Crank -> Wheel HP losses?

[benVFR]

Why is it that people say all bikes lose 10-15% of the power going from the engine -> rear wheel?

Why is it a percentage..

My question is this...

If an SV650/EX-500/whatver has a six speed transmission, and a chain drive...

And a Gixxer 1000 has a six speed transmission and chain drive...

What is it that causes the Gixxer to lose a greater amount of horsepower going from the engine to the wheel? The transmission and chain are going to work similarly and have about the same amount of friction and inertia right? Where are the extra losses coming from?

E.x. if the smaller bike loses 10hp, what makes the bigger bike lose 20hp. Why wouldn't they both lose 10hp?

(Note I'm not comparing a chain drive bike to a shaft drive bike, or a car)

So why do we say, "Bikes lose 10-15% of the power, rather than, all chain drive bikes lose 10hp" ??

Ben?

[Zero]

Probably because the more power you put through it, the more friction you are going to generate. If you think in extremes cases say a bike has 10HP, then how can it lose 10HP. I know there will be better explanations, but the percentage makes sense to me. Just like when a speedometer is off by 10%.

[benVFR]

I was told by someone else it has to do with the horsepower being made at a higher RPM as well.

Should have thought of that.

Ben

[beet]

ben

[JJ]

Drivetrain robs hp. The more hp you make, the more % you will lose.
It's the same as cars/trucks/bikes/snowmobiles/etc... The more power you make it puts more strain on chain (stretching)/clutch (more of a chance to slip) and all out wear and tear.

Not a real scientific answer but it should get the job done.

Edit

I was told by someone else it has to do with the horsepower being made at a higher RPM as well.

You make more power at higher rpm's so back to the more power creates more strain and slippage=more of a loss in hp.

[RandyO]

I am not familiar with calculating drive train losses, but I am familiar with fluid dynamics in calculating dymanic heads for shit system pumps, in theory, the principle is the same, so the more faster you go, the more friction loss, all the way from the rolling friction of the tire on the pavement to the gearbox losses

[jsven007]

Very good question, interesting article:

http://www.superstang.com/horsepower.htm