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Old 07-30-2009, 03:42 PM
carl2.0 carl2.0 is offline
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Default THE Gear Ratio Dilema !!

Ok Ive acquired all the parts fr my first ebike build but now Im stuck at deciding what size cog do i need for my 44 tooth sprocket which is mounted on the back wheel.... Im lookin for something that will provide decent spend 20 mph and wont put too much pressure on the motor.... Where do I start !!??
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Old 08-02-2009, 09:55 PM
mcgyver28117 mcgyver28117 is offline
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Default Re: THE Gear Ratio Dilema !!

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

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