I got a rim here that is a 15 inch with a 6 1/2 width. Im trying to see what optimal width tires can I put on. Would this make the tires perpendicular to the road with 225?

 

Hunh?

Yes you can put 225/50/15's on a 15"x6.5" wheel. It's not ideal (works better on a wider wheel), but it'll work.

 

So is 215 the widest I can go while still having the tire wall as straight as possible?

 

If you want straight sidewalls something like a 185 or 195 will be better, but if you want grip the 225's will be better. There's not much available in 215's.

 

im running 225/50 on the rear, and 205/50 on skyline GTS-T wheels. im pretty sure they are 16x6.5. i love how it grips in the *** end. it handles great and i love the way it feels turning in. i got fresh yokohama's all round as well.

 

The best answer to this question is to consult the spec sheet for the specific tire, in the specific size that you are considering. Tire Rack has the spec sheets online. Here's an example (215/60-15 Yokohama ES100):
http://www.tirerack.com/tires/Spec.j...e1=yes&place=3

Rim width range: 6-7.5

That means that this particular tire, in this particular size, is approved for use on 15x6.5" rims.

Remember: It varies from tire to tire, and it varies by the size and aspect ratio. Be sure to look at the right line in the right spec sheet.

-Max