Trailer Hauling ebike conversion

[AdrianKe]

I need some help with whether my plan will work. I have not purchased a bike yet but am thinking either a relaxed position bike (dutch style) or ladies urban bike like a specialized sirrus or alike. The bike will be for my wife.

I live in the Netherlands currently and it's mostly flat bike lanes, asphalt and cobble. The only challenge is that we have a steep hill between our home and my daughter's school, incline is about 5deg/8% over a stretch of 350m, the total commute is short 3km in total per round trip. My wife needs to travel that route twice a day with both our kids in a thule kid trailer (trailer total weight of +-40-45 kg loaded). Going up the hill I would like to have her cycle with minimal effort on high support level and flats she can drop the support level and have more own effort. On other days we will just have casual longer trips but the hill incline is not a big issue then, those trips will not easily exceed 35km.

The Netherlands have a 25km/h assistance limit legally but my need is more torque than speed.

This is what I was thinking of doing:
- I have not purchased a bike yet, looking for a second hand bike with a relaxed riding position
- Bafang BBS02
- Brake sensors
- Shift sensors
- 500c display
- Battery, not sure of voltage and ah rating

So my questions:
1. Will the Bafang BBS02 achieve my goals? (the hill must feel like a flat at worst)
2. What battery rating and size would you suggest?
3. Is it a bad idea to use internally geared hubs in this application?

 

[m@Robertson]

1. Yes it will. A BBS02 is rated on paper for around 120 Nm of torque, which yields quite a lot less when measured at the wheels. Still, if its torque you want thats the motor to get it from (and the method, being able to downshift) in the more-restrictive EU jurisdiction. A direct drive or geared hub motor would be perfect if it weren't for that hill, and even so a geared hub may still be enough... but maybe not as hub motors provide much lower torque output. This is borderline in terms of whether a mid drive is even needed... but if you want a certain solution the first time, then the '02 is it.

If you can swing it, I would purchase the higher-output BBS02 motor. 48v and 750w. I'm well aware of the regulations associated with same. That motor has an upgraded controller which is much more robust and my goal would be longevity not high power. Its far better to use a motor/controller at 35% of its capacity than it is to be always redlining it. The lower power BBS02s have been known to be a bit delicate with respect to their controller internals. A BBS02 can be downrated very easily via access to its settings interface. See below. I entitled the article for the BBSHD but the BBS02 has the identical interface and procedures. If you are concerned with limiting peak output, you can do so with this.

BBSHD Programming For The Pedaling Cyclist (2023 Update)

Explore enhanced BBSHD programming for pedal assist settings that don't let the bike run away from you, and throttle settings gentle on the drivetrain.

talesontwowheels.com

2. The biggest 48v pack you can afford. In The Netherlands you are the last people on Earth (perhaps literally) who need new ideas on how to ride bikes, but generally, as you put an ebike to use and it broadens your thinking on what you can use the bike for, your use case expands. And so will your battery capacity needs. Absent that, 6 km daily and one very small hill (by my local standards at least) and you should be able to utilize even the smallest battery to good effect. 3 km is not enough to drain anything and you can charge in between rides, so literally anything will work.

3. The short answer is yes, IGH's have known weaknesses, but you are working with much lower power levels than the ones I would expect to cause trouble. Still, I don't know what IGH you are talking about and there are so many. Only a few are known to work well with a mid drive in the kind of power range we are talking about. Here again, the certain solution is to not use one and go with a derailleur, but a likely successful build can have an IGH. Since this bike has to be reliable because it has a job, I would not use an IGH without some certainty on the IGH's specs.

 

[AdrianKe]

Thank you for the information, really appreciated the input. Seems that the BBS02 and external gears/casette will be the best option. External gears also allows for some torque adjustments by replacing the gear ratios.

 

[m@Robertson]

Thank you for the information, really appreciated the input. Seems that the BBS02 and external gears/casette will be the best option. External gears also allows for some torque adjustments by replacing the gear ratios.

Before you go down that rabbit hole...

A mid drive changes the game when it comes to picking drivetrain components. In particular, its generally better to pick less-expensive steel clusters that are pinned together. The steel is for durability when faced with high torue, and the 'pinned together' part creates a single monolithic component that distributes the force of torque across the entire cassette body, which helps prevent the cog from digging into the poor cassette body and killing it. The good news is that steel 1-piece clusters like this are inexpensive. For 9s with a narrow range, a Shimano HG-400 is only a couple of dozen Euro. For 9s wide range, you can't beat the Microshift Advent although for your terrain I can't see a big need for a pie plate in back. 10s is an Advent X cluster, and for 11s my go-to is a Sunrace CSMS7, also all-steel and pinned. They can be hard to find so the Sunrace CSMX8 is a close second with an alloy big cog, which is fine in your use case.

Take it a step further and you want a steel cassette body too. I have seen incredible differences where a DT Swiss steel MTB body after 1500 miles doesn't even have a scratch in it, while the alloy road version after 50 miles is dug into enough I can't sell it on Ebay anymore (I got lazy and didn't replace the cassette until a few days after build was completed).

The more you do on this list the less you will have to concern yourself with parts replacement due to excess wear/tear.

How To Build a Mid Drive Ebike That Doesn’t Break

Mid drives up the ante on the required competence of the builder. Read this so your bike lasts without things breaking or wearing out early.

talesontwowheels.com

 

[HaroldPE86]

Thank you for posting the link to your blog, Matt. Great stuff.

How To Build a Mid Drive Ebike That Doesn’t Break

Mid drives up the ante on the required competence of the builder. Read this so your bike lasts without things breaking or wearing out early.

talesontwowheels.com

 

[AdrianKe]

Before you go down that rabbit hole...

A mid drive changes the game when it comes to picking drivetrain components. In particular, its generally better to pick less-expensive steel clusters that are pinned together. The steel is for durability when faced with high torue, and the 'pinned together' part creates a single monolithic component that distributes the force of torque across the entire cassette body, which helps prevent the cog from digging into the poor cassette body and killing it. The good news is that steel 1-piece clusters like this are inexpensive. For 9s with a narrow range, a Shimano HG-400 is only a couple of dozen Euro. For 9s wide range, you can't beat the Microshift Advent although for your terrain I can't see a big need for a pie plate in back. 10s is an Advent X cluster, and for 11s my go-to is a Sunrace CSMS7, also all-steel and pinned. They can be hard to find so the Sunrace CSMX8 is a close second with an alloy big cog, which is fine in your use case.

Take it a step further and you want a steel cassette body too. I have seen incredible differences where a DT Swiss steel MTB body after 1500 miles doesn't even have a scratch in it, while the alloy road version after 50 miles is dug into enough I can't sell it on Ebay anymore (I got lazy and didn't replace the cassette until a few days after build was completed).

The more you do on this list the less you will have to concern yourself with parts replacement due to excess wear/tear.

How To Build a Mid Drive Ebike That Doesn’t Break

Mid drives up the ante on the required competence of the builder. Read this so your bike lasts without things breaking or wearing out early.

talesontwowheels.com

Great advice thanks, makes alot of sense mechanically

 

[AdrianKe]

Thank you for posting the link to your blog, Matt. Great stuff.

Thank you, appreciate the link!