Also been reading up on motor "red lines". The tag on "Otis" (the motor's nickname from now on, now that I know who made it
) doesn't say what it is.
I think it's safe max speed is in the neighbourhood of 3-5K RPM for typical series wound motors from a few things I've read. We need to know these things to plan what gear to be in
Here's a good account (with great pics) of someone blowing apart his Civic Wagovan's motor about a week after he got it on the road. He calculated afterwards that he spun it up to about 6K when the commutator went kablooie and blew its brains out on the pavement. (He also perservered in good humour and just had it rebuilt by the same motor guru who explained Otis' brush timing to me.)
Some of the good purpose-built EV motors are apparently good to 10k (kevlar straps on the rotor, etc).