Recommendations for 20" electric cargo bike / moped build


1 µW
Jun 20, 2023
Hello forum,

i am looking for some pointers from the experienced folks here for the build of an electric 20" cargo bike / moped.

As being based in southern europe and bike infrastructure is lacking to say the least, bike will be ridden on normal roads inside the city.

I have ridden cargo bikes (electric / non electric) for years and the goal of the project to build an electric cargo moped "sem pedales".

In a nutshell: "A cargo moped that can climb smaller hills and go around 30mph tops for up to 40km on mixed terrain"

1) Basic Needs:
speed and power

- fast enough to keep up with city traffic on paved roads, 30mph tops is enough (45km/h for us europeans)
- enough power to climb steeper hills from 5% to 15% in the city without bogging down a lot (portugal can be hilly).
- System weight around 170kgs = 85kg human + 30kg doggo + 45kg bike with motor and batts
- NO pedals, NO pedaling - throttle only
- it is, for now, a proof of concept and feasibility study of new mobility, so no need to look "flashy", open running cables are ok
- about 30 - 40km / 20- 25 miles on mixed terrain is enough, not always going to ride full throttle
Mid or Hub drive:
hub drive motor for now as the frame is not prepared for mid motors
No real limit, but would be nice to stay under 1200 € / 1300 dollar for the electric setup. Used parts are ok as its going to be a prototype. I dont include wheels , brakes and other parts in the calculation
Bike weight:
no big concern, i live in a house on ground level and the monster can be stored in the living room like it deserves ;)

2) Constraints
Battery size

- i would be willing to compromise on range / battery size as i want it to be tucked underneath the cargo box left / right
Rim size
- needs to be either 20 or 19 inch to work with the frame geometry

3) Bike Basis:
- "short john" cargobike frame with 20" wheels front and back , just short of 2m in length
- frame has detachable dropouts, wider axle motors would be possible
- no fat tires, Frame takes 3,0“ tires max


4) Good to know re: safety:
- talked extensively to the designer of the frame and its sturdy enough to take the power of stronger motors with torque arms
- i have enough knowledge around stopping power and what kind of brakes are required for the total system weight to not kill myself :)
- police doesnt care about throttle powered bikes that are not pedaled if ridden on the road

Looking for....
1) Advice on volts and amps
2) rear vs dual hub motors
3) motor types / brand
4) avg Newtonmeter requirements
5) controllers

Thanks upfront folks , Cheers from Portugal :)
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Rear 1500 watt motor kit, 48-52 volt/20 amp battery should get you what you want, except the range. 25 mile range without pedaling is impossible imo for 20" fat tire with extra cargo weight, especially if you're riding constantly at 30 mph.
My 29er e-bike with a Leaf 1500W motor matches the OP's goals for top speed and typical load, and exceeds the range goal. It suffers on steep climbs and needs lots of help at the pedals. I use a 44V 47Ah battery and a controller limited to 40A.

I think 2 kWh of battery would buy adequate range at the implied performance level. To get enough climbing torque, the controller and motor will have to be much more than powerful enough to maintain the desired top speed, but have an unloaded speed only a little higher than that. With an unloaded speed of 50-55 km/h and say 4000+ watts of maximum electric power, there should be enough torque surplus at lower speeds to climb most steep paved roads (but not enough torque at higher speeds to greatly exceed the speed target).
Since you're in Europe:
  1. what do you have for cargo bikes to work off of?
  2. To add onto 1, do you already have one?
  3. what is your skill level with fabricating things?
  4. Can you Weld?
  5. What tools do you have?
  6. How much is it to ship or purchase batteries in your area? Recycled EV cells are a great option, but some EU nations can have shipping fees nearly the cost of the battery itself.
Thanks so much for the answers already given, i see i have a lot to learn :)

1. basis is a veloader cargo frame , the frame has detachable dropouts with can accept wider axle motors
2. yes, its currently sitting in my car, picked up at the source in germany
3. no skills, but i have people at hand
4. see 3.
5. Drill, Grinder, Volt meter etc. I would have someone custom make connector and batteries for me for €
6. good question ! at the moment i am thinking about picking them up in person while i am visiting family in germany (bigger market and more readily available)

Is this assumption correct?
60v vs 52v will give a higher top speed mostly and both would be sufficient torque wise with a powerful enough motor.
Asking because i have someone at hand who could build me 2x 52v 26ah batteries what can be tucked neatly under the cargo box and could possibly be wired in parallel.

My impression is that the higher you go in voltage the more it gets complicated battery (size) wise...

>>>> added some photos to the start post for reference <<<
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Is this assumption correct?
60v vs 52v will give a higher top speed mostly and both would be sufficient torque wise with a powerful enough motor.

Your question is too limited. For any given motor architecture, you can trade battery voltage off against RPM per volt (which is a function of motor winding turn count). So once you commit to one, that dictates what you will need for the other.

Leaf Motor is beneficial for having custom winding count at no extra charge. So if you know what battery you will use and how fast you want to go, then you can get them to wind a motor that corresponds to those other factors.

My impression is that the higher you go in voltage the more it gets complicated battery (size) wise...

Again, you can trade off the number of cells in series against the number of cells in parallel (or the size of cells) to get different voltage batteries with the same total energy. 14S x 20P is the same number of cells (therefore size, weight, energy) as 20S x 14P.
I think I will but the battery topic aside for some time as its going to be a custom build pack that needs to fit under the cargo area, and most likely have it shipped or get built locally from someone who knows what theyre doing

Re: motor
I am currently in germany before travelling back to PT and could get my hands on the following motor for quite cheap (second hand, which is fine as its going to be a prototype / feasibility study, looks like if buying everything new i would blow through the budget in NO time)

I tried to learn about motors today and from my limited understanding lower winds (t´s ? ) require less battery size ultimately as a lot can be done via a good controller ?

Thats the one i could get. Thoughts ?

QS 205 V3 50H 30 x 4t 760rpm​

For what it’s worth, I frequently ride a juiced ODK v3 cargo bike with child in the back. This uses a 500W Bafang geared front hub and 52v batt with 22A KT controller.

It will go up any hill and has a top speed on the flat of about 40kph, which is fast enough with 20in wheels and no suspension. It’s fast off the line too which makes it fun to ride.

The good thing about a hub is that it’s completely independent from the rest of the bike, you can pedal along or not, up to you. Also really reliable and low maintenance.

Range is good although it needs a 14s 6p battery to use the full power (1000W peak).