The difference between 225/40 and 225/45 is 3.43%. This means your speedometer and odometer will read 3.43% too high, and you shorten your final gearing by 3.43% also. IMO the aesthetic difference between 225/40 and 225/45 isn't big enough for most to even notice, but by doing this you are effectively racking up and extra 3 and a half percent more miles on your car roughly.

I am no proffesional racer, but I can't imagine that shortening your final drive by that amount will make a huge differnce, and certainly the performance benefits on the street are marginal at best. Not to mention that you are much more likely to damage your wheels.

At 50,000 actual miles your odometer would read 51,715 miles.

Wouldn't be my choice.

 

Maybe Im wrong...but the dimension of your wheel didn't change so your speedo should be right on. And am I wrong in thinking that changing the "profile" of the tire is to adjust the thickness between tread and rim, not inner and outer wall?

 

The profile is the ratio of your sidewall height to your tread width, so a reduction in profile without a corresponding change in your tire width means the outside diameter of your tire is shorter. This in turn means that the shorter tire has to make more rpm to cover the same distance, but the speedometer and odometer are actually measuring how many times your wheels go around, so it is assuming stock tire diameter. So then you are reading a higher speed and racking up miles faster than your actual speed and miles travelled.

 

the only real difference your going to get is the look and ride quality difference. It will be more rough. The speedo may be like 1/2 of a mph off and you wont see a difference in your gearing. In theory it makes them smaller but you wont be able to feel it. I would just stay with stock, you wont get any gains out of it other then crappy ride.

 

This should help:

http://en.wikipedia.org/wiki/Tire_sizing

 

you need to have the outside diameter of both tires. the stock tire is 25.9". a 245 40 18 tends to fall in at 25.8. very very close.

beers