Winfried

Hello,

Shimano recommends not going lower than a ratio of 2, eg. 40T chainring and 20T cog so that the Nexus/Alfine hub doesn't get too much torque.

I read that a Nexus is meant to withstand a maximum torque of 50Nm, and even the 250W Bafang BBS01B mid-drive can add up to 80Nm to the mix.

Provided I pay super attention to never shift gears under load — stop pedaling, wait for the motor to stop, shift gear, resume —, could a Nexus 7/8 take the torque of a 40/23 combo (ratio of 1,73)?

And out of curiosity, what part(s) can break when applying too much input torque?

Thank you.

Winfried

Thanks. I know about the Nexus5, but its range would be too narrow for use in hilly terrain and a 250W mid-drive.

Still curious what parts break when over-torquing.

tcs

Horses for courses.

Enviolo Trekking: 85Nm rating. 380% gear range. Other models up to 100Nm.

https://enviolo.com/products/

Winfried

I'd rather use a Nexus/Alfine

Moe Zhoost

I think Shimano have an e-rated Alfine in both 8 and 11. I haven't looked at them in a while, but I was considering one of them when I add a motor to my trike. They would likely still have that 2:1 limit (as does Rohloff). In any case, your gearing range will be more limited than that provided by a derailleur/cassette system. The Enviolo hub is quite nice, but heavy. According to their specs, the Trekking hub is not compatable with e-bikes. You'd have to opt for a HD one.

Winfried

Thanks

https://bike.shimano.com/en-EU/produ...G-S7001-8.html

Elsewhere it says "With Centerlock disc mount. V-brake compatible", so possibly not Roller Brake-compatible.

base2 

For every action there is an equal & opposite reaction. The torque rating so far as I can tell has to do with the reactionary forces the axle transmits to the dropouts via the anti-rotation washer.

3 speed IGH axle by Richard Mozzarella, on Flickr

My memory is foggy on the details of some long-lost internet link I read one time, so please forgive my uncertainty about the shifting dog also being so close to the axle that makes it susceptible to failure from excessive input torque as opposed to near the hub shell like a Rohloff. I think this was addressed with the latest C-7000 series Alfine hubs where a bit of torque actually helps complete the shift. But C-6000 and below remain the weaker design.

Pratt

My guess would be the checkbook.

veganbikes

I would also recommend going for an Enviolo hub. Less to really no maintenance and plenty of range and they make a heavy duty and cargo version that would be perfect for your situation if you are looking for ultimate reliability. A Shimano Nexus hub is about the last hub I would want for an e-bike.

squirtdad

this seems like a variant of a classic

Choose 2 out of the 3

Durable
Desired Gear range
Lower cost

Winfried

So at this point, we don't know what breaks inside an over-torqued (Shimano) gear hub whose axle nuts are correctly greased and tightened ("30 foot-pounds/40Nm each MINIMUM!").

shelbyfv

^^^That sounds about right.

Winfried

If that's the case, it's so simple that it shouldn't prevent people from using a < 2 chairing/cog ratio if they need to (40/23 in my case).

Dan Burkhart Do you think it's a crazy idea?

base2 

Well, in addition to the axle spinning inside the anti-rotation washer (pic above) there is the driver unit that can sometimes have problems.

Chipped & broken by Richard Mozzarella, on Flickr
Notice the chunk missing, not from the pawl on the right, due to an errant power-shift, but from the part that constrains the pawl due to the torque transmitted? The near pawl with the missing half-moon shaped chunk above it is actually sitting at an angle, too and no longer moved freely.


This is the component that left-most, in the center row in picture 1 of post one of this thread. Next to the e-clip.

Winfried

Not sure what I should look at, but then, it's 1) a "3 speed IGH axle", so not a Nexus 7/8, and 2) the axle spun — were the nuts properly greased and tightened and/or the anti-rotation solid enough to handle the extra torque?

Indeed, I thought about pawls breaking… but although the Nexus 7 does have pawls, the latest Nexus 8 only have rollers so that's one worry less.

Big brand e-bikes with mid-drive motors + Nexus 8 are not unknown.

Once the axle nuts are properly set and the user pays attention never to shift under load, a < 2 ratio might not be such a risk after all.

base2 

Well, you do have me on the rollers engaging with the hub shell. I'm not sure if there would be anything other than slippage or exceeding the hub shell integrity failure due to internal pressure or some other such theoretical conceivable failure.

But something has to engage and disengage the various sun & planet carriers. The engineering philosophy and execution is very similar to all products in Shimano's line.

You asked what part would fail. My bet is the ones with the same function as the ones in the pictures up thread, no matter which version any Shimano hub is used.

The 3 speed is reputed to be the toughest of them all. So, there is that.

The Nexus 8 big-bike brand bikes all have shift sensors inline &/or Di2 programming that disengages the motor when a shift is detected. The 7000 series are overbuilt to handle e-bike torque. The operative take away is e-motor torque is much smoother (less cyclical than human generated torque) and the shifting pull is reversed so that when an errant shift happen under load the shift is assisted instead of impeded.

Winfried

I'll include screenshots in case that page on Flickr goes MIA one day

anga

This is what I gathered from various forums and not based on experience. Use at own risk

If you spin rather than mash and stay seated while pedaling, one can go down to a ratio of 1.3

The justification goes something like this. The minimum ratio of 2 is not linked to the wheel size. If a ratio of 2 is acceptable for a 20" wheel and a 28" wheel, then the hub can handle a ratio lower then 2.
622/406 = 1.53
2/1.53 = 1.3

Standing on the pedals and mashing at a ratio of 2 can produce a torque higher than spinning seated at a ratio of 1.3

I plan on a triple crank (alfine 8-speed at the rear) with the ratio going down to 1.3 on the smallest chainring.

Winfried

Thanks for the input.

Indeed, I always spin, and with a gear hub, never stand on the pedals because I read somewhere it's risky — it the hub slips, it can get messy.

Good to read that the ratio could then be lower.