Quote:
Originally Posted by Vettezuki
My sheet does three things a little differently. It calculates circumference exactly on input tire size. A 275/60x15 is slightly less than 28 inches. Additionally for reasons I can't remember and forgot were in there it has built in corrections altering the revs per mile and revs through the transmission. Hence the reduction from your completely accurate pure calculation. I can alter my sheet to remove these built-in corrections and we'll come out to the same numbers exactly. But this would be a totally idealized, perfect circumference, no slop kinda situation. I suspect my sheet may model reality a little more closely, but I certainly can't give you the logical proof for the constants that are used. There, aren't you glad you asked?
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So how many tire revs per mile does your sheet calculate? Because I calculated the revs per mile using the exact circumference of what a 275-60-15 tire should be. I don't allow for any variances and frankly I don't know how your spreadsheet could do that accurately, considering different variances between tire, tranny, and rear-end manufacturers.
Here is my calculation.
(((275/25.4)*.6)*2)+15 = 27.992125 (Tire diameter)
27.992125 * 3.1416 = 87.940059 (Tire circumference in inches)
87.940059/12 = 7.3283382 (Tire circumference in feet)
5280/7.3283382 = 720.49076 (tire revolutions per mile)