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If you have a 44 tooth sprocket, and a 26" rim with average sized rubber, then use this equation to find your engine RPM:

**RPM = 226.7885 * MPH**

This is what I did:

Rear sprocket is 44, front is 10. On the flipside of the engine there is a 20 tooth crank sprocket running an 82 tooth sprocket. So:

**(#1) 44/10 * 82/20 = 18.04**(This is your ratio of engine rpm to rear wheel rpm)

1mile/hour * 1hr/60min * 5380feet/1mile = 88feet/minute (per MPH...read on, you'll use this later)

I measured how far my bike travles in one rotation, pretty much exactly 7ft (7 feet = 84inches, and 84in = 2(pi)r, r = 13.36inches, just about right)

**(#2) 2(pi)r = x feet/rotation**

Therefore:

**(#3)]88ft/min (for 1mph) / 7 feet/rep = 12.5714 tire rpm (for 1mph)**(your tire will travel 12.57 feet in one minute going one mile per hour)

and

**(#4)12.5714 tire rpm * 18.04 (from equation #1) ratio = 226.7885 engine rpm per mile per hour**

so if you have a speedometer like I'm sure you all do, just multiply out whatever speed you want to get your engine rpm (ex. 20mph * 226.7885rpm = 4535.77rpm @ 20mph)

To get more accurate, measure the circumference (or diameter and use eq #2) of your wheel and plug it into equation #3 to get an accurate wheel rpm per mile per hour.

For a different sprocket size, just use equation #1 to adjust the ratio. Check this:

a 22 tooth rear sprocket would yield a 9.02 ratio, so instead of 4535.77rpm at 20, you'd be at 2267.88rpm.

THAT ALL BEING SAID...does anyone know the max rpm a broken in engine should be run at? what about while breaking in???

Ciao for now,

-Chas