Electrifying Your Rohloff-equipped Bike

[Andre Jute]

Max torque values I have seen for Shimano 8-speeds are 50 nm, which seems to me too low for even an entry-level Bafang mid motor. I have seen 130 nm quoted for the Rohloff.

Concur with all of this. These are the exact considerations that led to me choosing the Rohloff as the basis for the electrification I knew was coming when despite advancing age I moved up an even steeper hill.

The Bafang BB series of mid-motors are a development of a motor called the BPM, nicknamed "the little hill-climber", in which which everything was subordinated to torque maximization.

Torque is why I advise Bafang owners to grasp, understand and honor the concept underlying the Coulomb, and buy the biggest battery they can afford, because it will offer more instantaneous Coulombs at any point during any ride.

The base Bafang BB, legal in most jurisdictions, puts out about 60 per cent more torque than a common Shimano Nexus 8 can handle. I trashed a Nexus 8 and a Premium in only 5000 miles between them, before I electrified. I'm not surprised Shimano had to make a stronger version for electric bikes.

The Rohloff shrugs off what I estimate to be approaching a 100Nm of torque from my Bafang BB: no graunching or grinding noises, no bits of broken teeth in the gearbox oil when I change it.

One caveat of possible influence: My Rohloff was about half run-in when I fitted the electric mid-motor, not brand new. Thoughtful bedding-in before hitting an expensive gearbox with big torque makes sense.

One more thing. Before I fitted the Bafang centre motor, I invested Stg425 in a complete Bafang front drive kit including a bottle battery as self-instruction, but fitted where it would not interact directly with the Rohloff. This motor, with between 60 and 70Nm, had three large plastic gears, fully enclosed.

I trashed this system in less than two years riding. The gears melted and took the electronic controller out with them.

I could have rebuilt it with steel gears (generally available from the Chinese aftermarket) and patched up the controller or bought a new one -- they're not expensive -- but I couldn't be bothered as I had extracted the educational value I expected from the kit, and anyway, I suspected the steel gears would be noisy.

It is likely that the current more powerful Bafang BB motors, which belong to the same design development as my front motor but are generally packaged with more sophisticated controllers, has similar plastic gears to keep them quiet.

Here's the punchline: in case of abuse or overload accident, I believe that Chinese plastic gears will melt before any plastic gears that may or may not be inside the Rohloff. In short, that the BB motor, which is cheap to replace, acts as a protective cutout to the more expensive Rohloff.

I should stress that nothing remotely concerning has happened with either my Rohloff or the somewhat more powerful Bafang BB motor I chose on hand of the experience with the front-drive  motor. Neither has ever become more than lukewarm even in strenuous use, and mostly they run cold or just off-cold, unstressed.

Legal questions where you live aside, I would have no hesitation in recommending the 350W Bafang BB as the best-value load puller or hill stormer with the Rohloff, whatever sort of riding you do.

Above the 350W are 500W and 750W motors, the latter a glorious one horsepower.

I have had a ride on the 750W on a familiar stretch of road and I wouldn't entrust my Rohloff to it, though there are plenty of successful matches on the net from America.

The 750W is unnecessary unless you're building a fast commuter with the pedals as a fashion accessory.

Below the 350W are 200W (?) and 250W BB kits. I was happy with a similar 250W motor in the front wheel riding with other social cyclists, until riding alone and faster up a hill hauling a hefty easel in the pannier basket, it burned out.

I wouldn't go over 250W for a front wheel motor because a bigger motor would very likely upset the high, safe cornering cability of my bike by nudging it into oversteer.

After all this experience, and for all these reasons, it seems to me the divide between the pedalists and the electric motorcyclists falls at 350W.

Or perhaps, living in the Rome of West Cork, I'm just not seeing the monuments for the hills.

[martinf]

I don't yet need electric assistance, but have started looking into it. At the moment I have about 3 kilometers of riding experience with electrical assistance and have only needed to sort out mechanical issues on electrically assisted bikes - a loose headset and play in a rear wheel due to loose cones.

For myself when the time comes :

- Plan A is to convert one of my existing bikes. I don't see the point in electrifying one of my Bromptons, this would add several kilos of motor/battery to a bike that needs to be carried. None of my large wheel bikes are suitable for a mid motor, my Thorns have bottom brackets with eccentrics, one of the other two has a chamfered bottom bracket and the old utility bike is French thread. Front wheel drive is said to be a bit less intuitive than rear wheel or mid motor drive on a bike, but I am not worried about that for my own use.
- Plan B is to build up a mid-motor bike starting from an old ladies-style mountain-bike, ladies-style in case I have difficulty getting my leg over a diamond frame bike.

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My wife could already use an electric bike as she is increasingly finding it hard to cycle and uses her bikes less and less. Two problems here :

- she thinks electric assistance is cheating.
- electric bikes are heavy, and she already has difficulty pushing a non-assisted bike into the garage at home, or getting our small visitor bike at our island flat over the small step before she can use it on the road.

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For the nature reserve where I look after the bike park, my original idea was Plan B. But I found two lightly used second-hand mid-motor bikes for slightly under the price of two front motor conversion kits. They won't be as good as a high-end mid-motor bike with belt drive and suitable hub gears, but the frames are sturdy and the brakes and transmission can be improved when they wear out. And for use by people who are not necessarily experienced cyclists I reckon mid-motor is safest.

[Andre Jute]

Martin, about your Plan B, I bought a crossframe-mixte because of its load capacity (oil painting gear is heavy) and after 15 years I'm wondering if I shouldn't have bought one of those Dutch "ouma" frames with a deep curve of very thick tube. I looked at them at the time and decided they were unnecessary and would anyway interfere, given their low clearance, with my preference for downhill speeding because the low pedals would strike the road. Also it wasn't quite clear to me how a mid-motor, which I already knew would be my eventual destination, could be made to fit. But if I ever buy another bike, it will be one of those very low stopovers, and I'll just give up leaned-over speeding; I've already cut back by 5km pieces per annum from 60kph on the steepest hills to 35kph, because the worst thing would be a broken hip which, statistically, is a real killer.

I understand your wife's problem with the weight of the bike and by extension of electrification. But the default controllers for the Bafang motors you're considering, and presumably most other electric bike controllers, have an uphill walking/stair climbing/parking mode. To use it, you select it, then walk beside the bike to steer it, and it rolls up ramps at 6kph and lifts itself over low steps and up stairs if they aren't too narrow. I find 6kph too fast so this is one of the reasons I fitted a thumb throttle. (The other reason was to give me finer control hanging the bike on the edge on rough roads taken at speed before I started considering the possibility of a broken hip or shattered femoral bone like the one that ended Jobst Brandt's cycling and clearly ended his life early.} However, even without the throttle, the Bafang default control has nine "gears" under the rider's control, with a switch under one's thumb, which can work together with the Rohloff gears to set a speed for parking maneuvers anywhere within reason.

The problem of the weight of the motor and the battery remains, but is reduced to merely keeping the bike upright rather than keeping it upright while pushing it forward. It makes a big difference because once the bike is moving it suddenly doesn't seem so heavy.

There's another problem with controlling the weight of the electrical gear: starting on an incline. I live up a steep hill, and the countryside is on the uphill side, and the same applies if I'm returning in heavy stop-start traffic from the downhill side. There's a sort of a weave barrier speed when starting uphill. Here my powerful motor and massively over-specified battery are useful. I stand across the bike with one foot on a pedal at the top of crank rotation, with the Rohloff in one of the lower 7 gears (which otherwise I hardly ever use) depending on how steep the hill is, the electronic control in the most powerful of the "gears" I actually use (you can reduce the 9 available electronic gears to whatever number you find most practical*), and shoot off with the thumb-throttle hard down, raising my foot from the ground to start pedaling as well, overcoming the tendency to weave by applying enough power to reach straight-line speed in a couple of  paces.

I can imagine that the same procedure would also be helpful on the flat if the bike is already too heavy for one. Also, when I'm riding in light traffic, even if it is stop-start traffic, I try to keep some space in front of me so that I never need to put my foot down before the cars start moving again.

By these tactics I've kept all the desirable optional components on my bike, and haven't yet had to cut back on painting gear or shopping, compensating for their mass by using the motor, its battery and its controller mindfully.

So a carefully chosen electric motor/battery/controller has extended my cycling life more than ten years.

* Ex-factory these controllers come with lots of useful, clever features, and they're programmable not only with the multi-way handlebar switch, but by programming with a laptop through an interface you can buy in China. The aftermarket thumb-throttle gives further fine control, so I didn't see the need of the interface because the available features are pretty comprehensive, but a genuine nerd would probably want it to play with. You can however use the interface to unlock a crippled controller. Better still, you could ensure that you don't buy your gear from the sort of clown who thinks he's an adjunct of the police; lots of British sellers I spoke to, the sort of people who lecture one on going green, were horrified by my polite request to have the full operability that I was paying for. The guy I found who didn't cripple the controller OS also happened to be easy to deal with, ultra-efficient and helpful, and cheaper than the ones who thought they knew better than their customers; most of them aren't in business any more.

[martinf]

Plan A (front wheel hub motor) - probably based on the Thorn Raven in the first photo. I currently have drop bars on it, but I expect to go back to roadster bars in a few years time. If it was still available I would probably have bought the 47ST (largest step-through) version of the Thorn Nomad Mk3 frame to get a lower stepover height. For this type of conversion I rather like the idea of the offer from the British supplier Cytronex - this seems to be very easy to fit and relatively light at about 4 kg. But a bit more expensive than the heavier Bafang equivalent.

Plan B (mid-motor) - probably something like the second photo. This is one of the old mountain-bike frames I built up for the reserve, old-fashioned steel tubing, quite stiff even in the ladies style frame, clearance for at least 50 mm tyres. This example can't be easily converted to mid-motor as the bottom bracket is Italian thread for some odd reason (Lejeune is/was a French firm). Though small, the frame is quite long, so with a long seatpost it is quite comfortable for me to ride. With a Tubus rear rack fitted, it is also quite a good load carrier.

But the default controllers for the Bafang motors you're considering, and presumably most other electric bike controllers, have an uphill walking/stair climbing/parking mode. To use it, you select it, then walk beside the bike to steer it, and it rolls up ramps at 6kph and lifts itself over low steps and up stairs if they aren't too narrow.

Yes, this is a feature in quite a lot of the kits I looked at, including at least one of the front hub motor kits.

* Ex-factory these controllers come with lots of useful, clever features, and they're programmable not only with the multi-way handlebar switch, but by programming with a laptop through an interface you can buy in China. The aftermarket thumb-throttle gives further fine control, so I didn't see the need of the interface because the available features are pretty comprehensive, but a genuine nerd would probably want it to play with. You can however use the interface to unlock a crippled controller.

I've found a French supplier for Bafang kits. They propose all 3 main types - rear wheel, front wheel and mid-motor) and have quite a lot of options. Not sure about the thumb throttle, which is probably not street-legal here. They also assemble their own battery units, which means they can repair or refurbish them.

[Andyb1]

I fitted a 250W front wheel hub motor to my wife’s hybrid a few years ago.   Having drive to both wheels was very useful on muddy tracks - and of course put no extra load on the chain.

A couple of things:
- it is worth fitting torque arms to the wheel axle.  These are little stainless brackets that bolt to the mudguard eyes so there is no chance of the axle spinning in the fork. I think most hub motor axles are 10mm, I had to file the forks out from 9mm.
- she had a thumb throttle on the LH bar.   No pick up at the crank.  This was (is still?) legal on a conversion and it meant one less thing to go wrong (I was worried about water damage to the crank sensor).  To get space on the left hand handlebar (she had 2 x 8 gears) for the thumb throttle I removed the front mech so the bike became 1 x 8 speed so no LH gear lever was needed.  Obviously not relevant to a Rohloff geared bike.
- the battery was on the rear rack which sort of balanced out the weight of the front wheel hub motor.

With external wiring the conversion was not as tidy as a proper ebike but it worked OK.
 

[Andre Jute]

With external wiring the conversion was not as tidy as a proper ebike but it worked OK.

I used a length of that crocodile tubing sold for tidying cable in offices to keep all the cables together, with cables being led out of the main trunk when they arrive at their sockets, and excess cable length folded over also hidden in the main trunk. Not a perfect solution but better than many loose cables giving the bike an amateur vibe. The conduit that I had is battleship grey, which goes with any bike colour but you can paint it bike colour and I've seen some that came in other colors. About one inch in diameter is suitable, just, for all the power and controller cables for a Bafang central motor with hydraulic brake interruptor cables to brake handles, and all its controllers, as well as a thumb throttle. Inch and a quarter or inch and a half would likely be neater but no bigger. The conduit is stiff enough to stand by itself, and the one I got from a local pound shop seems pretty durable, lasting so far eighteen years.

PS: BTW, further to your point about a well balanced bike, I wrote a decade or more ago, on this forum I believe, that my Gazelle Toulouse has a sort of ABS braking system simply by using a simple cable disc brake on the front wheel plus an old design of roller brake, which was pretty weak compared to the disk, on the back.