Originally Posted by BillyShope
Originally Posted by dparker
...take your roll out and divide it by 3.1416 and that will give you a exact tire height.
A more convenient number is obtained by dividing the rollout into the number of inches in a mile. This gives you wheel revolutions per mile.
Then, draw a long horizontal line and start inserting the things you know, with the goal of canceling values that appear both above and below the line. You have N wheel revolutions per mile, S miles per hour, and G axle ratio (ratio of engine revolutions to wheel revolutions). So, when you multiply these out, the "mile" of N cancels the "mile" of S and the "wheel revolutions" of N cancels the "wheel revolutions" of G, leaving engine revolutions per hour. Divide by 60 and you have engine rpms. (Or, more rigorously, divide by the number of minutes in an hour, which cancels out the hours. Fewer mistakes are made when the problem is completely set up and the units have been reduced to those desired BEFORE picking up the calculator.)
I sorry but there's no way that's more convenient way to get the diameter of a circle. The Greeks derived this equation thousands of years ago. And I have yet to see a simpler version.
Pi R squared will get you the area.
BUT WHY!!!
Diameter of a circle = Circumference divided by Pi (3.14159265).
And there is no more convenient way to derive the diameter of a circle. Even Albert Einstein used the Greeks version of how to find the diameter of a circle.