20

I have a 3 mile daily commute that I bike in Toronto. I enjoy it very much, but there are times I'd like a bit of an e-boost; for example when a car cuts me off while I'm in the middle of climbing a steep hill. I'd like my e-bike to weigh as little as possible, and to be inexpensive. I would be happy with a battery range of about 1 mile, but the smallest ones I can find are at least 10-15 miles. Is there a reason why this range segment of the market does not exist?

15
  • 7
    If you want it, build it, Get an electric motor kit for your existing bike, and run it off the smallest battery pack you can make that provides the required voltage (36 volt will need 8x 18650 in series, and a 24V will only need 5 in series)
    – Criggie
    Jan 8, 2023 at 1:42
  • 21
    Perhaps some solid rocket boosters could be an alternative solution :D
    – MaplePanda
    Jan 8, 2023 at 3:28
  • 48
    @Criggie To bike 3 miles in 10 minutes you need an average speed of 18 miles per hour or around 30 km/h. That corresponds to a well trained individual with no elevation and zero traffic. OP already hinted at steep hills and cars cutting them off, ie dense traffic. Your comment sounds needlessly arrogant.
    – quarague
    Jan 8, 2023 at 7:08
  • 17
    How heavy is the battery in a 10-15 mile range e-bike? I suspect reducing that by 80 or 90% doesn't change much in terms of total bike wieght.
    – quarague
    Jan 8, 2023 at 7:11
  • 4
    A minor comment -- if you get a bike that will only last up to exactly what you need you'll run into problems when 1.) It's very windy, 2.) You weren't able to plug it in last night 3.) The battery has started to degrade. A 5 mile ebike degraded 50% would still allow you to go your route and back with some wiggle room for wind, a single mile ebike wouldn't get you halfway there and you'd start to see performance losses very quickly in the life cycle of the battery.
    – Sidney
    Jan 10, 2023 at 15:14

11 Answers 11

43

I think the ultimate issue boils down to a lack of demand for such a short-ranged product. Looking broadly at the entire electric vehicle market, range anxiety is fairly common. Most people are worried about not having enough range (even when it's an unreasonable or unwarranted concern)--very few people are actively seeking a short-ranged product when longer-ranged versions are available for little additional hassle. The bike still needs all the wiring, the motor, the controller, etc. None of those get simpler or go away due to a smaller battery. Hence, if you're going to go through the effort of motorizing a bicycle, you might as well give it a nice big battery. Also, pateksan points out in a comment that the manufacturer's pricing model would be disrupted by such an addition. To quote them:

A bike with 1 mile range would probably only be very slightly cheaper to make than one with 10-15 miles. It could therefore be hard to price competitively and without undermining the overall pricing model. If the 10-15 mile bikes were substantially pricier, nobody would buy them. And if the 10-15 was only a little extra, most people would prefer them, so few would buy the 1 mile.

There might be technological issues involved as well. Note that the electrical power needed to provide a given acceleration is independent of what battery capacity you use. Also, under a given load, a smaller battery is being used "harder" than a larger one. For example, to provide 1A of current, a 1000mAh battery is discharging at 1x its capacity, whereas a 100mAh battery would be draining at 10x its capacity. 1 mile is a very short range, and so a very low-capacity battery would be involved. I would not be surprised if the required current draw is infeasible for such small batteries.

Of course, with lithium-polymer technology, such current draws are possible, but lipo batteries tend to be delicate and have an increased fire risk. I believe existing ebike batteries all use regular lithium-ion technology with arrays of cylindrical cells for safety (and cost). Supercapacitors would be a good solution if this product was actually created.

8
  • Yeah - range anxiety is a thing. But a bike has the pedals as primary power and the electric is only an "assist", not a feature possible on an e-car.
    – Criggie
    Jan 8, 2023 at 4:09
  • 8
    Lol, one thing I've noted is that pedalling the bare minimum required is almost immediately a thing with most e-bikerists Jan 8, 2023 at 7:22
  • 7
    @LamarLatrell: I've noticed that too, and yet I don't understand it as I seem to be incapable of not hustling at all times regardless of e-assist or not. Jan 8, 2023 at 7:44
  • 6
    @LamarLatrell it depends on the bike - very upright city e-bikes lend themselves to pedalling at low effort and relying on the motor in a way that designs based on other geometries don't seem to
    – Chris H
    Jan 8, 2023 at 9:45
  • 10
    +1 but I think it may help to put it another way: a bike with 1 mile range would probably only be very slightly cheaper to make than one with 10-15 miles. It could therefore be hard to price competitively and without undermining the overall pricing model. If the 10-15 mile bikes were substantially pricier, nobody would buy them. And if the 10-15 was only a little extra, most people would prefer them, so few would buy the 1 mile. Naturally, I'm just speculating.
    – pateksan
    Jan 8, 2023 at 11:55
20

From a convenience point of view, a 1-mile e-bike would need to be charged every ride, for the use mentioned in the question (that would be a red flag for me, I have already enough batteries to manage in my life, but that's personal). For people living in cities, charging is very often a constraining aspect of e-bike ownership, as the bike is often parked outside the owner's premises – whether outside or in bike rooms. For such users, the minimum considered range required is not 1 ride, but the commuting distance of several days, or one week (+ a margin to consider battery wear, and cold-related discharge, if applicable). On top of that, charging takes time, but that point is not an issue with a pure commuter.

Another reason is that it would make such a bike only usable for that particular use. Some people prefer to buy specialized tools, but I would also assume that the vast majority still prefers general-purpose tools, especially if they get more expensive. From observations around me, an e-bike increases the bike use, and just for that reason I would not consider a bike that I can "only use" for my commute, and that I would have to charge after each ride. For instance, that would defeat the purpose with grocery shopping, if above that range: one of the legs of the journey would need to be done without assistance.

Now in terms of weight, not sure it would make a significant difference. A Bosch Powerpack 500 weighs 2.6kg. Typical ebikes using them weigh around 21-25kg. A battery with 10 times less capacity would probably weigh 2kg less (you still need housing, connectors and weather protection if the battery is removable), that would still make the bike too heavy for most people.

7
  • 3
    If parking outside, it would make a lot of sense to choose a model with a removable battery, fir security reasons as well as charging. These were the default until recently, and still seem to be in the utility e-bike market. Then it's easy to charge every night, and even under your desk.
    – Chris H
    Jan 8, 2023 at 9:50
  • 2
    +1 for the weight issue. It doesn't make sense to make your bike substantially more heavy to pedal all the time just to make it easier to pedal only for short distances when the motor is turned on. With most e-bikes, if you want to increase range and/or have more of a workout, you can still run them on a low power setting to help counteract the added weight of the motor and battery while still contributing much of the energy to by pedaling yourself. With a one-mile e-bike, ironically you might well need to use the e-assist for more than a mile just because of all the weight you added. Jan 9, 2023 at 2:37
  • My workplace has charging places for e-bikes (either plugging in the bike directly, or lockers with chargers inside for loose batteries). Bringing the battery inside for charging in the office is prohibited. I've never seen the charging places in use.
    – gerrit
    Jan 9, 2023 at 7:10
  • @gerrit dedicated e-bike charging at the workplace is probably a good indicator of a country that tends to be pretty advanced in its bike infrastructure. In the UK I've only heard of that for a workplace that used e-bikes to visit clients (inner-city healthcare), and my impression of urban cycling in Canada is that it's no better than we've got, possibly worse.
    – Chris H
    Jan 9, 2023 at 11:50
  • 1
    @gerrit I'm inclined to agree, but I can think of one very good use case: Those for whom charging at home is difficult (e.g. living in flats with fixed batteries and no power in the bike store). Another less likely one is old e-bikes after their battery has degraded - both the capacity and the internal resistance get worse, so hill son the way home can be tedious. But making e-bikes last longer is a worthwhile goal and replacement batteries for some brands exist only in theory.
    – Chris H
    Jan 9, 2023 at 13:00
12

A small battery does not provide enough power, as there is a limit to speed of discharge

The largest safe continuous discharge rate for lithium ion batteries is about 10C, i.e. fully discharged in 6 minutes. So for a 1 mile range, the top speed of the bike would be 10 miles per hour (16 km/h).

And even that rate is only safe in the sense that the battery doesn't overheat. Discharging at 10 C and always to 0% charge would wear out the battery much sooner than a larger battery discharging at e.g. 1 C and to 50%.

Different battery models have varying maximum discharge rates, but the effect on the cycle life (number of charges before battery capacity falls to 80% of original) is dramatic. At the 10 C discharge and a daily charge, a typical battery would be degraded within one year of use:

enter image description here

(Image: batteryuniversity.com)

5
  • 3
    What unit is C, and how is it related to miles per hour?
    – ojs
    Jan 8, 2023 at 19:15
  • 4
    @ojs C-rate, I added a link. If it takes at least 6 minutes to empty the battery fully (which in OP's case is just 1 mile worth of energy), that gives an upper limit of velocity.
    – jpa
    Jan 9, 2023 at 6:01
  • 1
    @ojs: 1 C is one battery-capacity per hour charge or discharge. It's a good way to normalize against capacity if you have larger or smaller cells. So yeah, 10C is a full discharge per 6 minutes. (You don't have to go the full 6 minutes, and in fact hopefully don't, because deep discharge is really bad for an Li-ion battery). Jan 10, 2023 at 16:18
  • 2
    @PeterCordes it would be nice if it had different symbol from coulomb
    – ojs
    Jan 10, 2023 at 17:34
  • 2
    @ojs: Yeah, that was my first reaction, too. :/ Jan 10, 2023 at 23:20
9

There are two limitations on a battery, that are quite strongly linked, in any given technology and price point at least

  • Capacity
  • Power

You need the battery to be able to provide enough power to assist the bike, say 100 W absolute minimum, preferably twice that.

You cannot get this power handling in a small, economical, battery. Once you can handle the power, the capacity will be up into double figures of miles.

Another way to look at this is how long it will take the battery to discharge. How long does it take you to go one mile? A battery that fully discharges in 4 minutes is working way down on its discharge rate / capacity curve, is discharging very inefficiently.

4
  • 3
    All this, plus you’ve got the fundamental problems that a small-capacity battery along the lines of what the OP is asking for requires the user to religiously recharge their battery, with little margin of error for forgetting one night, or for making any changes to their riding patterns.
    – RLH
    Jan 8, 2023 at 8:02
  • 1
    Yes, but if you forget to charge it, you've still got a bicycle, so you're fine.
    – user68083
    Jan 8, 2023 at 19:28
  • 6
    @user68083: e-bikes are heavy. Riding one with the battery dead is demoralizing. Jan 8, 2023 at 22:54
  • 1
    @whatsisname or even riding uphill with the battery really rather low. I used to occasionally borrow one, and ride it with no assistance on the flat, but riding uphill without proper assistance was harder than riding my own hybrid with my daughter on the back, despite a similar weight
    – Chris H
    Jan 9, 2023 at 11:52
5

For a 36V motor, you need 10x18650 batteries. With all the equipment to make an e-bike, the additional weight would be over ~3kg's, at best.

Such a bike would look weird on a catalogue, and price would still be too high for a 1 mile range e-bike.

With so much cost, effort and additional weight involved, no one would bother. But there's a DIY option as always. Or, you can buy an e-bike with no battery, and build a smaller battery pack, which would definitely give you more than 1 mile range, as it would be 1.5Ah at worst.

1
  • I'm not sure what the max current of a 14500 cell is but that would allow lower capacity - but save very little weight again
    – Chris H
    Jan 8, 2023 at 9:47
5

I would buy a bike with a reasonable range - if it only has a 1 mile range, then you will be recharging every day. Because you are fully cycling the battery pack every day, it will only last maybe a couple of years max, and show range reduction within months.

If you have a bike with a range of 10 miles, you will be recharging 10x less frequently and so the battery will last many years.

The motor and speed controller will still be the same weight as it still has to deliver the same power. All you save is the weight of the battery pack, and as others have stated, each cell has a maximum allowed current drain.

Which means for a given power output, the lower limit on the battery pack capacity is defined by the peak motor power, not the range.

4

The reason you cannot find an e-bike with such a small range is probably due to the lack of demand for that short of a range along with an inability for costs for a reduced capacity model to be lowered much if at all from the 10-15 mile range costs. The 10-15 mile range IS the bottom of the current market based on current battery capacity, motor efficiency, and general customer demand. A one-mile range e-bike is simply not practical (or profitable) to produce commercially.

16
  • 1
    An analogous example of this is seen in the removable/solid-state storage market. I recently was looking for some small capacity micro SD cards (for an older item that could not support the larger capacity cards) and had to search to find them. I could find plenty of 8, 16, 32 GB and more, but I had to get creative in my search to find what I needed. It just is not practical to produce the small capacity cards anymore, just like it is not practical for a company to produce the e-bike range you are seeking and still make a profit.
    – Ted Hohl
    Jan 7, 2023 at 22:25
  • 2
    There are in fact e-bikes that are close in weight and handling to their conventional counterparts and have concealed batteries, but they're very expensive. And have >1 mile range. Presumably the companies that are selling e-bikes have done market research and have designed their bikes accordingly.
    – Adam Rice
    Jan 8, 2023 at 2:09
  • 2
    @user68083 - the problem there is you're assuming there is a significant, or even reasonable cost-savings to be had in making the battery smaller. I rather doubt there is. After all, you still need the same capacity motor and electronics (they're dictated by the total weight of the bike+rider, where the rider is the major contributor). It might work out that the 1 or 5 mile version is $50-$100 cheaper (at most!), but that's such a small discount on the overall cost there's no reason to have the separate product.
    – Fake Name
    Jan 8, 2023 at 8:49
  • 2
    Further to what @FakeName says, it wouldn't be cheaper at all, because something so much less popular would lose economies of scale compared to typical models. Then by ruling out a detour to the shops on the way home, or a ride to somewhere interesting on a sunny weekend, such a short range shrinks the market dramatically. As does the need to charge at work as well as at home (so for most 1-mile commuters, a 2-mile range is the minimum). No cheaper, not appreciably lighter, much less useful for most users. Why would anyone sell them?
    – Chris H
    Jan 8, 2023 at 13:07
  • 1
    Also adding to what @FakeName is saying, once you get to that scale, the battery is such a tiny contributor to the total mass of the bike that you’re talking maybe a few dozen grams lighter for the reduced range, or probably less than 1% of the total mass of the bike plus the rider, which just does not matter unless you’re racing (and if you’re racing, you either can’t use an e-bike, or will want one that is much longer range). So not only would the cost savings be minimal, so would the mass savings. Jan 8, 2023 at 13:22
2

It's unusual to find cells that small in the ebike segment. Depending on the voltage, you have to join the batteries in a series to get i.e. 24 volts. If you join 6 18650 cells together, you get 2.5 amps at 24V, which is 2 miles. The problem is that arrangement would get very hot. You can use a 15 mile range ebike to do 1 mile aday for 15 days in a row before you recharge, and the price between 6 and 12 batteries is like 20 dollars, so why not pay 20 dollars for the extra batteries and top it up less frequently?

2

My "40 mile range" electric skateboard goes a real-world 15 miles when on full-throttle and going up and down hills in San Francisco. That's 15/40 = 37.5% of the "sticker rating".

After 5 years, I expect the range to reduce by half, down to 7.5 miles. That's 7.5/40 = 18.75% of the original "rating".

So, a "1 mile sticker range" electric bicycle (75 lb kid, flat smooth streets, 7 mph speed, 1 mile range) might have a real-world range (180 lb person + gear = 205 lbs, 15 mph speed, uphill) of 0.38 miles. After 5 years you'd get 0.19 miles. That's 0.19 miles x 5280 ft/mile = 1003 ft, or about 3 times the length of a football field.

Pretty useless, right? So is the complexity of an electric bike that has a near-zero range. The time it takes to get out your bike and gear is about how long it takes to just walk the 1000 feet.


Better answer:

The amortized component weight. You need a motor, speed controller, wiring, and battery. Getting the battery down to be tiny still leaves a decent amount of other components, weight, and complexity. You might as well make the battery big enough to actually provide the power you need.

Smaller-capacity batteries also have smaller currents, as the max deliverable current is directly proportional to the capacity of the battery as a "C-rating multiplier." Ex: a 20-C discharge battery rated for 4 Ah can discharge at a maximum of 20 x 4 = 80A. So, if you make the battery too small, the max continuous and burst output current gets too small to be useful, and you might as well choose a larger-capacity battery to be able to supply more current. You can offset this by getting a smaller capacity higher-C-rating battery, but then you increase cost to get higher C-rating. You might as well lower the C-rating and increase the capacity for the same cost.

Ex: two equivalent-cost and equivalent-max-discharge batteries might be these:

  1. $100 4Ah 37V 10S Li-Ion 15C discharge (max continuous current = 15*4 = 60A)
  2. $100 1.5Ah 37V 10S Li-Ion 40C discharge (max continuous current = 40*1.5 = 60A)

As you can see, they can each deliver the same max continuous current, and they cost the same, but one has 4Ah/1.5Ah = 2.7x the capacity. You might as well get a bigger capacity and have 2.7x the range for the same price and max-current capability.

0

I can imagine that a short range e-bike with with minimum features would really be suitable for a huge number of casual commuter cyclists.

Why there isn't a market for it? Probably because of "range anxiety" as other have mentioned. But also I think it's a bit of a chicken and egg scenario: nobody has offered the product, because the perceived demand isn't there, and nobody wants it because it isn't something to be had.

I can imagine strapping a cheap cordless circular saw to one of the front sprockets with a chain, could achieve basically what you're asking for... save for all the details that make that less viable in practice.

1
  • Welcome to the site - yes range anxiety should be less of a thing for an ebike, because the motor is only the secondary/assist source of power. One can always ride a flat ebike to destination.
    – Criggie
    Jan 11, 2023 at 3:36
0

The e-bike market is just a mess of businesses trying to make huge profits off something that should be very cheap and simple. To get what you want, you need a DIY/kit solution where you supply your own battery and it's easily removable. This also solves the objection some answers have raised that "it would be hard to charge the battery because you parked your bike somewhere outside not at your home": you just carry the battery inside with you wherever you're going and plug it in. (Aside: this also completely solves the risk-of-theft issue.)

Put a friction coupling or hub motor kit on a normal inexpensive road bike, connect a battery of the appropriate size, and you're done.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.