FFV8 -- thank you!! Do you think I'll be all right if I have 11/60 > 10/28 ?? Thank you again for all your helpSprocket choices depend on how much fabrication skill you have, and what soer of equipment you have to use.
You should do most of your reduction i the first stage. You are planning on using the bottom bracket bearings for a jackshaft, and they are not high speed items. I would really recommend replacing them with sealed ball bearings.
The 28T final sprocket limits you to a few choices, none of them easy bolt up stuff.
12/65 > 10/28 just makes it. A 65T #35 chain sprocket would have to be fitted to the jackshaft input, and a 10T sprocket on the output.
12/72 > 12/28 works too, but the 72T #35 sprocket is over 9" OD with a chain wrapped around it.
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EDIT: the pedal cranks on the bike I'm using are sealed bearings
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