Hacker News Reader

Comment by logicallee | Hacker News Reader

are those actual numbers or are you just showing it is high?

I'd have guessed it's more like 99%. isn't anything that isn't heat or noise = perfect efficiency? a normal bike chain doesn't get hot or make much noise at all, does it? seems to me just about 100% efficient. maybe transfers a bit of vibration to the rest of the frame? but not 8%-4% of its transferred force....

View on HN

This paper gives a very detailed analysis of chain drive efficiency:

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

Wow, thanks. I only had a quick look but Figure 2 seems to show 91.5%-95% efficiency depending on configuration. Very detailed study and it sounds like it would answer all my questions if I spent an hour reading it.

An athlete will only generate ~200w which isn't a lot for a fairly large metal part with plenty of air cooling. Even if it was only 50% efficient you might struggle to notice an appreciable change in temperature.

Motorcycles can have 150hp engines (~100kw) and even then the chain doesn't get particularly hot.

I might be a bike fanatic, but I'm no professional athlete and I can sustain more than 200W for hours, so my guess is the pro's are quite a bit higher again. (Your point still stands, though)

You are right, serves me right for going by memory. 200w is closer to an average cyclist, a pro is closer to 500w. Still, the orders of magnitude don't change.

During a sprint in 2018, Andre Greipel averaged 1,600W, and hit 1,900W peak. Those are the kind of numbers engineers have to take into consideration when designing for maximum torque, although obviously they are not sustained for hours.

Wait, you're saying 1 human = 2.5 horses?

Fun fact. Peak horse power for a horse is 14.9hp :)

I think the GP is right, I did a quick Google and found sites saying 93-97.5% and it depends on power output. I would expect a dirty chain to be worse.

thanks, that is certainly interesting.

Reply on news.ycombinator.com