Power question

[seb421]

How much power on average do you loose though the drive train on a bike?

If the RWHP was 110hp, what would the true Crank BHP be?

[Wicky]

http://www.springerlink.com/content/bj274q1060h31xn3/

SPORTS ENGINEERING
Volume 7, Number 2, 65-73, DOI: 10.1007/BF02915918

Optimisation of the chain drive system on sports motorcycles
Stuart Burgess and Chris Lodge

Abstract

This paper investigates the optimisation of the chain drive system on sports motorcycles. Recently there has been the development of a chain transmission efficiency model that is suitable for motorcycles. The new model is used to predict the efficiency of 600cc sports motorcycle at different speeds. The transmission efficiency is estimated to be between 96 and 99% for speeds less than 75 mile/h. Between 75 and 150 mile/h the transmission efficiency can be as low as 85% due to inertial tension. The transmission efficiency model presented in this paper enables optimisation of sprocket and chain sizes. In general, large sprockets are better at low speeds and smaller sprockets are better at high speeds. The optimum chain size is the chain with the smallest pitch that can meet the torque and power requirement. The sprocket centre distance also has a big effect on efficiency and it is important to use an effective installation procedure. In particular, it is important to set a chain up when the rear wheel axle, front crank and swing arm bearing are all in-line.

[seb421]

Yes thanks for that,

can you give a ruff guess at power at the crank then? if the RWHP was 110hp with a standard chain and sprockets

would a 520 chain make much of a difference?

[tony.mon]

Not really, there's more difference whether it's lubed or not, and correctly adjusted.

[Styler4077]

Wicky's right in that chain is an efficient power transfer mechanism loosing at best 2% but at worst .......
Well loads of things have a detrimental effect, such as a tight chain, no lub ( oh Er misses) incorrect alligment.
On my dyno I add between 8 and 10% for a chain drive and 15% for a shaft drive. So 110 BHP ATRW would be between 119 and 121 BHP for a chain drive 126.5 BHP for a shaft drive.
All a best guess as with out an engine dyno strapped directly to the crank to gather the engines true bhp and then on to a roller dyno to get the ATRW BHP. You can the work out with simple maths, Engine BHP minus ATRW BHP = gearbox, clutch and chain loss in BHP.

Then consider are these true BHP figures or DJ adjusted BHP figures?? Most people do not want true BHP figures
What ISO or Din standard ( or a special spec for Japan) are we testing with?
And then add in variables such as air temperature, air pressure and humidity.

Problem is unless you test when all three of the above are the same tun the same bike on the same dyno can vary between 1% and 3% at a guess on my part.

Hope this helps