Transmission Parasitic Power Losses

Trying to get at the point, “Just how much power is lost in a transmission?”, I’ve been reading about dynamometers and such.  It seems a no-brainer that a) A transmission sucks power from the system with friction and weight, and b) the only way to know exactly what this parasitic loss is, would be to measure it on a dyno, with and without a transmissh.

In my travels on the interwebs I found this pretty concise explanation of how dynomometers work and how they’re used.  Most importantly, the difference between a flywheel measurement and a measurement by a “chassis” or “rolling road” dynomometer.  (Simply, a flywheel measurement is done with the engine out of the vehicle, reading directly from the flywheel with no transmission.  The “chassis” dyno reads it from the tires, on rollers…  faster and easier, but not as accurate.)

…and this statement:

So is there any way of really measuring the true transmission loss of a car? Yes – only one – by measuring the flywheel power on an accurate engine dyno, the wheel power on an accurate chassis dyno and taking one away from the other. There is no way on God’s green earth of finding out the true transmission loss just by measuring the power at the wheels.

Now, it seems like an electric motorcycle takes a little of the sport out of this, since you can hook up the motor directly, then hook up the motor coupled to the transmission.  I think.  Maybe.

So, for everything you’ve ever wanted to read about dynomometers, hit up Puma Race Engines.

…or, you can just assume a small transmission is going to suck about 10 – 15% of your available power.




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