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I am building an EBike. The motor manufacturer said I must replace the existing cassette with a freewheel. Why do I need to do this?

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    Is the motor a hub motor design? or a bottom bracket mounted design? If it is a hub motor, it may be that it is designed to accept a freewheel. A link to the manufacturer's product page would be helpful. – renesis May 15 '18 at 20:29
  • Guessing - a freewheel axle design is pretty poorly supported on the right hand side, and axles are prone to bending under impact. A cassette-based wheel has the RHS bearings further out. Your ebike kit will require batteries, probably on the rear carrier, which increases overall weight and therefore likelyhood of bending the freewheel's rear axle. – Criggie May 15 '18 at 20:38
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    @Criggie, but OP said the kit requires a freewheel – Argenti Apparatus May 15 '18 at 21:42
  • @ArgentiApparatus ewww - that IS weird. Good spotting! Perhaps the instructions have errors, or perhaps the motor is a replacement for the rear hub and only fits freewheels as per Renesis's comment. – Criggie May 16 '18 at 1:12
  • @rpeter12 Could you please use EDIT to add a photo of your motor, specifically where the mounts are? – Criggie May 16 '18 at 1:13
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That does not make much sense.

A freehub/cassette combination has the same function as a freewheel. You cannot replace a cassette with a freewheel unless you replace the wheel hub as well.

The only reason I can think of is that the manufacturer thinks freewheels are stronger and can resist the extra torque of the motor better.

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