Ive had my 996 for just under a year now and its time for new shoes. Ive done a fair amount of reading on the subject and there are lots of threads out there saying that the rear tires need to be smaller than the front in order to transfer power to the front and not ruin the viscous clutch.
Ive also seen a lot of people talk about how they aren't following that piece of advise. With 19's it seems like 225/40 295/35 is your only choice, but there is lots of people out there running 235/245 fronts and 305/315/325 rears that don't play by those rules....


Is there anyone out there that has actually had any kind of failure or noticed any measurable ill effects from not keeping the "correct" tire diameter ratios?

 

They are supposed to be the same size or very close. If not the same size I think the fronts should be only just a bit bigger. I haven't heard of a failure happening but it is probably causing premature wear and there are probably people running around with worn out diffs who don't know it. It isn't that hard to find tires, there are a few good combos that work. Look around on Tirerack, they have a the sizes all listed nicely. I think I am going with Bridgestone RE-11 245/40/19 and 325/30/19 for my next set. They are both listed at 27.7 inches diameter. The 305 is listed at 26.3 in this particular tire so with a 245 front it is pushing it a bit but it should work fine.

 

27.7 in tires? That is a huge jump over the factory 25ish" tires, does that even fit without modification?

 

Just rolled fenders and maybe melting the liners back a bit.

 

I run 20" wheels in 245/30 front and 305/25 rear (on stock suspension & no body nor fenderliner modifications. ) . They look/fit/ride GREAT. I will never run 19s again. It's dubs or stockies for me- nothing in between!!! It probably goes without saying, I don't track my car.

 

26.7 not 27.7. The 245/40/19 will not fit in the front. Only way to run a 325/30/19 rear is with rwd. You can run a 255/35/19 front and 305/30/19 rear though with all the mods to the front liners and radiator brackets.

 

That extra .7 inch is too much for the front?

 

Yep it's a huge different, especially up front where you have to deal with turning.

 

So much for that plan then. I'm thinking about modding the front now.

 

Here are 255/35/19 (26.0 tall) at a slight turn with missing the radiator brackets. No more room for something 26.7 tall. I may even mod mine more this winter as well.

 

Yah that is close. The 225 will fit but I want to go wider. I hate it when my car plows a tight corner.

 

you can run a 275/35/18 front and a 315/30/18 rear. I'm a 19 a 245/35 and 295/30 is really the easiest to fit setup that's grip well with awd

 

Hrz2 tires in a 295/30/18 235/40/18 fit and the rolling diameter is within spec.
Shawn

 

I have a set of 19 inch rims with 12 in wide rears. I think the 255 and 305 combo will work best for me.

 

All good info but we are a bit off topic. Have any of you that run a larger diameter rear tire than front experienced any ill effects?