cbzzoom

I'm thinking of switching my 997 C4S to 18's. Mainly for more sidewall to absorb bumps on the road & track more, but two other things I'd like to get out of it are : wider tire in the front for less understeer and less weight.

I'm trying to figure out exactly what my 18" options are.

I think for the 4WD the important thing is to keep the ratio of the diameters front to back roughly the same.

The C4S OEM fitment is :

235/35/19 Diameter: 25.47 in
305/30/19 Diameter: 26.20 in
Rear/Front ratio = 1.0287

The C4 OEM size is :

235/40-18 Diameter: 25.40 in
295/35-18 Diameter: 26.12 in
Rear/Front ratio = 1.02835

Obviously I could go with the C4 size, but I'd like to go wider in the front if possible.

One options is to go with the OZ wheels that are 8.5" front and 12" rear and fit :

245/35/18 Diameter: 24.75 in
315/30/18 Diameter: 25.44 in
Rear/Front ratio = 1.028

this is a very good ratio match but they are quite a bit smaller overall.

Any suggestions or other options? How wide a front rubber can I fit on an 8.5" wheel? Are there any good/cheap/light 18x9" wheel options? Will I have any trouble with rubbing with wider fronts?

cbzzoom

Front options : there seems to be no problem getting tires in the front sizes, they are very common

235/40/18 Diameter: 25.40 in - OEM C4 - 8" rim okay
245/35/18 Diameter: 24.75 in - 8.5" rim
245/40/18 Diameter: 25.71 in - maybe too much sidewall
255/35/18 Diameter: 25.02 in - wants 9" rim
265/35/18 Diameter: 25.30 in - wants 9.5" rim

Rear options : more of an issue here :

295/35/18 Diameter: 26.12 in - OEM C4 - lots of these and cheaper, fits nice on 11" wheel
305/35/18 Diameter: 26.40 in [x] tire doesn't exist
315/30/18 Diameter: 25.44 in - mostly high end & race tires - 12" rim
325/30/18 Diameter: 25.67 in [x] tire doesn't exist
335/30/18 Diameter: 25.91 in - mostly high end & race tires - 12.5" rim

Front sidewall heights :

235/35/19 sidewall 8.22 - OEM C4S
245/35/18 sidewall 8.58
255/35/18 sidewall 8.92
265/35/18 sidewall 9.28
235/40/18 sidewall 9.40 - OEM C4
245/40/18 sidewall 9.80

brad@tirerack.com

295/35 on a 10 or 11" Allegerita, and 245/40 on an 8.5 is most popular for high performance street and or track.

Please give me a call if interested. Thanks!