibit the same diameter ratio as stock. In other words, if all the stock diameters were the same, and the new tires' diameters were the same TO EACH OTHER, NOT to the stock tires, then it would be fine.

 

Yep.....agreed.
Maintain approx front-rear relationship and no issues.
I know about how much my speedo is off and that's the only dif.

 

My manual is in my car which is in the shop but look closely at the AWD car at the Winter drive school Porsche has in Finland . They sure look like 19's to me.
http://www.youtube.com/watch?v=2dFo0HCqFog

 

As long as you keep the diameter between the 18 and 19's the same I do not see what the problem would be. Due to your car being AWD then if you differ from the outside diameter then I could see the problems you could have especially keeping the ratio betwen front and rear the same as 19" stock diameters.