I have done a lot of searching and I have seen that most people who vary from the OEM tire size on the stockers have gone with the 245/40/18s for the obvious reasons (sidewall ratio, speedo, etc...)
BUT, with that said, I am looking to get new tires after being on 225/45 Kuhmo SPTs for 20K. Didn't like them that much to say the least. I've been doing some searching for a while and have decided I want to go with the Kuhmo ASX. Put a set on our BMW and really liked them. Great treadwear, good noise comfort, and responsiveness...
So here's the dilemma, I am going to get the tires off of tirerack, my local installer orders from there, and I wanted to know opinions on going with a 235/40 against a 245/40. My only reason for debate is because of the $83.00 a piece against the $113.00 a piece for the 245s.
Will I be kicking myself for the difference in sidewall, diameter, small speedo change, etc...?

 

on the stock wheels that will b fine....it might b a little rougher but not bad I'd go for it you wont' hurt anything

 

ok. should a smaller profile make for a shorter tread life?

 

what? no i dont think so.

it will make the ride slightly stiffer. the upside is that you will also accelerate faster with the smaller 235/40 tire.

 

I run 235/40/18
My speedo is off by about 3 mph. No problems though.

 

^Not too bad I guess, If you can get used to it.

 

The speedo wil read 3 mph faster than what your actually going.

 

235x40 is actually a pretty good size, as 245x40 is a bit wide sidewall support-wise for the stock 18x8 rims.

My next tires will be Michelin Pilot Sport 2's. All around goodness (but a bit pricey).

 

A Tire Size Calculator will help you make your decision.

 

Oh ja, save money!