Our round-up of the best mountain bike stems in both 31.8mm and 35mm clamp sizes
Mountain bike stems are an important factor when it comes to the control of your mountain bike, but which one should you choose?
It is possible to measure differences in weight between models of stem, and if you’re really in tune with your bike, there are subtle differences in stiffness to evaluate. It’s not easy, but keep all the components the same, and ride the same trail over and over again with different stems, and the nuances begin to become apparent.
Equally, get up close and it becomes obvious which stems are really well thought-out and have the best combination of construction, material choice, geometry and even the fasteners — something that’s important on a component that needs to handle big forces.
Know your mountain bike stems
First job is to work out what stems will actually fit on to your bike. You’ll need to know your forks steerer size and handlebar diameter.
Your fork steerer is almost certainly going to be the usual 1-1/8th” diameter (the other option is 1.5in but it’s very rare these days). Use a tape measure to measure the diameter of your headset top cap and you’ll instantly see if it’s not for a 1-1/8th” fork steerer fork.
Handlebar and stem clamp diameter
Handlebar diameter is a bit less straightforward. Modern era mountain bikes will either have the more-common 31.8mm diameter handlebars or the newer 35mm diameter handlebars. Older bikes may still be sporting skinny 25.4mm diameter handlebars. Again you can use a tape measure to quickly assess what diameter your bike has. You need to get the same stem clamp diameter as your handlebar diameter ie. 31.8mm clamp stem for a 31.8mm diameter handlebar.
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. Cheaper bolts round off more easily, and anodised bolts can lose colour. Stainless steel or titanium bolts maintain looks and are more resistant to corrosion.
The vertical real estate the stem demands on the steerer tube. It can be an issue if your fork steerer is too short, and can also relate to the handlebar height achievable and overall stiffness of the stem.
30mm is about as short as you can go on a standard stem. There are some newer designs – such as Pacenti PDent – that enable even shorter stems but they require specially designed handlebars. Stubby stems are something we’re big advocates of here, since reducing the distance the bar extends beyond the steerer will sharpen the steering response, provided your bike is roomy enough. We recommend fitting the shortest stem you can get away with but bear in mind that some older bikes with short top tubes may end up with cramped reach and compromised bike control, in which case we wouldn’t go shorter than 50mm and we’d also think about fitting wider handlebars as a means of widening your reach and improving balance, control and comfort.
Zero gap fastening
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.
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.
CNC v 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.
Syntace Megaforce 2
mbr review: “With a low stack height, six-degree rise (that can be flipped), and 10mm length increments, there’s a range of bar positions for all frame sizes. In this respect, Syntace really has ticked all the boxes. It’s hard to believe how rock-solid this stem is on the bike. The steering precision, sensation of control, and lack of vibration in the hands feels perfect. The Megaforce 2 is mega expensive, but comes with a 10-year guarantee and, if money were no object, would be our first choice.”
mbr review: “You never need worry about stiffness with Truvativ stems and, true to type, the Descendant feels like it’s hewn from girders. Basically, you lean on the bars and the bike turns with a solid, near instantaneous response with no discernible twisting or rotating between the grips. It’s not the lightest, but it’s still perfectly acceptable for trail riding, or even XC, and the price is excellent considering the quality.”
mbr review: “KS has opted for a more unusual steerer clamp, with the one-sided wraparound design putting bolts out of harm’s way to prevent knees from knocking against sharp edges. We’ve had mixed experiences in the past with similar offset designs, but this one worked fine. The Ether’s ride feel is great, with good stiffness and connection to the bars, without being jarring and transferring too many vibrations. For a first effort this stem is very good, and if 50mm is short enough, also offers fantastic value for money.”
Race Face Ride
mbr review: “The Ride range is aimed more at general cross country riders and light trail use, rather than the more heavy duty stems in Race Face’s range. But that aside, we had no issues with it at any point during our test period. We rarely had to think about it, and it happily kept our bars held tight and pointing in the right direction; all without a single complaint. If you’re after a top performing, no-fuss stem then look no further! The Race Face Ride really does fit the bill for a stem perfect for general trail duties. And at under £25 it’s a total steal.”
mbr review: “The Crossfire cannot be faulted in performance. Very little flex could be perceived during riding even when hauling on the bars. Setting up was simple and despite running all the bolts dry (sorry!) and riding it in desert conditions it never developed a creak. There are plenty of colours to choose from and it has a style suited to any bike. There are slightly lighter stems out there but the Crossfire is hard to beat on every other factor.”
Pacenti PDent system
mbr review: “The PDent design works by allowing the bar to overlap into the space taken up by the fork steerer and, with regular stems bottoming out at around 30-31mm, this allows Pacenti to run ultra-stubby stem lengths. In terms of pure function, the PDent bar/stem combo is stiff and comfortable with an overall quality that’s reflected in the top-end price. It doesn’t suit shorter bikes with steeper head angles, but on modern trail bikes with slacker geometry, it ultimately requires less effort to control the bike, particularly in the tight stuff. PDent’s elegant design brings something truly unique to the whole steering geometry debate, and we rate it very highly.”
The best mountain bike stems: verdict
All five of these chosen stems are worthy of your money.
Our favourite, money-no-object, stem for 31.8mm bars is the Syntace Megaforce 2, the main issue might be tracking one down. The same goes for the rare but excellent KS Ether.
The three stems from more mainstream brands are the logical all-round choice: the sorted Funn Crossfire, the solid Truvativ Descendant and the bargain Race Face Ride.
If you want a whole new cockpit for a modern long-reach bike then the Pacenti PDent system really is excellent.