I found this and might be of some use to explain the "measuring" rim spec (that rim width figure generally in the middle of three numbers on a tire spec page).

There is also some info on what the consequences of going with a "too narrow" or "too wide" rim are...

Tire Width, Rim Width And Aspect Ratio link:

http://www.dunloptire.com/tiretech/W...tire_width.txt


General Tire Info Link (Tire Tech 101 – this is the main page):

http://www.dunloptire.com/tiretech/

 

Goond info there, thanks Eric, Chod should add some of that info to the faw perhaps?

 

That's good info that's hard to find - I did a lot of searching for narrow rims and couldn't find it. I put 235/45's on my car a few weeks ago and I love it. As the article says, the ride is less harsh, the sidewalls absorbing more of the bumps. It moves the CL-S more toward the luxury side of the luxury/sport equation.