Just like our buyer's guide to road bike groupsets, this guide is designed to explain the components of a groupset, and the different options offered by the two main manufacturers: Shimano and SRAM.
It is more common to see complete groupsets on road bikes. When it comes to mountain bikes, however, brands usually mix and match parts from various groups — and in some cases different brands — to suit the bike's intended use and meet a specific price point.
There are three types of front cranksets found on mountain bikes. Commonly, the type of crankset fitted will depend on the bike’s designed use, price point and even wheel size, with bigger wheeled bikes (such as 29ers) often have lower gearings to compensate for longer roll-out measurements.
The first is the triple – the old classic. It consists of three front rings, the largest often being a 42- or 44-tooth outer ring. The middle ring is usually a 32 or 34 and the smallest, inside ring, is often a 22- or 24-tooth. This setup offers the largest range of gears, but there is significant redundancy in terms of gear ratios. Cross-chaining is also a concern with a triple. Triple cranksets are seldom found on on high-end mountain bikes and they are disappearing from the entry-level market as well.
The second, more common type of crankset on modern mountain bikes, is a double. This uses a smaller inner ring (24- to 28-tooth), while the larger outside cog offers a gear that’s generally well-suited to faster riding, this is usually between a 36- and 42-tooth size. It’s lighter than a triple and offers a better angle for the chain in order to use all the gears. A double features less gear ratio cross-over compared to a triple.
Over the past few years, mountain bike drivetrains have been trending toward a simpler, single chainring setup. By removing the front derailleur and corresponding shifter, a single-ring setup is less complex as well as lighter.
Commonly referred to as a "1x", this arrangement has been popular on downhill mountain bikes, where large gear ranges aren’t needed and chain security (that is, no dropped chains) is very important. Following SRAM's launch of XX1 and the introduction of subsequent wide-range 1x11 and 1x12 groups, the single-ring drivetrain is becoming the norm on high to mid-level mountain bikes.
A crankset isn't very useful without bearings to spin on. These bearings are pressed or threaded into the bottom bracket shell. Bottom brackets are available in a staggering array of configurations – you might find our complete guide to bottom brackets useful.
Cassettes come in a wide range of sizes and speeds. Like the crankset, cassette choice is often determined by the bike’s intended riding style and price.
Mountain bike cassettes can be found in seven through 12-speed versions. They are often referred to by the smallest and largest cogs to provide an indication of the total range. E.g., 11-32 or 10-50t.
Aside from downhill bikes, which often use very narrow range cassettes, most mountain bikes favor a cassette with a wide spread of gears to make climbing easier. The most commonly found ranges on bikes with double or triple cranksets are 11- to 32-, 34- or 36-tooth.
Single-ring drivetrains go much wider, with SRAM's XX1 and X01 Eagle 12-speed drivetrains providing a 10-50t spread, while Shimano offers an 11-46t range on its 1x11 XT group.
The groupset brand and number of gears dictate the chain. In general, as the number of gears increases, the spacing between the cogs shrinks and the chain must become narrower as well. Because of this, you should only run a chain designed specifically for the number of cogs on your cassette - i.e., don't use a 9-speed chain on a 10-speed drivetrain, or an 11-speed chain on a 12-speed drivetrain.
The more expensive chains often have smoother, more durable and corrosion-resistant coatings and save weight with hollow links and pins. With that in mind, chains are the first part of a drivetrain to wear out, so it's often best to invest in a mid-level chain.
Derailleurs are the components that move the chain between cogs on the cassette and chainrings on the crankset. Each brand offers its own design, but the principle is generally the same. When pressed, the shifter pulls or releases a cable, which moves the derailleur, derailing the chain and repositioning it in a different gear.
Cables are no longer the only way to control derailleurs. Shimano now offers electronically-actuated derailleurs on XTR Di2 as well as XT Di2. Both these groups use wires to send electronic signals from the shifters to the derailleurs to actuate the derailleurs.
As previously mentioned, shift levers are use to operate a bicycle's derailleurs. Shimano and SRAM use different designs, and while they all shift gears, they each have a particular way of doing it.
While mechanically different, both SRAM and Shimano offer "trigger shifters." This name is a bit misleading, as both companies have refined the lever ergonomics to shift both levers with the thumb, rather than also relying on the rider's trigger finger. The benefit of this approach is that it allows a rider to shift while also braking.
SRAM offers two systems, trigger and Grip Shift. The trigger system is much more common. Grip Shift functions like a throttle, twisting back and forth to shift. This system has lost popularity in recent years, but still holds a loyal following in cross-country racing since the system is very light and allows riders to shift across the cassette quickly.
Shimano's Di2 electronic shifters also throw a spanner into the mix as technically they're electronic switches, rather than a mechanical component. This means Di2 levers can be customised and programmed to behave in ways that aren't possible with conventional shifters. A great example is Shimano's Synchroshift technology, which emulates an intriguing mechanical system of old by controlling a two derailleur setup with just one synchronised shifter.
Like most components, groupsets vary in price a great deal. So what benefits do more expensive groupsets bring?
Keith Bontrager famously said of bicycle parts: "Strong. Light. Cheap. Pick two." A lighter bike will always accelerate, climb and brake better than a heavier one, but without giving up strength, something has to give. Whether you're looking at groupsets, wheels or even complete bikes, reduced weight is often the major contributor to increased cost.
Generally with mountain bike groupsets, the more you spend, the lighter they get. Often the performance of the groupset plateaus at the tier from the top, with reduced weight being the reason for the extra expense. For example, the difference between Shimano's top two tiers, XT and XTR, is around 230g (excluding brakes), while the difference between SRAM's top-range XX1 and second-tier X01 single-ring options is closer to just 30g (excluding brakes).
These weight differences are the result of more expensive materials and refined, or more time-consuming, manufacturing processes. In addition to further machining, hole-drilling and high precision, more expensive components often use materials such as carbon fiber, titanium, lightweight aluminium and ceramic bearings to achieve the pinnacle in low weight.
If you're spending more money on a mountain bike groupset, you'd expect it to outlast a cheaper option. Durability does improve with price, but our experience is that durability also plateaus at the second-tier options, and in some ways, actually starts to decline at the most expensive option.
The more expensive technical components are built with greater precision, refinement and materials that lend themselves to greater longevity. This is apparent in derailleurs and shifters, where the cheaper options will develop play and slop overtime, whereas better parts often remain like new.
Wear items, such as cassettes and chainrings, however, are often the reverse of this. Cheaper options are made of heavier, but more durable steels, while the more expensive versions are made with lighter, but softer, aluminium and titanium metals.
In addition to the benefits of reduced weight, more expensive MTB groupsets find other ways of increasing performance. Most noticeably, higher priced options provide a smoother, more precise and quicker shift between gears. This includes reduced effort at the lever, something that becomes apparent once you've been on the bike for a few hours. It's an area where electronic gears are going to set a new benchmark; ultimate precision and speed at the simple push of a button.
Another performance example is increased crankset stiffness to provide crisper shifting and more efficient power transfer from the pedals to the rear wheel. This is achieved with more complex designs and materials that increase strength and stiffness, but don't add weight.
Besides offering extra gears, it's common for the more expensive groupsets to offer additional features, however subtle they may be. Clutch-equipped rear derailleurs, such as Shadow Plus from Shimano or Type-2 from SRAM are primary example of this. The clutch keeps the chain taut, which offers enhanced control of the chain, keeping the drivetrain quieter and with less chance of a dropped chain over rough terrain.
In reverse of this, gear indicators are a feature often lost as the groupset price increases. The theory being that more experienced riders use gears based on ‘feel’ and don’t need numbers or indicators to help them.
With mountain biking spanning so many individual disciplines, it shouldn’t be too surprising to find that what works perfectly for climbing steep hills in cross-country may not be ideal for descending cliff faces in downhill.
This is why discipline-specific groupsets now exist for the more extreme riding styles. We’ll cover these below in the individual brand hierarchies.
Japan's Shimano offers the widest range of groupsets for mountain biking.The range starts with the most budget Tourney, which is usually found on kids’ and entry-level bikes. While it's included in the mountain bike groupsets, we don’t consider Tourney to be off-road worthy outside of occasional and light use. Tourney is a 6- or 7-speed system (six or seven gears at the rear) combined with a triple crankset.
Next is Altus, which is sold as a 7-, 8- or even 9-speed system. No matter how many gears are featured out back, this group is always supplied with a triple crankset.
Acera follows, and starts to introduce corrosion-resistant materials such as stainless steel on certain components.
Shimano Alivio sits just above Acera and introduces a few performance features such as RapidFire Plus shifters with push/pull trigger action. Like Acera, this 9-speed group is available with a triple ring crankset only. We consider Alivio Shimano’s starting point if you’re seeking a focused mountain bike.
Next in line is Shimano Deore, widely considered to be the Japanese company's first performance-ready off-road groupset. It's 10-speed and shares many of the designs and technology of the higher priced groupsets. Deore is offered in both double- and triple-crankset options and also spells the introduction to the clutch-style rear derailleur.
Long considered the workhorse group in Shimano’s mountain offerings, SLX is a third-tier offering from the Japenese giant. Generally speaking, SLX offers many of the features and function as the upper-end XT, but at a higher weight and marginally lower shift quality.
The first of the discipline-specific groups, Zee, is Shimano’s entry-level gravity groupset, a cheaper version of Saint (see below). Available only with a single-chainring crankset, Zee is designed for fast and rough downhill riding. It’s built heavier (and sturdier) than the similarly-priced SLX offering.
Shimano Deore XT sits one below the professional-level XTR. This 11-speed group has nearly all the top-end design features as the range topping XTR and offers all the performance most riders will ever need, but at a weight penalty compared to XTR. XT is available with either single, double- or triple-ring cranksets.
Sitting as a top-level offering for those who race downhill is Saint. Saint, like Zee, is a gravity-focused groupset that is built incredibly strong to handle the abuse of freeride, downhill and other extreme forms of mountain biking. Only offered with a single-ring crankset, Saint also has additional chain retention features.
XTR is the pinnacle of Shimano's range and is often used for racing purposes. For 2016, it offers 11-speed gearing with either single-, double- or triple-crankset configurations. XTR combines top-end design with lightweight materials such as high-grade alloys, carbon fibre, and titanium. It’s common for XTR to offer features that no other groupset level receives, such as multi-shift release when downshifting.
XTR is split into two separate groupset offerings – Race and Trail, with the brakes, rear derailleur and crankset options being the difference. Race is all about absolute weight savings, where features such as tool-free brake lever adjust and Ice-Tech brake cooling fins are removed in favour of saved grams. Trail is the more ‘everyday’ and feature-packed option, where a few additional grams get you greater brake power, adjustability and even chain retention.
Shimano also offers XTR in its latest electronically-operated Di2 design. This system does away with traditional cables in favour of a system that's actuated by motor driven mechs powered by a battery, which can either be frame mounted or hidden within the seatpost, seat tube or steerer tube. The advantage of the electronic system is consistent gear shifts and very low maintenance. Another perk of the XTR Di2 is sequential shifting, in that both front and rear derailleurs are operated with a single control, and the system decides whether to shift at the front or rear for the next closest jump. As previously mentioned, Di2 technology has now been confirmed at Shimano XT level.
The downsides are mainly the cost, but there’s also a minor weight penalty and remembering to occasionally recharge the battery.
The Di2 groupsets shares the same crankset, cassette, chain and brakes of the respective mechanical groupset.
Shimano's groupsets are designed to work with each other (providing they share the same number of gears), so for example, you can easily upgrade Deore with a mix of SLX and XT parts.
SRAM's mountain bike groupset range is split into two, with single-chainring groupsets (many of which get a ‘1’ featured in the name) separate to the double and triple options. Currently SRAM’s highly popular single-ring options are only for performance-level bikes. Like Shimano, SRAM offers a discipline-specific option too, in the form of X01 DH.
While SRAM’s recent success story is its dedicated single-chainring groupsets, the brand was a strong advocate of double chainring setups over triples. SRAM calls this 2X10.
Another detail to be aware of with SRAM is trickle-down technology. The cheaper components from SRAM are often the same as more expensive options from a few years prior. As well as to this reuse of technology, it’s common for SRAM groups to be very close in function, with material changes accounting for the weight differences.
SRAM’s mountain bike groupsets kick off with X5, X7 and X9 transmissions which are available in 9 and 10-speed, double and triple configurations with technology that’s trickled down from the top.
Sharing many design and internal features of the top-level 1x offerings, SRAM NX and GXcomponents are a popular choice on mid-priced bikes. The latter is, rather confusingly, available in 2x11 and 2x10 configurations as well as the better-known 1x11 version.
Higher up the ladder of SRAM’s single-chainring groupsets is X1. X1 is an 11-speed groupset that will only work with a single chainring, afforded by the massive 10-42T cassette. Introduced in 2015, X1 offers nearly all the same features as X01 and XX1 but at a higher weight.
Long considered as SRAM’s best option if you don’t race, X0 is a 2x10 groupset that introduces carbon fibre for weight savings, among a few other small features.
Arguably the most popular single chainring groupset on the market, X01 offers all the features of X1, but more expensive materials and manufacturing processes substantially reduce weight.
X01 DH is a purpose-built groupset for downhill racing and is available as either a 7- or 10-speed setup.
SRAM XX1 is the groupset that kicked off the whole single-chainring phenomenon. It remains as SRAM’s pinnacle off-road groupset and is popular among everyone from gravity-seeking enduro riders to gram-counting cross-country racers. With approximately 30g separating X01 and XX1, it’s mainly for those who just want the best.
Sitting as a cross-country race specific groupset, XX is SRAM’s pro-level 2X10 offering. Since the release of XX1, XX isn’t used or seen as often.
New for 2016 is SRAM's XX1 and X01 Eagle 12-speed drivetrains that both offer a 500% gear range through huge 10-50t cassettes. Eagle components are currently priced at a point that'll only reach those with deep pockets but knowing SRAM's approach it shouldn't be too long before its ultra-wide range makes its down to a price that's easier to swallow.
For more on Eagle XX1 and X01, check out our first ride review video.
Also new for 2016 is SRAM's EX1 group, developed specifically for the growing phenomenon that is e-mountain biking.
Electric assistance and its associated rapid shifts put greater stress on components. To counter this, EX1 features an 8spd cassette, with the big cog 7mm inwards of where it would be on an 11spd setup to reduce cross-chaining, and an extra-strong chain that's positionally synced with specific teeth to ease strain on the drivetrain while changing gear.
EX1 also comes with its own brakes – the Guide RE – which are similar to downhill units in order to keep the extra weight of an e-bike in check. We're looking forward to getting some proper miles in on EX1 soon to see how it measures up.
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