What I've read says car type alternators need a minimum of 1000 rpm to
produce usable voltage.
Could you put magnets directly on the wheel and pickup coils around it?
Kinda like a big old synchronous motor?

Shaun

Car alternators spin pretty fast compared to what you would probably
do running it with a bike. Anyone know if there is a speed (slow) that
it will not produce enough to spark up the diode triode? Anyway, you
may have to consider/ponder a different lower output generator. Just
guessing here, maybe someone else knows.