A buyer's guide to stems

Looking to change the stock option on your bike? Find out what to look out to find the perfect fit.

How to choose your bike stem

In the ratio of simplicity to significance, no other bicycle component comes close to the importance of a bike stem. This of course means picking the right one has a crucial effect on your riding experience.

The humble bike stem does one simple job: it connects your steerer tube – and, therefore your fork and front wheel to your handlebar, and it's a crucial part of your bike.

More than providing just the basic mechanics of effective steering and control, the stem’s height and length also have a massive effect on your position and comfort in the saddle.

So choosing and fitting the correct stem is an important business, but it’s not complicated – and we’re here to help.

Why change stem?

The obvious reason to change your stem is that your existing stem got damaged and you need a straight replacement. In fact, due to their simplicity and strength, stem failures are extremely rare.

More likely, you’ll want to change your stem for either better comfort or control. When it comes to positioning, stem length is vital. A stem that's too long will have you stretched out too far and reaching for the handlebar. Too short a stem will have you too hunched or cramped on the bike. Height is important, too, with some people preferring to sit more upright in the saddle, while others are eager to get low and streamlined.

Stem length can also affect control. For example, mountain bikers who require instant, direct control like to fit ultra-short ‘stubby’ stems to feel more connected to the front wheel. At the other end of the scale, leisurely road riders might be happy with a longer stem for a more relaxed ride.

Quill or threadless

Before we go any further into looking at your replacement stem options, we need to explain the two main stem systems.

The first and oldest is the quill stem, which is still found on less expensive and more traditional bikes. A quill stem is an L-shaped design, one end of which slides inside the steerer tube and is secured in place by a wedge or expander, which you tighten via a top bolt. The other end is used to attach the handlebar via a clamp or faceplate.

The vast majority of high-quality modern bikes, though, use an aheadset stem, which is a far simpler design than a quill. An aheadset stem is just a metal tube with a vertical clamp at one end to tighten around the steerer tube and a faceplate at the front for the handlebar.

Most people tend to stay with the same system that came with their bike, although you can convert from quill to aheadset with products such as our BTwin aheadset converter.

Quill stems

One of the advantages of quill stems is that you can adjust their height quite easily by inserting more or less stem into the steerer tube before tightening – a bit like the way you would adjust the saddle height. Just pay attention to the minimum insertion marker and make sure a safe amount of stem is left inside the steerer!

One of the biggest negatives of quill stems, especially nowadays, is that replacements can be hard to find. We are helping to overcome this with a great range of quill stems, such as our quill stem for 1" steerer tubes or our quill stem for 1 1/8in steerers. Like most quill stems, both of these will fit only 25.4mm handlebars.

For added practicality and to get your handlebar height even more finely tuned, you could use an adjustable version, such as our BTwin Adjustable quill stem. This fits 1 1/8in steerers and you can alter the stem height and angle to get your position just right.

Lastly, in our quill stem range, we have some specialist replacement options. Our range of 2-in-1 stem and bar combos are perfect for children’s bikes, while our wide range of folding quill stems, such as the Workshop Tilt 500E stem is great for specific commuter bike repairs.

Threadless stems

Threadless stems, sometimes called Ahead or Aheadset stems, are simpler than quill stems and simply slide into position on the steerer tube. You can adjust their height by fitting spacer rings underneath and secure them in place by tightening the bolts on the collar.

Such simplicity means swapping different threadless stems in and out is super easy: unbolt the faceplate to detach the handlebar; untighten and remove the old stem; fit a new one and tighten its bolts; then refit the handlebar.

That also means you can go stem buying without any major worries except for one important detail: make sure the faceplate clamp is compatible with your handlebar size – normally either 25.4mm (non-oversize) or 31.8mm (oversize). One thing to be aware of is that many stems, handlebars, and steerer tubes come with a recommended torque setting for tightening – usually around 6 N m. Over-tightening a stem onto a carbon steerer is not a good idea. Our BTwin 500 Torque Wrench can help you here – it’s an ideal tool to have, particularly if you ride a lightweight road bike.

Road and hybrid threadless stems, such as the BTwin High-Performance road bike stem, are straightforward items and typically come in a choice of lengths from about 60mm up to 130mm. Mountain bike stems tend to be chunkier and shorter, even going as short as our 35mm BTwin oversize stem.

Whichever threadless stem you choose, be aware that it probably won’t be perfectly perpendicular to the steerer tube. Most stems feature a modest angle or rise, and some are designed so that you can flip them to alter the position of your handlebar. If you want to get that angle even more honed you could use our BTwin non-oversize adjustable threadless stem for 25.4mm handlebars or our BTwin oversize adjustable threadless stem for 31.8mm handlebars.

Vital stem information

Before you buy a new stem there are a couple of key pieces of information you need to know, aside from whether it is a quill or a threadless design.

First, what size is your bike’s steerer tube? The most common sizes are 1in and usually older bikes that take quill stems; 1 1/8in. The most common size; and 1 1/2in – is found on some gravity mountain bikes. A few bikes have a 1 1/4in steerer tube. All of our stems are either 1in or 1 1/4 in. You’ll also need to know your steerer tube size if you want to fit spacers as they’ll need to be the right diameter.

Second, what diameter are your handlebars? This is the diameter of the section of tube that the stem will be clamping to. Handlebars come in two main diameters: 25.4mm and 31.8mm, the latter are usually called oversized bars. Your stem needs to be the appropriate size for your bars.

And while it’s true that most handlebars come in either 25.4mm or 31.8mm sizes, there is another option: 22.2mm BMX handlebars. Naturally, we have a BTwin threadless stem for that, too.

It might take a little bit of deliberating before you know exactly what stem length and height will suit you best, but once you have that idea in mind, we have all the kit to make it a reality – even for a hesitant home mechanic!