Bike Input torque, Was: speculation on the future of belt drive
An example would be the NuVinci hub. It is specified as able to accept up to 130NM of torque or about 96 pound feet.
Lets examine this 96LbFt limit. With 170 mm cranks (6.69") this is 172 pounds of force at the crank arms and then multiply it by 2 due to the NuVinci specified minimum input ratio which halves the torque actually seen by the hub so the actual force applied at the pedals would need to be 344 pounds, with the pedals horizontal, to match the Nuvinci specified input torque limit! That sounds pretty strong to me.
A strong rider when out of the saddle and pulling down on the bars can generate effective weight on the crank arms considerably above his own body weight. That is a torque level in excess of that generated at the crankshaft by a 2 liter car engine at its torque peak. A bottom bracket gearset has to be able to withstand it repeatedly for years. A rear wheel gearbox such as an IGH is subjected to lower torque in direct relation to the input ratio used.
A humans power output is more like a steam engine than a car engine. The car engine puts out maximum torque at higher RPM while the human, or steam engine, puts out maximum torque at very low RPM or cadence in comparison.
--- In Geared_hub_bikes@yahoogroups.com, Joseph Shaul <spasticteapot@...> wrote:
> I'm surprised that the gearboxes are so heavy - I would think they would be