Shimano, SRAM and MicroShift – the complete hierarchy explained

By Alex Evans

Published: Thursday, 23 March 2023 at 12:00 am


BikeRadar‘s buyer’s guide to mountain bike groupsets is here to tell you everything you need to know about your bicycle’s components.

A group or groupset are all ways of describing the collection of parts that make up a bicycle’s drivetrain.

The components include the shifters, crankset, bottom bracket, front and rear derailleurs, chain, and cassette. Brakes are sometimes included in component series, but, for this article, we’re going to stick to the items that comprise the drivetrain.

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.

Components of a mountain bike groupset

Mountain bike crankset

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Shimano offers its XT group in versions with one, two and three chainrings.
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Mountain bike cranksets can be divided into three categories by their number of chainrings.

Triple

The first is the triple – the old classic. As the name implies, it consists of three chainrings, 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 can offer the largest range of gears, but there is significant redundancy in terms of gear ratios. Cross-chaining is also a concern with a triple if the lowest or highest chainring is selected with the opposite lowest or highest sprocket on the cassette.

Cranksets with three chainrings aren’t found on modern high-end mountain bikes. They are disappearing from the entry-level market and double- and single-ring drivetrains are quickly becoming the most desired setup and the new normal.

Double

Cranksets with two chainrings overtook the triple as the most popular mountain bike crankset when SRAM and Shimano introduced 10-speed drivetrains. Double cranksets offer a narrower gear range with less overlap than a triple.

They use a smaller inner ring (22- to 28-tooth), while the larger outside cog offers a gear that’s generally well-suited to faster riding (34- to 36-tooth).

Double cranksets are found from entry-level bikes through to high-end models but their popularity is on the wane too.

Single

The most significant trend in mountain bike drivetrains over the past five years has been the movement toward wide-range 1x drivetrains with a single chainring.

Commonly referred to as a ‘1x’ (one-by), this arrangement has been popular on downhill mountain bikes for years, 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 1×11 and 1×12 groups, the single-ring drivetrain has now become the new norm on high- to mid-level mountain bikes, and is increasingly found on entry-level bikes too, thanks to the introduction of SX Eagle and NX Eagle 12-speed drivetrains.

Chainring size ranges vary widely, depending on the intended use, from 38-tooth chainrings for strong cross-country racers down to 28- and even 26-tooth chainrings on some fat bikes. Most bikes with 1x drivetrains come with 32- or 30-tooth chainrings.

One key attribute of 1x drivetrains is the use of a chainring with tall, unramped teeth (since there’s no need to shift between chainrings) and alternating tooth widths that match up with the inner and outer links of the chain.

Both of these features are designed to keep the chain in place without the aid of a front derailleur or chain guide.

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The ramped teeth help to keep the chain on the single ring without the need for a chain device or chain guide.
SRAM

By removing the front derailleur and corresponding shifter, a single-ring drivetrain is less complex as well as lighter. Many novice riders find 1x drivetrains easier to operate as well.

Mountain bike bottom bracket

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Different frames use different bottom bracket systems, including threaded (left) and press-fit (right).
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A crankset won’t get you very far without bearings to spin on. These bearings are pressed or threaded into the mountain bike’s bottom bracket shell.

Bottom brackets are available in a staggering array of configurations — you might find our complete guide to bottom brackets useful.

Mountain bike cassettes

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Shimano’s widest range 12-speed cassette offers a 10-51t spread, while SRAM offers a 12-speed group with a 10-50t range.
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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 7- through 12-speed versions. They are usually referred to by the smallest and largest cogs to provide an indication of the total range, e.g. 11-32t or 10-50t.

Aside from downhill bikes, which often use very narrow-range cassettes, most mountain bikes favour 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 34- or 36-tooth.

Single-ring drivetrains go much wider, with SRAM’s 12-speed Eagle-branded drivetrains providing up to a 10-52t spread (11-50t on SX and NX Eagle), while Shimano offers an 11-46t range on its 11-speed SLX and XT groups and a 10-51t option on its latest 12-speed XTR, XT and SLX groups.

Mountain bike chains

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Higher-end chains often feature hollow links or pins to save weight over more affordable versions.
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The groupset brand and the number of gears dictate the type of chain you need. In general, as the number of gears increases, the spacing between the cogs shrinks and so the chain becomes narrower as well.

Because of this, you should only run a chain designed specifically for the number of cogs on your cassette – don’t use a 9-speed chain on a 10-speed drivetrain, or an 11-speed chain on a 12-speed drivetrain. Some chains are even directional and need mounting in a specific orientation, so check upon install.

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.

Mountain bike derailleurs

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.

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Front derailleurs move the chain between the chainrings.
BikeRadar

When pressed, the shifter pulls or releases a cable, which moves the derailleur, derailing the chain and repositioning it in a different gear.

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Rear derailleurs move the chain between cogs on the cassette.
BikeRadar

Cables are no longer the only way to control derailleurs. Shimano offers electronically actuated derailleurs on XTR Di2 as well as XT Di2, which use electrical wires connected to the shifter(s). SRAM’s AXS groupsets are completely wireless.

Mountain bike shifters

As previously mentioned, shift levers are used 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.

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Current shifter types: left is Shimano’s RapidFire trigger system, in the middle is SRAM’s Grip Shift, and on the right is SRAM’s trigger shifter.
BikeRadar

While mechanically different, both SRAM and Shimano offer ‘trigger shifters’. This name is a bit misleading because both companies have refined the lever ergonomics to shift both levers with the thumb, rather than also relying on the rider’s index or ‘trigger’ finger.

The benefit of this approach is that it allows a rider to shift while also keeping their index finger on the brake lever.

SRAM offers two systems for its mechanical shifters, Trigger and Grip Shift. The trigger system is 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.

SRAM AXS introduced a new design with three buttons, two of which are operated by a paddle that rocks up or down, with the third being a button on the back – the buttons’ operation is customisable in SRAM’s dedicated app.

Shimano’s Di2 uses electronic switches too and can also be customised via its app.

Di2 can, for example, make use of Shimano’s Synchro Shift technology, which allows the rider to use a single shift lever to control the front and rear derailleurs. The system’s computer shifts into the optimal chainring and cassette sprocket to keep the rider’s cadence relatively constant.

Choosing a mountain bike groupset: price versus performance

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The SRAM derailleur, despite being wireless, carries a 144g weight penalty because of the battery.
Tom Marvin / Immediate Media

Like most components, groupsets vary in price a great deal. So what benefits do more expensive groupsets bring?

Groupset weight

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 sacrificing strength, something has to give. Whether you’re looking at mountain bike drivetrains, wheels or even complete bikes, reduced weight is often the major factor in increased cost.

Generally, with mountain bike groups, the more you spend, the lighter they get. Often the performance of the groupset plateaus at the second 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 300g (excluding brakes), while the difference between SRAM’s flagship XX1 Eagle and second-tier X01 Eagle drivetrains is closer to 46g (excluding brakes and bottom bracket).

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 fibre, titanium, lightweight aluminium and ceramic bearings to achieve class-leading low weights.

Groupset durability

If you’re spending more money on a mountain bike group, 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. XT in the case of Shimano and X01 in the case of SRAM.

In some instances, component durability can actually decline at the most expensive option, where absolute weight savings sometimes trump product longevity.

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 for many years of use.

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.

Groupset performance

In addition to the benefits of reduced weight, more expensive mountain bike 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 without adding weight.

Additional groupset features

Besides offering extra gears, it’s common for the more expensive groups to offer additional features.

Clutch-equipped rear derailleurs, such as Shadow RD Plus from Shimano or Type-3 Roller Bearing Clutch from SRAM are an example of a technology that is offered on these brands’ groupsets, from Deore and NX Eagle upwards.

The clutch keeps the chain taut, which improves shifting over rough terrain, keeping the drivetrain quieter, and reduces the likelihood of dropping a chain.

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Both SRAM and Shimano mechs now come with a clutch mechanism to help reduce chain slap.
BikeRadar

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.

Discipline-focused options

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.

Shimano’s mountain bike groupsets

Japanese manufacturer Shimano offers the widest range of groupsets for mountain biking.

Shimano’s mountain bike groupset hierarchy, from least expensive and technologically advanced to most, is as follows:

  • Shimano Tourney
  • Shimano Altus M2000
  • Shimano Acera M3000
  • Shimano Alivio M3100
  • Shimano Cues U6000
  • Shimano Deore M6100, M5100, M4100
  • Shimano SLX M7100
  • Shimano Deore XT M8050
  • Shimano Deore XT M8100
  • Shimano XTR M9050
  • Shimano XTR M9100

Shimano also offers two downhill-specific groupsets:

  • Shimano Zee M640
  • Shimano Saint M820

Shimano Tourney

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The Tourney groupset is Shimano’s budget 6- and 7-speed offering.
Shimano

The range starts with Tourney, which is usually found on department-store or children’s bikes and comes in a few different configurations depending on its intended application, whether that’s touring, road or very light mountain biking.

Tourney received its latest update in 2020 getting two new 6- and 7-speed mechs and further updates to the shifters, front mechs, cranks and cassettes.

The groupset is available in 6-, 7- and 8-speed systems combined with triple or double cranksets.

Shimano Altus M2000

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Altus is the group you’re likely to find on entry-level mountain bikes.
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