If you go with 215/40-18 front and 245/35-18 rear, you will be about 0.05" lower to the ground, which is nothing. Because these 18" tires are about 0.1" smaller in diameters than 16" OEM.

 

The 225/40R18 and 255/35R18 are within .1" of the stock diameter. They will not change the gear ratio at all. If the 18" wheel is lighter it can actually be quicker and brake easier.

 

After further review......I agree that the difference is minimal on the plus size example.

I apologize for stating misinformed or incorrect information. Just trying to help

 

I'm confused as to how it could be quicker...even a lighter overall wheel, would still have exponentially more rotational mass...inhibiting acceleration and braking.

The bigger wheels will have less compliant sidewalls making it a stiffer, (and in the case of racecars) more controllable and tuneable ride....personally dont see how it could be quicker in the straight line sence.

might be missing something though.

 

What is the heaviest part of the rim/tire combo? The tire, right? With a 18 inch rim, you are pushing that weight further away from the axis of rotation, increasing the inertia exponentially.

Although it should theoretically slow you down in terms of acceleration and increase braking distances, you also benefit from a stiffer/shorter sidewall, and a wider tire selection for potentially more overall grip. In terms of daily driving though, i doubt you'd beable to notice much difference at all between the two.

 

The comment was made if the 18"wheels/tires are "actually lighter" then you would see improvement. Most 18" setups are not though...