it's also usually the mixing of tires front to rear, and/or new to old that seems to cause the abs/psm cels which are often associated with *mismatched* sizes or inequal tread depths. the ecu ( usually ) adjusts. or not, if the match is way off. +1 that was great info on the 19" tire size choices..too bad i'll probably never be able to use it.

i would think the 807/792 would be fine. that max 3% differential btw frt/r is myth, for a reason.

 

I understand how rim width can impact rolling diameter, however it's not feasible for me to mount and measure different tire sizes before purchase. I think the specs provided by manufacturers provide enough information to make an educated purchase.

Thanks for the feedback.

 

True to a point But you do have knit pickers that make a point about the size difference differences between front and rear solely by specs given, so they should be accurate when they knit pick,,, LOL..

 

I wonder if we could run 245/35ZR19 on 9" wheel and 325/30ZR19 on 12" wheel with Michelin Pilot Super Sport tires.

 

I went with the 305/30/19 in the back and 345/35/19 in the front. Car is fairly low, no issues in the front so far. The back was VERY tight, I had some very slight rubbing on the inner fender liner on the first drive. Happy with the tires so far.

I have BBS CHR, 19x9 ET51 in the front, and 19x12 ET45 in the rear. Hope this helps. Good luck, I suppose anything is possible, but you may have to modify or change the fender liners, I *think* the GT2 liners may provide more clearance, research this.

 

Thanks looks like I found another option
Nitto NT01 235/40/18 and 315/30/18
or
Nitto NT01 235/40/18 and 305/35/18

 

Your other post mentioned ZR19 .. So I thought you were on 19's ?

 

I would have had to get 19's, I all ready have 18's
Looking at tire selection options with higher widths then stock are difficult with 18's so was thinking I had to go with 19' to get more selection choices.

 

Just mounted techart 19s with 235/40/19 and 305/30/19s on 996tt lowered to gt2 specs. I'am getting considerable rub, any suggested fixes? Please help, thanks!

 

commonly recommended the combo of 245/35/19 in the front and 305/30/19 in the rear or alternatively the combo of 235/30/19 in the front and 315/25/19 in the rear. There are other options as well, but these are common option that should keep you within spec front to back.

 

First, this was an immensely helpful thread - great info.




I've worn out my 225/35/19 - 315/25/19 PS2s and am probably switching to 245/35/19 - 305/30/19 Pilot Super Sports (based on this and another thread where the 315/25 vs. 305/30 was debated at length). The rolling diameter of my existing setup is 25.2" F&R and the diameters for the new setup are 25.8"F & 26.3" R. Being that I'm adding between .6 and 1.1" in diameter or ~25-30 revs per mile, how will that affect the speedometer?

 

You will actual be going faster then what your speedo reads.
I run close to that size with my 245/40/18 and 295/35/18 sizes.
There is a formula for correction with tire diameter changes which I will look up when I get home.

 

That's what I thought. My radar detector and GPS will tell me the correct speed so I can reference them, but I'm not a fan of not having an accurate speedometer. I wonder if there is a way to calibrate the speedo?

 

Just thinking this through out loud...if the speedo runs off the front wheels, the OE 18" tires had a diameter of 25.3" vs. the 25.8" I'm going to, so it's an increase of just under 2%; so if my speedo reads 70 I'm really doing about 71.4. Not a big deal I guess. Now at 150 I'm really doing 153...I might get a ticket for that, LOL.

 

I was told there was away to compensate for a tire change in our ECU management settings But that was not the case, as I brought my car to dealer.. But 997turbos have that.