Originally Posted by
Bonzo Banana
I think you have that reversed. You can have a larger rear cog or a smaller front chainring as this will put less torque on the IGH but require a higher cadence by the rider to maintain the same speed.
No, Steve has it right. As you gear lower you're relying on mechanical advantage to move your bike, instead of your own muscles. 2.1 is the recommended minimum ratio quoted by Shimano for their Nexus/Alfine hubs. But, not all the hubs are built/designed equally, and there are many Nexus/Alfine 8 users who run ~1.5 ratios with no issues. While the Alfine 11 is known to be pretty sensitive to high torque.
Originally Posted by
Bonzo Banana
Besides isn't it how Shimano configures nexus/alfine hubs if you have a smaller rear wheel (20") you can have a larger front chainring but if you have a larger rear wheel (700c) you need a smaller front chainring?
That's just a matter of creating equal development metrics between two differing wheel sizes. The smaller wheel bike requires a larger gear ratio to achieve the same speed at a given cadence.
edit: whoops. Just noticed that Tourist already said the same stuff.