I bought AG Mesh 20 inches wheels. The supplier (to rename nameless, for now) said that 295/25 and 245/30s would be ok.. roughly even diameters, so about 3% less rear drive than stock.

Of course, this gave me the PTM inactive error.

Bumping up to a 305 rear gets me to 2.3%. From my reading on this forum, <3% should be ok.. so this should do it?

a 315 rear would get me to 1.1% difference... but 315/25s seem pretty rare..


Thoughts?

 

why wouldn't you just run a 305 width like the stock set-up?

305 rear with a 235 or 245 front or if you went wider 325/25/20 and 245/30/20 seems to be pretty common also. Not heard of anyone really going narrower than stock, especially on the rears.

 

Working with the supplier to resolve this in exact that manner.

However, a 315 out back even with a 235 up front (in 20s) still have a smaller % split. Unfortunately aspect ratio is just an 'estimate' of real sizing. still a 2.3% difference from stock.

 

I'm running 315/25 and 245/30 Toyo with absolutely zero problem. I wanted 325/245 setup like everyone recommend but my rear wheels are only 11" wide so 325 would be too much. However I found that my 315 Toyo has same exact diameter(26.3") with 325 PSS according to Tirerack website.

 

What year/model car?

 

997.1

 

I ran 245/30-20 (9 inch) and 325/25-20 (12 inch) on a 997 C4S with no problems. I realize the AWD systems are different between the C4 and the TT but I think the front to rear ratios were OK and didn't cause any differential problems. You have to be careful with tire sizing since the wrong sizes can cause your AWD to "blow-up".

 

Wish I could do a 325, but wheel is too narrow. guess I could widen it. Done that before back in the day.

Looking at 305s for the rear, but that will still put me at 2.3% different than stock. I am wondering if it really hurts anything. I mean, its just a diff. if the PTM turns off because its hot.. it should just freewheel, and unless you are running tires that are WAY different.. I would think it woudl be ok.

Dunno enough about how it works exactly! Vendor is being awesome. Hopefully we can figure it out.. Anybody know if 305s will do it?

Tempted to throw in the towel and go back to 19s :-(

 

What do you mean by blow up? Just curious

 

Destroy center diff(front diff on Pcars?) and /or PTM.

 

Looks like tires in the size I need are non existent right now. May have to return the setup and go to 19s

 

For 20's, go 245/325 only. That's the only combination people run. And it will kill your center diff - not to mention the car just doesn't run right if the ratio isn't correct.

 

Yup, working on that right now with the vendor. he has been good. Trying to find 325s right now!

 

On a 997/1 turbo you can run 235/30r20 FR and 305/25r20 RR.
100% safe and within every tolerance.

 

+1 and it can also cause issues on some cars in the rear as well, IE tips with the crown and pinion area.