guido wrote:oh yes I call the small sprockets on the motor and rear wheel sprockets and on the crank blades, sort of a direct translation from dutch, but I guess they are all called sprockets then?
I think the big ones are generally called ' chainrings' in the bicycle community, and the rear,sprockets . In a mechanical / farm engineering scenario, they would all be called sprockets, chain wheels or probably others too, but blade is one Inhad not heard before.
Ah, now you have given us that one extra bit of info that there is no sprung chain tensioner and you have to change to a smaller chain makes the situation far clearer. I could not understand why you were not just changing down to the 32 when you needed it. I understand about Nexus hubs and no rear dérailleur, but since there is two usable front chainrings, I automatically assumed the rest of the gear change system for that front pair of rings had been fitted also.
So to me, the solution is to fit a rear dérailleur tensioner unit if the bike has a mounting bracket for it, and fit a front gear change unit, to enable changing from a 39 to 48 while riding.
If there is no mounting bracket, then I am sure some other chain tensioning system is available
And as I said earlier, and spinningmagnets repeated with a picture of the device, fit the cooling fins to the motor. If cyclone manufacturer them ready to go then that makes job even easier.
Temp probe great idea, then you can compare your motor temps to that on the yclone website; I am sure I gave seen reference to temps on their FAQ page.
Another fixed gear alternative may be to change the rear sprocket on the Nexus hub, a quick google for them shows them available in 16, 18,19, 20 or 22 teeth. Or at the front, change the 48 tooth secondary drive primary gear for a smaller one