Hybrid with internal gear hub: mid-drive or front hub kit?

[alx]

I live in Bristol, UK, and though I'm fine getting about town on my bike, I'd like to have something to help me extend my range so that I can go further afield (up to the Mendip hills etc), and get away more while towing a trailer (Burley Nomad).

The bike I'm considering converting is a Scott SUB 35 hybrid, which has an internal gear hub (Shimano Nexus 8) on the rear wheel, so I'm limited to mid-drive or front hub kits.

From what I've read, it sounds like a mid-drive kit might not be the best idea with the hub, as it could put too much torque through it - is that right? Either way, I'd appreciate advice on a suitable kit that'll give me a decent extra range, and in particular help boost me through hillier terrain.

 

[Benjahmin]

I have no experience with mid drive. There are many threads on here that deal with them. Chain line difficulties crop up alot, also reliability seems lower than other systems. If the motor has an internal controller this seems to be a weakness from an overheating point of view. Mid will put extra strain through the drive train leading to greater chain and sprocket wear. Whether the hub gear can take it....?
The forks on the bike are specced as alloys, so you will definately need torque brackets. The dropouts need to be inboard with 100mm clearance. I would fit a disc brake if possible.
Some will say that front hubs suffer from grip issues. It's true, on greasy, loose, steep climbs there can be some scrubbing, also on gravel paths under sudden accelaration. But, really, I've never found it to be a big issue and is actually quite enjoyable on millstone grit paths like the Tissington trail.
Hub motors tend to be fairly bullet proof, I have two. I've had to change two case bearings and one motor connector plug in a combined mileage of around 12k.
With hilly Bristol and Mendip terrain then buy the biggest, highest quality battery you can afford to get the range.
Lower rpm motor will give higher torque but top speed will suffer. In practice if you can keep the motor at or above 50% of it's top speed, when climbing (7-8mph), then there shouldn't be any heating issues.
I have an 8fun bpm and an Ezee , both big front hubs that get me around the hills of West Wales. Both known to be high torque motors. I think there are now physically smaller motors with similar torque.
Have a look at Woosh's offerings as a start point.

 

[peterjd]

I would endorse Benjahmin's comments but similarly only from experience of a front wheel hub motor kit. When I first became interested in battery assistance I thought a mid-drive kit would be the answer but had doubts about my fitting skills so went for a simple front wheel kit (a Swytch Mk 1). Although easy to adapt the bike I disliked the weight distribution with a fairly large (and heavy) battery on the handlebars so adapted to have a battery on the rear pannier. This has worked well in less hilly Leicestershire and indeed I more often use a 36V 5Ah lawnmower Li-ion battery as motive power for journeys up to ~25 miles (carrying a second 2.5Ah similar battery in a pannier or rucksack as a reserve for such distances). Weight distribution is then very acceptable for me. I still tend to think mid-drive well designed ebikes (not kits) are almost certainly more efficient but then there is the cost and less adaptability. Good luck. Peter

 

[matthewslack]

It depends on your aspirations, which will likely change as you go along.

You could do worse than get a front hub kit to begin with, something fairly chunky for the hills and trailer weight, and learn from that at fairly modest cost whether that is sufficient.

If that proves to be not enough, then mid-drive will do anything you need because of the ability to choose gearing to suit the use. A low power BBS01 was noted in a recent thread to be OK probably with a nexus hub, although your additional payload with the trailer might change that. BBSHD or BBS02 probably avoid unless you remove the nexus.

Get a really good battery and it will work with both systems, keeping the overall cost down.

 

[alx]

Thanks for the advice all. Plenty for me to chew over here

 

[Woosh]

From what I've read, it sounds like a mid-drive kit might not be the best idea with the hub, as it could put too much torque through it - is that right? Either way, I'd appreciate advice on a suitable kit that'll give me a decent extra range, and in particular help boost me through hillier terrain.

I'd recommend a 250W TSDZ2 or BBS01 crank drive kit.
The weight distribution is better, the torque range is also better suitable for hills.
Avoid high power BBSes, they are the ones that can damage your hub gears.

 

[Bonzo Banana]

Nexus 8 is definitely more reliable than the Nexus 7, the Nexus 7 is actually a 9 speed hub with 2 gears mapped out that you cannot use. Also the Nexus 8 has a direct drive gear which is number 5 and using this gear reduces wear on the mechanism. I have a Nexus 8 in my Subway 8 bike but I haven't used it in recent years. At the time, as a conventional bike lifespan was somewhere between 8,000 and 20,000 miles or kilometres. I think it was miles as the sites were mainly US but can't remember for sure. However many people had early failures before the 8,000 miles.

The thing is a front hub motor massively extends the life of the Nexus 8 because it takes a lot of wear off it because the motor helps so much on the hills etc and they work independently. Even a low power mid-drive motor will probably be delivering 2-3x the power through the drivetrain compared to a normal bike so you should expect a reduced lifespan out of the Nexus. However its one of those things that you never can tell until you try it, you may get away with it and it lasts a long time.

One of the positive things about a combination of Nexus and mid-drive is on a Nexus you typically or should stop peddling to change gear and you will do the same with a mid-drive fitted so it prevents the aggressive cog and chain wearing you get with a derailleur system when the motor is still engaged plus of course you have a stronger single speed chain and all steel rear cog. The concern really is about the internal mechanism of the Nexus 8 which is neither that easy to service or repair.

I seem to remember someone on a forum specifically made their Nexus bike an ebike because the hub gears were worn and some gears weren't working but didn't want to change the bike and getting a ebike kit meant he could easily cycle without those gears, I think there is something like 3 moving sections in a Nexus 8 and one section had seized into one position so instead of 2x2x2 it was 2x1x2 or something like that. I think in the end he replaced the rear wheel with a 3 speed Nexus or someone suggested that, can't remember. I think at the time the difference between a new Nexus 8 wheel laced for his bike and an ebike kit were fairly equal or at least not that much more for a basic ebike kit.

I definitely think if you do destroy the Nexus 8 hub then a 3 speed replacement is the best option, those are very simple and more robust and much easier to service and repair. Also their pricing is quite low and the motor should easily compensate for lack of gears and you can gear it a bit lower too safely.