SRAM's pivoting chainring could provide its future 1x drivetrains with the perfect chainline

Could wobbly chainrings be the next big thing?

SRAM, arguably the king of 1x, has a new patent filing aimed at further refining one of the major problems 1x-drivetrains face.

The issue with wide-range cassettes and a single chainring is the potential for poor chain lines at each extreme end of the gear range. That can lead to reduced efficiency and increased wear and load on your chain, chainrings and cassette.

We previously reported on patents from SRAM and Shimano that feature a split chainring and a sliding chainring mechanism respectively, which tries to address this.

However, we’ve come across this new patent from SRAM that touts a pivoting chainring as an alternative solution to the problem.

Various alignments of the chainring at different positions on the cassette
Various alignments of the chainring at different positions on the cassette

An assembly places the pivot ahead of the bottom bracket. The effect of this offset, which SRAM has dubbed trail, is to prevent a pivoting chainring from wobbling during pedalling.

The pivot location is ahead of the bottom bracket, apparently reducing chainring wobble
The pivot location is ahead of the bottom bracket, apparently reducing chainring wobble

In some examples, SRAM also suggests a “rotation resistance device” to act “as a damper in reducing wobble about the chainring.” This can act in various ways: one example suggests that the chainring can pivot in steps, slotting into detents (362) as it pivots more or less, in turn providing more stability in each position.

In order to achieve this, SRAM has had to come up with what we feel is quite a complicated mechanism to allow simultaneous pivoting and pedalling.

The pivoting assembly (inside) is fixed, whilst the chainring carrier (outside) sits on a bearing and rotates around it
The pivoting assembly (inside) is fixed, whilst the chainring carrier (outside) sits on a bearing and rotates around it

The pivot (352) is effectively attached to the bottom bracket shell, keeping it in the same orientation. The chainring must rotate around this fixed pivot.

The chainring sits on a carrier (314) that rotates on a bearing (320) around the pivot assembly. Torque is transmitted to the chainring with a drive pin (400) that protrudes from the crank arm.

A drive pin transmits the torque to the chainring
A drive pin transmits the torque to the chainring

This allows the chainring to pivot independently of the pedalling action.

It's clear that SRAM is putting a lot of time and effort into addressing the chainline issues that surround current 1x drivetrains, whether or not we'll ever see a design like this make production is still anyone's guess.

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