Go on any e-bike forum and you will find countless numbers of e-bike enthusiasts “over-volting” geared hub motors to massive wattages. However, in our world of delivering container loads of safe, reliable and consistently low warranty products, we just don’t have that luxury…
Most 5:1 reduction BPM’s are rated at 500-750 watts nominal and can be over-volted to peak at 1000 watts reliably. A few rare exceptions like the MAC and BMC motors can be over-volted much higher than 1000 watts (but usually below 1500 watts.) This is partly due to wider composite gears and more robust clutches. However, the manufacturers will say when being used as a mass production motor, 1000 watts is really the peak limit to operate safely without a lot of warranty phone calls. Also, these two motors cost more than double most other BPM’s.
We have tested a beveled corner, helical cut, metal planet gears with a matching helical cut ring gear but found that the motor noise just screams at anything over 500~750 watts. http://www.topsecretev.com/helical-cut-steel-planetary-gears-for-hub-motors/
Now, there is a patented nylon planet “spur gear” with matching profile reinforced steel scrim plates on each side. It’s a good idea to increase strength while reducing noise but we think the max hub motor limit will also be under 1000 watts.
We are also using double reduction, geared hub motors. Which nearly doubles the reduction to 9.6:1 and almost doubles the torque for any given input wattage under 1000 watts (over a traditional single reduction, spur gear BPM’s.) These have proven to be quiet and reliable with a much smaller footprint. However, the safe and reliable wattage is 750 watts nominal/ 1000 watts peak (for short periods of time only.) This motor operating at 750 watts would produce nearly 70Nm of torque, in a hub shell about 35-40% smaller than a traditional BPM.
Then there’s the next generation “large footprint” direct drive/ gearless hub motors. These are really moped or e-scooter motors in bicycle OLN frame widths. They can handle a lot of current but the torque output for the given wattage required is much lower than any geared BPM (when operating at under 1000 watts.) So these types of motors really only start to make sense when operating well above 1500watts. Given the added costs of the extra wide magnets, more copper, a larger 18~24 Fet controller and a substantially bigger battery required, it just doesn’t make that much sense in a street legal production model e-bike.
So until we can find a reliable, moderately priced geared hub motor that can operate between 1200~1500 watts safely and quietly for large scale production e-bikes, our search continues… Of course middle drive motors will provide the torque needed at lower voltages, but the off-the-shelf bicycle drive-trains are not really designed to match these large torque applications.