The folks at Friction Facts are at it again, this time investigating how gear selection affects drivetrain drag. Just as racers have been saying for ages, Friction Facts has now proven that it’s more efficient to stay in the big ring, saving nearly three watts of effort in certain combinations – but there is a tipping point where it’s still better to drop down up front.
Friction Facts’ earlier study on rear derailleur pulley size suggested that larger-diameter chainrings and cogs would produce less friction than smaller ones, and this latest exercise confirms that hypothesis. Despite the fact that bigger chainrings and cogs create higher chain speed (which slightly increases friction), Friction Facts says the lower chain tension and reduced individual chain link rotation more than offset lower frictional losses overall.
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Generally speaking, bigger chainrings and cassette cogs produce less friction than smaller ones for an equivalent gear ratio
A 53-15t combination, for example, yields almost the exact same gear ratio as a 39-11t but the latter requires an extra 1.5w to maintain the same speed – and that’s in a lab setting where the chainline can be perfectly aligned.
Things get even more interesting – and the potential energy savings double – when accounting for chain angle on a real-world drivetrain.
You can read more at BikeRadar.com
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