Gregory Bender

Miles Per Hour calculation

Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models



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I extracted this information from Charley Cole of Zydeco Racing on the Yahoo! Loopframe_Guzzi news group. In Charley's own words:

(RPM × 60 × Circumference of Rear Tire) ÷ (5280 × 12 × Overall Drive Ratio) = MPH

The circumference of the rear tire should be entered in decimal form and in inches.

Example...24 inch, enter 24.75 inch

Circumference is 2 × 3.14 × radius of your tire. Measure with the tire/wheel absolutely vertical (check with level) from the contact patch (ground/floor) to the center of your axle.

The overall drive ratio is your primary ratio × your gear ratio × your final drive ratio. All of these values are in the factory manuals and also Guzziology.

You can use this formula to calculate your speed in any gear, at any RPM, with stock or non stock combinations of any gearbox, rear drive or wheel/tire size. It is useful to predict the effect of gearing changes such as a different rear drive ratio or to know your precise speed at any time. It is only accurate when your bike is vertical since your effective tire radius is reduced considerably at full lean due to the profile of your rear tire.