Need some help. I'm a little confused with tire sizing. I have stock 265/70/17s on factory 7.5" rims. If I want to go one size taller and one size wider, what size tire do I need? I know the "265" is part of that equation and the "70" (I think) is the other part but its all greek to me. Thanks for the help.

 

This site should tell you what you need to know. http://www.miata.net/garage/tirecalc.html

 

The "265" is the width of the tread in millimeters. The "70" is the percentage of tread width which determines the tire height (think of this as the height the tire raises the bottom edge of the rim off the ground).

So a "50" profile tire would have a tire height equal to one half (50%) of the tire width.

> e.g. 265 x 0.70 = 185.5mm

you divide this by 25.4 to get inches:

> 185.5 / 25.4 = 7.3 inches

Then to get you overall tire diameter, you double the tire height (tire height at top and bottom of rim) and add to the rim diameter.

> 7.3 + 17 + 7.3 = 31.6 inches.

So, going to a wider tire (say 285) and keeping the same profile (70) would also give you a larger diameter tire.

285/70 would give you a 7.85 inch tire height (about 1/2" more truck height) and and overall tire diameter of 32.7" (7.85 + 17 + 7.85).

If you want a wider tire but do not want increased tire diameter, you'd have to go with a lower profile (e.g. 285/65).

Hope that helps (and that my arithmetic is right )

..........................Scott

 

Here's a really helpful link to tire sizing.

http://www.therangerstation.com/Metr...nch_Tires.html