Drivetrain Efficiency

["Neil Deshpande" <Ndeshp@xxxxxxxxxxxx>]

Michael:

As far as I know, the power loss is in the gearing, not the driveshaft.  Gear
teeth should ideally roll on each other and have no rubbing, but in practise
they rub and use up power in friction.  The rubbing provides strength via
increased contact area as opposed to line contact for the ideal rolling case.
The number of gears between the engine crank and the wheels is pretty similar
on most cars, hence the lack of easily available comparisons.  An auto has a
power absorbing torque convertor, hence the difference.

Neil Deshpande
1988 325 iS
1989 325 iC
www.neilwerke.com

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"Michael Ting" <lupin@domain.elided>

I've never been into any Dyno shop, so correct me if I'm wrong. From what I've
heard, HP@Wheel = .85 HP@Crank. (approximation) For automatic trans, it's more
like HP@Wheel= .80 HP@Crank.  The constant (.85, or .80) comes from the energy
loss through the driveshaft(Is this the proper word to use??). Well, my
question is do people actually measure the different driveshaft efficiency on
different cars??

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