Help! Lightweight e-kit for coaster brake bike - alternate e-bike and 'normal' bike experience.

[LauraEG]

Hi there!

I want to electrify my bike but I'm unsure what kits would be compatible. It is a Swedish bike, Monark brand, with a back pedal brake. I used it as my usual means of transportation when I lived in Malmö, and I transported my two children in it, in total they weight about 40kg (one 3 years old in a front seat, and the other, 7 years old, in the luggage rack).

Now I'm in Barcelona and have to make longer journeys (about 15-20km a day) with quite a lot of hilly parts. Doing that carrying the children is hard for me.

Ideally, I would want as light a kit as possible allowing me to alternate power assist with zero assist. I would like the assistance for the climbs above all, but I want to continue having the experience of riding a 'normal' bike and I don't want to depend solely on the battery. And as I said, it shouldn't weigh much, so I wouldn't want a super powerful battery and motor (the idea is rather to have some help at specific times, but not all the time).

I don't know if there's even such a kit? If there isn't, I'm also open to other ideas you might have!

I attach some photos of my bike. (Btw, I've changed that chain by now )

Thank you very much in advance : )

 

[Az.]

What is your budget? Is starting from scratch with new bike an option?
If not, then front hub motor with torque sensor would be best option I think.

...and welcome.

 

[saneagle]

Before anythingthing, your chain needs tightening. In case you don't know how to do it, loosen off the two wheel axle nuts and pull the wheel baxk and up, then re-tighten the nuts making sure that the front of the tyre is in the middle of the frame.

I'm wondering whether you should get a different bike because your brakes are not really good enough if you want to carry a couple of kids and have the extra speed from an electric motor. It might be easier to get another bike with disc brakes. the cost of the bike is normally small considering the cost of the electric kit.

With your present bike, you're more or less limited to a front wheel motor, which is OK, but not the best. A different bike would give you more options..

The nearest kit to what you ask for is the latest Swytch Go kit, but waiting times are quite long and support is not as good as we'd hope, though the Go kit should be more reliable than the previous ones. I can't see it on their website, so you'd have to ask them about it. there's been plenty of hype about it in the media:

Swytch Go - a new, even more affordable e-bike conversion kit

Swytch are well-known for their affordable and extremely popular front hub retrofit conversion kit which fits a very wide range of bike designs. In April 2022 they announced an even lighter, smaller version based around distinctive large-smartphone-sized batteries and we reviewed and liked this...

ebiketips.road.cc

https://support.swytchbike.com/hc/en-gb/articles/20493029580561-Which-extras-do-I-need-for-my-Swytch-GO

Apart from that, we'd need to know about your level of competence to fit kits, make adjustments, fabrications and things like that before maling other recommendations.

 

[saneagle]

If not, then front hub motor with torque sensor would be best option I think.

It has a coaster brake. Does a torque sensor work with one?

 

[LauraEG]

What is your budget? Is starting from scratch with new bike an option?
If not, then front hub motor with torque sensor would be best option I think.

...and welcome.

Thanks : )

I don't really have a budget in mind, what matters the most to me now is to find a solution that allows me to keep using and enjoying my current bike...

 

[Az.]

It has a coaster brake. Does a torque sensor work with one?

KT controller then.

 

[LauraEG]

Thanks @saneagle for all your comments!

The chain has been changed now, but yes, it was way too loose... Thanks for the tips anyway.

I'm familiar with the Swytch kits (I should have mentioned that in my post) and they seem to tick some of the boxes of what I want, but unfortunately as per their customer service they are not coaster brake compatible : (

From what you say, I understand it's not the safest option to electrify a coaster brake bike? In my case, I'm not really looking to increase speed with a motor, but rather to have some help for the climbs in my biking itineraries with the kids. Would that change your recommendation?

And if I were to use another bike (I have another one, it is an old city bike with disc brakes, but needs some update), are there any kits you'd recommend (lightweight, etc)?

My level of competence for fitting kits and bike mechanics in general is quite average (or quite low, actually ) but I have that covered because my partner is a bike mechanic - although with little knowledge of e-bikes : )

 

[Waspy]

I'm sorry to be the party-pooper but three humans on one bicycle does not sound very safe to me, and a seven year old is getting quite big to fit on a kid's bike seat

Have you considered one of those bike trailers that are specifically designed for transporting kids?

An electric motor would make towing a trailer much easier.

 

[Az.]

I see no reason why Swytch kit might be incompatible with your bike. Having that said I don't think Swytch is a good option at all.

Do you find riding your bike safe? I have absolutely zero experience in that matter, but with child seat so high, your bike looks to me very unbalanced. If I were you, safety would be my primary consideration.

Installation of conversion it will be like walk in a par for your partner.

 

[saneagle]

Thanks @saneagle for all your comments!

The chain has been changed now, but yes, it was way too loose... Thanks for the tips anyway.

I'm familiar with the Swytch kits (I should have mentioned that in my post) and they seem to tick some of the boxes of what I want, but unfortunately as per their customer service they are not coaster brake compatible : (

From what you say, I understand it's not the safest option to electrify a coaster brake bike? In my case, I'm not really looking to increase speed with a motor, but rather to have some help for the climbs in my biking itineraries with the kids. Would that change your recommendation?

And if I were to use another bike (I have another one, it is an old city bike with disc brakes, but needs some update), are there any kits you'd recommend (lightweight, etc)?

My level of competence for fitting kits and bike mechanics in general is quite average (or quite low, actually ) but I have that covered because my partner is a bike mechanic - although with little knowledge of e-bikes : )

For your specific application you need a mix and match kit. The motor needs to be low speed (around 180 - 201 rpm). Most standard kits are around 250 -260 rpm, which are not so efficient for low speed and heavy weights, especially if you want a lightweight one..

You should measure the distance between your forks first to get the axle length. Most front motors are 100mm. Some are narrower if you need one.

The motors that come to mind are the Q100 or AKM 100 (100mm axle) or Q70 or AKM 85 (75mm axle).

I'm not sure why Swytch says their kit is not compatible with a coaster brake. It should be fine with your bike. There's a small channce you'd have to get a different pedal sensor, which would only cost about 10 Euros.

 

[LauraEG]

@Az. @Waspy thanks for your comments! I understand your concerns, but I do find my current setting safe (it's only exhausting with the climbs now ). I have the younger one in the front child seat (which is supposed to be placed as high as it is) and the older one on the luggage rack, with feet supports and a minimalist but sturdy structure to support his back. The bike is very balanced when I ride with both, as the weight is distributed all over the front and the back.

We do have a bike trailer that we love but for my day-to-day, I prefer to carry them on the bike (lighter and easier to move around).

 

[peterjd]

Hi, Congratulations on achieving what you do with an extra 40kg of no doubt lively youngsters onboard. So it sounds as though you only need limited assistance at present on the more hilly terrain around Barcelona. It might be possible with something like the relatively light Swytch Go kit. Like Saneagle I can't see why the pedal speed sensor shouldn't work with the back pedalling brake except that the power would stop immediately you brake, which could be a problem with the sort of weight (plus hub motor and battery) you would be carrying . What does your bike-mechanic partner think about it?

 

[Benjahmin]

I would be very wary of switch kits. There have been many problems reported on this forum, Their waiting times, after paying for it, seem ridiculously long and their customer service, in the case of faulty equipment, almost none existant.
The front hub motors that Saneagle mentions are available from Topbikekit, as are the controller, brake switches etc. You may need to look elsewhere for a battery.
I bought an AKM 128 from them and built it into a rim myself (first time) this keeps delivery costs down and should be something your partner could do. I found it a very enjoyable experience.
With a front hub you could put a battery in the frame (keeping weight as low as possible) and the controller under your front basket.

ebike hub motor,front motor,24V/36V/48V motor,200-350W motor,500w motor for electric motor

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topbikekit.com

However I too would be concerned about the braking. You will be adding extra mass with the kit as well as growing kids and you are now living in a place with steeper hills perhaps leading to much more front rim wear from braking. I'd go with discs every time.

 

[Tony1951]

I see no reason why Swytch kit might be incompatible with your bike. Having that said I don't think Swytch is a good option at all.

Do you find riding your bike safe? I have absolutely zero experience in that matter, but with child seat so high, your bike looks to me very unbalanced. If I were you, safety would be my primary consideration.

Installation of conversion it will be like walk in a par for your partner.

All true. And thinking about safety, I winced the other day driving in Newcastle to see a bloke towing two little kids in a trailer made of next to nothing, right down near the road and maneuvering in busy traffic. It wasn't that I thought the rider was going to crash and hurt his kids, but I thought he was putting a massive amount of trust in other drivers. Those kids could so easily end up under the front of a car driven by some coked up, or drunken idiot, or ordinary petrolhead psycho. We've all seen them haven't we?

I used to ride about with my own sons in child seats back in the day, I'm not sure I would do now. Too many knackers in cars, or is it that my risk appetite has changed? I don't know.

 

[saneagle]

Hi, Congratulations on achieving what you do with an extra 40kg of no doubt lively youngsters onboard. So it sounds as though you only need limited assistance at present on the more hilly terrain around Barcelona. It might be possible with something like the relatively light Swytch Go kit. Like Saneagle I can't see why the pedal speed sensor shouldn't work with the back pedalling brake except that the power would stop immediately you brake, which could be a problem with the sort of weight (plus hub motor and battery) you would be carrying . What does your bike-mechanic partner think about it?

Having thought about it, the motor cut-off wouldn't work with just back-pedalling unless you used an in-line cable switch (HWBS); however, that wouldn't be a problem as long as you use the front brake at the same time. I can't see any issue with the pedal sensor that couldn't be overcome by the normal means.

 

[Nealh]

Tongsheng tsdz2 mid motor have a coaster brake variant of the motor.

 

[matthewslack]

Just to clarify: some PAS sensors will decide you are pedalling and so the motor should be ON even when you are pedalling backwards (for your coaster brake). That's not safe, and you need a 100% reliable workaround for that before you add a front hub motor to your bike.

A brake cutout only on the front brake? I would not regard that as safe on your bike. You will need a reliable brake cutout triggered by the motion of your back pedalling rather than the position of a brake lever, so a non-standard sensor, a non-standard solution, which is why kit manufacturers in general do not support coaster brake bikes.

 

[saneagle]

Just to clarify: some PAS sensors will decide you are pedalling and so the motor should be ON even when you are pedalling backwards (for your coaster brake). That's not safe, and you need a 100% reliable workaround for that before you add a front hub motor to your bike.

A brake cutout only on the front brake? I would not regard that as safe on your bike. You will need a reliable brake cutout triggered by the motion of your back pedalling rather than the position of a brake lever, so a non-standard sensor, a non-standard solution, which is why kit manufacturers in general do not support coaster brake bikes.

I heard of one once, but I've never seen one in 14 years of working with ebikes.

 

[guerney]

coaster brake

Isn't that terribly dangerous when the chain breaks? I strongly suggest you convert a different bike which doesn't use coaster brakes, to transport your children with.

 

[saneagle]

Isn't that terribly dangerous when the chain breaks? I strongly suggest you convert a different bike which doesn't use coaster brakes, to transport your children with.

What if your cable breaks or you drop your bike and the lever snaps off? Cables break more easily than chains.