ok i forgot how it is measured say a tire is 215/55
what numbers for what? and what to divide? i forgot this i'm sorry guys. =(

 

215 is tire width in mm, 55 is ratio of sidewall to width.

 

215 means it's 215 mm in width. 55 is the height in perspective of the height...in your case, 55% of 215. hope that helps.

 

so how do i convert the width into inches. bad at math!!

 

hmmm...if i remember correctly, it's something like 2.54 cm for every in. don't tell me u can convert cm to mm!

 

25.4mm to the inch.

But, dont try to convert tread width to find rim width. Look up the tires specs to find the recommended rims widths.

 

You should probably just email my friend's 3rd grade son, he could probably do the calculations. He's investigating for me right now whether or not I should refinance my home!

just joking, but it's amazing how smart kids are nowadays. It's like that whole burn-out thing of the early 90's has been replaced by these super smart competitive kids. No joke, he was calcualting the area of a rectangle for homework, yes, in the 3rd grade.

anyway, the most important thing is the overall diameter. and if you didn't want to do any math at all you could look at charts on the tire rack website to find diameter right down to the model of the tire. just look at the RS-A's diameter for a 215/55-16. Then you can see the 235/45-17 and 235/40-18's are the closest matches.

 

and over...

here you go:

http://www.tirerack.com/tires/tiretech/general/size.htm