OK, let's ask this question here.......

Does anyone know if the computer will complain about a 2" (or more) diameter difference ?

If so, what is the maximum allowable difference ?

 

I believe it would, anything over 1 inch starts getting problems

 

I was running a 1.4" difference on my 07Z. Only warning I got was Engine Drag Active on decel. No big deal.

 

Since you don't specify what size is 2" different than another size, here's how to calculate if they'll work.

New OEM tires have a rear diameter that's 1.04 times larger than the front. Since the car will still operate correctly when the fronts are bald and the backs new or vice versa, you can do the calculations of tread depth differentials to find the ratio limits. If you are on the ragged edge of the ratio limits with new tires, you could have a problem when they begin to wear.

 

Patriot,
thanks.
On my '08 Z, my A7 tires are 1.4 inches rear to front and no issues.
But I am thinking of getting Toyo R888R tires...
305/30/18 25.3"
345/30/19 27.1"

1.8 inches difference.... Hmmmm ????

Sam Strano runs a little bigger front and the same as this rear in the A7 for his C6 Z, and has no problems. His difference is 1.7"

 

27.4 tall rear tires (305/35/r19 Michelin Pilot Super Sports) and 25.6 tall front tires (275/35/r18 Michelin Pilot Super Sports) for a 1.8 inch difference and NO issues whatsoever Gary.

I've driven over 6.5k miles on two long haul trips (from GA to WA and back) and the only problems I had were from the 2 to 3 inches of water on the roadways in Oklahoma on the way back here to GA.

 

Thanks Kenny