Dutch bakfiets (cargo bike) conversion help

[pajtaz]

Hello,

You have helped me select a kit for my Kona Sutra commuter. Can you help me do the same for my possible next conversion?

We have just purchased a used bakfiets (cargo bike) for hauling kids around town. Exact model is Bakfiets Cargobike Short from 2012, photos are below. It is easy to ride speed is low so it takes much longer to get around town and it does get tiring quickly. I am considering converting it to ebike but only if it is not too expensive AND it must be done with front hub motor.

Unlike my Kona Sutra conversion where I was looking for speed, a rear hub motor, and did not care too much about final cost, here I am looking to just get assistance - to get to places faster and to reduce fatigue - but with as low cost as possible. If that means 36V instead of 48V or smaller battery or smaller motor then it is fine as long as it helps with pedaling. I already have a charger for my other 48V battery, maybe I can save money there also.

Can you please help me first understand what kind of a front motor do I need? This bike is not too heavy but with two kids and the rider it gets easily to 150 kg (40 kg bike, 40 kg for kids and baggage, 70 kg rider). Front wheel is 20". I am clueless what kind of motor do I need and what kind of torque. Please help me with specific make and model suggestions.

Front wheel has a brake I am not familiar (I think it is called roller brake). Would I need to get the wheel and the motor and change the type of brake or is it possible to just get the motor? Or do I need to get the motor and change the brake but have someone install the motor in the wheel? What kind of brake would be adequate - normal disc brake or hydraulic disc brake?

Does it matter whether system is 36V or 48V? Can I save money with 36V motor and battery?

Which controller?

PAS would go on the left side, there is no space on right.

Seems 11 Ah battery is enough since most rides will be 15 kms round trip max. Actually it will be used daily for taking kids to school and back and this is only 1 km away so maybe 4-5 kms per day max.

All of the above would need to be max 400 EUR with shipping and taxes. If I can't get the motor and wheel shipped from Europe then it will be already too expensive. Maybe I can get just the motor and have someone install it in the wheel? Any suggestions are welcome.

Thank you in advance for any help.

 

[vfr400]

Roller brake motors have nearly died out now and most of those that are available are too weak for what you want. I found this one on Aliexpress. It's 255 rpm. which will be quite slow in a 20" wheel - probably about 12 mph with a half-charged battery, so that would be good if you want to ride around at 10 mph. If you want 15mph, you should use a 48v battery and controller.

Just one thing in the listing doesn't add up. At the top it says 255 rpm, but lower down it says for 20" wheel, which normally would mean that they made a mistake with one of those numbers, so maybe test it with your present controller to see what its actual speed is before getting a battery.

Obviously, you need to check that it's the right width for your forks.

113.67￡ |Dgw12r 36v250w Black Front Hub Motor With Roller Brake 255rpm Speed Sensor Integrated - Electric Bicycle Motor - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

One other thing. Maybe it's a crooked photo, but it looks like your lower head-race is shot and needs replacing. You should check it out.

 

[pajtaz]

One other thing. Maybe it's a crooked photo, but it looks like your lower head-race is shot and needs replacing. You should check it out.

Thanks. What is a head-race?
EDIT: I guess you mean the space between circular parts of the fork/headset in the third photo? I'll check but I haven't noticed any problems yet.

 

[sjpt]

Thanks. What is a head-race?
EDIT: I guess you mean the space between circular parts of the fork/headset in the third photo? I'll check but I haven't noticed any problems yet.

Yes, it's the bearings where the fork is attached to the frame.
If you apply the front brake and rock the bike forward and backward there shouldn't be any play.
Normally if wrong it really hurts the handling of a bike. It could be that with the rather indirect steering mechanism and probably slow speeds it doesn't affect handling so much on that bike; but worth fixing anyway to prevent wear.

 

[pajtaz]

Ok, thanks. Handling right now feels very good but maybe it’s something to look at in the future.

So at what kind of motor should I be looking? I guess 250W is enough but what size, torque, voltage? What battery and controller? Any recommendation on LCD? Does battery have to be 48V if I want use existing charger?

 

[Benjahmin]

For 20 inch wheels I believe you normally look for a 325rpm motor to get 25kph capacity. That's if you use a 36v battery.
If you were going to use a 48v battery, then a 36v motor wound for around 250rpm will get you to full speed.
You need to check the distance between your front forks (normally 100mm) and how many spokes your current wheel has 'cosd it needs to match the spoke holes in the new motor.
There are no disc brake mountings on your current forks and it's hard to see if a caliper brake could be fitted.

 

[pajtaz]

What about this kit? Yosepower 20" kit
Says max torque is 30 Nm so this might not be enough for the bakfiets?

On another forum person used this kit for their bakfiets conversion: Chamrider ebike kit
This kit is perfect except that cost is about 90 EUR more and it is not clear when it would arrive and whether it is shipped within EU.

Or this kit: Greenbikekit

 

[vfr400]

You still haven't checked the gap between your forks. You're wasting your time until you have!

What are you planning to do for a brake with those motors you just suggested? Are you planning on changing the forks?

30NM in a 20" wheel is the same as 43.5NM in a 29" one.

 

[pajtaz]

You still haven't checked the gap between your forks. You're wasting your time until you have!

What are you planning to do for a brake with those motors you just suggested? Are you planning on changing the forks?

30NM in a 20" wheel is the same as 43.5NM in a 29" one.

Gap is 100 mm, same as the other guy who made similar conversion with his bakfiets. However I will change the fork since I will need a new fork with mounts for disc brakes. The new fork has the same gap of 100 mm.

 

[vfr400]

However I will change the fork since I will need a new fork with mounts for disc brakes. The new fork has the same gap of 100 mm.

You can use virtually any geared front motor you want. the bigger the diameter, the more robust they are. For 15 mph, you need around 300- 330 rpm in a 20" wheel. For any other speed, you need rpm in proportion. That's important.