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# Building an electric bike, how can I calculate my top speed and battery life? Answered

I'm in the process of building an electric bike to commute back and forth to school, as well to the store. I plan to mount the motor on a rack above my rear wheel, and re-rout the chain from the peddles to the motor above.

I've been looking at this (http://www.monsterscooterparts.com/24vo500wamow1.html) motor, and I hope to power it with this (http://www.monsterscooterparts.com/12-volt-yt12b-bs-scooter-motorcycle-battery.html) battery (will be using two of these). How to I calculate the battery life using this motor, and is there any way I can calculate the max speed?

The bike is predicted to weigh aprox 50 pounds, i'm about 160 plus 20-30 pounds of books and the like in my pack.

Thanks in advance!

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## Discussions

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first off, that motor will not work. the sprocket attached is a #25, and you will need a #40 to mesh correctly with the bike chain. to calculate top speed, take the teeth of the motor sprocket divided by the teeth of the driven sprocket, and then multiply that by motor rpm, and then multiply by PI*Diamater of rear wheel. example: 5 tooth drive sprocket, 10 tooth driven sprocket, 20inch wheel and 1000 motor rpm = (5/10)*1000*(pi*20)= 5000pi inches/min. then you will need to convert that into mph.

From a sheerly practical point of vies with 500 watts and a 2 x 12 volt battery at perhaps 74 A/hr you might get about an hours run from the battery pack.

500 watts is way over for a light bike. 250W should be plenty, try to arrange gearing so that the motor maintains it's optimal speed to minimise battery draw.

24 volt battery pack will add excessive weight can you manage to get a 12 volt motor and use it to assist peddling.