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

Really handy tool someone developed to provide you upfront options on wheels and tires if you are looking at keeping the same OD

Apologies if this has been posted before.

Z

Cool tool! I like how the change in the actual speed is indicated. Helpful to all of us that needed to replace the Sport Pak "summer only" tires that came with the car. Choices in the exact OEM tire size is not huge for All Season tires, and requires some adjustments to get certain tire brands. This tool lets you know what changes with the different size. Thanks Chief!:thumbsup:

You are welcome...glad you like it...I got it some years ago and have it set in my favorites on the computer. I didn't see it mentioned on this forum and thought those that are looking to upgrade may find some good use for it.

Z

Here is another one... few different features...

Calculator (http://www.1000rims.com/rt_specs.jsp)

Here is another one... few different features...

Calculator (http://www.1000rims.com/rt_specs.jsp)

Excellent...I like this one too...thanks.

Z

This is the one I use:

http://www.wheelsmaster.com/rt_specs.jsp

You can also figure it out pretty simply on your calculator:

Tire width X Sidewall, divided by 25.4, + rim diameter = Overall Tire Diameter

Example: 245-45-18

245 X .45 = 110.25 divided by 25.4 = 4.34 + 18 = 22.34

You can also figure it out pretty simply on your calculator:

Tire width X Sidewall, divided by 25.4, + rim diameter = Overall Tire Diameter

Example: 245-45-18

245 X .45 = 110.25 divided by 25.4 = 4.34 + 18 = 22.34

You forgot a step, since there are two sidewalls to consider in overall diameter (top and bottom sidewall). So your equation should be:

245 X .45 = 110.25 divided by 25.4 = 4.34 X 2 = 8.68 + 18 = 26.68 overall tire diameter

or there is www.1010tires.com