Rohloff Hub: How Much is Too Much Watt-Wise?

PeteCress

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I am contemplating a tadpole etrike build with a Rohloff hub and a Bafang mid-drive w/shift sensing.

1,000 watts is calling out to me just for CYA, since I know so little and weigh so much (215#).

But I wonder if I might be overloading the Rohloff with all that torque (120 nm) - especially on the 1.25 mile 9% grade that most of my rides end with.

Does anybody have some thoughts on this?
 
PeteCress said:
I am contemplating a tadpole etrike build with a Rohloff hub and a Bafang mid-drive w/shift sensing.

1,000 watts is calling out to me just for CYA, since I know so little and weigh so much (215#).

But I wonder if I might be overloading the Rohloff with all that torque (120 nm) - especially on the 1.25 mile 9% grade that most of my rides end with.

Does anybody have some thoughts on this?

The specified maximum torque for a Rohloff Speedhub is 130 Nm. Don't use it all up with motor power if you intend to pedal as well.

Keep in mind that the torque from your mid drive is modified by the gear ratio. So for instance if you use a 42:18 chain drive and the mid drive makes a maximum 120 Nm, then the torque into the hub would be 120 Nm / 2.333 or about 51.4 Nm. That would allow you almost 80 Nm torque you could add using the pedals before you risk shearing off the torque limiting pins in the hub.
 
Unless you are spinning fast enough for centrifugal forces to rip something apart or starve something in an oil bath from oil, watts mean absolutely nothing. Calculate your torque and worry about that only. Lowering torque by varying gearing will let you push more power.

Also as you will be restricted in torque, pedaling hard while hard launching will be a no go.
 
Yep. Calculate torque and don't worry about power too much.

Power ratings on motors are a decent initial guide to what the motor can handle. But they don't tell you much about actual performance. Get the specs on the motor and (if possible) use a simulator to see what sort of torque you will get, what kind of hills you can climb, what kinds of temperatures you'll see and what speeds you can achieve.
 
Chalo said:
... before you risk shearing off the torque limiting pins in the hub.
That is the first time I have heard about those pins.

I already have a couple Rohloffs on my non-electric diamond frames.

Maybe I should but a few pins just in case.

Are those pins replacable in the field?

My guess would be "No Way Jose'"...
 
PeteCress said:
Chalo said:
... before you risk shearing off the torque limiting pins in the hub.
That is the first time I have heard about those pins.

I already have a couple Rohloffs on my non-electric diamond frames.

Maybe I should but a few pins just in case.

Are those pins replacable in the field?

My guess would be "No Way Jose'"...

They don't need attention unless they shear (which saves the gears from breaking). Replacing them is a job for a Rohloff service center like Rat City Bikes of Seattle.
 
PeteCress said:
Tommm said:
Lowering torque by varying gearing will let you push more power.
And riding in a higher gear will reduce torque, right?

I guess this because my two Rohloff hubs came with a caution not to use a front chain ring smaller that a certain size...

Right. It doesn't matter what internal gear of the hub you use, but the external gear (chain drive or belt) must not apply more than 130 Nm (motor and pedal combined) to the input. The higher the chain gearing, the less torque goes to the hub.
 
If somebody can afford a Rohloff drive they could afford to put two Grin All-axle motors on the front wheels.

That way you have a AWD Trike. If it's got proper 20 inch front wheels then it would essentially make you unstoppable. Could climb a 25% degree slope at 20mph.
 
If you do use a rohloff hub with a mid-drive, you need to specify the tandem variant and not have gear ratios outside 2.5:1, and 1.9:1
 
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