Originally Posted by
steeltrap21
Thanks prj71, I have seen both links. Neither one provides actual data on single speed vs geared. Intuitively, I would think single speed is more efficient mechanically, but is there a significant difference? I think we are pitting the efficiency of the human body at a reasonable cadence (geared) against the mechanical efficiency of SS. Of course, in hilly terrain and strong winds, I would think geared always wins. On flatter courses and light wind, the SS might win. I am interested because I sometimes go with a nearby informal race that is relatively flat. I am 75 and need all the help I can get (at least 20 years older than anyone else out there), so if SS would give me 2% or so that could be significant. Similarly for a time trialist.
I think the answer is difficult to determine because efficiently depends on many factors including the lube used on the chain, the actual interaction of the cog and roller in the chain, and the ratio of the gears. Here is an article that details the difference between geared hubs and derailleurs but also outlines some challenges to measuring small differences in efficiency:
http://www.whpva.org/HParchive/hp55p11-15.pdf
There is also “Effects of Frictional Losses on Bicycle Chain Drive Efficiency” by Spicer et.al. (You can use a search to find a full pdf copy of the paper) that is also interesting. All things being equal bigger cogs in the back are more efficient than smaller ones by a larger amount then I would have guessed so it pays to have your favorite gear in a straight line and set up the gearing so this is a largish cog. So if your favorite gear is 46-15 switching to 50-16 would be slightly more efficient by about a 1%. Also if you favorite gear results in a lot of chain deflection consider a cassette that would have a straight chain line.