TIL #3: Drivetrain ‘Trim’

Bikes are simple.  They have two wheels and a chain, a derailleur that moves said chain from gear to gear, allowing you, the rider, an easy (or easier) time when riding your favorite routes.  As technology continues to evolve in the industry, improvements such as expansion of the drivetrain has occurred.  With this in mind, chainline, or the angle in which the chain is at from a cog on the cassette to a chainring on the crankset, has begun to experience some changes.  While some gear combinations are not the best for the bike, namely, the large chainring and largest cog on the back, or the dreaded small and small combo, the rider may need to put the bike into these combinations during times of peril.  In addition to a speedier means of wearing out the drivetrain, these combinations and others showing a similar chain angle, tend to make some noise…the solution, mostly found on ‘road bikes’ is the ability to ‘trim’ the front derailleur, these half-shifts allow the front derailleur to be best placed in relation to where the chain is lined up on the cassette.

Below, we can see an example of a drivetrain in a ‘big chainring and big cog’.  The chain is angled in a manner that it is rubbing the inner plate of the front derailleur, causing noise and also vibration that will both bother the bike and the rider.

Wow, that chain is rubbing the inner plate of that front derailleur to the point that you’re going to go crazy.

This has an easy fix, the front shifter on this particular bike has more than two positions, the ability to ‘trim’ the front derailleur to better accommodate the narrow tolerances of this drivetrain, allow both precision and drivetrain flexibility.  Next is an image of a half-shift of the front derailleur.  This allows the derailleur to be repositioned over the large chainring and offer a mostly noise free gear combination.

The result in this half-shift is the repositioning of the front derailleur, depicted below:

When properly setup, your bike can comfortably utilize every gear combination.   Wondering if your bike has this feature? Play around with the shifter, or stop down, we’re happy to help show you a few hidden tricks that you may not have known about!