Best Front Hub 20inch wheel kit for a tandem

[KenR]

I would appreciate some advice on the best kit for my tandem. It has to be front hub as a mid drive can't be fitted and I want to keep the Rohloff gears. We have several ebikes in the family and all use 36v batteries so I am looking at 36v 500w set ups being the most powerful geared motors I can get for 36v. I looked at a Bafang kit on Aliexpress but as far as I can see from the Bafang web site their motors are only designed for 26inch wheels, i.e. they don't rev fast enough for 20inch wheels. CSC offer a kit with a 20inch wheel running at 360rpm which looks ok but is it strong enough for a heavy tandem. Any help appreciated.

 

[Nealh]

A 500w is no different to a 250w at sub 20a the only advantage is if you want to pump 25/30a in to one.

 

[KenR]

Thanks for your reply. I would like the maximum power that I can get with 600wh 36v battery. This is mainly for hill climbing as the tandem is very heavy. I have fitted several kits on other family bikes but do not have much technical knowledge so any further help appreciated.

 

[sjpt]

I would appreciate some advice on the best kit for my tandem. It has to be front hub as a mid drive can't be fitted and I want to keep the Rohloff gears. We have several ebikes in the family and all use 36v batteries so I am looking at 36v 500w set ups being the most powerful geared motors I can get for 36v. I looked at a Bafang kit on Aliexpress but as far as I can see from the Bafang web site their motors are only designed for 26inch wheels, i.e. they don't rev fast enough for 20inch wheels. CSC offer a kit with a 20inch wheel running at 360rpm which looks ok but is it strong enough for a heavy tandem. Any help appreciated.

Depends a lot on how you want to use the tandem.

We have a 700c tandem with an XF07. That is underpowered for a tandem (as we were warned), but it was the only legal kit easily available at the time. It is great on the level (we never use it above setting 2 of 5, and rarely go above 12mph except downhill). It struggles on the hills but still gives us that important extra push that means we can make lots of hills we wouldn't be able to otherwise. For us a lower geared hub would be better, we don't need the speed on the flat, but we would like the extra help we would get on hills at say 6mph. The efficiency of the XF07 has really dropped off by 6mph; it would probably be better for what we need on a 20" wheel.

p.s. I see you say 'mainly for hill climbing' in a crossed post. So you may not need the higher revs you think you need.

 

[Nealh]

The max power depends on the continuous rating of the battery discharge (not the peak current ) and the controller max current rating. Pointless buying a controller with a 20a max draw if a battery continuous rating is equal or less. So before deciding on the kit one needs to know the limit of the battery rating.

 

[KenR]

Thanks again Neith, how do I work out my battery rating?

 

[KenR]

Depends a lot on how you want to use the tandem.

We have a 700c tandem with an XF07. That is underpowered for a tandem (as we were warned), but it was the only legal kit easily available at the time. It is great on the level (we never use it above setting 2 of 5, and rarely go above 12mph except downhill). It struggles on the hills but still gives us that important extra push that means we can make lots of hills we wouldn't be able to otherwise. For us a lower geared hub would be better, we don't need the speed on the flat, but we would like the extra help we would get on hills at say 6mph. The efficiency of the XF07 has really dropped off by 6mph; it would probably be better for what we need on a 20" wheel.

p.s. I see you say 'mainly for hill climbing' in a crossed post. So you may not need the higher revs you think you need.

Thanks, I currently have a 250w Bafang hub motor in the tandem and get a very similar experience to you. I live in a hilly area and want a bit more help on the hills. I prefer to be legal but with a touring tandem......

 

[matthewslack]

Thanks, I currently have a 250w Bafang hub motor in the tandem and get a very similar experience to you. I live in a hilly area and want a bit more help on the hills. I prefer to be legal but with a touring tandem......

Have a look at the motor simulator at ebikes.ca. Many motors in their list, so quite informative. The GMAC functionally might be good, but 250W rated it is not.

The problem with a tandem is twice the weight nearly but still only allowed the same motor rated power, so on hills speed will be low which is no good for any hub motor that can help up to 25kph. A slow wound hub will help at low end, but may run out of its rev range at a horribly low speed.

You have probably already found some red line which makes a mid-drive bafang kit unworkable, but you need the sort of help that gears provide, so is there a way?

 

[matthewslack]

Thanks, I currently have a 250w Bafang hub motor in the tandem and get a very similar experience to you. I live in a hilly area and want a bit more help on the hills. I prefer to be legal but with a touring tandem......

I missed the front hub bit... try the GRIN in the sim.

 

[Nealh]

Thanks again Neith, how do I work out my battery rating?

The rating is usually spec'd by the seller/manufacturer and will depend on the cells and BMS used.

 

[KenR]

Have a look at the motor simulator at ebikes.ca. Many motors in their list, so quite informative. The GMAC functionally might be good, but 250W rated it is not.

The problem with a tandem is twice the weight nearly but still only allowed the same motor rated power, so on hills speed will be low which is no good for any hub motor that can help up to 25kph. A slow wound hub will help at low end, but may run out of its rev range at a horribly low speed.

You have probably already found some red line which makes a mid-drive bafang kit unworkable, but you need the sort of help that gears provide, so is there a way?

Thanks, There is always a way but it would need really major work as it is both belt drive, low step through and folding. Even then I don't think a Bafang mid drive would fit in the bottom bracket shells......

 

[KenR]

The rating is usually spec'd by the seller/manufacturer and will depend on the cells and BMS used.

Thanks, My main battery is made up from six Grin Ligo units but I also have another which is six 36v 84wh skateboard batteries wired together in parallel. That way we can take our bikes by air.

 

[KenR]

Thanks all that has all been a great help. Just had a look at the simulator. Unless someone says different it confirms what everyone has said above, ie that with my 6 Ligo battery units the output of a 250w motor is very similar to a 500w motor. Looks as if the power is restricted by the LIGO BMS. Looks as if there is nothing I can do to get more power if I want to take my bikes by air.

 

[Nealh]

The main marking of 350/500w is to satisfy the US market where everything has to be bigger and so called better, they simply won't purchase 250w marked hubs on mass.