Along with suspension and disc brakes, bicycle drivetrains are one of the things that make mountain bikes so incredibly capable. Having a wide range of gears is what allows us to pedal our bikes up to towering peaks, and descend steep trails with confidence.
While they offer an incredible amount of convenience, drivetrains can also be a point of confusion and frustration – even for seasoned riders. We’ve all fumed in anger at dropped chains, skipping gears, and stubborn derailleurs. So with that in mind, we at Jans want to help explain drivetrains in a way that would make your riding experience as smooth and enjoyable as possible.
The Evolution of the Drivetrain
In the early years, it was common for mountain bikes to have both front and rear derailleurs. This means that there were not only multiple rings comprising the cassette in the rear of the bike, but also two (2x) or three (3x) chainrings on the drive side of the cranks. This gave riders multiple combinations of gears to help get them up and down hills.
These different-sized gears are referred to as high and low.
High gears are made for descending, and consist of a large gear in the front, and a small gear in the back. This ratio provides a high amount of wheel rotation for each revolution of the cranks. It creates more resistance against each pedal stroke, but also allows the bicycle to maintain a high speed.
Low gears are made for climbing, and consist of a small gear in the front and a large gear in the back. This ratio provides a low amount of wheel rotation for each revolution of the cranks. It creates less resistance against each pedal stroke, but doesn’t allow the bicycle to maintain a high speed.
While this system made bikes more capable than they had been in the past, it also had its pitfalls. Having a front and rear derailleur required riders to have shifters on each side of their handlebars, which not only took up space and made bicycle maintenance more cumbersome, but also tended to confuse riders and distract from the ride.
Less is More
In recent years, a solution to this issue has been found in the 1X drivetrain. Since rear hubs have become wider, engineers have realized they could make cassettes capable of carrying the full gear range necessary to get people up and down steep grades, and in doing so, have eliminated the need for a front derailleur. This not only simplifies shifting, but streamlines bicycle assembly and maintenance as well.
The 1X drivetrain uses similar high and low gear ratios as its 2X and 3X predecessors, but keeps the chainring static while allowing all the shifting to occur on the cassette. Because newer cassettes are handling all the shifting, they are required to be larger and have greater gear ranges than older models.
A typical 1X drivetrain may consist of a single 34T or 36T ring in the front, and an 11 or 12-speed cassette with a range of 11-46T or 10-50T rings. For example, a 10-50T cassette has 12 rings which increase in size up to the biggest ring. The smallest ring is comprised of 10 teeth, and the largest has 50 teeth. One way to help visualize this is by thinking of a cassette like a mountain. If you turn a cassette sideways, you’ll notice it has a conical shape. The low gears at the base of the mountain have the biggest circumference, and the most teeth. At the peak of the mountain you have the high gears with their small circumference and few teeth. The smaller (high) rings allow riders to pedal at speed, while the larger (low) rings make climbing steep grades much more manageable.
Along with simplifying the drivetrain, the 1X system also frees up space on the handlebar by eliminating the front shifter. This allows riders to mount other components on their bars, like dropper post levers or suspension lockout levers.
If the convenience of a 1X drivetrain appeals to you, there’s a few things you should keep in mind before you run out and buy yourself a new group:
- First, speak with an experienced bicycle tech. This will allow you to make sure that your cranks, frame, and wheelset are compatible with 1X drivetrains.
- Do not blend groups. Manufacturers like SRAM and Shimano make drivetrain components that are specific in their design. This means that for example, a SRAM Eagle 12-speed cassette will not function properly with a Shimano XT 11-speed chain. Therefore, it is important to make sure that all the components in your drivetrain are compatible.
- Don’t set yourself up to drop chains. Since 1X drivetrains do not have front derailleurs, they can leave chains vulnerable to falling off the rings. There are two popular techniques to prevent this from happening. The first is by running a narrow-wide These are specially machined chainrings that have alternating narrow and wide teeth which adhere to the links of a chain to prevent it from popping off the ring. This technique is especially popular for trail, all-mountain, and enduro bikes. The second technique is to install a chain guide. Chain guides consist of a ring and a backing-plate that sit on either side of the chainring, so the chain can’t bounce off in rough terrain. This technique is typical for downhill and freeride bikes, and requires that the frame has compatible ISCG mounts.