alt Hacker NewsYou can't "easily" modify an electric brushless motor to go faster than its Kv limit, to handle more current than its magnetic saturation limit, or to exceed the limits of back-EMF.
99% of the people whinging about ebikes have no idea what they're talking about.
There are people claiming in this very thread that kids are modding their "e-bikes" to go "45mph."
The power levels required to push a hybrid bicycle to 45mph is north of 3000W and thus well beyond the capabilities of the motors and battery packs in nearly all electric bicycles. Even the e-motos struggle to hit those speeds; you need a pretty high end, expensive one to do so.
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Nobody is building ebikes that are physically speed limited by the motor windings. The top speed of a motor depends on load, and it's impossible to predict the exact load of a motor in a bike with a rider. Even if you could, the amount of excess torque available as you got near the top speed would be tiny - it wouldn't be fun to ride.
Speed limits are universally based on measured speed - either at the wheel or motor.
Well, you can switch from high efficiency to field weakening once you run out of supply voltage to handle full field back EMF as you increase speed.
That can readily double your speed on flat or downhill terrain if normal torque is sized to give good acceleration from standstill.
No, what the modders do is just disable the velocity dependent power limit on the standard e-bike power controllers. The easiest/hackiest way to do that is to install a pulse rate divider on the tachometer cables - bike goes 30mph, controller thinks it's going 10mph and delivers full power. This messes up the mileage counter and is trivially easy for the cops to spot, but it'll work.
> The power levels required to push a hybrid bicycle to 45mph is north of 3000W
Yeah, 45 mph is hyperbole. 45 kph is very easily doable on a standard 750W e-bike motor with <$1 of additional electronics. At that point it's all aero, so going even faster is mostly about rider position and bike geometry (those scooter looking things are going to be slower than a proper bike on 29" wheels).