Help! Recommend me a front hub motor

[Bikes4two]

• I’m looking to convert our tandem which is fitted with a Rohloff IGH and both bottom brackets are therefore eccentric.
  
• The eccentric clamps are castings on the underside of the BB which therefore excludes the possibility of a mid drive motor like the Bafang BBSxx series or Tong Sheng TSDZ2 (the latter currently being my favourite but I’m keen to understand and experience a hub motor given those on here who favour them over mid drives).
  
• Thus I’m looking for recommendations for a front hub motor, OLN 100mm for a 26” wheel
  
• I know that front motors are not as powerful as rear hub motors but fortunately we are fairly able cyclists still and so just looking for a bit of assistance when the need arises.
  
• Spoke count isn’t critical as I shall build a wheel to suit.
  
• Brakes are caliper so no worries about disc mounts
  
• I’m looking at using 36v batteries as that is what I already have – so what motor RPM should I be looking at? (or persuade me to go 48V?).

Controller/Display

• My limited experience with a hub motors comes from a Pendleton where I upgraded the controller and display (I posted about this HERE.).
  
• I do recall that the Kung Teng (KT) controller I upgraded to was Torque Simulated (like this one HERE)and the power delivery gave a much more satisfactory ride than the OEM one, so I’m aiming to get a similar ride experience for this project.
  
• Obviously the display goes with the controller but something minimalistic is the goal (battery level indication and power up/down/off is all I am looking for).

Brakes and PAS

• The brakes are hydraulic (Magura HS33) so something neat for the levers: in-line or stick-on?
  
• PAS – there seem to be some fancy alternatives to the normal magnetic discs but I’m not up familiar with what’s what so guidance please. Further, on the tandem the front cranks have the chain wheel on the left (it’s the sync chain linking front to back) so that is a consideration.

Thanks very much in anticipation,
Cheers, Bikes4two

 

[saneagle]

Front motors are noisy and course compared with back ones, so whatever you do, make sure you get a KT controller to quieten it down and smooth it out. LCD4 won't break, but the buttons are a bit small for winter gloved hands. It's Ok for the summer.

Motor choice depends on how fast you want to go, how much power you want and what sort of forks tou have. The same applies to voltage.

 

[Benjahmin]

Have a look at Topbikekit, many motors to be had, I've just used them with no problems. Or you could talk to Woosh and get a kit to suit.
For a 26 inch wheel, something specced as 250rpm will get you legal speed at 36v, however most seem to be specced as 201 or 328 rpm.
However a 48v 328rpm motor run at 36v will get you in the right ball park. I've just done it ( with loads of help from here) with a rear motor and it's worked a treat.

 

[Bikes4two]

Thanks @saneagle for the info

• the KT LCD4 or 900S are topping the list at the moment
• Forks - the tandem is a Santos Double Travel - proprietary forks - I'm guessing you're thinking of torque and stress on the forks? They look beefy to me (not very technical eh!).
• So far the motors I've spotted in my research (Akiema SX75, Bafang Q100H, G370) all seem to have around 30nm
• Speed - I'm keen to keep power assist to the 25kph limit - we're not fast riders so I'm thinking torque at lower speeds will be more beneficial than higher speeds - does that point me to around 200rpm then?
• Some other tandem riders in my area have deeper pockets than mine and have the Cytronex C1 kit (about £1000 - eek link) and derive enough power for their needs which will be similar to my own - what motor is that kit do you know? (did I read somewhere that it was an Akiema of some sort?).

 

[Sturmey]

Thanks @saneagle for the info

• Forks - the tandem is a Santos Double Travel - proprietary forks - I'm guessing you're thinking of torque and stress on the forks? They look beefy to me (not very technical eh!).

Are they the forks in photo below? Are they alloy or steel? Is there room for hub?

 

[sjpt]

We've got an XF07 (700c) on the front of our tandem. We'd certainly like more power but it has been a great success over the 5 years we've had it. It was the only legal one we could find when we bought it. For our use it would have been better with a motor wound for lower speeds: more torque on the hills at the expense of less assist as it gets near 15mph. We rarely go above 12mph on the level even with assist, and the motor is definitely well below good efficiency as we slow to 8 or even 6 mph on hills. XF07 in a 20" wheel would be about right for us from that point of view.

Woosh show a 250w BPM front (https://wooshbikes.co.uk/?hubkits#frontbpmkit), but I'm not sure they still actually stock it.

As Saneagle says, front motors are noisier, more accurately they seem noisier to the rider because of where they are. I don't think they are any courser. Do make sure your forks are up to a front motor.

p.s. If you'd find a Cytronex enough the XF07 (42nm) should certainly be enough. A lot cheaper than the Cytronex, much more choice of batteries, and no lockin to proprietary parts. Heavier and not so neat though.

 

[Woosh]

We still offer XF07 and bafang BPM in 26in rims. In general, front hubs are a little noisier and the BPM with bigger gearbox is also noisier.

 

[saneagle]

Thanks @saneagle for the info

• the KT LCD4 or 900S are topping the list at the moment
• Forks - the tandem is a Santos Double Travel - proprietary forks - I'm guessing you're thinking of torque and stress on the forks? They look beefy to me (not very technical eh!).
• So far the motors I've spotted in my research (Akiema SX75, Bafang Q100H, G370) all seem to have around 30nm
• Speed - I'm keen to keep power assist to the 25kph limit - we're not fast riders so I'm thinking torque at lower speeds will be more beneficial than higher speeds - does that point me to around 200rpm then?
• Some other tandem riders in my area have deeper pockets than mine and have the Cytronex C1 kit (about £1000 - eek link) and derive enough power for their needs which will be similar to my own - what motor is that kit do you know? (did I read somewhere that it was an Akiema of some sort?).

Show a picture of the forks from the front and left side. There are more characteristics than beefiness to worry about.

The motors you mention are all a bit on the weak side for a tandem. If you want 15 mph, you need one with a max speed around 250rpm for a 26" wheel. If you want it only to assist climbing, 201 rpm would be better.

You get 30% more torque with 48v compared with 36v using the same current. 48v will always be more efficient than 36v as long as you choose a suitable motor. You can use a 36v 201 rpm one at 48v to get good torque and efficiency for 15 mph riding. When you have a motor that can give high torque, you don't have to use it all, but if you have a weak motor, you can't turn up the torque when you need it.

 

[Nealh]

What terrain are you using the tandem on Alan ?

 

[Bikes4two]

Thanks gain @saneagle

Show a picture of the forks from the front and left side. [

Are the pics below enough? The fork material is an aluminium alloy of some description.

There are more characteristics than beefiness to worry about.

I guessed that - had to laugh at myself when I said what I did - exactly what is it that makes forks OK (or not)?

And thanks for the motor info - I'm thinking that torque at lower speeds is going to be more beneficial to our sort of riding (long tours are no longer on our agenda !).

The torque advantage at 48v - I'll pick a motor and controller that can work at both 36v and 48v so that if my 36v battery packs aren't giving me enough torque, I'll go for 48v (Another self build battery pack - yipee!).

Fork pics - the black metalwork is the front pannier rack.

 

[saneagle]

Thanks gain @saneagle

Are the pics below enough? The fork material is an aluminium alloy of some description. I guessed that - had to laugh at myself when I said what I did - exactly what is it that makes forks OK (or not)?

And thanks for the motor info - I'm thinking that torque at lower speeds is going to be more beneficial to our sort of riding (long tours are no longer on our agenda !).

The torque advantage at 48v - I'll pick a motor and controller that can work at both 36v and 48v so that if my 36v battery packs aren't giving me enough torque, I'll go for 48v (Another self build battery pack - yipee!).

Fork pics - the black metalwork is the front pannier rack.

View attachment 54052

View attachment 54053

Bad news I'm afraid. Your drop-outs are in the middle of the tube, which means that the tube will rub on the side of the motor. You will have to spread your forks and use washers to get most motors in. It might be an idea to change the forks, which will give you the opportunity to fit a disc brake, which will be much safer too.

 

[Bikes4two]

Are they the forks in photo below? Are they alloy or steel? Is there room for hub?

Forks are alloy (Edit - they are STEEL - durgh!) - is there room for a hub motor? That's a good question - not a factor I'd considered until now - hmmm!

I'm going to have to see if I can find a 26" wheel with a hub motor in it to see what's what. Thanks for the 'heads up'.

My forks:

 

[saneagle]

I edited the above post to add the last sentence.

 

[Bikes4two]

Bad news I'm afraid. Your drop-outs are in the middle of the tube, which means that the tube will rub on the side of the motor. You will have to spread your forks and use washers to get most motors in.

Ah, well that answers the question posed by @Sturmey

 

[saneagle]

They look like steel forks to me, so should bend easily. Test with a magnet.

 

[Bikes4two]

I edited the above post to add the last sentence.

They look like steel forks to me, so should bend easily. Test with a magnet.

Magnet applied and .......... yes, STEEL forks (do you ever get those moments when you feel a bit of a twit -I'm getting one right now!).

 

[Bikes4two]

What terrain are you using the tandem on Alan ?

Hi Neal,
I live just south of the South Downs area (Havant) so nothing worse that South Harting and that would be a rare ascent (there are easier ways/hills to get back home ), more like through Ditcham Park or the cycle path Buriton to QE Park (that's south of Petersfield) , ways I suspect you might be familiar with?

Edit: I went around the Isle of Wight Randonee route last week after a 4 year lay-off - the first time on my ebike and thank goodness for the motor. I doubt that we'd attempt that on our tandem now (although we have done it before but a good few years ago and my wife was not impressed by my choice of route and curses me about it even now!).

Edit 2: I know Neal that you like your G370 - what is it that stood out from the others for you?

 

[Nealh]

If no serious hills then yes I can recommend the Bafang g370 but there are cons and pros with it.

My one has towed my 100kg laiden trailer with no problem (and even managed 0ver 125kg once) , though the route is the flat Worth way route the only real incline I have is in the local village where I keep my bees and it is only slight for about 0.5km.
I use mine at 44v so likely it runs at about 250rpm and not the 201rpm.

Pro;
Small /lightweight hardly noticable.
Fitted strainght in to my Surly DT drop outs with out fettling.
Quiet with the Kt 9 fet controller, tbh I haven't even used it out of PAS 1.
Power is more then ample for a legal set up, (those wanting 500w or more just for tootling around don't understnd power ratings or controller outputs).
Rides nicely without power utilises a higher gearing ratio 14.6.
36h to suit most rims.
Laser marked and rated 250w .
Rim or disc compatible.

Cons;
Probably not one for very hilly terrain.
Cost (one might consider an Akiema at a cheaper cost).
No torque arms can be fitted as the axle is 10mm dia and no flats, the only flat is inboard in the drop out .
Only one A/R/W can be fitted as the wire exit is in board at the drop out.
Only use a steel fork.
Keep max power lowish 15a should be ok possibly a bit more (never needed to put test it to the test).
Only model I have seen is 201 rpm at 36v .
Spares (though TBK appear to offer them).

 

[Sturmey]

Forks are alloy (Edit - they are STEEL - durgh!) - is there room for a hub motor? That's a good question - not a factor I'd considered until now - hmmm!

I'm going to have to see if I can find a 26" wheel with a hub motor in it to see what's what. Thanks for the 'heads up'.

I have got an extra few mm's of room with a xf07 by removing the disk screws and plastic spacer and fitting the tabbed washer on the outside on the disk side and extra washers on the other side . The six holes needs to be sealed (I used short very flat headed screws) and the wheel re-centered (reduce the offset/dish).

 

[Benjahmin]

Topbike kit have motor drawings on their pages. Here's the one for the AKM75:

https://www.topbikekit.com/75SX%20Drawing.pdf