LanceK

Thanks Teflon.

I guess the 17's are out...

LanceK

Teflon I just checked the ad of a guy who is selling 17"s and it states that the wheels will "clear any big red brake system".


Are you sure the 17"s won't work?


Thanks.

Viken

Maybe, the seller is referring to the older 993 red big brakes. Porsche does make it very clear that you cannot use 17" wheels on the C4S in their winter wheel and tire TSB. It shows that all 996 cars can use a 17" except the C4S, Turbo, GT2 and GT3.

Riad

Hmm... this is interesting. I have 17" snow tires for my 01 C4 that I was planning on keeping when I get my C4S. I'll plan on selling them now... good to know.

Rob

LanceK

I spoke to a Porsche tech briefly and he said that the 17" rim TSB may be valid but doesn't necessarily apply to ALL wheels i.e. aftermarket.


So I guess if there is a 17" wheel that clears the calipers you could still use it.

RSRRacer

Here are your options (based on lots of personal experience)

I use:

245/35/18 plus 285/30/18 rear; OR
245/40/18 plus 305/30/18 rear.

FOr slicks, I use 235/650 front and 280/650 rear or 305/645 rear.

Bottom line, keep diameters as close to the same as possible.

LanceK

Thanks RSR...

If I use your first combination of 245/35/18 for the front and 285/30/18 in the Hoosier auto-x compound the overall diameters are 24.5" front and 24.6" rear. I believe that should be more than close enough.

For comparison tire rack lists the diameters of my stock Pirelli Asymmetricos as 25.2 front and 25 rear.

So if anything the Hoosiers are actually closer in size front to rear.

RSRRacer

I didn't even see the auto-x reference..... for that I would definitely use the 285 rear setup for 2 reasons.

1) better setup vs the 305 rear to rotate the car;
2) shorter tire which provides better acceleration vs. taller 305 tire.

Good luck.

LanceK

My thinking exactly.


What a great forum.

JimB

Obviously I agree with RSR (look back about 40 posts) with the exception of the notion that shorter tires accelerate faster. I only bring this up because it seems to be a common idea that doesn't hold up at the track. Certainly if you are accelerating from a given speed in the same gear the shorter tire will be faster but the difference between 285s and 305s is enough that you frequently run into situations where you can be a gear lower with 305s. The trick is to have the right final gear ratio, not the lowest. A 996 on 305s in second gear at 5800 rpms is a whole lot quicker than the same car on 285s in third at 4000 rpm. (these numbers are just made up to make a point. I have no idea what the actuals would be.)

Having said that, 285s are still likely to be your best bet for auto-x. Now stop hanging out on this board and go buy your tires.