[Sccabrz192]

I'm not too sold on the 235/40 myself... The car has a short second gear, and that limiter is devastating the way it cuts out and takes so long to rebound. With the smaller circumference of the 235/40 you are going to be hitting that cut earlier.

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
215/45-17 3.8in 12.3in 24.6in 77.3in 819 0.0%
225/45-17 4.0in 12.5in 25.0in 78.5in 808 1.4%
235/45-17 4.2in 12.7in 25.3in 79.6in 796 2.9%
235/40-17 3.7in 12.2in 24.4in 76.7in 827 -0.9%

I have 235/45 ZII's on order.

My theory is, the car is already underpowered, and likely will already be an underdog on power courses to the Z-cars nationally... so I am going to hedge my bets on the fast flowing courses by getting the most I possibly can out of the top end of second. Additionally, with the taller 45 A/R, the sidewall will be less pinched than the 40, creating a more ideal tire dynamic and sidewall. The ideal rim width range of the 40 A/R has a min of 8", the 45 A/R has a min of 7.5"... I figure only being 1/2" out of bounds isn't going to exhibit as much negative effects due to pinch as being a whole inch out.

That's my theory, we'll see how it goes... FWIW it should be right around a 2.25 MPH difference between the 235/40 and the 235/45 in 2nd.