Tire Size Formula

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babyarm85

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Hey guys I'm a new member to the forums but not new to here. I always come here to solve any technical questions I have until I ran into a problem that I couldn't find by using the search function. I always see people wondering if they're tire/rim size combo will fit on there vehicle. and then I ran into this same problem myself. So after a lot of searching I actually found a method/formula for figuring out tire sizes that would benefit a lot of people and i felt it was time to contribute back to the community that I have been quietly using the knowledge of. If there is thread like this I apologize or it is common knowledge I apologize again. so here it goes.

If you take the tire width and convert it into inches and then multiply by the decimal thickness then double that number and add the rim diameter you should get the overall diameter of the tire.

In order to convert MM into inches you have to divide by 25.4 (number of millimeters in an inch)

For example:
If your tire is 285/55/22
285(mm) / 25.4 = 11.22"(inches)
11.22"(inches) x .55 (sidewall thickness) = 6.17"(inches, rim to outer tire)
6.17"(inches) x 2 + rim diameter = 34.34"(inches, overall diameter of tire on rim)

That way all you need to do measure the clearance on your vehicle (wheel well and suspension travel) and you will know if the tire(s) size will fit.

I hope this helps anyone that it can and if this is basically a useless post I apologize for wasting your time. Thank You.
 
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babyarm85

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Sorry I keep forgetting they have an automatic calculator for everything. maybe they should make a sticky for that link or develop an app specifically for this site. I've just seen too many people go "will these fit my ride"?
 

ChrisAU

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That's still good to have a basic knowledge of for on the fly approximations. I HATE when people refer to metric tires as 285's, 305's, etc...you are telling me nothing but the width.

I hate that people think that 315=35" and 305=33" etc.
 

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