Having realised that the gearing is not helping the motor work with it's current drive system, I decided I could either change rear sprockets (could be expensive to get one made), or try doubling the pack voltage.
I had read somewhere in the past that the EV10 24-48V controller I have can actually switch 72V packs, as long as a limiting resistor is introduced between the 72v supply and the controller logic board. I calculated a suitable resistance, reconfigured the pack for 84V max voltage and turned the throttle.
I can do a tyre smoking burnout now !
Riding the bike the acceleration is exceptional, like a good 400cc or 600cc bike. To save the pack I've wound back the current limit to where it is enough to get the bike rolling at a reasonable rate.
I'll have to reconfigure the headway pack from 12s2p to 48s, and then that means I'll also have to look at some battery management for that, but on the upside I have a pile of contactors, fuses and other electrical ancilliaries from a Lansing 72V forklift which I can now use, so I've saved a bit there.
The bike has a soft rear tyre and the chain is the largest 530 sized chain. Together these two things are adding up to a fair loss of power. perhaps I'll look at changing to a 520 size, or even smaller, chain and sprockets, in the future.