I ran the #25 chain on my old bike for about 5000 miles and by then the chain and sprocket were really worn out.
Actually, I could run a regular bicycle chain if it was a 14 tooth on the front. (14-55)
Since I already bought the #219 chain and sprockets I figured it's worth a try. I can always change things later.
The RC motor (that I bought, but am not using) needs to spin really fast so the smaller #219 would be better for that.
My rear sprocket #219 is 100 teeth.
Just trying to keep my options open... dialing in a bike takes time.
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From the science I know, friction is a function of number of teeth. When you use small sprockets (less than 12 teeth) the efficiency goes way down. The #219 chain is obviously superior in quality to the #25 that I used and I doubt there's any truth to the #219 being "too big". Also, with the motor current limiting the acceleration will be very gradual, and that means the inertia will be less difficult to move. Top speed is more important than 0-20 mph times.
Probably the main thing is long life... I want at least 10,000 miles before needing a replacement. Seems that most of the ebikes I read about last less than 1000 miles before major repairs are needed. The RC motor builds seem to last about 100 miles before throwing a bearing.
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Things went well on building the front sprocket today. Yesterdays attempt failed, but this one is looking better. No one talks about the days you "attempt" something and you have to give up on it.