What’s a modern day mountain bike without a groupset? Well, it’s a frame, suspension fork, wheels and control items, but it’s not a bike, it's nothing more than a fancy scooter. Thought of as the bike’s engine room, the drivetrain consists of the cranks, chainring/s (front cogs), chain, cassette (rear cogs), derailleurs and shifters. Simply put, it's a closed circuit that propels the bike forwards.
In this article, you’ll learn what you need to know when it comes to mountain bike groupsets including what each part does, the critical difference between various price points and other information you’ll need to make an educated decision on which groupset is best for you.
- Related Reading:Ultimate Guide to Buying a Mountain Bike
Components of a groupset
The crankset is what the bicycle pedals attach to and are what your legs spin in circles as you pedal. On modern mountain bikes, the crankset consists of the crank arms, chainrings (the front cogs) and the axle that connects the two crank arms.
The crankset and its number of chainrings dictate how many forward gears a bike has. Modern mountain bikes have one, two or three, with the latest trend being the fewer, the better.
The length of crank arms does vary, but not as much as seen with road bikes. Crank length in mountain biking is typically more standard to help with leverage at an average lower riding speed. With this, smaller bikes will often use 170mm crank arms, with medium-sized bikes and up using a 175mm crank length. Downhill bikes and similar will use shorter 165mm cranks for improved ground clearance.
The crankset spins on a set of bearings, these are known as the bottom bracket. The bottom bracket attaches within the frame, and so there is a large array of options to suit various frame designs. The two key types include ones that thread into place (threaded) and ones that are pressed into place and rely on tight tolerances, these are known as ‘press-fit’ bottom brackets.
The cassette is the rear cogs that connect to the rear wheel. These rear cogs dictate how many gears a bike has at the back, with most modern mountain bikes typically offering between eight to twelve gears.
The chain is what connects the front crankset to the rear cassette. Without the chain, the bike has no drive. A chain is usually made of steel and features a series of interconnected links that rotate smoothly but are difficult to twist laterally.
Derailleurs are the components that guide the chain between the cogs. These usually work by having a cable, or hydraulic fluid pull them in one direction and then relying on spring tension within the derailleur to pull opposite direction.
With the rear derailleur made of a series of springs, rough terrain in mountain biking can see this component slap around, often leading to lots of noise and the potential of a dropped chain. In recent years "clutch" equipped rear derailleurs have become the standard for intermediate and better mountain bike derailleurs. This clutch creates a one direction friction in the cage that the chain runs through, and offers a quieter ride with a significantly reduced chance of a dropped chain.
New electronic technology sees small servo motors added to some derailleurs, which control the movement; this is known as electronic shifting. Such technology comes at a premium price but removes the risk of mud, water or general wear affecting shift performance. This is because a cable-operated (mechanical) system relies on precise cable tension and cable condition to accurately move the derailleur between gears.
Sitting at the handlebars within easy reach, the shifters are your controls for enacting a gear change. The shifters are linked directly to the derailleurs, typically by way of mechanic cable.
The most common type of shifter on a mountain bike is the ‘trigger’ shifter. Here, either your thumb or forefinger is used to actuate a shift. A less common design is that of grip shift, which works by twisting the grip to make a shift. Each brand offers a different style of shifting; we’ll explain this later.
Traditionally part of a groupset, mountain bike brakes have broken free into their own category in recent years. In many cases, you’ll still be able to match your brakes to your desired groupset, but it’s far more common to mix-and-match in this regard. This is due to disc brakes becoming the standard choice in mountain bikes. Where over a decade ago rim brakes were still popular, disc brakes now are featured on just about any mountain bike selling for over AU$500.
Disc brakes are easily segmented into two categories: Hydraulic and mechanical. Hydraulic borrows its technology from the automotive world and uses a fluid system to transfer force from the brake lever to the brake pads. Being a sealed system, it’s incredibly low maintenance and easy to operate.
Mechanical disc brakes remain the standard choice for lower-end mountain bikes where the hydraulic systems are too expensive. Here, a wire cable is used to transfer the force at the brake lever to the brake pads. This system is not sealed and is susceptible to dirt, rust, cable stretch and other wear factors. As the brake pads wear, a simple manual adjustment will be needed; whereas with hydraulic systems, such modifications are generally automated.
Gears, ratios and numbers
Much like the engine and transmission found in a car, bicycle gears are used to allow your motor (legs) to cover a range of speeds and gradients efficiently. Here, different gear ratios change how far the rear wheel spins in relation to crank at the front. Easier (lower) gears result in a rear wheel that turns less with regard to the crank, while harder (higher) gears will see the rear wheel travel further for a single revolution of the crank.
Mountain biking often involves low gearing to scale steep hills and overcome loose terrain. Due to this, mountain bikes use specific gear ratios that are best suited to the rugged terrain, and generally lower average speeds compared to other cycling forms. Bigger wheel diameters effectively make the gearing harder, and so as mountain bike wheels have increased in size, the gearing has become relatively more comfortable.
The critical thing to know is that the available gear range and number of gears are not the same thing. The gear range refers to the span from the very hardest (high) to the easiest (low) gear. A bike with only 11 gears can potentially have the same high and low span as a bike with 30 gears.
The number of gears is calculated by multiplying the number of cogs at the back wheel (cassette), with the number of cogs (chainrings) at the front crank. For example, a bike with nine gears at the cassette and three at the crankset is a 27-speed. And a bike with ten gears at the cassette and two at the crankset is a 20-speed.
Understanding gear range is becoming increasingly important in mountain biking as it’s how and why many modern bikes are moving away from three chainrings on the front, and moving to two or even just one. This new approach comes from new cassettes that offer a significantly increased range.
There are multiple reasons to have fewer front gears on a mountain bike, but the main reasons include greater simplicity, more effortless operation and improved reliability. Additionally, where two or three chainrings are involved, there are always going to be overlapping/redundant gears, so for example, a 27-speed drivetrain may only offer 18 truly different ratios. Reducing the number of chainrings reduces this overlap.
The number of teeth on the individual chainrings and rear cogs calculate the exact gear ratios of a bike. The smaller (fewer teeth) a chainring has, the lower the gear is. Out back, it’s reverse of this, and the lowest gear will be biggest (with the most teeth) cassette cog.
Reverse this, and you have the highest gear. This is the most prominent front chainring matched with the smallest rear cog.
It can be confusing to get your head around, but generally speaking, chainrings are smaller, and cassettes are bigger on mountain bikes when compared to other popular bike types.
There are two key groupset brands in mountain biking that control a large share of the market – Shimano and SRAM. Below we outline the hierarchy available for each brand.
The market leader in all cycling categories, Shimano has the biggest range of mountain-specific groupsets.
Most of Shimano's groupsets are designed to work together (as long as they share the same number of gears), making it possible to mix componentry, although for optimal performance it's best to keep uniformity.
Shimano’s mountain bike shifters use ‘Rapid Fire’ technology, where your thumb operates one shift lever to move the derailleur in one direction, and your forefinger works the other to send the derailleur the opposite direction. From Alivio-level and up, that forefinger lever can also be operated with your thumb. Rapid Fire allows multiple gearshifts to be made with the large thumb lever and on more expensive models, both levers can shift multiple gears in a single push.
Below is a brief breakdown of Shimano's mountain bike groupsets.
Tourney: Shimano's most budget groupset, often seen on basic recreational and even kids bikes. With basic stamped steel and plastic components, it’s not designed for the rigours of off-road riding. Expect a plastic grip shifter and 3x7 gears at this level.
Altus: Altus is Shimano’s entry-level groupset and is occasionally seen on budget mountain bikes. Again, it’s not designed for mountain biking, but light off-road use is applicable. Shimano RapidFire trigger shifters are found here, and a 3x7 or 3x8 gear setup is typical.
Acera: Acera appears on many entry-level bikes and offers either 8 or 9-speed gears at the back, and three at the front. More aluminium is starting to be seen at this price, with higher rust resistance compared to the models below.
Alivio: Alivio is top of Shimano’s ‘recreational’ mountain bike groupsets. It offers several features and shared aesthetics of groupsets above it. This groupset is found on entry-level mountain bikes that are designed for off-road use; however, the 3x9 gearing and lack of a clutch-equipped derailleur are the critical limitations for genuine off-road thrashing. Higher rust resistance and more easily serviced components are seen at this level.
Deore: Deore is aimed at the entry to an intermediate level mountain biker and is perhaps the most popular too. Deore is durable, reliable and features much of the technology found on the more expensive SLX and XT. Deore currently has ten cogs on the cassette and a choice of two or three gears at the front. Some bike brands do equip Deore on bikes with a single chainring, but Shimano themselves don’t offer the groupset in such a setup. Deore is Shimano’s first groupset to offer a clutch-equipped rear derailleur.
SLX: SLX is to mountain biking as what 105 is to road cycling. It’s the workhorse groupset that shares many of the same features and performance as models above, but with a higher weight. This is often due to the greater use of steels instead of advanced alloys. Current generation SLX offers 11-speed shifting at the rear, with a choice of one, two or three chainrings on the front. In a ‘1x’ setup (one chainring), the most popular cassette choice is an 11-42T ratio; however, options up to 11-46t exist.
Zee: Explicitly designed for downhill and freeriding, Zee sits at a similar price to SLX. Current generation Zee is a 1x10 drivetrain, it's now a little dated compared to current SLX and so has lost popularity, although its brakes are still commonly found on bikes that require greater stopping power.
XT: One of mountain biking’s most popular groupsets, XT is commonly thought to offer all the performance of the top-tier XTR version, but with a price that’s far more palatable. Just about all the technology is there, including heavy use of aluminium and high-quality stainless steels. Many enthusiast level race bikes feature Shimano XT components. Current generation XT 8000 is most commonly used with either a single or double chainring setup. For the single-chainring, either the use of an 11-42 or an 11-46T cassette is widespread.
XT Di2: XT also comes in an electronic version known as 'XT Di2'. Unlike the mechanical version, which requires cables to change gears, Di2 uses motor-driven mechanics at the front and rear derailleur to provide a crisp, perfect shift, every time. The Di2 version is slightly heavier than mechanical (about 90g) but is impervious to dirt and grit. Once set up, it also never requires re-adjustment. XT Di2 shares the same chain, crankset and cassette options at standard XT.
XTR: The gold standard of mountain bike groupsets from the Japanese company. The groupset was revamped in 2018, now featuring in both 1x12 and 2x12 configuration. XTR uses a mixture of carbon fibre, titanium and high-grade alloys to reduce weight without sacrificing reliability. XTR RapidFire Plus shift levers have a marginally smoother operation due to the use of an internal bearing. Tolerances are tightest on Shimano XTR, and so while it’s marginal, there is an improvement in shift quality over XT in addition to being a couple of hundred grams lighter, and for over double the price, you’d hope so too. It's worth noting that the latest XTR M9100 is not cross-compatible with any other Shimano components at this time.
Saint: Similar in level to Shimano XTR, Saint is considered a gravity-orientated ‘specialty’ groupset. It’s most commonly found on pro-level downhill race bikes. Current generation Saint is a 1x10 drivetrain.
SRAM has multiple mountain bike groupsets available, and in many ways is the more progressive company in the mountain bike sector with having first introduced 2x and then 1x drivetrains to the mainstream mountain bike world.
SRAM’s groupsets are not as clearly defined as Shimano’s and so mixing, and matching of components is typical at the lower end. SRAM is fast moving toward 1x-specific drivetrains on nearly all of its intermediate to premium groupset options. Assuming the number of gears match, SRAM parts are typically interchangeable between series.
Shifting with SRAM comes in two styles – trigger shifter or grip shift. Grip shift, which works by twisting the handlebar grip to shift is where SRAM started but isn’t as popular these days and isn’t found stock on new bikes – although it’s readily available as an aftermarket option. Trigger shifting is now the standard choice for SRAM users and works similar to Shimano’s Rapid Fire system, but your thumb operates both levers with a push. It was SRAM’s system that prompted Shimano to add the option of thumb operation on its more expensive shifters. Such a design allows shifting in both directions and brake control at the same time.
Below is a basic breakdown of SRAM's groupsets. Mentioned below are the models you’re likely to find on 2018 model bikes.
X5: This entry-level groupset from SRAM features both 9 and 10-speed options and two or three chainrings. X5 components are rarely seen as a complete groupset, but the parts are commonly found on basic hardtails.
X7: This groupset was once a staple on intermediate hardtails and entry-level dual suspension bikes. It offers dependable trail performance on a tight budget. The groupset now is mostly found in a 10-speed setup with two chainrings (2x10). X7 is SRAM’s entry into offering a clutch-equipped rear derailleur for additional chain security. Many bikes that would have previously used X7 are now using SRAM’s 1x11 NX groupset for 2018.
X9: Building on the features of X7, X9 introduces more aluminium and higher-end steels. X9 is commonly set up as 2x10 and was once a popular groupset for intermediate mountain bikes. For 2018, SRAM NX and GX is far more widely seen for where X9 once was.
NX: NX is the lowest price entry into a 1x specific drivetrain on the market. Designed to imitate the function and features of more expensive options, 11-speed SRAM NX offers an 11-42T cassette for a wide range. This cassette is a big part of the cost savings over more expensive 1x groupsets as it fits onto a standard hub, whereas more premium 1x SRAM cassettes require a unique "XD Driver" hub body to host a wider-range 10-42T cassette, such a component is part of the rear hub and so often requires a more expensive wheel too.
NX Eagle: Released in mid-2018, NX Eagle is SRAM’s latest 1x12 speed groupset. Although very similar in operation to its more expensive counterparts, NX Eagle is aimed at the entry-level and therefore sees cheaper, heavier materials used than its more expensive stablemates. NX Eagle groupsets are likely to find their way onto a wide range of entry-level to mid-level mountain bikes for 2019.
GX: GX confusingly overlaps closely with X7, X9 and X1. For this, GX is offered in four variants: 1x7, 1x11, 2x11 and 2x10. It’s the 1x11 version of GX most commonly equipped, and the group introduces the use of a wide-range 10-42T cassette along with greater use of aluminium components (like X9 and X1). The limited range of the 1x7 option is designed for downhill racing.
GX Eagle: Released mid-way through 2017, GX Eagle is a 1x12 speed groupset that brings all the benefits found on more expensive XX1 and X01 Eagle groupsets, down to a more modest price point. Although very similar in operation to its more costly counterparts, GX Eagle makes use of slightly cheaper materials and see’s a slight weight increase to hit its extremely competitive price point. Expect to find GX Eagle groupsets on a wide range of mid-priced high-value mountain bikes.
X1: First introduced in 2015, X1 has now been commonly replaced with SRAM GX Eagle on many bikes for 2018. X1 is a fully featured 1x-specific groupset with components featuring aluminium construction and a proven track record for being capable of severe abuse. X1 offers similar shift performance to more expensive groupsets but at a higher weight. X1 is a tad lighter than GX.
XO1: SRAM’s first offering of carbon fibre and a little premium performance, SRAM X01 is a high-end groupset that is 1x-specific and uses a lightweight 11-speed 10-42T cassette. X01 is typically considered SRAM’s pinnacle for trail, Enduro racing and other aggressive riding styles. SRAM X01 is also available in a 1x7 variant which is specially designed for downhill racers in mind, and it’s the groupset SRAM’s sponsored downhill riders to use.
X01 Eagle / X01Eagle eTap AXS: Recently updated to accommodate wireless shifting, X01 Eagle has a 12-speed setup and runs off SRAM's new AXS wireless protocol. Eagle is SRAM’s statement to make front shifting redundant, and the Eagle 10-50T cassette offers an incredible 500% gear range. While no longer sitting atop the hierarchy, X01 Eagle is still a premium groupset featuring high-end aluminium, CNC-machined steel and carbon fibre construction.
XX1: Where X01 is SRAM’s finest for the Enduro and trail riders, XX1 takes it a notch above for the cross-country riders and racers counting grams. The differences between X01 and XX1 are subtle, but the scales don’t lie. XX1 was SRAM’s first 1x-specific 11-speed groupset. It uses a 10-42T cassette.
XX1 Eagle eTap AXS: SRAM’s latest and most premium groupset, XX1 Eagle shares all the same features as the 12-speed X01 Eagle eTap AXS groupset but saves weight at every possible corner for a groupset that’s aimed at the cross country racer or trail rider seeking the very lightest, wide-range 1x groupset on the market.