Having trouble computing overall tire diameter . . .

[treeguy]

I am trying to compute overall tire diameter. Here is my logic: 215/85R16 1) Multiply 215 by .85 = 182.5 mm 2) Divide by 10: 182.5 mm/10= 18.3 cm 3) 2.54cm = 1 inch so . . . divide 18.3 cm by 2.54cm to find inches: 18.3 cm/2.54=7.19 inches 4) Now add half the rim to it (7.19 + 8= 15.1 inches) this yields radius. Now to multiply by 2 to find diameter (15.1 x 2= 30.2 inches) . . . Is this reasonable??

 

[Sasquatch_Ryda]

I use this site for that stuff.

http://www.1010tires.com/tiresizecalculator.asp?action=submit

30.38 in is the overall diameter.

 

[shane96ranger]

I know this isn't part of the question you asked. But, I have one I use, very similar to Sasquatch's - but it calculates the MPH difference if you are switching sizes.

http://www.discounttire.com/dtcs/infoTireMath.dos

 

[Sasquatch_Ryda]

So does the 1010tires one.

 

[exbass94]

I am trying to compute overall tire diameter. Here is my logic: 215/85R16 1) Multiply 215 by .85 = 182.5 mm 2) Divide by 10: 182.5 mm/10= 18.3 cm 3) 2.54cm = 1 inch so . . . divide 18.3 cm by 2.54cm to find inches: 18.3 cm/2.54=7.19 inches 4) Now add half the rim to it (7.19 + 8= 15.1 inches) this yields radius. Now to multiply by 2 to find diameter (15.1 x 2= 30.2 inches) . . . Is this reasonable??

Your math is correct. That's how I figure out tire diameter.

 

[4x4junkie]

I get 30.39"

215 × .85 × 2 ÷ 25.4 + 16 = 30.389763"

 

[treeguy]

Thanks for the correction 4x4junkie! You're right, my early rounding in my calculations contributed to my inaccuracy. I reworked the numbers and came up with the number you did. Thanks!