Currently I have a 235/45/17 tire on the front wheels. I want to get a 245 tire, but which sidewall, 45 or 40, will have the same height as my current tire setup?

 

Neither... 245/45 will be taller, 245/40 will be shorter...

255/40-17 is as close as you are gonna get...

 

Thanks... I guess i'll go with a 245/40.

 

Stock- 235 x.45 = 105.75mm
245 x .40 = 98mm
245 x .45 = 110.25mm
255 x .40 = 102mm

Personally, I would go with 235/45 just the like factory recommends. Like Mitsu said, 255/40 is the closest you are going to get to a 235/45 but it will look really "fat" and ugly. 245/40 is too short, and 245/45 is too tall.