Background

It has been hypothesized that lateral chain misalignment (also known as ‘cross-chaining’) causes significant frictional losses in the drivetrain, and these frictional losses increase as the angle of misalignment increases.

It has also been hypothesized that a larger chainring is more efficient than a smaller chainring, given the same final effective gear ratio.

When riding in the front big ring with larger rear cogs, at what point, as the chain climbs up the rear cassette (shifting to larger-toothed cogs), does the potential frictional advantage associated with using the big ring become a disadvantage due to the increasing angular misalignment (aka heavy cross-chaining while in the big ring)?

In a derailleur-style drivetrain, the overall frictional losses can be affected by both lateral misalignment and ring selection concurrently.  As multiple similar final gear ratios can be achieved by using either the big ring or small ring, it has been hypothesized that some gear ratios are less efficient based on the ring being used, whether big or small. It has also been hypothesized that an ‘optimal’ shift sequence exists by using only the most efficient ring/cog combinations, while still providing for a full range of final gear ratios.

This test analyzes the frictional losses of the 22 ring-cog combinations of a 2 x 11 speed drivetrain, as well as the effects of frictional losses based solely on chainring size. 

Results Summary

1) Lateral chain misalignment creates frictional losses, and the losses increase as the angle of misalignment increases.

2) A larger front chainring creates less frictional losses than a smaller chainring, given the same effective gear ratio, power output, and cadence, when tested with the chain in a pure coplanar manner (no chain misalignment introduced).

3) The data shows that optimal big ring-to-small ring and small ring-to-big ring shift points exist.  When the chain is in the big ring, the frictional losses created by the lateral misalignment become greater than the big ring savings at the 9thcog of an 11sp cassette (with the small cog being the 1stcog).  In practice, when riding in the big ring and shifting the rear derailleur to larger cogs, it’s advisable to avoid the use of the 9th, 10th, and 11th cogs.  Beyond the 8thcog, it is more efficient to shift the front derailleur down to the small ring in conjunction with a shift of the rear derailleur to a cog that maintains a similar final gear ratio.