Tire sizes for a C4 with 19s ?

I am looking at replacing the tires.on my 99 C4 with 19" 8.5 front and 11 rear. It looks like 235 35 19 front and 295 30 19 rears are recomended. But I have read that the C4 sould have 5% smaller dia. Tires in the rear to allow the viscous coupling to provide the proper torque to the front wheels. The tire combo above has the rears at 26 and the fronts at 25.6. Just the opposite What size should I run with 19s and 8 in front and 11 in the rear?

The rear tyres should not turn slower than the fronts; the do not have to be 5% smaller.

A little bit more information would be helpful. Here are a couple of questions and comments: - There's not an official recommended tire size for 19" wheels on the 996. Porsche only recommends sizes up to 18". You can find recommendations online and on web forums, and you'll have to pick the one that sounds the most credible to you. - What year is your 996? Early 996s sometimes need to have the rear fenders rolled to accept larger sized wheels and tires. There's a Porsche TSB on this... - Is your suspension stock or has your car been lowered? - What kind of look are you trying to achieve? Are you simply wanting larger wheels or do you also want to push the wheels out a little bit? - What are the offsets of the 19" wheels that you'll be using? - I've always heard that the difference in diameter between front and rear should be 3% or less. I'm not sure which number is correct, but I'd certainly try to get them as close as possible. My biggest concerns with your switch to 19" wheels would be the viscous coupling as you've noted and tires rubbing.

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I have a 996 C4 my tires are Front 235/35/19 with nearly 2 1/2" lip; Rear 275/30/19 with 3 1/2" lip. I have had them on for since 2008 with deep dish Rims, and no problems at all. You will need to have a" tight" suspension springs and shocks. If your suspension is not tight you might have to find a experience body shop and have the rear fenders rolled ( Fender Lip tucked under flat against the inside). My tires are no protruding from the fender either. Gives an impressive look.

More info. I bought the car recently with the 19s on it. It has 135K and stock suspension that is in good shape. The PO has 265 30 19s streched on the rears and it looks ghetto. Another member posted that he had the 295 19s on the rear and it fit perfect. If I am reading the numbers on the wheels correct they are 50 offset. If I need to have the fenders rolled I will. In my research into the function of the awd system, they mention the rears being slightly smaller to make them turn faster and thus provide a small torque bias to the fronts during normal driving. My wify who normally does not any "non-stock" kind of look likes these wheels. So the wheels stay. Thanks for the inputs.

I'm running 295's on rear and have no issues whatsoever. The fronts rub a teeny bit if I turn the wheel more than 75% in one direction, but that only happens once in a blue moon..... Btw, mine is a 99 C2 with OEM 996 GT3 suspension; 997 GT3 wheels (non-RS wheels); and lowered about 1"