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Note that some links in this question go to sites with a metered paywall, i.e. you can access something like 4-5 free articles per month. While the question mentions a bike manufacturer, the problem very likely spans all manufacturers of low-cost e-bikes.

Recently, Molly Steinsapir died while she and a friend were riding a cargo e-bike downhill. This was covered in mainstream and cycling media outlets, e.g. on Bicycling magazine's site. Her friend was unable to stop the bike, because the brakes did not engage. Why the brakes failed to engage during the accident sequence is not known. This Outside magazine article says that Molly's friend, who was controlling the bike, applied the front brake, but it didn't slow the bike and caused the wheel to wobble. As covered in both articles and this Tweet by cycling journalist Peter Flax, there may be widespread problems with the brakes on lower-cost cargo e-bikes. These may stem from any combination of the following:

  • Cheaper disc brakes may generate less power
  • This may be exacerbated by lower-quality cables and/or poor routing
  • Low-quality brakes may come out of adjustment faster, wear faster, or otherwise be unreliable
  • Novice consumers may not realize they should keep adjusting their brakes, or adjust them wrongly, or be dissuaded from taking them to a store repeatedly because of cost

For the record, cable (aka mechanical) disc brakes are specced on lower-end bikes because they're cheaper than hydraulic disc brakes. Hydraulic brakes self-adjust, and the system requires little maintenance if set up properly and the bike is in tolerance (e.g. disc brake mounts are flat). This Cyclingtips article after a 2022 bicycle field test argued that you could get good braking with cheaper mechanical disc brakes, although many bikes have low-quality cable housing or routing that robs braking power.

E-bikes in general are heavier and faster than unpowered bikes. This translates to more kinetic energy to dissipate while stopping. Cargo e-bikes are considerably heavier and can carry much more load than their peers. For the record, the Radpower model involved in the accident claimed a capacity for 300 lbs total weight. It has Tektro mechanical discs with 180mm rotors.

Question: What spec changes would suffice to ensure adequate stopping power on e-bikes? Would these raise the price of such bikes enough to affect demand?

Note that the original motivating issue was e-cargo bikes, which can carry significant loads. However, it seems warranted to discuss both cargo and non-cargo e-bikes if posters feel it's warranted.

Weiwen Ng
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  • Today I learned there exist e-bikes for less than 3000 €/$/£. I wonder if the bike in question would have been legal to sell in the EU. – gerrit Feb 07 '23 at 07:34
  • 750W motor, 30 kg bike, $20 brakes. – gschenk Feb 07 '23 at 11:18
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    Is the linking of this question to a real world death at all necessary? Imagine if a family member or friend stumbles across this? Since the question is hypothetical in nature (I would say speculative and of poor quality too) why the needless linkage to a death with no confirmed root cause? – Secret squirrel Feb 07 '23 at 12:08
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    @gerrit (non-cargo) e-bikes at 1/3 of that price have been legally compliant and sold for many years. You can build a BSO for £50-100, leaving you several hundred for the motor, battery, and controller. – Chris H Feb 07 '23 at 12:57
  • @ChrisH The question title mentions a cargo e-bike, though. – gerrit Feb 07 '23 at 13:02
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    The incident happened on a (steep) downhill. How does it matter that the bike was electric — apart from the fact that in such hilly terrain, some people wouldn't ride bikes at all if they weren't electric? – gerrit Feb 07 '23 at 13:07
  • @gerrit I modified the title also. The point is that in general, e-bikes allow people to get faster, possibly with much more cargo, than they could on their own. They then need to stop. Keeping the price point constant, the components on an e-bike should be worse than on an unpowered bike, because you need to pay for the battery and motor. – Weiwen Ng Feb 07 '23 at 13:13
  • @gerrit your comment didn't mention cargo, so I wasn't sure if you were referring specifically to cargo bikes – Chris H Feb 07 '23 at 14:41
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    Disc brakes don't generate power, so it's unclear why they may generate less power (than what?). Are you talking about the amount of power they can dissipate? Or are you confusing with braking force? – Toby Speight Feb 07 '23 at 16:13
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    @TobySpeight “power” has long been used as a synonym for “force” in the context of bike brakes. End of the day, all we are concerned about is the rate of slowing down ability. – MaplePanda Feb 07 '23 at 17:25
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    I think it's important that the incident happened on a 65-pound (~30kg) bike going down a 14% grade with a pair of pre-teen riders who had probably never ridden an e-bike before (it was a new bike belonging to the sister of one of the girls). – shoover Feb 07 '23 at 18:43
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    I don't understand the problem. Your bike either stops in good time, in which case the brakes are fine; or it doesn't, in which case the brakes need adjustment. This is the user's responsibility and is no different from a non-electric bicycle. – Ian Kemp Feb 07 '23 at 20:21
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    @IanKemp the problem is that, according to the article, many e-bikes of that brand require weekly adjustment of the brakes. That's a lot unless you're riding professional competition. It's a valid question to ask how to improve on that. – SQB Feb 07 '23 at 22:18
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    @TobySpeight similar to what MaplePanda says, it can help to think of brakes as a power sink, so "less powerful" means "capable of absorbing less power". Slightly sloppy but useful terminology, and related to force rather than synonymous. You need both decent force and decent power(-handling) ability. – Chris H Feb 08 '23 at 11:33
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    @shoover the bike weight isn't ridiculous. It's similar to my tourer with a very light touring load or even a heavy commuting load. I probably weigh a similar amount to the 2 riders, so the same total weight. But I'd be very surprised if a pre-teen kid had my grip strength - though that may not matter if the brakes needed adjusting. If you run out of range, brute force doesn't help. – Chris H Feb 08 '23 at 11:38
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    @ChrisH And you’d be extremely qualified to talk about running out of brake adjustment range. – MaplePanda Feb 08 '23 at 17:31
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    Notably, the bike in the fatal accident had two passengers who were going down a 14% slope. That's a brake check for any bike that not all of them will pass. That it was an electric bike is probably not very important. Note to self: Don't do that. Note to parents: Keep an eye on your children. – Peter - Reinstate Monica Feb 09 '23 at 01:10
  • @Peter-ReinstateMonica I completely agree with you that it's a situation that asks a lot of a braking system. But in this case, the two passengers could easily weigh the same as a larger adult+child seat+kid (+backpack, +some groceries in panniers, etc...), and descending 14% grades is well within the intended and marketed use case of an urban utility e-bike (granted, we don't know at what kind of speed they tried to stop). – Zach Lipton Feb 09 '23 at 05:27
  • @SQB My TRP Spyres on a gravel bike would require a weekly adjustment if I ride a lot. Perhaps even more often. When I were on bikepacking and did over 100 km everyday, a weekly adjustment would not suffice. Still the pads lasted very long. As long as the rotors, above 6000 km in the back and were still usable at 10000km in the front. Just the adjustment is very fine. – Vladimir F Героям слава Feb 09 '23 at 09:57
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    Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on [meta], or in [chat]. Comments continuing discussion may be removed. – jimchristie Feb 09 '23 at 13:41

5 Answers5

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The problem I see constantly is lack of maintenance. It's very common for ebikes of all varieties to come into the shop I work at with brakes that the user has treated essentially as an automotive brake, i.e. with the expectation that maintenance and wear needs to be addressed only very occasionally. These users often fail to advance the pads on mechanical brakes, and wear through the pads to the back plates or pistons on hydraulic ones.

The power level when most ebike brake systems are in sound mechanical state is acceptable.

Fixing the situation on the behavior/education end is impractical. Ebike buyers can be hard to reach, since direct-to-consumer and other low-interaction business models are so predominant. Beyond that is the fact that ebikes to date have needed to largely adopt normal bicycle brakes and the mounting/spatial standards that go along with them, which were not designed for the purpose. The braking needs of an ebike are much closer to that of a moped, which have more overbuilt brakes. The best avenue to pursue is brake systems that have much longer life on their wear parts at the expense of weight and/or cost.

Getting to much longer wear life for brake components (pads and rotors) has both material and form factor considerations. There's a further question here that deals with where the point is that new or different frame spacing, rotor mounting, and/or caliper mounting standards may be necessary to accommodate needed form factor changes, and at what cost in tradeoff factors like wheel strength and minimum q-factor if making rotors and pads much thicker was needed, such that either the left hub flange needed to be closer to the frame centerline or the frame spacing needed to be increased respectively. This topic has a lot of ins and outs as it applies to both future designs and/or retroftting.

At this point most disc brake pad makers have ebike compound offerings on the market designed for longer wear life, but some seem to be getting there at the expense of power (friction). This suggests there are tradeoffs involved in the formulation of the compound where more thickness and/or contact area is the only solution for applications that need both power and longevity, as is often the case for hilly, fast, and/or load-carrying ebike applications.

Many ebikes with hub motors have a rear caliper where the inner pad adjuster can't be accessed in the intended manner because the hub is in the way. Mechanics usually can figure out simple enough workarounds for this issue, but average users often cannot. If mechanical brakes keep appearing on hub motor bikes (ideally they wouldn't, but they probably will), it would be ideal to abandon the conventional design completely and replace it with an external hex bolt so that, for example, a simple small combination or adjustable wrench could be used to make the adjustment.

Some may propose replacing all the cheap mechanical brakes in the world with good hydraulic models. This would be better than what we have, but doesn't fix everything. Automatic pad advancement and extra power are welcome, but it's common for users working with the same low-maintenance expectation to simply go through all the pad material on hydraulic brakes, until they're running the back plates against their rotors.

Nathan Knutson
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  • If you're willing and if you have the info, do you have examples you can give? E.g. I see that Deore M6100 brakes retail for US$85 at Jenson, and that's only a 2-piston setup. – Weiwen Ng Feb 06 '23 at 21:42
  • Add a third brake as a last-resort, like a coaster or roller brake ? If weight isn't an issue. – Criggie Feb 06 '23 at 21:46
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    My own crash a few years back was partly caused by advancing the fixed pad to the limit, followed by faster than expected wear. The drop-off in performance on mechanical disc brakes can be quite sudden, and the adjustment stiff and hard to do with roadside tools. I couldn't budge a fixed pad recently, to replace it, until I got home to a socket set. That's BB5s, and I've found some tektro discs to be even fussier. – Chris H Feb 06 '23 at 22:30
  • You believe that The power level when most ebike brake systems are in sound mechanical state is acceptable. Is that still the case with e-cargo bikes, which can carry a significant payload? The question was initially written about those, but maybe it should be clarified. – Weiwen Ng Feb 07 '23 at 00:54
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    @WeiwenNg There are a lot of e-cargo bikes around now so there are counterexamples, but yes I would say from what I've seen that baseline power level out of the box and with sound adjustment is usually acceptable, even loaded. Manufacturers tend to be pretty good about putting bigger rotors on when appropriate, which is the piece of the puzzle that has the most bearing on power level. One can argue that all of them could use some more power to spare and that may be true, but it's not what causing the biggest and worst problems with ebike brakes. – Nathan Knutson Feb 07 '23 at 03:07
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    @Criggie: You’d need enough time (and presence of mind) to switch to the third brake in case both normal brakes fail. If the third brake only acts on the rear wheel it might not stop you in time anyway. If customers are stupid (or uneducated) enough to neglect maintenance to the point where brake pads are completely worn down (or cable tension not adjusted at all) a third brake doesn’t really prevent such negligence. – Michael Feb 07 '23 at 08:03
  • Hydraulic brakes for me have have a big advantage: thanks to automatic advancement, they will keep braking if not maintained. If the user goes too far in term of pad wear, there will be a distinctive sound to indicate there's a problem (and rotors might be ruined too). But at least the brake keeps working, instead of failing quitly. – Rеnаud Feb 07 '23 at 18:32
  • @Renaud Unfortunately, people don't always take the sound of brake pad backing plate on rotor (or even worse, bare piston on rotor) to be an immediate problem. Surely, if the brake pads on a car can last many tens of thousands of km without having to touch a thing, the brakes on a silly ol' bicycle couldn't require any maintenance, right??? – MaplePanda Feb 08 '23 at 07:25
  • @MaplePanda If people ignore a new noise that appear when applying brakes, that is another problem. If I were to choose between two systems, I prefer the one with a warning sound that keeps working over the over that fades quietly. People on e-bikes that do not care about brakes usually have other "traits", like cheap rigid/stock tires under-inflated. In their daily use, stopping to pedal is a good "brake" too (the rolling resistance being compensated by the motor), but the real brakes wouldn't be ready in case of emergency. – Rеnаud Feb 08 '23 at 07:48
  • Coming back to my recent slight scare - I'd adjusted the brakes to good performance on the Friday night. By Saturday afternoon the pads had worn to the point where the back needed further adjustment and the front needed new pads. That was in 150km, on BB5s with sintered pads, but filthy riding conditions with muddy water all over the place. @Renaud, I actually like the need to adjust my mechanical pads, because I inspect them too. The hydraulics on my MTB feel really nice, but it's harder to remember to get the wheel out (needed on that model) and check the pads when they self-adjust – Chris H Feb 08 '23 at 11:42
  • Personally I'd spec TRP Spyres for a cargo bike; I like them on the tandem, which is a similar load, and the maintenance is neither too frequent nor too onerous. – Chris H Feb 08 '23 at 11:45
  • TRP Spyres are reasonably good and do not have any fixed pad. Both pads can be quickly adjusted on the roadside with a 3 mm hex key. They still share the drawbacks of all cable brakes, any cable stretch makes them spongy. – Vladimir F Героям слава Feb 09 '23 at 09:52
  • @Michael a lot of motorcycles have 2 front rotors that are simultaneously engaged. With hydraulic brakes, this is pretty easy to set up. – Adam Rice Feb 11 '23 at 14:43
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Problem with all E-Bikes generally - from the article the only people riding down those hills pre -E-Bike would be people who rode up, and to ride up, you have enough cycle time to know how to descent safely. E-Bike takes novices to places and at speeds, that novices should not be going. Focusing on one thing (in this case forcing better brakes on cargo bikes) does not address the root cause of the problem.

User education is the key here. It does not matter how highly speced the brakes are, poor maintenance and/or poor braking technique and lack of understanding of how brakes work and what their limitations are will lead to failure, accidents and deaths. Better brakes will give bigger margins for errors and reduce these accidents to a minimum. In the case of children, the parents are the ones who should be educated.

Manufacturers have all the responsibility though here. They are selling their product to a target audience that is naive, who want a utility item, rather than the enthusiast. This should be reflected in the product they offer which should be safe and robust. Why is it acceptable that bikes can be delivered with crap brakes that always need adjusting when car brakes 'just work, all the time, every time'.

If people cannot afford a bike with good enough brakes, they cannot afford a bike. If that affects demand, so be it. Is it not better to have fewer bikes and fewer accidents (as a percentage). (If cars were cheaper, more people would buy one, but we don't let the manufacturers sell unsafe cars so more people can buy them.) If the manufacturers are trying to meet a price point that means their product unsafe, and do so anyway, it is 100% on them. Often regulation is needed to keep people safe from these unscrupulous manufacturers, although (in the US particularly) the civil legal risk may be enough that regulation is not needed. (I am removing from my discussion any idea that morals will prevent a for-profit selling an unsafe product)

mattnz
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    to ride up, you have enough cycle time to know how to descent safely — I don't follow. I don't need my brakes at all to ride up. – gerrit Feb 07 '23 at 07:28
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    @gerrit: Mattnz is talking about overall time spent on the bike (riding experience), not just the time taken for this single trip. – Michael Feb 07 '23 at 08:06
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    @mattnz: I’ve heard your argument often (usually in the context of older persons who supposedly ride eBikes at ridiculous speeds while being – supposedly – unable to control them). I don’t buy it. You can get into plenty of dangerous scenarios on a normal bike, you can get to high speed (or at least higher than the 25km/h threshold) on a normal bike. In the end it’s all about riding responsibly and at a safe speed, doesn’t matter if your kinetic energy comes from muscle power or a battery. – Michael Feb 07 '23 at 08:13
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    @Michael many people wouldn't be riding at all, if it was not for e-bikes. More people riding = more accidents. I dont know if E-Bikers are statistically more prone to crash, but at least in some regions of the alps, mountain rescue regulary needs to pick up older people stranded on the way down. These people would never go up the mountains with normal bikes. – airace3 Feb 07 '23 at 09:02
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    @Michael Although I find the argument plausible that (older) people ride faster on e-bikes, the incident linked in the question is on a downhill, where this doesn't apply. On flat terrain on utility bicycles, many (older) people don't usually ride faster than 15 km/h unless they have a strong tailwind. – gerrit Feb 07 '23 at 13:06
  • The part of this that actually answers the question ("improve user education") really ought to be more prominent. I wasted too much of my life sifting through to find it. – Toby Speight Feb 07 '23 at 16:18
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    I think the argument is that those people are not in the shape to ride up mountains without electric assist and by the time they are fit to do it under their own power they would have enough experience to descend safely – ojs Feb 07 '23 at 21:34
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    Yes, typically to be fit enough to ride up a hill takes time on a cycle, that time builds the required experience to ride down safely. There are always outliers - the person who is uber-fit with no cycle experience. – mattnz Feb 07 '23 at 23:55
  • I also want to mention a point about braking technique. I've heard that a lot, especially at the beginning of my MTB'ing. Then, i had discs 160mm, while i'm 90kg, people told me "its just your technique". First, that "160mm=enough" was plain wrong, and second- I don't see the point of constantly having to think about how to brake to not overheat it. A brake is such an essential part of a bike, it should "just work"- largely independent of techniqe. – Apfelsaft Feb 08 '23 at 10:04
  • @ojs you sum it up nicely, but I'm sure we've all met strong cyclists with no clue about maintenance (and some like me who are basically capable of the maintenance, but suffered premature learning experiences). If there's a unusual maintenance requirement with the brakes specced on some cargo bikes, no amount of riding skill will overcome it. – Chris H Feb 08 '23 at 21:26
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    An important thing to keep in mind for the Europeans on this site: the E-bikes from Radpower in the US and Canada are significantly different from the E-bikes common in Europe. They have a throttle and can be ridden w/o pedalling up to a speed of 20mph (32km/h). (The regulators in the EU had the foresight to heavily restrict such bikes and only treat pedelecs, i.e., bikes that do not have a throttle and can only assist pedalling (up to 25km/h), as equivalent to regular bicycles. End of rant...) – user2705196 Feb 08 '23 at 21:50
  • @ChrisH yes, we have all met the type but it is very rare compared to the type who ride as fast as they can everywhere, and when electric assist finally allows them to go above jogging speed, they bumble everywhere at 25 km/h (or faster if they are not the law-obeying type) – ojs Feb 08 '23 at 22:34
3

Storytime:

Years ago I bought a bike (in France) and was surprised to find it had very weak brakes. After almost rear-ending a car with it on the way from the shop to my home, I disassembled the brakes and discovered they had been fitted with a braking limiter, some sort of spring assembly that got squished when pressing the brake handle, thus limiting pulling force on the cable. Once this was removed, the brakes worked as they should.

I immediately assumed lawyers and/or lawsuits involving someone flying over the bars, or worse... regulation... had been somehow involved in the otherwise unexplained apparition of this murderous device on my brand new bike.

They are no longer selling bikes equipped with this sort of self-destruct device, so I presume someone sued the manufacturer because they crashed.

So yeah, it's risky to be alive. And quite often when cowards panic about something they're not doing anyway, the result is over-regulation which makes the regulated thing impossible to do. Or in the case above, "safety features" that make it a lot deadlier.

Anyway. First, regulation! I will translate choice bits about brakes from the French code, it is quite simple:

  • Bicycles must have two independent brakes acting on two different wheels
  • Brakes must stop the bike under reasonable circumstances including in wet conditions
  • Brakes shall be designed to not lock the front wheel if they break
  • Usual maintenance operations (changing a tube, putting on some lights, fenders, rack, etc) must not force the user to disassemble or unset vital safety parts of the bike (braking, steering, etc). (this mandates quick releases on V-brakes so you can pull the wheel out without having to unscrew the screw holding the cable).

So, for this cargo bike, "reasonable circumstances" would an emergency stop, at reasonable speed, with the rated load weight plus some safety margin, on the steepest slope available, which should be about 20-25%, since it's not a mountain bike. Either it can or it can't, and if it can't, it's illegal to sell it, and the manufacturer is liable.

What spec changes would suffice to ensure adequate stopping power on e-bikes? Would these raise the price of such bikes enough to affect demand?

I have very little information about the accident you're talking about, so I'll hand-wave it: 13 year old girls are not very heavy, so it is extremely unlikely they overloaded a bike rated for 300lbs.

However a 13 year old girl does not have the grip strength of a grown adult either.

So, unless the accident was caused by a mechanical failure, defective assembly, etc, it would be interesting to know if the brakes have enough leverage to stop the bike at its rated load, under reasonable circumstances, taking into account the low grip strength and small hands of a young rider.

The fact it's an ebike actually matters here because it allows a child to ride it with a lot more weight on it that they would would be able to without the help of the motor.

So it might make sense to overspec discs and brakes on a kid bike, or at least check if the levers fit their hands and they can stop properly with an acceptable level of hand effort, not too much.

I would also like someone to invent brake pads that screech loudly when the pads are worn out, to warn the user it's time to change them.

Of course training is essential, but no-one does it.

bobflux
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    Oh, brake pads make plenty of noise when they’re worn out. It’s just that not everyone takes the noise to be a problem. – MaplePanda Feb 08 '23 at 17:37
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    @MaplePanda can't hear the brake pads over the earbuds.... therefore No Problem ! ? – Criggie Feb 08 '23 at 18:37
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    I wonder if the "braking limiter" was a power modulator like this one. I'm far from an expert, but I know Shimano's instructions call for them in certain configurations, and I presume a manufacturer who disregards the recommendation to include a safety component without a rather good reason is opening themselves up to liability. There were some crashes of bike share bikes in the US that were blamed on lack of power modulators. – Zach Lipton Feb 09 '23 at 05:08
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    @ZachLipton yes it was this thing. With V-brakes it ruined the performance of the brakes: if the pads didn't rub there was not enough cable pull to both compress the spring and then brake properly. Also makes brakes feel very spongy and hard to control. However it may work differently with drum brakes as in your link. – bobflux Feb 09 '23 at 08:06
  • For the record, the US Consumer Product Safety Commission regulates bicycles, and the regulations do have some wording on testing requirements for brakes. However, it's a static, one-time test. It may not cover cases of brakes going out of adjustment due to poor assembly or poor component quality. https://www.cpsc.gov/content/bicycle-requirements-business-guidance – Weiwen Ng Feb 09 '23 at 19:08
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It may be possible to design brake pad wear indicator of one or another kind as some motor vehicles have. It could simply make lots of noise when braking if worn, or, having advantage of electronics readily available, show the warning on the control panel when metal base of the brake pad touches the rotor. I would be happy to have such.

nightrider
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-1

Uh oh, rant ahead...

Disc brakes work just fine, even affordable mechanical ones. They do of course consume pads though. It's not a big problem, but as Nathan remarked the average E-bike rider doesn't exactly maintain their bike well.

There is one way this aspect could be rendered far less relevant: if manufactures properly implemented regenerative braking, as they should. It makes so much sense if you're anyway going to have an electric motor anyway to also use it for braking, because this both extends battery range (or allows for a smaller/lighter/cheaper battery) and gets rid of pad wear. There's a lot of nonsense talk regarding that regen wouldn't work on bikes because the motors are too weak or that it wouldn't be useful because bikes are too light. Those arguments are particularly nonsense when it comes to cargo bikes, which are a lot heavier (which is bad for friction brakes but actually good for regen), strongly powered (which means there would also be more torque for regen braking), and usually ridden at low speeds (which means less energy is consumed by drag, despite the non-great aero).

The regen braking wouldn't be enough for coming to a stop or for emergencies, but should be plenty for 50-80% of everyday use, which would mean the disc brake pads stay in good shape for longer. Plus, the regen could even make the front braking ABS, which by itself would be a large safety boon for inexpert riders. And front-wheel drive could be quite handy for maneuvering a heavily loaded long-wheelbase bike up curbs as well.

Unfortunately of course, even most cargo bikes nowadays use mid motors which aren't suitable for regen braking at all. Mid motors have some merit for full-suspension e-MTBs, but for cargo bikes they don't really make sense at all – a strongly geared hub motor would work just as well; for a cargo bike it wouldn't matter that it can't cope with high speeds and incurs a lot of drag when turned off.

Cost of this? Very little actually. Any standard motor controller can also be used in reverse to feed back energy into the battery. The main changes needed is to get rid of any freewheeling mechanisms between wheel and motor, to double-check that the gear mechanics are sound also under reverse load, and include some safety circuitry to avoid overloading the battery. (The last point is possibly the main reason manufacturers aren't doing this... they're afraid that batteries might go up in flames and create a publicity disaster, and shy of the testing effort to ensure it doesn't happen.)

leftaroundabout
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  • I suspect ABS would merely change a 'front wheel lockup and wipe out' accident (falling in the direction of the turn) to an 'over the side/bars accident' (thrown in the direction of the outside of the turn) – mattnz Feb 08 '23 at 00:12
  • @mattnz well, ABS ensures that the steering stays responsive. Steering itself is always up to the rider. I don't see any reason why it would make over-the-side accidents more likely. Experience from motorcycles suggest that ABS does significantly improve safety, perhaps not as much as in cars, but that's likely because MC riders tend to be quite savvy in situation-dependent brake modulation. Similar for sportive cyclists, but hardly for most people using an E-bike to do their shopping. – leftaroundabout Feb 08 '23 at 08:08
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    There's a charging circuit there already: e-bike chargers are just power supplies with the clever stuff done on board (the same is true for phones BTW). The control system that would be harder is dealing with a single brake lever for the user when the battery fills up. That adds complexity to the simple mechanical system you want to be reliable. And braking with a full battery is likely if you live (charge) at the top of a hill. I looked into dumping the power into resistors, but you'd need quite a lot - and that would have been using a hub motor as a third (drag) brake on a tandem – Chris H Feb 08 '23 at 11:51
  • @ChrisH the way I'd design the brake lever is as a pressure-sensitive pad on top of the ordinary mechanical lever. So that pressing without moving only activates the regen drag, but actual lever movements directly control the mechanical brakes as usual. — You're right about the charging circuitry, but those aren't designed to handle large overvoltages which could arise when the regen tries to dump more energy into an already full battery – precisely your living-on-top scenario. (Though that could of course be addressed by only charging the battery to 80% at home, which is anyway a good idea.) – leftaroundabout Feb 08 '23 at 11:59
  • That at least has the advantage of an intuitive user interface (squeeze harder=brake harder) But would be prone to false switching when covering the brakes. Some e-bike brake levers use a magnetic switch to cut the motor drive on even very light braking; that could perhaps be repurposed or a 2nd switch could be added. – Chris H Feb 08 '23 at 12:07
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    80% charge at home would have to be automatic - but living on top of a hill you'd want max assistance for the end of the journey home, so decent charge at the end of the day. You & I may be happy to optimise (taking into account likely traffic and load, even temperature), but it's a big ask for naive users – Chris H Feb 08 '23 at 12:07
  • Electric cars usually have a charge cap of 80% as the default setting (more because it reduces battery degradation than because of regen considerations); this could be done for a bike just the same. Most users don't actually need the full battery charge and might not even notice, those who do could manually raise the cap (or buy a bigger battery, which would probably be better than relying on a complete unhealthy charge cycle on each journey). – leftaroundabout Feb 08 '23 at 12:19
  • And, yes, resistors as a backup solution would also make sense; they would need to be quite powerful but not unrealistically so. An aluminium frame is a pretty good heat sink. – leftaroundabout Feb 08 '23 at 12:22
  • This raises a question: what proportion of e-bike battery management units implement smart charging features like setting the initial maximum charge at 80%? I don't know how widely this is implemented in consumer electronics. If I look at my Apple gear, there is an option to do smart charging, but this implementation frequently charges my laptop to 100%. I have to leave the laptop on the charger for a very long time to avoid this. – Weiwen Ng Feb 08 '23 at 15:51
  • @WeiwenNg I rented once a Giant, that has this "feature" enabled by default. I discovered it by having the bike partially charged the next morning, which lead to a cancellation of the ride. – Rеnаud Feb 09 '23 at 07:34
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    @leftaroundabout Some bikes were sold at some point bike with regen braking. The range increase was counted in percent, and those were an hassle to ride without assist, because basically you could not disconnected the "regen" - it's a different wiring of the motor, if I understood correct. So in practice limited to 25kph, and it needs to be charged all the time (above 25kph or if the battery is empty, the regen kicks in). It would also require a hub motor, which is less suitable for cargo bikes (because of the available power at low speed), while central motors can take advantage of gearing. – Rеnаud Feb 09 '23 at 08:09
  • @Renaud well, I countered these arguments already in the answer. To repeat: 25 km/h is all you need on a cargo bike, running with empty battery is anyway kinda game over, and a hub motor works just as well as a mid motor. (In fact, a hub motor needs less gearing to generate the same torque as a mid motor except in <1:1 gears. The only reason mid motors are available with more torque is that they're very aggressively geared.) – leftaroundabout Feb 09 '23 at 09:19
  • And as for range increase, 1. that's not even necessarily the main reason for regen (at least not in this context) 2. how much the range increase is depends entirely on the riding style. If you're using the motor full boost all the time but only brake as little as possible (as most cyclists are used to doing) then sure, it'll buy you almost nothing. OTOH, if you use the motor properly only for the steeper climbs and otherwise merely let it coast with the pedals, and also consequently regen-brake on all descents to never exceed 20 km/h, then the range can be infinite. – leftaroundabout Feb 09 '23 at 09:27
  • Not sure why the downvotes, I was about to write the same answer: keep disc brakes but reduce their maintenance needs, possibly using aggresive regen (triggered by brake handles, not just coasting). I know that regen is not very useful in recharging the battery, but it could be used to slow down the bike much more aggresively, and save the brake pads for longer. – Ekus Feb 09 '23 at 20:57
  • There may be some technical obstacles to using regenerative braking on bikes. You'd be adding a lot of weight. The amount of recovered energy may be small, and it will heat up the battery and increase wear. It doesn't appear widely implemented now, but technology may improve if there's sufficient demand. – Weiwen Ng May 22 '23 at 19:55