What is Cm?

[philatlondon]

There is a variable that can be changed called Cm, but there is no explanation in the manual of what this represents . Could someone please explain what it is?

[travispape]

There is a variable that can be changed called Cm, but there is no explanation in the manual of what this represents . Could someone please explain what it is?

Cm is a factor that represents the mechanical efficiency of turning rider power into propultion power using the same convention as used here. A Cm = 1 means no loss, and larger values of Cm mean more loss. The default value of Cm = 1.02 is the same thing as saying that the drive train is 98% efficient on average--a good typical number for most bikes. A badly worn drive train might results in a larger value of Cm. A tandem or recumbant might also have larger values of Cm.

Travis

[rruff]

Based on chain efficiency tests I've seen, 2% is about right for high power outputs (400W+), but it drops substantially at lower power levels... in fact it behaves very much like a constant offset of 8-10W at powers of 100W+.

[racerfern]

Based on chain efficiency tests I've seen, 2% is about right for high power outputs (400W+), but it drops substantially at lower power levels... in fact it behaves very much like a constant offset of 8-10W at powers of 100W+.

That's a huge jump not a decrease. 8-10% is massive.

[rruff]

Sorry... to clarify, it is the efficiency that drops a lot. Some test data here:
http://www.bhpc.org.uk/HParchive/PDF/hp50-2000.pdf