Found while searching the vast internet:
Speed = (RPM x rear tire circumference x front sprocket) / (primary gear ratio x selected gear ratio x rear sprocket x 1056)

Is this correct? Where does the "1056" number come from
This is different from the automotive one I have:
Speed = (RPM x rear tire circumference) / (R&P x selected gear x 336)

Appears to be correct, not sure where the 1056 comes in... conversion from inches of tire circumfrence to MPH perhaps?

Also note the tire circumfrence changes pretty drastically w/ a bit of lean so 6000rpm straight might be 120mph, but 6000rpm dragging knee might only be 90mph...

BJH

Unit conversion
12 (inches per foot) * 5280 (ft per mile) / 60 (min per hour) = 1056

Knew that # looked familiar... I'm just too lazy to have done the math...

BJH