Feenix

I'm planning to go from a 245/50r16 on the stock 16s to 18x8.5 front wheels and 18x10.5 rear, and running 255/35zr18 front and 295/35zr18 rear.

My question is would I need to combine the differences in the staggered new tires to come up with the diameter change for the speedo or how would I go about figuring that out?

I tried to search for this answer for a few days now and I just can't find what i'm looking for. So I apologize if this is beat to death question.

hrlyhnx

iTrader: (3)

I'm not a mechanic but what i heard was it needs to go on the Dyno for accuracy. Might want to check there first.

Feenix

Nah, I know what to do if it were all the same size tires. The part thats throwing me off is the staggering. I don't know how to go about figuring that out. Do you mix the values? Or what?

trans_am7935

iTrader: (15)

why dont you go with a 255 40 18 up front instead, it should put them both just around 26". if you went with these tire sizes in BFG tires, the rear would measure 26.1" diameter and the front with my suggestion at 26" diameter. the speedo would be so close there would be no real difference. i have included a chart so you can see the difference

also if you have a Diablo Sport, HP Tuners or other tuning software you can just input the tire size and the computer will adjust itself. Also any Tuner can should be able to take care of this issue.

Feenix

Thank you for the solid feedback. So 255/40 it is. I have potenza re760's planned. Dunno how much difference that would make.

I do plan to have a mail order tune from frost once I put headers on, so I'll take care of it then. Thanks alot for the post.