What is a drivetrain or groupset on a mountain bike?
A MTB drivetrain is the group of components that transfer the power from your legs to the wheels of a bike. A drivetrain is sometimes called a groupset - these two terms are basically interchangable.
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What is included in a MTB drivetrain?
What is a 1x drivetrain?
What is a 2x or 3x drivetrain?
How do I know if a new drivetrain will fit my bike?
How do I know if a cassette will fit on my wheel?
How do I know if a chainring will fit on my cranks?
What makes a modern 1x drivetrain better than 2x?
What are the advantages of the different number of gears?
How do I look after my MTB drivetrain?
What is included in a MTB drivetrain?
- Shifter
- The shifter is attached to your handlebars & pressed by the rider which signals the derailleur to change gears.
- Derailleur
- The mechanism that moves the chain up and down gears on the cassette. Modern mountain bikes have one rear derailleur. Some older bikes and road bikes also have a front derailleur.
- Cassette
- The large metal cogs attached to the rear wheel. The number of cogs on the cassette determines how many gears your bike has.
- Cranks
- The metal arms connected to your pedals and chainring.
- Chainring
- The smaller toothed gear at the middle of your bike, attached to your cranks. Bikes with a front derailleur will have two or three chainrings. Modern MTB have one single chainring.
- Chain
- The metal links that connect the chainring to the cassette & derailleur.
Sometimes people include the brakes as part of a "groupset" as they may all be sold together as a package by major brands like SRAM and Shimano. However, brakes are not part of the drivetrain.
What is a 1x drivetrain on a mountain bike?
A 1x drivetrain (pronounced "one-by") means that a bike has a single rear derailleur and a single front chainring. All gear changes are made by moving the chain on the cassette.
A 1x12 drivetrain has 12 gears on the cassette. Modern MTB drivetrains range from the budget-friendly 1x8 Microshift Acolyte and the strong and simple 1x9 Shimano Cues all the way to the top-end 1x12 SRAM and Shimano drivetrains.
What is a 2x or 3x drivetrain on a mountain bike?
2x or 3x drivetrains ("two-by" or "three-by") have front and rear derailleurs. They also have 2 or 3 front chainrings. Gear changes are made by a combinating of moving the chain on the cassette and changing which front-chainring is being used.
How do I know if a new drivetrain will fit my bike?
There are three questions that affect whether a drivetrain will fit your bike.
- Will the drivetrain parts work with each other?
- This isn't an issue if you are buying a groupset of the same brand & number of gears (e.g., all parts are 9 Speed Shimano Cues)
- If you're only replacing some parts, you need to ensure that your new cassette is designed to work with your derailleur, shifter, and other parts.
- Keeping the correct number of gears is vital, but you can sometimes mix and match brands.
- Will the cassette fit on my wheel?
- Will the chainring fit on my cranks?
How do I know if a cassette will fit on my wheel?
Bike cassettes mount onto the freehub body of your rear wheel. This is a part of your rear hub (the centre of the wheel) that is designed to a certain standard.
The easiest way to know which freehub type your wheel has is to find the model of cassette that is currently on your bike. By searching the model name or number, you will find what freehub type it uses.
There are 3 main mountain bike freehub types.
- Shimano HG
- The most common type on older and budget-friendly bikes
- The smallest cog has a minimum number of 11teeth - no smaller.
- SRAM XD
- Designed so that cassettes could have a small cog with 9 or 10 teeth (instead of 11 on Shimano HG).
- SRAM XD cassettes can be 10, 11, or, most commonly, 12 speed.
- Shimano Microspline
- This was designed for Shimano 12 speed cassettes.
- Small cog can have 10 teeth.
If you need help working out your freehub body, please reach out to our super-knowledgeable customer service team for some help!
How do I know if a chainring will fit my cranks?
Chainrings can be mounted via 4 (or 5) small bolts or a variety of 'direct mount' standards.
Direct Mount Chainring and Cranks
If your cranks have no visible bolts like the image above, then they will be direct mount. You need a direct mount chainring that is designed for your cranks. This is usually the brand of cranks (e.g., Race Face direct mount, SRAM direct mount, Shimano direct mount).
4 Bolt Chainring and Cranks
If your cranks use a 4 or 5 bolt system, then you'll need to discover your Bolt Circle Diameter (BCD). Check your chainring - it might have the BCD written on it somewhere! If not, you'll need to measure it. To understand how to measure your BCD check out this excellent guide from our friends at Wolf Tooth.
What is 'chainring offset' or 'chainline'?
You want your chainring to be in the correct position to help your chain run smoothly over to the cassette. This is called the 'chainline'. Some cranks and chainrings adjust this position through moving the chainring to the side slightly, 'offsetting' it.
The ideal chainline depends on your bike design - mostly how wide your rear hub is - commonly referred to as "Boost" or "Non-Boost" spacing.
If you're not sure of your hub spacing, the Shimano Cues cranks & chainring have a chainline designed to work with all mountain bikes!
What makes a modern 1x MTB drivetrain better than 3x?
A modern 1x drivetrain is more reliable and quietier than an older 2x or 3x drivetrain while maintaining a similar gear range - the range from easiest (good for going uphill) to hardest (good for going downhill) gears - as 2x or 3x drivetrains.
But this wasn't always true! For many years in the mid 2010s there were many arguments about whether 1x or 2x drivetrains were better - especially for people climbing steep mountains!
However, the release of Shimano's 1x12 drivetrain in 2019 to catch up with SRAM's 2016 release signalled the end of 2x drivetrains in the mountain bike world.
What are the advantages of the different number of gears?
In general, a drivetrain with fewer gears (e.g., 9 or 10speed) will be cheaper to buy than one with more gears (11 or 12speed). I'll give examples for 9 and 12 speed - as the advantages to 10 and 11 sit inbetween these two.
12 Speed
12 speed drivetrains have small 'steps' between each gear, which makes shifting between gears smoother. However, because they fit the more gears into the same physical space, they can be harder to adjust. If your derailleur gets out of alignment or your shift cable gets old the quality of shifting will get worse quickly.
12 Speed drivetrains have the widest gear range - but this isn't as firm of a rule as it used to be. Some 9 speed drivetrains are now almost the same as 12 speed.
The SRAM NX Eagle 12speed Groupset is an example that is considered relatively cheap for a 12speed drivetrain.
9 Speed
A 9 speed drivetrain will keep working longer if the derailleur gets bent. If you don't want to spend time tinkering with your bike - this is a great option.
A modern 9 speed drivetrain can offer a similar gear range to 12speed, however there will be big "jumps" between gears. This means it will take your derailleur longer to move between gears, resulting in a less smooth ride.
The Shimano Cues 9 Speed drivetrain below is super durable and about half the price of the 12speed NX Eagle linked above!
It's designed to work with the common HG freehub, is compatible with both Boost and Non-Boost frames and is even rated strong enough for eMTB!
How do I look after my MTB drivetrain?
MTB drivetrains can be expensive! Riding around in the dirt and mud will wear down your chain and the metal teeth of the cassette & chainring. Keeping your drivetrain clean and lubricated will make your bike faster, quieter, and make your drivetrain last longer!
Check out our Ultimate Drivetrain Maintenance Guide for a run-down on how to take care of your drivetrain.
Still confused? Need help confirming your freehub type?
Reach out to our friendly and knowledgeable Customer Service crew for help finding the perfect drivetrain for your bike and budget!
Email us at help@mtbdirect.com.au, click the chat-widget in the bottom corner, or fill out our Contact Us form with all your details and we'll get you sorted!