bigger is not always better. Bigger probably means the gear ratios go taller. Bigger sometimes means heavier and this is bad.... and either way your probably putting on bigger rubber which is more weight located 8.5" or so from the center or torque.

 

I had these on my first S they looked great but they are soooooo heavy. Also the rolling diameter was slightly higher. On a driver training course with 3 other S's I was getting higher top speeds in each gear and taking slightly longer to get there!

So two factors to consider. Weight and diameter!

 

Just make sure you get the proper size tire and you won't have an issue with the diameter. I run 255/35R18's and I'm only .x inches off from stock diameter. Weight of my wheels are the same as my 16s. I feel no difference going back and forth between my wheels aside from the obvious more grip with the 255 SO tires on my 18s.

 

I think 17s look best

 

"Proper" means what the car came with originally. See if your 18" tires match these diameter and/or width specs:

 

My rears are approx .2 inches off from the OEM "proper" size. If you going to say that you can feel a difference in two tenths of an inch, hah no comment


If your just asking me a question if they match, then sorry for me being rude


As for width, I can't say. My tires mounted on my 18s are packed away till winter.

 

that chart does not account for the contact patch which is different for each manufacturer. This is the reason the SO2 is so bad with standing water - low on the water channel count

 

No problem, just checking. The 245/40/17 RE050 rears are actually listed at 24.6" in diameter. Most 255/35/18 rears are 25.2" and larger. I could definitely feel the difference, and I was running BBS RGR 18" wheels so they were about the same weight as the stock wheels.

Which tires are you running?

 

You better stick to the older ones then. Or put a turbo on your car.