Headset spacers – small rings of aluminium or carbon fibre that slide on to your forks’ steerer tube – are another of those small, inexpensive but crucial bicycle components that play a key role in determining how well your bike fits you and consequently how comfortable and efficient your on-bike position is.
Put simply, headset spacers enable you to easily adjust the height of your handlebars, which is an essential element of bike fit for BMX, MTB and road riders. In the particular case of the latter (road cycling), the correct bar height is key for comfort and performance. Racing cyclists, for example, will typically opt for a low bar height (where the handlebars are lower than the saddle) to enable them obtain the ‘flat back’ racing position for optimum aerodynamic efficiency. Higher handlebars (typically level with or even higher than the saddle height) are however viewed as being more comfortable for long-distance cycling and beginner to mid-level riders, who may find the ‘flat back’ position difficult to attain and/or sustain.
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When choosing headset spacers the three most important things to consider are diameter, height and materials.
Headset spacers can be used with both threaded and threadless headsets/steerer tubes (see our buyers’ guide to headsets for a more in-depth explanation), with the latter type (also called an ‘Aheadset’) being commonplace on modern bikes.
When choosing headset spacers the most important thing is to match the size to the diameter of the fork steerer tube. The most common steerer diameters are 1”,1 1/8”, 1.5” and tapered.
• 1”: Typically, the older-style threaded headsets will be found on bikes with a 1” threaded fork steerer (although 1” threadless headsets are available).
• 1 1/8”: The standard fork steerer diameter for most BMX, MTB and road bikes is 1 1/8”.
• 1.5”: Some modern gravity bikes or speciality road bikes use 1.5” fork steerers and correspondingly larger head tubes for extra strength and front-end stiffness.
• Tapered: A new trend has emerged in road and MTB for tapered head tubes with a steerer diameter of 1.5” at the bottom and 1 1/8” at the top. These will use ‘normal’ 1 1/8” headset spacers.
Headset spacers are generally available in a variety of heights enabling you to fine-tune your bar position through use of a combination of multiple spacers. Using different height spacers allows you to adjust your stack height, the term used to describe the total height of the headset components (including spacers) that are outside your frame. Spacers will typically be sold in a pack with a selection of different heights e.g. 3mm, 5mm, 10mm and 20mm.
In terms of materials, headset spacers are generally made from lightweight aluminium alloy or carbon fibre. The former are generally precision-engineered to exacting tolerances to ensure even distribution of force and perfect alignment between the bottom of your stem and the top of the headset. Although alloy spacers are already lightweight, some riders keen on shaving every extra gram opt for carbon fibre as being even lighter. That said, the differences are minimal and some riders who exert considerable force on their components – e.g. BMX and MTB gravity riders – regard carbon as having inferior performance under compression when compared to high-grade aluminium.
Replacing or adjusting headset spacers.
Replacing or adjusting headset spacers is a relatively easy job. For threadless headsets/steerer tubes (more than likely the kind you have) simply loosen the pinch bolts that attach the stem to the steerer (using an appropriate Allen key) as well as the bolt in the centre of the top cap which tensions the star-fangled nut (SFN) inside the steerer tube. You can remove the top cap and stem/bars, and add or remove spacers as necessary to adjust the stem height. Once you’re happy, replace all parts and tighten (paying attention to the recommended torque). You can adjust and re-adjust your headset spacers to your heart’s content until you achieve a bar height that is comfortable for you – many road riders, for example, may find that as their riding progresses they may wish to periodically lower their bar height, while BMX and MTB riders may be more likely to find a height and a fit that’s comfortable for them, and stick with it.
NOTE: Headset spacers can be positioned both above and below the stem (for aesthetic reasons some riders prefer to have no spacers above), but it’s important to use enough spacers so that the lip of the top spacer sits a little (1-2mm) above the top of the steerer tube so everything is compressed together when the SFN is retightened. If you don’t have enough spacers to enable this clearance you will need more – or alternatively you can cut the steerer tube to size. This is a precision job though that may require specialist tools such as a vice/pipe cutters or in the case of carbon steerer tubes a special saw blade so if you’re not confident or equipped it might be best left to a mechanic.
Adjusting bar height on the older type of threaded headset is a little different, as any spacers are positioned between the top race and the locknut. However these headsets are often used in conjunction with a ‘quill’ stem, where a long bolt runs down the centre of the steerer tube and is connected to an expanding wedge. If you have one of these stems, loosening the bolt releases the wedge and enables you to move the stem up or down, so you may not even need headset spacers.
• Alloy spacers
Precision-engineered from high-grade aluminium alloy, these offer exacting tolerances and good performance under compression for a minor weight penalty.
• Carbon spacers
The lightest of the light, carbon spacers are the choice for weight-conscious riders keen to save every gram possible.
• Conical spacers
Conical in shape as opposed to the classical ‘ring’ design, these are often found on road or MTB bikes with integrated or internal (semi-integrated) headsets, where the headset top bearing sits inside and flush with the top of the head tube. They are mainly an aesthetic consideration offering a clean visual line and neat junction between head tube and steerer, and are often used in conjunction with ‘normal’ spacers which sit on top (see our buyers’ guide to headsets for more on integrated/internal headsets).