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Comment by IshKebab | Hacker News Reader

The problem with max speed is that while big legit ebike manufacturers respect it (e.g. you can't buy a Bosch ebike in the UK that will go above 15.5mph), you can easily get Chinese models that don't care, or you can mod other bikes that do fairly easily.

I don't know what the solution is tbh.

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Why not just define the law in terms of maximum speed and be fine with it? Why nitpick over control modes?

I can guarantee that if I asked 10 random cops what the restrictions are of a Class 2 e-bike not more than 1 could answer, but if I asked them to stop people who were going over 30mph on the bike trail they could figure it out.

I agree the control mode restrictions are dumb. Lime-style ebikes have their assist set so high that you don't need to put any effort at all into pedaling. Effectively the pedals are the throttle.

But anyway that's nothing to do with the problem of ebike hooligans. The law is also defined in terms of maximum speed. Anyone going over 15.5mph (without pedaling really hard) is breaking the law.

It's not ambiguous when this is happening; it's just impractical for the police to do anything about it.

You 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.

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).

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.

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