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Old 05-09-2010, 11:20 AM
KCvale KCvale is offline
Motorized Bicycle Elite Member
Join Date: Feb 2010
Location: Phoenix,AZ
Posts: 3,552
Default Re: Is it possible to Motorize a bike with coaster brake?

I read a very informative and detailed web page about coaster brakes.
Overhauling a Coaster Brake Bike

I have noticed that newer Beach Cruiser coaster bikes seem to have a weak coaster brake, so I went looking for why and how to fix it.

Turns out it is a matter of gear ratio, not the brake itself.

Coaster bikes tend to be geared a little high so you can get up to a fair speed without gears.
But this means it takes more effort to get them started.
The reverse is also true, it takes more effort to apply sufficient braking force.

The simple solution for a better coaster brake seems as easy as just lowering the gear ratio a bit by swapping in a rear sprocket with one or two more teeth.
It's a fairly easy job, and the sprockets are only about $15.

Since the vast majority of the pedaling you do is low speed, it would seem to be a win win, especially on the those days when the motor is stubborn to start and you have to keep pedaling to turn over the motor.

I am aware the pedal chain will need to be longer, that is not an issue for me, I already size the pedal chain to match the drive chain so I don't need to use any tensioner.

Has anyone already done this?
If so, how many more teeth? One, two, maybe even 3?
I suppose it would depend on the current gear ratio, but a little trial and error won't hurt ;-}
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