Hi, I've did some search and got mixed information about tire sizes for the 996 turbo.

Currently running 235/35/19 front and 315/25/19 rear.

Looking to change to 235/35/19 and 305/30/19 rear.
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Will this be okay on the drive train and not ruining the differential?

Car is for weekend spirited driving. Want to have something that rides a bit smoother on bumpy roads.

Thanks
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Go to the 245 front if you are running 305 rears. The 235 is a bit small in comparison to the rear. The 997 runs the 235 front but has different gearing to make it work.

 

I run 245/35/19 and 305/30/19 rear in Bridgestone S04 without issue.

 

If I keep the front 235 that would be an issue in the future?

 

Do 315s in rear require rolling the fenders?

 

It is thought to possibly over heat the front diff as they will be working against each other. The Porsche tolerance I thought was something like .3 inches and the difference between the 235 and 305 is quite a bit more than that. You could possibly do the 295 rear with the 235 front but even then you would still want to do the 245 front.

 

No they do not since the profile is 25. Like riding on rubber bands and nowhere close to rubbing.

 

Would i be able to fit 235 30 19 front and 325 30 19 rear?

 

No way 325 is way too tall. Look at the diameters of the tires, they need to be closely matched.

 

I just bought a 996tt with this exact same tire combination and wondering the same thing, from what I gathered in the service records the car has been running this setup for a while but doesn’t seem to have had problems with the front differential or VC (or at least there’s no records of it).

For what it’s worth a PPI was also done about 5k miles ago does not show anything regarding the front differential and/or VC.

 

Yah it might be fine and it might not. Just going with the recommended specs. We joke around about there being a lot of 996tt with front diffs that are worthless/ruined but we really don't know. Next time you buy tires just get the 245 fronts if you go 305 rear. Might save you on gas, might save your diff.

 

For the rears:
Looking at Michelins the 305/30 is 26.3 inches diameter, 295/30 is 26.

For the fronts
225/40 is 26.1 might be a tight squeeze but pretty tall, though too narrow for a car that already under steers
235/35 is 25.2 really short tire
245/35 is 25.8 much closer to the 295 and 305 rears

So when you go 245/35 front you are within .2 of the 295s and .5 of the 305s with good width. The 235 and 305 combo is 1.1 inches apart which I believe is significant.

 

and as much as i can understand - not recommended? thanks

 

Make sure your front tires are always a little taller than your rear tires. I chased a "tank slapper" issue for years, until I realized with was caused by the fact that my rear tires were trying to push my front tires down the road. After finally changing my tires sizes, the problem is completely gone.

Old setup 245/35R19 F (25.8" tall) and 295/30R19 R (26.0" tall) DO NOT DO
New setup 235/40R19 F (26.4" tall) and 305/30R19 R (26.2" tall) This is taller than most people will want to run, but worked great at eliminating the tank slapper issue.

Later, Steve

 

Here's the link, if you want to see my pain,

https://www.6speedonline.com/forums/...lp-needed.html