I recently purchased a Diablo Predator programmer and it is asking for my tire size in the language that I don't know what is but it ain't what's on the tire.

I've got BFG M/T's 35x12.5 on 17" rims. Can you help me convert or tell me how to get this in that "305x70" or whatever thing it is?? thanks in advance...

 

I believe it would be 315 70R 17.

 

Search on 'metric tire calc' or metric tire conversion' with your favorite internet browser.

Or just go to the mfg's website and look at the big specs list. It will have both metric and standard sizing in one easy to read list.

 

The first number is the width in mm.

In your case 12.5x25.4=317.5 or approx 315mm

The second number is the ratio of the sidewalk to the width of the tire

Tire height minus rim height divided by 2 gives the side all height in your case 9" or 228mm

228mm divided by 317.5 = 71.8 or approx 70

The last number is the rim height. In your case 17.

So basically the answer is 315/70R17. But if you want to know how see above.

 

Doing it from metric to inches-

315-70x17

315 divided by 25.4 (metric conversion)= 12.40
The sidewall is a 70 (or 70% of the tread width) so you'd use a 12.40x.7= 8.68" sidewall.
2x the sidewall of 8.68"=17.36" + the 17" wheel equals a total height of 34.36".

 

Jeez, lots of smart fellow jeepers we have !! me no so smart........thanks a zillion !

 

I came up with 317.5/72R17 which closest actual size would be the 315/70 that others have stated, I just felt like posting what I came up with. you all use different math i divide the inches by 0.03937, I think thats right but I guess it equals out the same as the others.