Energy Loss Numbers

Quoted message said:

So, if a cyclist riding on the brake hoods traveling at ~25 mph (flat,
calm winds) is putting out ~300 watts, and ~90% of the effort is
overcoming aerodynamic effects, then about 30 watts of the effort is
due to rolling resistance and mechanical friction, correct? Is tire
rolling resistance on the order 90% of that 30 watts? Which leaves ~3
watts for mechanical friction, and I would imagine that the next
biggest consumer of that 3 watts would be the chain, maybe 2 of the 3
watts? Is this close to being in the ballpark?

Dear JCQ,

Here's calculator whose default is 300 watts and about 23 mph on level
ground with no wind:

http://w3.iac.net/~curta/bp/velocityN/velocity.html

You can kill a drag factor by setting it to 0. Then reduce the watts
until the speed drops back to its original value. How much you reduce
the watts suggests how much power was used by that drag factor.

With chains, power is tricky. In general, higher chain speed (lower
tension and higher cadence) is less efficient at transmitting the same
input power. Smaller sprockets also reduce transmission efficiency.
The first article in this link has extensive chain efficiency testing:

http://www.ihpva.org/HParchive/PDF/hp50-2000.pdf

Cheers,

Carl Fogel

Aero will be about 80% under those conditions, rolling resistance 15%,
and drivetrain losses 4%, bearing losses 1%.