A Guide to
MTB & Road Groupsets
Aside from the frame, a specific type or level of groupset is what defines a bike and what a lot of people will look for in a bike. It is the collective term for the mechanical parts found on your bicycle and its role is one of two things, either to make you GO or to make you STOP. Your groupset comprises gears and gear levers, brakes and brake levers, chain, cassette, chainset and in some cases the bottom bracket as well as hubs and wheels.
Both mountain bikes (MTB) and road bikes have groupsets that are made by two industry-leading brands, SRAM and Shimano, with Campagnolo focussing on making road groupsets only.
For both road and MTB there are different quality level groupsets available (by Shimano and SRAM) and bikes for both disciplines offer a wide range from entry-level groupsets, all the way up to professional level groupsets which are used by the pros in the big races such as the Tour de France for road and the World Cup for MTB.
All the parts of a certain groupset are designed to work best together. Meaning, for example, a Shimano XT rear derailleur/mech will work best with XT shifters, an XT cassette and an XT chain.
Some manufactures now produce different variations to their groupsets such as 2x10, 2x11, 1x10 or 1x11 (‘1’ being the number of chainrings on the chainset and ‘x 11’ being the number of gears or cogs on the cassette). A further high-end option today is a groupset which offers electronic gearing, which is currently available from Shimano and Campagnolo.
Road bike cassettes can be found in a huge range of sizes. Professional riders and time triallists favour a rear cassette with as little difference between gears as possible. Having close ratios between gears makes it easier to maintain a consistent pedaling cadence as you accelerate or climb.
These close ratios are most commonly 11 to 25. That means that in an 11-speed cassette, the lowest gear (easiest to turn) has 25 teeth, while the hardest gear has 11. Cassettes can be found as low as an 11-23, which will only have a maximum jump of two teeth between gears.
Road bike cassette sizes
Most people will favour a road bike cassette with a wider spread of gears to make climbing easier. The most commonly found on standard bikes is 11 or 12 to 27 or 28. Recently, all of the gear component companies have released even wider cassettes designed for serious mountain climbs. SRAM have their PG cassettes which go as large as 11-32, Shimano offer a 32 in their 10-speed systems and a 30 in 11-speed, while Campagnolo offer up to 30-tooth options.
A fresh mountain bike cassette can transform a clunky, heavy mountain bike drivetrain into one that runs as smooth as butter.
Mountain bike cassettes generally have a wider range than road bike cassettes, with wider-spaced gear ratios generally ranging from 11 to 32, 34 or 36-tooth options. A wider range MTB cassette might mean you can run either a double or single ring chainset, reducing weight and potentially the requirement for a front derailleur.
Cassettes fit onto the freehub of your rear hub, with splines on the freehub ensuring their alignment is correct to improve shifting. Unless you have a SRAM 11-speed drivetrain, any 9 or 10-speed MTB cassette should fit on your mountain bike wheels.
If you’re running a SRAM 11-speed system, such as X01, you’ll need to buy a corresponding cassette because the freehub body on your wheel will be different. The 11-speed cassettes cost more than regular ones because of the amount of machining that goes into their construction – it takes three hours of machining to create one cassette! Their benefit is that they run a super-wide range of 10-42. It’s the small 10-tooth sprocket that requires the use of a specific freehub body ‘driver’, because they don’t fit on wider diameter regular freehubs.
As prices rise, cassettes become lighter, and will start to use sprocket carriers. If you have an aluminium freehub body, as found often on lighter wheels, you might find that mountain bike cassettes made from individual sprockets are held together with pins that can dig into the softer aluminium freehub.
Road bike chainsets are available in a few different configurations. The first is called a double. It’s used by professional riders and consists of two front rings - one large 53-tooth outer and a smaller 39-tooth inner ring. The second (and most common) is a called a compact. The outer ring is a 50-tooth, but it uses a smaller inner ring with 34 teeth to provide a lower, easier bottom gear to make climbing steeper slopes easier. You can also get a front road bike chainset that’s a halfway house between standard and compact, called a pro-compact, which uses a ring combination of 52 and 36.
The remaining front chainset setup, and one that has fallen a little out of favour since the introduction of the compact is the road bike triple chainset . Road triples usually combine a 50-tooth outer ring with a 39-tooth middle, and an inner ring that’s just 30 teeth. Road triples offer the widest and lightest bottom gear, but nowadays are only really found on lower priced entry-level road bikes, though they are still highly favoured by touring cyclists riding bikes laden with the extra weight of luggage.
A decent MTB chainset is integral to the performance of your mountain bike groupset. A chainset consists of crank arms and chain rings, which transfer the power from your pedal stroke to the chain. Many different companies make mountain bike chainsets, including , Shimano and SRAM. There are loads of different options available, whether you are after something lightweight, stiff or strong.
A mountain bike chainset comes with one, two or three chain rings, depending on the range of gears you want to run. Most will take standard size chain rings, however some, such as SRAM’s XX1 chainset have a specific chain ring bolt pattern, which limits which chain rings you can run.
Generally speaking, as prices rise, MTB chainsets will become lighter and stiffer. Expect to see carbon options appearing at higher price points, such as the Race Face Next SL chainset. Other high-end chainsets such as Shimano’s XTR are still made of aluminium.
It’s important to remember that frames are built around varying bottom bracket standards. While most chainsets will work with most frames, if a chainset comes with a bottom bracket, make sure it will fit your frame, otherwise you may need to purchase an adaptor..
Road bike derailleurs, also called mechs, are the components that move the chain between rings at the front, and across the gears of the rear cassette. Each different brand offers their own design of road bike derailleur with Shimano and Campagnolo both offering versions that are actuated electronically.
Mountain bike derailleurs, also known as ‘mechs’, have a tough life directing the chain between the cassette’s sprockets and the chainset’s chainrings. MTB derailleurs also ensure chain tension is maintained - all while being sprayed with mud and water, and potentially being knocked against rocks and hit with trail debris along the way.
A mountain bike rear derailleur is specific to the number of gears you are running. SRAM and Shimano parts aren’t cross-compatible, so check which one you need before buying. Fortunately, front mechs are more flexible in this regard.
Other options include the length of cage you require – the cage is the part that holds the jockey wheels. If you’re running a single ring, you can get away with a short-cage mech, but if you’re running a triple, you’d be better off with a long cage – this is to account for the increased chain growth you get from running a wider range of gears.
Over time, the pivots and jockey wheels get worn out, when this happens shifting performance will suffer and it will be time to either replace the jockey wheels or purchase a new mech.
The most common is Shimano's STI system. The Shimano design uses two levers – a brake lever and another lever that sits just behind it. The brake lever doubles as a gear shift lever - swing the right hand brake lever inwards and the rear mech shifts the chain upwards on the cassette (to a lighter gear). When the inner lever is pushed inwards, the chain is shipped down the cassette (to a harder gear).
Shimano is designed to allow multiple shifts at one time, so the further you push either lever, the more gears you'll shift (up to a maximum of three). The left hand shifter operates the front mech - the brake lever swings inwards to move the chain onto the larger chainring, the small lever moves it to the smaller ring.
SRAM’s system called is called DoubleTap - you only have one lever on each side, which sits just behind the brake lever. Push the right hand lever in until its first click and the chain will drop into a smaller gear on the cassette, but keep pushing the lever until it hits a second click (or double tap) and it'll rise up the cassette to a lighter gear. One the left-hand lever, moving it until the first click will shift the chain to the smaller front ring, while two clicks moves it up onto the bigger chainring.
Campagnolo's Ergopower system uses a combination of a lever (which sits behind the brake lever) and a small button on the inside of the brake hoods (the rubber coated housing is referred to as the hood). The right hand lever swings inwards to make the chain rise up the gears, while pushing the button shifts the chain into harder gears. Pushing the lever further or the button through more clicks allows Campagnolo, like Shimano, to shift multiple gears at a time. The left hand lever lifts the chain onto the bigger chainring and the button trigger drops it onto the smaller chainring.
Your mountain bike shifters are what allow you to have direct control over what’s going on with your bike’s drivetrain. The shifters on your mountain bike control the derailleurs by pulling or releasing the gear cables – new shifters will help keep everything shifting sweetly and can transform how your gears feel.
Check before you buy whether you’re running a 9, 10 or 11-speed drivetrain, because mountain bike gear shifters are specific to the number of gears you run. You will also need to run the same brand mountain bike gear shifter as your rear derailleur.
Both Shimano and SRAM shifters use a big thumb paddle to pull the cable through, and a shorter thumb or index fingered lever, which quickly releases cable tension. Some MTB gear shifters, such as the Shimano XT I-Spec shifters can seamlessly integrate with brake levers, minimising bar clutter because they only use a single clamp.
While most people will use ‘trigger’ shifters, some prefer ‘twist shifters’, often found on SRAM’s groupsets. Because they are often lighter, they’re usually part of racier groupsets such as SRAM XX.