A bike’s stem performs a fundamentally simple job, its basic purpose being to ensure the handlebars are securely clamped to the fork steerer.
However the stem type, materials and dimensions – length of stem, degree of rise – play a pivotal role in how a bike fits and handles, so it’s important to choose carefully.
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Or, read on for more information on how to choose the right stem for your BMX, MTB or road bike.
The right stem for your MTB bike will depend on a number of factors, the most important being the stem type, materials and dimensions.
The vast majority of MTB (and road bike) stems on the market today are of the Aheadstem design (also known as ‘Aheadset stem’ or ‘threadless stem’) which bolts directly onto a fork’s steerer tube, the plug-in quill design being now only found on older or cheaper bikes.
Aluminium alloy still by far the most common stem material in low- to mid-budget stems, but carbon fibre models are available at the very top end of the market, with their appeal mostly among racers both on-road and off-.
Stems are available to fit a range of steerer tube sizes with 1 1/8” being by far the most common on both MTB and road bikes. However some models are also available for older bikes with 1” steerers (although a shim can also be used to make these fit standard stems) or for gravity bikes with 1.5” steerer tubes.
A range of clamp sizes is also available to fit the different handlebar diameters. MTB bars are usually 25.4mm (standard) or 31.8mm OS (oversize) in diameter, with the latter standard now actually the most common owing to its properties of strength and stiffness.
A critical question when choosing a stem is what length it should be. Whereas road riders tend to choose stem length based solely on overall bike fit and positioning, for off-road riders, the length of the stem is critical in determining how the bike handles. Shorter stems result in noticeably quicker and more responsive handling that is a definite advantage on technical singletrack and gravity riding. As a way of example, super-slack DH sleds typically sport stubby block-style stems of around 40mm, while at the other extreme, XC racers favour long (110-120mm stems) paired with narrow bars.
For many riders, a mid-length stem of 60-80mm provides the perfect balance of responsive steering and pedal-efficient positioning, but these shorter stems work best with the slacker frame geometry of modern trail bikes or long-forked hardtails, rather than the steep angles of ‘classic’ XC bikes. You may need to experiment with stem lengths to find the one that offers the right balance for you – a difference of 10mm can have a huge effect in terms of quickfire singletrack handling or all-day pedalling comfort.
The stem rise refers to the stem’s angle in degrees, relative to the fork steerer tube, and affects bike positioning and reach. A ‘zero rise’ stem, for example, is essentially ‘straight’, while a stem with a rise of 10° has a 10° angle between the steerer and handlebar clamp areas. Most stems will have a moderate rise (6° being quite common) and can be flipped to offer a lower bar position (so a stem may be referred to as having a rise of +/- 6°). As with stem length, you may need to experiment with stem rise in order to find your ideal positioning for a balance of pedalling comforting and handling response. Stem rise is however just one way of achieving your ideal cockpit positioning, with handlebar rise and number of spacers on the steerer tube etc. also being options.
Cross-country race stem
An XC race stem is typically long (100-120mm) and flat (zero-rise or a small degree of rise) to allow the rider achieve the stretched-out position that is optimum for racing. It may be made of carbon fibre to shed additional grams.
A typical trail stem is mid-length (60-80mm) with a moderate degree of rise (e.g. 6°) for a more upright riding position and quicker steering responses in high-speed, technical singletrack. A shorter stem also makes it easier for the rider to get his/her weight over the back wheel when descending. Most trail stems are made of lightweight, stiff and strong aluminium alloy.
Stems for Downhill (DH) racing are very short (40-50mm) for quickfire handling responses. Many DH stems are integrated (also known as ‘direct mount’) to match certain types of suspension forks, in that they bolt directly onto the top clamp of triple-clamp DH forks rather than onto the steerer tube. Again, most DH stems are made of aluminium alloy but carbon models are available at the top end of the market.
As with MTB stems, the right choice for your road bike will depend on a number of factors, the most important being the stem type, materials and dimensions.
The vast majority road bike stems on the market today are of the Aheadstem design (also known as ‘Aheadset stem’ or ‘threadless stem’) which bolts directly onto a fork’s steerer tube, the plug-in quill design being now only found on older or cheaper bikes. Some road bike stems may be designed with additional features such as adjustable rise or computer mounts, while others – designed for time trial and triathlon racing – may be integrated into single bar/stem units.
Aluminium alloy still by far the most common stem material in low- to mid-budget stems, but carbon fibre models are also a popular choice for racers and for anyone looking to shed weight from the their bike and add a little more comfort.
Stems are available to fit a range of steerer tube sizes with 1 1/8” being by far the most common (a shim can be use to make these fit older bikes with 1” steerers) A range of clamp sizes is available to fit the different handlebar diameters – 26/25.8mm are the traditional standard road sizes, but in recent years these have been largelysuperseded by the MTB-inspired oversize (OS) 31.8mm standard.
The most important consideration when choosing a road stem is the stem length, considered as a key factor in the overall fit of the bike. Riders looking to achieve a long, low and aerodynamic position on the bike – e.g. competitive racers – will opt for a longer (120mm+) stem for optimum ‘stretch’. However for the large numbers of casual riders for whom such a position is uncomfortable, a shorter stem allows for a more upright riding position.
Riders who don’t like to be too stretched on the bike may find that a stem 10mm shorter, or with a rise of a few degrees more, can result in a more upright riding position that may suit them better. Conversely, budding racers looking for pedalling efficiency and better aerodynamics may wish to add a few mm to stem length, or drop the cockpit down a few degrees. Experimentation will reveal what’s right for you.
Your BMX stem can have a significant effect on your bike’s handling primarily through influencing bar height and reach. You will need to have a stem that offers you the perfect balance of comfortable positioning and responsive handling – and you will need a stem that is strong enough to withstand the hard landings and tough punishment of street and park riding without failure.
Some of the common things to take into consideration are stem materials, type and dimensions.
• Materials: The vast majority of BMX stems are made from strong, stiff and lightweight aluminium alloy, with 6061 and 7075 being the two most common types. The latter is regarded as having a higher strength to weight ratio, but is more prone to corrosion. Most higher-end BMX stems will feature extensive CNC machining to shed weight without compromising strength.
• Design: There are two basic designs of BMX stem – front load (where the front plate is vertical, with horizontal bolts to clamp the bars) and top load (where the front plate is horizontal or almost so, and the bolts are vertical – basically where the bars go in from the top rather than from the front).
• Dimensions: As with all stems, BMX stem dimensions (length) will affect the handling characteristic of the bike.
The most important thing to bear in mind when choosing a new stem is the effect it will have on your bar position. And in order to understand this, you need to have some idea of what your preferred position is. If you prefer to ride with higher bars for more leverage over the back of the bike, a top load stem will help to achieve a slighter higher position. Conversely, if you like lower bars and a more ‘forward’ riding position go for a front load stem.
The length of your stem will also influence your overall reach on the bike. A shorter stem will give you a more upright position and sharper, more responsive handling but this may be at the expense of high-speed stability. A longer stem will be more stable at speed and will also allow for more leverage over the front wheel of the bike, important for doing certain tricks such as nose manuals. A longer stem may also be one way to get over the feeling of being ‘cramped’ on a bike with a shorter frame, and vice-versa.
Front load stems
Front load BMX stems feature a vertical front plate for bar installation, and result in a lower bar position.
Top load stems
Top load BMX stems feature a top plate that is removed to install the bars. These generally result in a higher bar position than front load stems.