I'm thinking about getting wheels that will run 215/45-17 tires and am wondering if it would be better to have 17x7 or 17x7.5? What's "really" the difference?

 

About the only difference that I can see is that the 7" rim would offer slightly more protection for the rim from curb rash. Other than that I can see no real difference. The 7" is also the recommended size for that tire.

The 7.5" may just stiffen the sidewalls slightly.

 

Not that much difference.

215/45-17 fits rims 7-8" wide, perfect fit for 7" rim so both rim widths will work fine.

You do get about 1/2" wider tread with the 7.5" wide rim.
You also will likely add a little more weight for the 7.5" rim.

Basically it comes down to rim selection as some will come in 17x7 while others come in only 17x7.5 or even only 17x8 sizes. Offset comes also into play as wheels with about +42 to +45mm offsets will fit better than rims with +38 offset or less depending on tire size and your suspension drop.

Performance wise you will be close and tire selection will play a bigger role than rim width.

 

I have 7.5 17 wheels and get a lot of rubbing on bumps and twisties if I have passengers now that my car is lowered with Mach V springs. I may switch back to JCW springs unless Dan can fix this. It is very annoying to hear the scraping all the time.

 

what offset and what tire size?

 

minihune, I agree with every single thing you wrote, except that. Although the WHEEL width is going to change by 0.5", the TREAD width will barely change -- more like 0.05". The tread width is basically fixed. The only thing that's different is the sidewall shape will change slightly from the wider wheel, resulting in an almost insignificant change in the amount of tread on the ground as the sidewall changes from this |_| to this \_/.

--Dan
Mach V

 

+1 to Mach V Dan

 

Yes, more accurately tire section width will change a bit with the wider rim while tread width is fixed more or less. You might be able to use more of the full width of the tread with a wider rim depending on tire pressure and alignment settings. 1/2" difference in rim is pretty close.

For 205 vs 215mm wide tires and 7 vs 7.5" rims it's pretty similar.
I'm not sure if you could really see or feel much difference with either tire mounted on either rim.

Yes, in theory you may get a slight mismatch as you push the limits of fitment. Yes, you do want a good match whenever you can.

\_/ more evident with 8" wide rim and 205mm tire. Some tires do vary with how they fit on a given rim.

Functionally for the OP, both rims will work for street use and daily driving.

Rubbing is at risk with lowered suspensions and with offsets that are at the limit of fitment usually about +38 mm with 17x7.5" rims and taller than stock diameter sized tires like 215/45-17 or 225/45-17.

 

Is an offset of 45 optimal when running 215/45/17's in a 17x7 wheel?

 

Stock offset is +48mm with 17x7 rim.

+45mm offset will work.

 

definitely 7.5's. the primary reason why i went with my current wheels
functionally is that they are 7.5's for my 215's. if you're going to sport
17x7, run 205/45/17's.

the differences are:

1) better sidwall stiffness for turn-ins, etc.
2) better appearance.