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I need to buy a new set of tires because Falken doesn't make my rears anymore. Have a 2004 996 C4S. So I'm looking new tires on Tire Rack and start comparing tires. I was looking at the Sumitomo's and noticed that front diameter/rev's per mile are different for fronts and back (25.1/826 v 24.9/834). So I'm thinking maybe because they're cheap. I then look at the Bridgestone Potenza's and they're worse at 25.3/823 fronts and 24.9/837 rears! And they are Porsche N3 approved. With the car being AWD, am I asking for trouble down the line? Thanks
I need to buy a new set of tires because Falken doesn't make my rears anymore. Have a 2004 996 C4S. So I'm looking new tires on Tire Rack and start comparing tires. I was looking at the Sumitomo's and noticed that front diameter/rev's per mile are different for fronts and back (25.1/826 v 24.9/834). So I'm thinking maybe because they're cheap. I then look at the Bridgestone Potenza's and they're worse at 25.3/823 fronts and 24.9/837 rears! And they are Porsche N3 approved. With the car being AWD, am I asking for trouble down the line? Thanks
The AWD depends on different front and rear tire diameters.
The "trick" is to stay within the wheel/tire sizes and the resulting different revolutions per mile numbers sanctioned by Porsche.
I dont think there will be any difference in any tire mfg for a specific size tire. if one mfg makes a 295/30 /18 the next mfg will be in the same spec
you go by the size that porsche recommends , do you think the front and rear are equal?
The "trick" is to stay within the wheel/tire sizes and the resulting different revolutions per mile numbers sanctioned by Porsche.
Originally Posted by Sneaky Pete
If I remember correctly you can have as much as a 5% diff in diameter from the front to rear and be good.
Yes. I went through this tire exercise recently with the Boxste', and had to try many combos before I could find one that was within Porsche "sanctioned" size and within 5% F/R.
I think OP was wondering if there is an acceptable range for variance in revolutions per mile...
There is but Porsche AFAIK doesn't publish the ranges. One can infer these indirectly by running the sanctioned wheel/tire numbers and obtaining the differences in revs per distance traveled or some other number and then taking the numbers of the setup one wants to use and seeing if its numbers fall inside that range of numbers obtained from the sanctioned wheel/tire sets.
If they do fine. If they do not I would be leery of using the non-sanctioned set of wheels/tires. That front diff and its viscous coupling is an expensive piece of hardware.