Curious about speed limiters

[whyarehillsgettingsteeper]

I have no plans to make my bike do 30mph, other than very occasionally downhill, but I know people sell expensive dongles to let this happen. I was, though, wondering how manufacturers allow for the size of an e-bike's wheels. I mean, if a system set to limit a road bike to 15mph were fitted to a folding bike with tiny wheels and the power still cut out at the same number of revolutions of the wheels per minute that would give a top speed of about walking pace. The other way round and the theoretical top assisted speed would be terrifying! So where is the calibration made and what's to stop the owner altering it or fitting a part designed for a bike with different sized wheels? Presumably, if you're buying a replacement motor, you have to specify which bike, or type of bike, or wheel size it has to match - either that or you'd have to 'tell' the system about your bike yourself. Or does it not work that way at all? I understand the Bosch set up allows you to adjust +/- 5% for different tyres, but that's obviously not enough to allow for very different wheels - or worth throwing out the speed and distance displays for the sake of an extra 0.75mph of assistance.

 

[flecc]

I was, though, wondering how manufacturers allow for the size of an e-bike's wheels.

By design to wheel size.

Wheel hub motors are made with different windings to give rotation speeds to suit each size of wheel for legality. Alternatively the wrong motor can be deliberately chosen. For example one maker produced a 20" wheel folder limited to 15 mph but also put the same motor into a 27" wheel bike which then assisted to 22 mph at the cost of worse hill climbing. Sometimes a hub motor for a large wheel is put into a smaller wheel to give better hill climbing or load pulling at the cost of less than 15 mph top assist speed.

Crank motors these days are similarly electrically specified for a certain wheel size with the chain sprockets also specified to give the correct road speed. One maker has internal Hall sensing of a crank motor gearwheel speed to limit the rotation to suit a given wheel size. Some older crank motor e-bikes have a magnet attached to a rear wheel spoke with a sensor registering it as it passes on each rotation and that is used to set the top speed allowed.
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[vfr400]

Most systems use wheel RPM to calculate the bike's speed. Some get that by measuring the wheel speed directly, and many hub-motors get it by measuring the motor speed.

In the old days, you could trick some systems by falsely setting the wheel diameter, but many many now only use that to calculate the speed for the LCD. The control for the actual speed is programmed into the system and not reachable with simple settings.

Yes, if you could physically get a 29" wheel into a Bosch 26" bike, the system would wrongly report the speed and allow it to go 10% faster.

There are still always ways to trick the system regarding the bike's actual speed so that it allows a higher speed, but you need more and more sophisticated ways to do it undetected.

 

[whyarehillsgettingsteeper]

Thanks for the info. I assumed they all had a magnetic wheel sensor and a motor could easily be fooled by fitting it to a bike it wasn't designed for, though I really didn't plan to do so myself. I've been hankering after an e-bike for years but want one with a long range which puts them pretty much out of reach pricewise. 625Wh batteries are new since I last looked. Now I'm craving a Cube Kathmandu exc, but it'll have to wait until I get my pension. Does anyone ride a trapeze frame? I wonder if it's a sensible compromise as I always think Easy Entry/step through bikes just look wrong but getting my leg over is getting harder.

 

[soundwave]

you can get the dealer to change the wheel size but if you go over 5% it will just come up with a 503 speed sensor error and cut power.

dongles work but they are a rip off.

 

[whyarehillsgettingsteeper]

you can get the dealer to change the wheel size but if you go over 5% it will just come up with a 503 speed sensor error and cut power.

You can adjust +/- 5% yourself on the Intuvia display. I see what you mean about rip-off though, not much there for the money and if you were to injure someone while speeding you'd be in serious trouble.

 

[soundwave]

E-bike cyclist cleared of killing Hackney pedestrian

Thomas Hanlon had denied causing the death of Sakine Cihan while riding a modified e-bike in 2018.

www.bbc.co.uk

 

[sjpt]

You can adjust +/- 5% yourself on the Intuvia display. I see what you mean about rip-off though, not much there for the money and if you were to injure someone while speeding you'd be in serious trouble.

You could be (and should be) in serious trouble, but history indicates you probably won't be.

In the most prominent case (see Soundwave above, posts crossed) where a cyclist killed a pedestrian the police only pressed fairly strong charges, and not the lesser charges (illegal bike, no insurance, etc). So when the cyclist got off on the strong charges (contributory negligence by the pedestrian) it was too late to charge him with the others. I suspect he paid a significant penalty in stress while awaiting trial.

 

[whyarehillsgettingsteeper]

You could be (and should be) in serious trouble, but history indicates you probably won't be.

In the most prominent case (see Soundwave above, posts crossed) where a cyclist killed a pedestrian the police only pressed fairly strong charges, and not the lesser charges (illegal bike, no insurance, etc). So when the cyclist got off on the strong charges (contributory negligence by the pedestrian) it was too late to charge him with the others. I suspect he paid a significant penalty in stress while awaiting trial.

I'd hope he's still paying a 'penalty' living with what he's done if he has any sort of conscience.

 

[vfr400]

I'd hope he's still paying a 'penalty' living with what he's done if he has any sort of conscience.

Why? It wasn't his fault. That's why he was found innocent.

He probably feels some guilt, like anybody would. He'd be thinking if only he hadn't paused to phone his mum before setting off, he wouldn't have been there at the time when the woman decided to make her suicidal dash into the road without looking and she might still be alive, but that's just the way the cookie crumbles. It was just unfirtunate circumstances and timing. He was going quite fast, but anyone might have killed her at a much lower speed. The guy on the fixie bike, who killed a woman, who did much the same thing, was only going 15 mph. He was found guilty of reckless cycling because he didn't have a front brake, which actually made no difference to the events, so he was jailed.