Help! 996 c4 tire options for the track
 

I really need the help of the tire guru's. I recently purchased a set of oz allegerita in 996 Gt3 spec (18 x8.5 and 18x11 as opposed to the 18x8.5 and 18x10 that were recommended) for my 99 911 c4. I purchased them with the intention of running a wider tire for the track. Now as I am ready to pull the trigger on tires I am receiving conflicting information that has caused me to second guess my wheel purchase. Due to the awd system, I was told that I can only run the recommended 225/40 and 265/35/18 tires. Anything else I will run the risk of causing damage to the differential and transmission. Does anyone know with certainty if this is true? If not what are some tire sizes I can run on my car to accommodate the wider wheels yet still stay within the correct tolerance that is recommended for my car. Your help is greatly appreciated. I called Porsche of North America and even my local dealership and they both informed me to stay with the stock tire sizes.

My C4S is a 997.2 and I have 11 rims with 305's and I believe the non-S has 295's. Are the 997 and 996 so different? What did you decide?

225/40 and 235/40 18 will work up front.

On an 11" rear, 265 is a bit narrow. 285/30 18, 295/30, and 305/30 18 are all better fits.

225/285 or 295 are closest matches in OD.

If using the 305 in back, it's best to match to the 235 up front.

The AWD restriction is due to tire height differential. Factory spec is fairly loose, I'd to actually look it up, but it's something like < 3 to 5% diff. The less the better though
225/40 & 265/35 are fine
235/40 & 275/35 are fine
245/35 & 285/30 are fine

A 26" tall front tire in a track squat environment is likely going to give you issues. 225/40 and 235/40 are better ideas.