Originally Posted by
likebike23
. . . In order to plan the build for what I want it to do, I need to figure out what is a good top speed for torque/hill climbing. The motor is 24V, 28Amp, 500Watts, and runs at 2600RPM according to the sticker on it. The total weight it would be pulling is 220 pounds. I figure that the motor won't be working too hard if it's geared for a 10MPH top speed. I also figure that 10MPH would be a reasonable in town/traffic speed.
So, to calculate gear reduction/rear wheel RPM which will determine my top speed, do you multiply or add the primary and secondary reductions to get the total reduction? Do you then divide the motor RPM (2600RPM) by the total reduction to get the rear wheel RPM?
You multiply the reductions of the two stages, you do not add them.
If you gear so that the motor is running at its full rated 2,600 RPM when the rear wheel is going 10-mph then your strongest hill climbing ability is going to be in the 5-6.7 mph range (1/2 to 2/3 max free running, no load RPM) and you will continue to get some assistance from the motor while pedaling above 6.7 mph up to 10 mph but the closer you get to that 10 mph mark the less strong the motor will be until it isn't doing any of the work and its all on you pedaling at 10 mph or above. Climbing at anything much less then 5 mph will start to make the motor overheat. It most likely will not go 10 mph but something a little less on the flat geared that way. Unless the RPM rating of the motor specifically says that is a loaded RPM then what they are giving you is a free running, no load RPM and you need to expect less RPM while its actually doing work and propelling the bike.
Do you have a speedometer on your current pedal only bike? Do you know how fast you currently go under pedal power only on the flat (and in town) and how fast you go climbing that hill back up to your house?