I don't know if anyone has posted this yet, but it is super usefull. This calculator will not only show a visual difference, but also give speed differences for two different tire and rim combinations. So one could enter the stock xB tire size of 185/60/15 in the drop down menu, and could enter 215/40/17 in the second drop down menu and would see that there is almost no difference between the two, even in speed! So one could find out how to upsize their rims without having to calibrate their speedometer. Helpfull thing to know.

http://www.miata.net/garage/tirecalc.html

 

on 215/40/17, is 40 the size of the outer diameter? IE the tire rubber part?

Is 215 the width?

 

215 is the width of the tread

 

215 is the width.
40 is the sidewall. You take 40% of the tire width & you get the sidewall height.
17 is the tire size.

Here's another tire calculator. Not only does it tell you tire size, but it also calculates offsets, wheel widths, & tire sizes combined! (^_^ )

http://gs.tolan-hoechst.com/tirecalc.htm

Yup. Have fun. ( ^_^)/

 

how do you calibrate you're speedo?

 

I geuss I'm not hard core enough, because either I did'nt understand some of the info on the other one, or it just was'nt needed. That's a great calculator for performance applications, but I jus want the basics. Still nice to know though, and a good contribution SR20 MAN. :D I bet the TC pilots would love that.

And the only way I know to calibrate the speedo is to take the car to a shop, usually 4X4 shops can do that. I'm sure some of these geniuses on this site know some ways though.