Well I did it. Changed my rears to a 245/35 18 and I am still running 225/40 18's.
Do I need to drop it down to 215/40 18's????

Also if the Speed rating is different does that effect handling too? Front's are Z's and Rears are Y's. They both have about the same treadwear rating. 20 points difference.

 

Are you using the same tire front and rear? If not that will cause the handling to be off. The best thing is to match the tires front and rear. Not may people make a 215/40R18 tire so that will be tough to find a matching tire.

Jim

 

Yeah unfortunately. Not many people make the 245/35 18's either. I haven't decided if I like these or not. To even get the front matching wheels. The wheels are 2 different brands.

 

I too am running 245/35R, 225/40F all four T1-S. Supposily, the tire diameter is a 1.32% difference and the speedometer difference is a 1.33% too fast. Also, comparing 255/35R and 225/40F the diameter difference is 0.24% and the speedometer difference is 0.241% too fast. I knew all this but the hell with it, i went for the 245 rears anyways. I saved $200 this way

 

Oh and i forgot, why did YOU change to 245 anyways?

 

actually the tire diameter of the T1-S at 245/35/18 is 24.8 which is same as the stock S0-2. You spedometer shouldn't be off(well except for how much it is from the factory )

Fronts diameters won't matter when it comes to spedo....

 

^ Ooooooh Yeeeaaaaa!!!!