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I'm considering to buy a pedal-assist electric bike with a mid-drive motor. I'm worried that if and when the drive unit fails, I might have to replace the entire bike, such as indicated in this answer, (or maybe that's not true and it's not quite as bad as I fear it might be). For a semi-recumbent tandem that costs around €6450–€8350 without electric assist and around €10000–€12000 with electric assist, it would be a pity to replace the entire bike already after around 10 years; if I spend €6500–€12000 on a bike, I hope it lasts much longer than 10 years. Google Search suggests that mid-drive retrofits exist. It would seem that if it's possible to retrofit a mid-drive engine, then it should also be possible to replace that retrofit after 10 years when the rest of the bike is still usable.

What are the advantages and disadvantages of retrofitting an electric engine to an existing bike, compared to a design where the electric engine was part of the bike from the start?

(One aspect is that retrofitting on a new bike might void the warranty.)

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  • I couldn't find it right away, but does the 10 k€ bike manufacturer not provide waranty for more than 10 years, such that they service/replace the engine themselves when/if it fails (for perhaps a fee from your side)? Jul 9, 2023 at 19:27
  • @SaaruLindestøkke No. Warranty is two years for the bike I'm looking at.
    – gerrit
    Jul 9, 2023 at 19:41
  • Oof... :( Didn't expect that for such a price, but I now better understand the question you have. Jul 9, 2023 at 19:49
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    Given the answer linked has a vote count of -2, not sure it qualifies as a statement of correctness. Check with the manufacturer if motor is replaceable, and how long they will support the bike for. (Being Shimano, I suspect yes and for a very long time).
    – mattnz
    Jul 10, 2023 at 1:01
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    side thought: with the pino the front driver sits pretty much on top of the front wheel, and so does the cargo in the cargo configuration. With this load on the wheel, even a front hub motor may be a consideration - which should be extremely easy to replace. To the point where you may consider to keep the non-electric wheel as spare part or use the electric one only for tours where you definitively need it. Jul 10, 2023 at 8:02

2 Answers 2

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You will need to replace lots of the ordinary components until the engine gets worn or you will not find a replacement battery on the market.

Also, €12000 is horribly expensive. You can buy three descent E bikes for this. The non electric part is seldom very high end.

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  • It is expensive, but I haven't found anything comparable on the market that is cheaper. Three decent ebikes are not useful for transporting loads or for riding a tandem where one person cannot ride a balance bike. The viewpoint is slightly cheaper than the cheapest version of the Pino and does not double as a cargo bike. The one from performer cycles does appear cheaper but also lacks several other features.
    – gerrit
    Jul 9, 2023 at 19:48
  • So if I'm trying to justify spending that type of money, I tell myself that it's sort of three bicycles in one: a tandem, so one can go touring with two people without needing two bikes, and I won't need to buy a separate cargo bike.
    – gerrit
    Jul 9, 2023 at 19:57
  • Looks like the Circe Morpheus is a cheaper competitor.
    – gerrit
    Jul 9, 2023 at 20:47
  • You write one of these two cyclists cannot drive a bike alone so I understand you need a tandem. Otherwise you could buy a bicycle per rider for this money.
    – nightrider
    Jul 10, 2023 at 5:01
  • Correct, + a 3rd bike as a cargo bike, and I think a semi-recumbent tandem with freewheel is more suitable for the "passenger" than a classical tandem. We've also test-ridden recumbent trikes, but the Hase Kettwiesel costs as much as the Pino and is only for one person, so de facto it's even more expensive. But I should look into the Circe Morpheus as a cheaper alternative. There's also the Velomo Hi-Life² but I'm not convinced it's cheaper than the Pino.
    – gerrit
    Jul 10, 2023 at 7:09
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I'd divide bikes into several classes:

  1. Ready-made mid-drive electric bikes
  2. Ready-made hub-drive electric bikes + maybe a ready-made mid-drive electric bike with a mid-drive system that uses a standard bottom bracket shell (apparently those exist, as indicated in the question)
  3. Retrofitted hub-drive electric bikes + maybe those mid-drive retrofits that use a standard bottom bracket shell

For (1) the general advantage is that they are the best when power and controllability are considered. For example you can get 85 Nm of torque from the best units. This combined with for example 28T/38T/48T triple and 11-51 cassette means you get 155 Nm of torque at the wheel -- and this is not at zero speed, but at whatever speed you are travelling. Also, all mid-drive electric bikes that don't use a standard bottom bracket shell but rather an all-in-one mid-drive unit include torque sensor. This means that you control the drive unit by varying pedaling power. If you want to go slower, you just pedal with less effort. You don't have to adjust the assist level at all.

For (2), the problem is that these almost always lack the all-important torque sensor. Also, the strongest Bafang hub drive I found is 95 Nm and intended for fatbikes (so probably not compatible with anything else), for regular bikes the strongest is 80 Nm. I think these pale in comparison with a strong mid-drive with low gearing. Also you have to remember that for hub-drives the torque they specify is the torque at zero speed, for mid-drives they specify torque at pedaling speed. So you cannot say that for example 85 Nm mid-drive with 1:1 gearing would be equivalent to 85 Nm hub-drive.

However, (2) has a massive benefit: most likely the frame is standard. This means if an important electrical system component fails and you can't find a compatible replacement, and you have to replace all electrical parts of the bike, you can do it. However, for mid-drives this is generally not possible since there is no standardization for the mounting of the mid-drive into the frame. You may find that for example Bosch drive unit of year X might be compatible with another Bosch drive unit of year Y, but this is not guaranteed, Bosch may change the mounting as they wish from year to year and from model to model.

For (3) you get all the benefits and drawbacks of (2) with four additional drawbacks: first, you (or someone else) needs to do a lot of labor to retrofit the bike, secondly since you are not a volume buyer you don't get the discounts volume buyers get, thirdly you need to throw away lots of components and labor, for example your old spokes, your old hub, and the massive effort the wheelbuilder spent to make the hub, spokes and rim into a complete wheel. Fourthly, frames and forks have a variety of axle standards, for example if you have a thru axle frame but the motor hub you want to buy is for non thru axle frames, you have a problem. I would consider (3) only if (2) is impossible for you due to some reason.

As for tandems, firstly from your other question you said the other person is not capable of pedaling with full effort. This means the electric assist would need to be very strong. This limits your options to maybe two: (1) a very strong mid-drive unit with low enough gearing, (2) a very strong hub-drive unit. Most units can be ruled out since they are not intended for tandems where one of the person cannot pedal at full intensity. Considering that tandems are very expensive you may not want to throw away the frame if a mid-drive unit fails, thus (2) might be preferable. About the torque sensor, I always advise selecting an e-bike with torque sensor, but in the case of tandems this may not be the case. The reason being that in tandems there are two persons pedaling, so you cannot control the pedaling effort all on your own. You must communicate with the other person, and this makes the adjustment of pedaling effort very slow. This is exactly the same problem that plagues every e-bike without torque sensor: you must communicate your intentions to the computer by continuously adjusting the assist level. But since the problem with tandems and e-bikes without torque sensor is the same, adjustment of power level is very slow, the lack of torque sensor will not probably bother you.

Thus, I might consider an e-tandem with a very strong hub drive in this case. Maybe a 80 Nm Bafang hub could be adequate, even if it doesn't give the full 80 Nm at speed, since anyway you need the maximum torque only on steep hills and you are going very slow on those hills anyway.

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  • NB: The front rider on the Pino has its own freewheel, so the front rider doesn't have to pedal at all. I don't know how that works with the torque sensor. Actually, I don't quite know how the transmission for the front rider works at all if they pedal slower than the back rider (who is the pilot in case of the Pino).
    – gerrit
    Jul 9, 2023 at 19:56
  • I feel like as someone who has a Bafang mid drive e-bike I need to add to this: I have found the lack of torque sensor to be no problem at all as long as you also have a throttle (in my case a thumb throttle). I find this to be even better than a torque sensor because I can actually pre-empt needing torque when for example starting from a dead stop. Also I have the very lowest power model and I find the torque to be more than enough for my needs.
    – Turksarama
    Jul 9, 2023 at 23:02
  • I confirm you need to change the level of assistance on Bafang each time you want to change the speed or start climbing. But this is possible to learn, not a disaster. I was however surprised how the controller on another bicycle does not need to be touched at all.
    – nightrider
    Jul 10, 2023 at 5:08

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