So what are people’s recommendations for the front and rear sprocket ratios for this motor with the built-in gear reduction?
Am I correct that QS says 1:3?
I’m looking to use the QS138 70H in a vintage scooter, with a 12” wheel. Scooter will probably weigh around 130-140kg (285-310lbs). Scooter would be mainly for commuting, but my commute includes a bit of motorway, so want to be able to do 100km/hr (65m/hr). Was thinking I’d probably just use the Votol EM150 or may EM200. Looking at CALB CAM72 batteries in a 23s 1p config for 72V 72ah, but should handle 150A continuous.
The scooter has a 40 tooth rear sprocket originally - which would be the easiest option. So the standard 14 tooth front sprocket that QS ships these with should be pretty close to 1:3. By my calculations, though, that’d only get me something like 75km/hr at, say, 5,500 motor RPM?
It seems like I’d need more like a 1:2 ratio (19 or 20 tooth front sprocket with a 40 tooth rear) to get 100km/hr at that sort of RPM. (This assumes a rolling wheel circumference of about 1529mm (for a 130/70 x 12 tyre).) Or am I calculating this wrong?
Is 5,500 motor RPM a reasonable assumption? It looks like that may be what QS has used to calculate the 100km/hr for their QS138 70H motor kit (with swingarm and belt drive).