Is 52T / 16T cog stressful on Nexus 8spd w/ BBS02 ?

[nukezero]

Which stresses the Nexus hub more? Using a 52T chain ring up front with a 16T rear cog or using a lower tooth count chainring, like a 46T ?

This is of course, paired with a 750w. bafang mid drive bbs-02 on 16 inch wheels.

If my understanding is correct, the 52T would stress the rear more, but logic says otherwise, as it will take more force for the bbs-02 to turn the 52T as opposed to a 46T or less.

What if I drop the 16T to a 14T rear cog and stick with a 46T or 52T, is the 14T rear cog going to cause more stress to the IGH and wear it out more?

 

[CmdrBond]

Firstly I don't think you can drop below 16t on the Nexus/Alfine hubs (I have the Alfine)

As to your question.

Torque to the hub, if I an correct, is torque output by the crank multiplied by the gear ratio.

Torque of the 750w is ~120N

52:16 is a ratio of 1:3.250, × 120N = 390.000N
46:14 is a ratio of 1:3.286, × 120N = 394.286N
46:16 is a ratio of 1:2.875, × 120N = 345.000N

So the best option for the hub, and the motor (as it will have to do less work) is the 46:16.

That will result in better hill climbing, but lower to speed.

 

[ferret]

It's the other way around, smaller chainring and/or bigger wheel cog will transmit more torque (think of the small "granny gear" chainring and biggest cog in the cassette for climbing):

16:52 is a ratio of 1:3.250, × 120N = 120/3.25 =36.9N
14:46 is a ratio of 1:3.286, × 120N = 120/3.286=36.5N
16:46 is a ratio of 1:2.875, × 120N = 120/2.875=41.7N

Avner.

 

[CmdrBond]

It's the other way around, smaller chainring and/or bigger wheel cog will transmit more torque (think of the small "granny gear" chainring and biggest cog in the cassette for climbing):

16:52 is a ratio of 1:3.250, × 120N = 120/3.25 =36.9N
14:46 is a ratio of 1:3.286, × 120N = 120/3.286=36.5N
16:46 is a ratio of 1:2.875, × 120N = 120/2.875=41.7N

Avner.

Quite correct - my apologies I replied in a hurry this morning and wasn't thinking straight.

Torque is inversely proportional to speed.

The LOWER the gear ratio, the LOWER the work the engine has to do, the LOWER the top speed, the HIGHER the torque applied to the hub.

The HIGHER the gear ration, the HIGHER the work the engine has to do, the HIGHER the top speed, the LOWER the torque applied to the hub.

 

[nukezero]

Ah, thank you for that explanation. Now it makes sense. I should stick with a 52T instead.