Best mountain bike stems: improve your fit and steering

Read our full test review of the Funn Crossfire stem

DMR Defy 35

A rare short stem with a low stack height

Weight: 174g | Colours: Black, silver | Lengths: 35mm, 50mm | Clamps: 31.8mm, 35mm | Stack height: 28mm | Rating: 9/10

Pros: Super secure. Raises your front end whilst having low stack height. Good price.

Cons: Typically robust weight. Square edge aesthetic may not suit some bikes.

The Defy stem is designed to be a perfect match (aesthetically speaking) with DMR’s own Wingbar, but has a few features that make it a very attractive package for any cockpit combination. Twin face plate clamps use a Top-Close clamp design where you tighten both top bolts until they touch the stem body before tightening the lower bolts, ensuring simple, safe and effective bar installation. The two-piece design does make things slightly fiddlier during installation (there are two face plates to drop on the floor, rather than one) but once fitted they do look very modern.

The shape tapers down to steerer clamp to create one of the lowest stack heights on the market. At just 28mm this makes the Defy perfect if you want to play a little more with stem/bar height (and thus you bike’s effective reach distance)  or have a fork with a less than ideal steerer length – or you’ve cut your steerer too short (we’ve all been there). Of course, you can simply add more spacers if you don’t fall into that camp. One of the best – and pretty unique – aspects of the Defy stem is that its stubby 35mm length also packs in a bit of rise (at least 5mm), which is really handy if you want to elevate your bar height without resorting to stem spacers or a new handlebar. Sure, this stem is not going to win any weight awards, but it’s crisply made, stiff as heck, offers a rare bit of rise for a dinky stem and looks stylish in the process.

Read our full test review of the DMR Defy 35 stem

Deity Copperhead

Great low-stack option

Weight: 142g | Colours: Eight | Lengths: 35 or 50mm | Clamps: 31.8mm, 35mm | Stack height: 33mm | Rating: 9/10

Pros: Great attention to detail

Cons: On the expensive side

What does “low-stack” mean you ask? It’s how much vertical space the stem takes up around your fork steerer. If a stem has low-stack height it can be a lifesaver in situations where the fork steerer has been trimmed down and there isn’t much real estate to fit a stem on there. In this regard it’s similar to the DMR Defy stem (above), but without the rise. Although the Copperhead is CNC’d from 6061 T6 aluminium and not cold-forged (which tends to be the construction method that results in the stiffest stems) it is nevertheless still impressively stiff. We attribute this stiffness to the relatively broad face plate with its 55mm width.

It’s not the cheapest option, but there is a level of quality and thought gone into the Copperhead stem that is well worth the money. For example, the bolts have deep-set recesses for Allen keys and this really does help prevent the bolts being rounded or otherwise damaged by ropey multi-tools or inattentive and rushed wrenching (we’ve all been there).

Read our full test review of the Deity Copperhead

Burgtec Enduro MK3

Available in ‘Goldilocks’ 42.5mm length

Weight: 155g | Colours: Nine | Lengths: 35, 42.5 and 50mm | Clamps: 31.8mm, 35mm | Stack height: N/A | Rating: 8/10

Pros: Unique length offering

Cons: Split front clamps are fiddly to install

Taking our reviewer’s hat off, there really isn’t anything to complain about with the latest Burgtec Enduro stem. Yes, the two-piece front clamp design is fiddly but, for heaven’s sake, how often do you actually install/remove a stem in the real world? For this, the brand’s third version of its Enduro stem, Burgtec has switched to a cold-forged construction method. This has really upped the stiffness quotient of the stem compared to the previous Enduro MK2 stem. The bar clamping width has also been increased. So too has the steerer clamp depth, which has resulted in a greater stack height, so this may no longer be a viable option for riders with minimal fork steerers.

Perhaps the main USP of the Burgtec Enduro MK3 is that it is available in a 42.5mm length. It may sound daft and all rather Princess-and-the-pea, but a couple of mm here and there with stems can certainly be felt by experienced riders. So if you’ve tried 40mm and 45mm stems and not quite gelled with them, here’s the (42.5mm length) stem for you!

Read our full test review of the Burgtec Enduro MK3

Renthal Apex

Renthal’s comprehensive size range has you covered

Weight: 110g | Colours: Black & gold | Lengths: 31, 33, 40, 50, 60mm | Clamps: 31.8mm, 35mm | Stack height: 40mm | Rating: 8/10

Pros: All of the lengths

Cons: Not the absolute stiffest

The Renthal Apex uses a twin face plate design, like many other stems. But the clamps here are 240° wrap-around affairs that help support the bar, but you’ll need to careful when installing the bar to avoid scratching it or ending up with a cockeyed alignment. It’s also a really good idea to use a torque wrench to ensure the bolts are done up just-so.

It’s also noteworthy for offering a bit of rise (approximately 6°), which is a welcome and all-too-rare feature on sub-50mm long stems. Secondly, as with Renthal’s handlebars, there is a tiny but noticeable flex apparent when really loading up the front end. Which could be an advantage or a disadvantage depending on your position. If you’re currently feeling like your 35mm standard front end is overly harsh, Renthal’s Apex stem could be the answer to your prayers.

Read our full test review of the Renthal Apex

Hope AM FR

Typically no-nonsense UK-made stem

Weight: 133g | Colours: Red, orange, blue, purple, gun smoke, black | Lengths: 32 and 50mm | Clamps: 31.8mm and 35mm | Stack height: N/A | Rating: 8/10

Pros: Hope’s signature CNC aesthetic

Cons: A bit flexier than some

Cutting straight to the chase, the pinstripe and crisp CNC vibe is either your thang or it isn’t. Truth be told, even if it is your thang, it may just simply not suit your bike. The swoopy, candy colour, gloss finish of certain carbon frames doesn’t lend itself to being paired with a chunk of lasered alloy.

For those of you lucky enough to have taste and a bike that does fit the bill, you’ll be served well by the Hope AM FR stem. Much like its fellow Brit brand Renthal, Hope’s stem is not the absolute stiffest option out there, if that’s what you prize in front end feel. The use of stainless steel bolts is a nice touch, as is the modern use of a zero-gap faceplate design. It all lends the AM FR stem the typical Hope vibe that will simply float a lot of people’s boats.

Read our full test review of the Hope AM FR

Stubby stems are now the norm, with anything longer than 50mm rarely seen

How we tested the best mountain bike stems

With plenty of stems to evaluate, we spread them between a mix of test bikes and trusted testers to put the miles in and assess long-term durability. If we have an outlier in terms of stiffness, we then go on to test it back-to-back against a benchmark model on the same bike on the same track to put the performance into context. All bolts were greased as necessary, and tightened to the recommended torque settings using a torque wrench.

What to look for with the best mountain bike stems

A mountain bike stem connects the handlebars to the fork steerer. They come in different lengths and different rises, allowing you to tune your cockpit position Modern stems are typically under 70mm in length, with 40mm and 50mm being the most popular measurements. Generally there are twin bolts to clamp around the steerer tube, and four bolts at the face plate to attach the handlebar.

First job is to work out what stems will actually fit on to your bike. You’ll need to know your fork’s steerer size and handlebar diameter.

Your fork steerer is almost certainly going to be the usual 1-1/8in diameter (the other option is 1.5in but it’s very rare these days). Use a tape measure or vernier calipers to measure the diameter of your headset top cap and you’ll instantly see if it’s not for a 1-1/8in fork steerer fork. You’ll also need to check the handlebar diameter. This will either be 31.8mm or 35mm on modern mountain bikes. Make sure you measure the area at the clamp, not the ends at the grips.

35mm stems can bring a stiffness boost, if that’s what you’re after

What’s best: 31.8mm or 35mm diameter?

Unfortunately there’s no simple answer here, as it depends on the bike, the rider and the terrain, as well as what you are trying to achieve. If you’re 95kg and riding a powerful e-bike on bike park trails and enduro tracks, the answer is probably going to be 35mm. But for most people, 31.8mm is going to be fine, and indeed preferable in terms of harshness. It’s rare we ride a 31.8mm bar/stem at 780mm wide and think it’s too flexy.

Thankfully the days of mile-long stems are behind us

What length do I need? Is shorter better?

Again the answer is not a simple one, but if we were to look at the average stem length across the mountain bike market in 2023, the answer would probably be 40mm. Then, if you want a snappier steering or feel like you have too much weight over the front wheel, you could go shorter. Conversely, if you can’t get enough weight over the front, or feel like the bike is too cramped, and have tried playing with the bar height and bar roll, then a longer stem might be worth trying. In this case, we probably wouldn’t go longer than 50mm. For more ways to tune your weight balance and your bike’s handling, read this article.

Neat spacers and clamp on Canyon’s G5 stem and bars, along with torque settings for the bolts

What size bolts are used on stems?

4mm and 5mm Allen bolts are most common on mtb stems, with the heavier, larger-diameter bolts typically enabling higher torques and subsequent clamping forces. Some stems come with T25 Torx bolts, which are less prone to rounding off.

DMR’s Defy stem has a really low stack height that’s perfect. for stubby steerer tubes

What is stack height?

This refers to the vertical real estate the stem demands on the steerer tube. In other words, it’s the height of the steerer clamp on the stem. This is important if your fork steerer is too short, and can also relate to the handlebar height achievable and overall stiffness of the stem.

Modern gap-less designs are excellent

What is meant by a zero-gap clamp?

More and more stems are now featuring a zero-gap bar clamp design, whereby one pair of clamp bolts fasten fully, and the remaining bolts tighten to lock the bar in place. The design prevents uneven tensioning and reduces the number of bolts you need to fix to a precise torque setting, making set-up easier.

A stem with a rise can be useful if you want a higher bar height, but don’t want too many spacers under the stem or a higher-rise bar

What is stem rise, and is it important?

Rise is the difference in height between the clamps. Most stems are zero-rise, which means if you flip them over they don’t change the bar height. However, a six-degree rise stem allows you to effect a plus or minus six-degree change in bar height by simply turning the stem upside down. It’s not critical, as cockpit height can be adjusted by moving the stem on the steerer, or changing the handlebars.

Most stems are cold-forged with some CNC finishing

What’s better? CNC machined or cold forged?

Stems are either 3D forged or CNC machined from an aluminium billet (basically a chunk of metal). Forging sees aluminium squeezed under immense pressures into (close to) the stem’s final shape. The technique compresses the material around high stress areas, and it’s argued produces a stiffer product with a better-aligned, denser grain structure. The initial forging cost is expensive and the finish is sometimes less angular, although you do see stems that are forged initially and then tidied up on a CNC machine.