# THE Gear Ratio Dilema !!



## mcgyver28117 (Dec 4, 2008)

Hi Carl,

Gear ratios are dependant on the motor specifications. Provided that the motor you intend to use has sufficient power for the application and you have a controller and battery pack that is also sufficient, then the 20mph is merely a function of matching the maximum motor speed to the tire size with perhaps 10-20% margin for the max. speed.

If motor speed max is 5000 rpm then 4500 rpm (10% less ) would be coupled against the rpm the tire has at 20 mph. At 20 mph * 5280 ft/mile = 105600 ft/hr.

105600 /60 = 1760 ft./min 

A tire diameter of 1 ft = 3.1416 feet in circumference

1760 / 3.1416 = 560 rpm

4500 / 560 = a gear ratio of approx. 8 to 1 

Sincerely,
Ron 
www.black-sheep.us


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