Has anyone actually used a 3x3 Nine or Revolute IGH (with or without a mid-motor)?

[TPEHAK]

Bigger cog at the same gear ratio reduces the force on the chain, prolongs the chain life and the cog life, that's the benefit.

 

[vklurk]

I would describe it the other way. It is a function of the Nine's higher output ratio relative to the Rohloff which requires a bigger input sprocket to slow it down.

Thank you! You even pointed it out in your post but still I missed that the sprokets were different!

 

[rscamp]

Thank you! You even pointed it out in your post but still I missed that the sprokets were different!

Yes. If the sprockets are kept the same then the overall drive ratios from crank to wheel (e.g. gear inches) are a factor of 2 different with the two IGHs. At least one system would be quite unsuitable for use!

It is important to consider what needs to change to keep the overall system drive ratio the same (customarily measured in gear inches). Since the chain ring isn't changing, the only option is to change the sprocket at the input of the IGHs. This means that when a rider is going the same speed with the same effort and spinning the crank at the same RPM and has selected an appropriate IGH ratio to do so the pedal chain speed and tension will be the same. However, the resultant torque at the hub will be 2X different because the radius at which the chain is pulling on the sprocket has halved or doubled. The torque in this case is the chain tension multiplied by the particular sprocket's pitch radius.

I hope this helps visualize what is happening.