Rope-Pusher wrote:Tire revolutions per mile follow the trend of tire circumference, but not directly. For the same circumference, different tire brands will have different revs per mile due to tire construction differences. Still, calculating the circumference gets you into the ballpark (on opening day).
You are, of course, talking about circumference calculated using the tire's size...actual
circumference (mount on vehicle, inflate to normal, put a thin line of paint on and drive until the wet paint leaves two lines on the pavement...or just wrap a tape measure) would be a different story. That is, unless I'm missing something about differences between constructions/materials that differently affect high-speed hysteresis, thermal expansion, or something like that. It would be crazy to try for that kind of precision though!
Happy Easter Cow! Aren't you glad the Ham is more the traditional meat at Easter than the Beef?
Speakin' of beefs (beeves?), yes, even using the actual measured circumference, a fudge factor is required to determine the actual Revs per Mile....and even then it will vary some depending on the amount of weight on the axle, the rim width, and whether it is a driven or non-driven wheel. One, or two might even find some difference due to the difference in road-load power. Maybe towing a trailer, or driving a big, blunt SUV might produce a different revs per mile than with the same tire mounted on a slippery sedan.
At what point would this difference be discernable? HaH! with proper instrumentation one, or two might measure the difference, but considering that a typical revs per mile might be in the 800's, even 8 revs per mile difference is only 1%.
Did I ever mention that I spent a summer at GM Tire and Wheel Engineering and four of the projects I worked on were related to revs per mile. One was in developing a more accurate formula for calculating Revs per Mile on "normal" tires, another was to study revs per mile on compact spare tires (they are different enough to need their own revs per mile prediction formula), the third was to look at the speed sensitivity of revs per mile (apparently, in the days of bias-belt tire construction, there was a significant difference at say 25 mph ("Twenty-Five Miles per Gallon") vs highway speeds.), and the forth was load sensitivity of compact spare tires for Revs per Mile.