Quote:
Originally Posted by serialk11r
I think that's gotta be transferring power through a set of gears vs. direct drive with no gears. There's no way e.g. 0.8 and 1 have a 2% difference in efficiency.
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Correct. The overdrive is running power through an additional set of gears, to get the output shaft spinning faster than the input shaft in top gear.
That's by definition, an 'overdrive.'
Any gear set costs a 2% loss in heat, from viscous shearing of the lube.
On top of the transmission loss, must be added the loss at the propeller shaft, ring and pinion, spiders, and wheel bearings.
General Motors measured their 1:1 powertrain under power transfer, reporting an overall 94% mechanical efficiency.
You'd have the main shaft bearing losses, propeller shaft losses, differential and rear wheel bearing losses.
Had it been an overdrive, it would have been 92.1%. Delta- 1.9%.
And all that was with mineral oil.
With full-synthetic gear oil, the loss is less than 1.9%.
The aerodynamic load hasn't changed at all.
When you add aero and rolling resistance, the difference in the powertrain begins to get lost in the noise of both aero and RR.
You'd be splitting hairs.
If you're going to lose 500-rpm at the rear axle, how are you going to do it? And what's it going to cost for the unknown quantity you'll attain?