I promised I'd post a photo of the alternative method I use to torque test PT hubs. It basically replaces a weight (body weight or otherwise) with the crank tensioned in the upwards direction via a digital scale. The crank is rolled back into the upstroke position and tension is introduced by rotating the rear wheel backwards till you get the desired force. The cranks don't need to be horizontal, but the tensioned cord running to the scale should be at right angles to the crank arms for accuracy. I slide a wooden dowel between a spoke head and the stays to lock the wheel off when the cranks are close to perpendicular to the scale cord and the scale force is about where I want it. If the cords are stretchy it takes a few seconds for the system to settle out and then you read the scale and the PT computer in torque mode and follow the stomp testing math:
Force(pounds)* crank length(mm)/25.4*cog_teeth/chainring_teeth = expected torque.
If the cranks aren't perpendicular to the scale cord your expected torque will be higher than what you're actually putting on the system since it effectively shortens the crank length regardless of which direction you're in error. But the angle doesn't have to be dead on. A +/- 5 degree angle error relative to perpendicular only results in a measurement error of 0.4% and +/- 8 degrees of error is ~ 1% in measurement error.
The biggest hassle is making sure the PT computer stays awake, the torque is zeroed and the scale is zeroed with just the weight of the connecting cords between tests. But it's a lot more portable than 50 pound barbell plates.
Anyway, if you don't like the bodyweight test (didn't spend enough time balancing on concrete forms as a kid ) or don't have a lot of weight plates lying around then this is an alternative method.
-Dave
Force(pounds)* crank length(mm)/25.4*cog_teeth/chainring_teeth = expected torque.
If the cranks aren't perpendicular to the scale cord your expected torque will be higher than what you're actually putting on the system since it effectively shortens the crank length regardless of which direction you're in error. But the angle doesn't have to be dead on. A +/- 5 degree angle error relative to perpendicular only results in a measurement error of 0.4% and +/- 8 degrees of error is ~ 1% in measurement error.
The biggest hassle is making sure the PT computer stays awake, the torque is zeroed and the scale is zeroed with just the weight of the connecting cords between tests. But it's a lot more portable than 50 pound barbell plates.
Anyway, if you don't like the bodyweight test (didn't spend enough time balancing on concrete forms as a kid ) or don't have a lot of weight plates lying around then this is an alternative method.
-Dave