BBS motor for slow cargo trike

Hello,

I have a cargo trike that I use to take my kids around (http://christianiabikes.com/). I live in a somewhat hilly area and would like some assistance at times. Bike+Kids+me+some cargo weights some 375-400 lb or 170 kg. I do not want or need to go fast (15mph/25kph tops), with some 5% hills (some parts steper, but of short length). The bike has hydraulic disk brakes and a nexus hub, and I think a mid drive will be the best application, but which one? Will the bbs01 or the 500w bbs02 be better than the bbs02 750W for my application?

Thanks!

I have a lot of experience with cargo bikes myself, although not specifically the bike you are using.

Sounds like the bike you are using has standard duty only drive components in which case it is best to keep the power on a crank drive down to 500 watts or less. A rider standing up on pedals putting their entire weight into each pedal stroke puts about the same amount of stress on a bikes drive system as a 500 watt mid-drive system. Once you start getting into more powerful drives then that power level you start putting more stress on the drive system.

Long story short, with a cargo bike that uses a standard duty drive system and isn't equipped with heavier duty drive components you want to choose a mid-drive system that operates at a power level that won't ever-stress the drive system and will force you to shift down to a lower gear and not try to power through in a high gear.

I have zero personal experience with the specific mid-drive system you are asking about but I have built a few mid-drives of my own from scratch and have used Cyclone brand mid-drive kits quite extensively in the kind of application you are asking about.

Another thing you want to watch is the RPM that the mid-drive kit you choose will spin the crank at, if you want to pedal along with the motor that needs to be within the human pedal range (about 60-120 RPM pedal cadence).

And also watch the sizes of drive chain ring (drive chain ring = the chain ring that the chain going back to the rear wheel uses) that the mid-drive kit comes with. If it has more teeth then your stock chain ring it will change your gearing to higher then before (which you don't usually want with a cargo bike) and if it has less teeth then your stock chain ring it will change your gearing to lower then before (which with a cargo bike isn't necessarily a bad thing so long as you don't get carried away with it). For example if your cargo bike comes with a 38-tooth chain-ring on it stock you don't want a mid-drive that comes with a 44-tooth chain ring because that will change your gearing and make it higher with you don't really want. On the other hand a mid-drive that came with a 36-tooth chain-ring would be fine and would actually probably help a little because of the slightly reduced gearing ratios. Obviously matching the same size works out the same.

Some mid-drives its fairly easy to change the size of the chain-ring used on the kit or can order the kit with different sizes of chain rings it comes with. Other kits you can be stuck with the size it comes with and that is that. So if you haven't already go count the number of teeth on you current stock chain-ring on your bike and keep that in mind when shopping.

daniel.. said:

Hello,

I have a cargo trike that I use to take my kids around (http://christianiabikes.com/). I live in a somewhat hilly area and would like some assistance at times. Bike+Kids+me+some cargo weights some 375-400 lb or 170 kg. I do not want or need to go fast (15mph/25kph tops), with some 5% hills (some parts steper, but of short length). The bike has hydraulic disk brakes and a nexus hub, and I think a mid drive will be the best application, but which one? Will the bbs01 or the 500w bbs02 be better than the bbs02 750W for my application?

Thanks!

Click to expand...

First of all if you put a 750W Bafang on your Christiania Cargo Trike It WILL NO LONGER BE SLOW, BUT VERY FAST.
I have made the conversion you are thinking off and I hit top speeds of 45km/h which is absolutely nuts with this bike, as it gets destabilized above 30km/h. What you want to get from a 750W conversion is the torque, no hill in the world with asfalt on will stop you. So go for the 750W but save your self and others from hospital bills and get the controller speed limited at 25-28 km/h.

It would be nice to see where you live, change that in your settings.

I need to see a picture of the model of Christiania bike you have, most of them need a blacksmith to be able to take the Bafang midmotor. Some older models don't and the 2-wheels neither. Place a big heavy (10-15kg) battery in the front of the cargo box and you get MUCH better riding stability.

/Philip

Here is a picture of my conversion, note how the triangle is remodelled.

Thank you both. Philip, that is very interesting! Good call on the frame modification. I was thinking of having the motor protrusion pointing down, but I guess floor clearance would be too small.

Can you please share what chain wheel battery and voltage you are using and what is your speed and mileage / W consumption?
What brakes are you using? Do you find them powerful enough?
I am really not looking for speed, and may go for a lower voltage / smaller chainwheel / larger cog configuration, but this, together with the frame modification and the motor and battery, may be a significant investment.

BTW, I am near Barcelona, Spain.

Thanks again,

Daniel

daniel.. said:

Thank you both. Philip, that is very interesting! Good call on the frame modification. I was thinking of having the motor protrusion pointing down, but I guess floor clearance would be too small.

Can you please share what chain wheel battery and voltage you are using and what is your speed and mileage / W consumption?
What brakes are you using? Do you find them powerful enough?
I am really not looking for speed, and may go for a lower voltage / smaller chainwheel / larger cog configuration, but this, together with the frame modification and the motor and battery, may be a significant investment.

BTW, I am near Barcelona, Spain.

Thanks again,

Daniel

Click to expand...

The motor won't fit under the frame, unless you remodel the frame.
You also need to make a dent in the horizontal main tube to fit the motor like I did. But none of this is a problem if you got the skills or know somebody that has.

I'm using the Bafang 48V 750W BBS02 motor with a original 46T cog in front and 22T cog at the rear (2.09 in gear ratio). The battery is a 48V LiFePO4 Pouch 30Ah giving me 1200Wh in practical use.

The rig uses between 10-20 Wh/km. With heavy loaded bike (total of 200kg) and at 25km/h I use 15Wh/km and have a minimum distance of 80km, which has proven to be correct at several bicycle tours with this bike. I have run this rig without problems for 1600km since 10. April. With nearly empty bike and riding to and from the city, keeping up with the other cyclist, I use 12Wh/km. The weight of the bike makes acceleration Wh-expensive.

The brakes need to be good because of the weight, so I changed the front mechanical disc brakes to hydraulics, the rear is still just ordinary rim brakes not so good, but hardly ever use it. The front brakes are Bengal Helix 7.5 I don't know if they ship to Spain but you can get a complete brake set (200€) to switch from the original mechanical disc brakes to hydraulic with ease.

/Philip