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Idler cog size, chain tension and drag
Last Post 06/21/2013 01:25 AM by Andy Eunson. 1 Replies.
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79pmooney

Posts:1082

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06/20/2013 10:29 PM
There is an interesting article in CyclingNews (http://www.cyclingnews.com/features/friction-facts-bigger-pulleys-really-are-more-efficient) about derailleur pulley size.  (Bigger is better and less drag.)  The article also talked about chain tension (less equals less drag).

All this interesting but not rocket science.  What is new is derailleur cages allowing idler pulleys up to 15 teeth!  I do have concerns about relaxing the chain tension.  The article talks of the small wattages saved with the lower tension.  But doesn't less tension + more dropped chains on bikes ridden and raced in the real world?

At the end of the article was a line about how this relates to single speeds and track bikes.  Apparently the writer never heard the advice I got many years ago.  1/2" of vertical play.  Ie, no chain tension.  (The fixie crowd here in Portland never got this lesson either.  But the velodrome crowd do get it.  "Sag" is visible on all their bikes.)

Ben
Oldfart

Posts:453

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06/21/2013 01:25 AM
Sure makes difference off road. I'm using clutch derailleurs and still drop now and then. Even one by ten with a top mount guide saw my chain come off. I know in rough road races pros have a guide or chain watcher at the front off the inside and often they lock out the lowest gear at the back. So yeah keeping the chain in place trumps fewer watts.
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