Originally Posted By: Jetronic
With manual transmissions you could push a trailer backwards all day at 2-3 miles per hour (so without fully engaged clutch) and never wear out a clutch. Just don't add throttle either, and let the idle speed regulation do the work
Or you could do it bad and burn out a clutch in minutes or even seconds....
I get your drift, and will explain how they work, and why you are nearly sort of correct.
The power transfer across a clutch is a "torque in = torque out" (torque converters have a multiplier effect, clutches are straight equal torques).
The power into the clutch is the torque x engine RPM.
The power out of the clutch is the torque x gearbox input shaft RPM.
The difference is that power that's being used to fry the clutch.
i.e. clutch frying power = applied torque x RPM difference (times 2 x pi/60, which we don't need to worry about here).
Your engine typically doesn't produce much torque at no revs, so needs some revs to match the tractive effort, and those revs create greater power loss through the clutch, and at a higher applied torque also.
So yep, you are really close.
My Nissan diesel had a LOT of EGR just off idle, and a "swirl control" butterfly that cut off one of the two inlet valves per cylinder to provide better mixing...it needed great gobs of revs and a clutch dance to get moving on a 1:10 gradient. No EGR and swirl valves later, you can let it out quickly at idle and away she goes...much much better for the clutch, maybe not so good for the big ends.