Just commenting on this, I just got 4 18" 5 spoke Dart wheels from one of my troops for super cheap, I'll be mounting some 235/40-18's on them and running them in the summer.

 

Check the back space! It shouldn't be more than 42mm

 

Will do! I did toss them on with his tires, 225/40-18, and the fit. But I am not sure if the offset.

 

So long as they clear the body and suspension, you're fine!
We need pictures!

 

Good deal, as soon as I get some rubber for them ill snap some pictures and post them.

 

225/40/18's are going to have a short sidewall and probably give you a rough ride. Spec out at about 25 inches.
255/40/18's would give you another inch of sidewall and the ride would be better. They would clear the suspension, providing the offset is OK.

 

You mean an extra 1/2" of sidewall, and just over an inch more in overall diameter, right?

 

Technically yes. But you have to add the 2x factor and multiple to achieve the upper and lower area of the increased sidewall height to end up with the overall height of the yada, yada, yada.

Oh Hail ! Now my brain hurts. Think I'll go cut some grass.
(Yes. Our grass is growing again. 82 degrees F. forecast for today )

 

I was looking at the 235/40-18 to keep the speedo within .5%. I have the ability to change the BCM to the 17" wheel option also. Not to worried about the sidewall height, I have the FE1 suspension, but the front struts have been changed to quick struts. So, the ride is kinda soft. In the end, I just want to keep the speedo accurate and the ride is secondary.

 

You gonna swap out those quick struts to KYB's and Canucks?