Important - DO NOT put 315's in rears!!!!
#17
03-11-2007, 11:34 PM
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#18
03-11-2007, 11:36 PM
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Originally Posted by Simba
As a general rule, you want to keep your tire rotational speed identical to the stock speed, and in effect proportionally stock tire height for the front and rear wheels. If you don't, the difference in tire circumference and hence wheel speed will quickly start roasting diffs.
The width of the tire doesn't matter. The overall height of the tire does. You can run 315/25/19 rear tires just fine, but you will need to size the front ones appropriately. I believe the closest you could get with commonly available tire sizes in 19" would be a 265/30/19 in the front. It would still be slightly slower than the stock front wheel speed, but much less so than 315's and 235's.
Alternatively, you could just rip the AWD system out and run whatever you want.
The width of the tire doesn't matter. The overall height of the tire does. You can run 315/25/19 rear tires just fine, but you will need to size the front ones appropriately. I believe the closest you could get with commonly available tire sizes in 19" would be a 265/30/19 in the front. It would still be slightly slower than the stock front wheel speed, but much less so than 315's and 235's.
Alternatively, you could just rip the AWD system out and run whatever you want.
#19
03-11-2007, 11:39 PM
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4% rolling dia, 15% total suspension geometry is max tolerence within spec on a 997TT/996TT/C4S awd system. Probably magnified a bit in the all electronic 997TT version.
#20
03-12-2007, 02:28 AM
I foresaw this problem when I was spec'ing out tires to run 18" wheels on the track. Divide the dia of the front tire by the rear and you get a percentage. Try to keep very close to that ratio and you'll be OK. My Hoosier track tires are smaller in diameter than stock - 24.8" vs 25.5" front, 25.6" vs 26.3" rear. Ratio-wise, the Hoosiers are 97.2% of the front and 97.3% of the rear. This has been close enough as not to disturb the differential, ABS, and stability programs.
Last edited by eclou; 03-12-2007 at 02:35 AM.
#21
03-12-2007, 12:41 PM
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Originally Posted by cayenne_ksa
I think the main thing is the diameter of the tire and it has to be as high as the front
#22
03-12-2007, 02:38 PM
Originally Posted by fredttx50
Hi guys,
More to follow but my car is in the shop as I have an over heated front differential clutch. This is not the actuall clutch, but a clutch in the differential. (this showed up while looking for fault codes). It shows up on the computer as an overheated clutch.
Porsche is looking into this but the preliminary diagnosis is that it seems to be related to the height of the rear tire, in relation to front/rear tire size. The front tire height is the same as stock, the rears are an inch shorter, which seems to have burnt out the clutch in the front diff.. They are saying that difference can definitely burn the clutch and is not warrantable.
Therefore I am going back to stock tires sizes.
More to follow but you might want to hesitate on going with 315's at this moment.
Thanks!
More to follow but my car is in the shop as I have an over heated front differential clutch. This is not the actuall clutch, but a clutch in the differential. (this showed up while looking for fault codes). It shows up on the computer as an overheated clutch.
Porsche is looking into this but the preliminary diagnosis is that it seems to be related to the height of the rear tire, in relation to front/rear tire size. The front tire height is the same as stock, the rears are an inch shorter, which seems to have burnt out the clutch in the front diff.. They are saying that difference can definitely burn the clutch and is not warrantable.
Therefore I am going back to stock tires sizes.
More to follow but you might want to hesitate on going with 315's at this moment.
Thanks!
#24
03-12-2007, 03:23 PM
Originally Posted by NormanM
Could not find the tire size calculator could you post the direct link
It would have helped if I had typed it correctly the first time. I also use the offset calculator often.
>?
It would have helped if I had typed it correctly the first time. I also use the offset calculator often.
>?
#29
03-14-2007, 05:10 PM
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Correct me if I'm wrong but 315 is the width... What does the width have to do with the heighth of the tire?
Before everyone starts removing their 315's someone needs to clarify what you are saying.
Before everyone starts removing their 315's someone needs to clarify what you are saying.
#30
03-14-2007, 05:53 PM
Yeah, this thread would be more helpful if the make and size of the tires were specified.
Does anybody know if there would be similar problems for the 996's models? I'm guess it would be ok because we have mechanical diffs?
Does anybody know if there would be similar problems for the 996's models? I'm guess it would be ok because we have mechanical diffs?