1x Drivetrains Explained – Gearing, Mechanics, and Optimization
The simplicity and effectiveness of a 1x drivetrain, which refers to a single front chainring with multiple sprockets and a rear derailleur, has many people converting their multi-chainring setups.
We will cover 2 main things in this Tech Document: 1) why 1x and why now, 2) What factors should I be aware of to optimize performance of a 1x drivetrain?
Why 1x and Why now?
The increased popularity of 1x drivetrains stems from a confluence of three different technologies:
- Wide range cassettes
- Clutch style rear derailleurs
- Chainrings that hold the chain on better
Wide Range Cassettes – this is the MOST important technology of the three. The 1x plots below say it all! 2x and 3x drivetrains have a LOT of gearing overlap whereas 1x covers nearly the same useful range given the wide range cassettes. In addition to the graphs below, our Gear Charts are useful in understanding what the optimal step will be for you.
Clutch Rear Derailluers – in four short years these went from being the the exception to the rule. Shimano’s Shadow Plus and SRAM’s Type 2.1/X-Horizon both have a roller clutch controlling the motion of the derailleur cage, which keeps chain movement over bumpy terrain to a minimum. Less chain movement means there is less chance for the chain to derail from the front chainring.
Chainrings – Without the wide range cassettes and clutch style rear derailleurs, we probably wouldn’t be talking too much about 1x specific chainrings. But given those two things, it is more exciting to talk about the improvements in the 1x specific chainrings.
Optimizing 1x Performance
Now that we have covered why 1x is being adopted by so many, lets discuss the key factors that affect 1x drivetrain performance:
- Free Chain Length
To be clear, these same 3 things affect 2x and 3x performance as well, but because it was much less common to modify 2x and 3x drivetrains, the stock engineered solutions were accepted as optimal. With 1x modifications/upgrades, riders have the ability to mix, match, and customize their drivetrain to their riding style, terrain, and strengths/weakness.
Chainline – this is simply the measurement in mm of the distance between the centerline of the chainring teeth and centerline if of the bike. Generally speaking, it is best to have the center of the chainring just to the outside of the center of the cassette. However, this is a much longer more detailed discussion when talking exact numbers because of different rear hub spacing (road, road disc, mountain, fat) and tire/chainstay clearance. This is partly covered here for modern mountain bike spacing and here for fat bikes. Chainline affects drivetrain life, which in turn affects long term shifting.
Chainwrap – this is one of the less talked about measurements but is very important to drivetrain life. Chainwrap is the measurement in degrees that a chain engages a cassette. This is most critical when talking about cassette wear, specifically the small cassette cogs. The more chain wrap, the longer the cassette lasts because the load is distributed over more teeth on the given cog.
Free Chain Length – this too is often not talked about but is very important for shifting precision. Free Chain Length is the length of chain that extends between the upper jockey wheel of the rear derailleur and the cog on the cassette. The shorter this length of unsupported chain, the more precise the shifting will be. This can simply be explained by the fact that adding more free chain length (links) allows the chain to flex more between the derailleur and cassette so shifting is less precise. Do note that some free chain and flex is needed to allow a shift so there is an optimal free chain length (generally accepted as stock length).
This is a redacted version of original articles published by Wolf Tooth Components; its main article which first appeared here