Headset Spacers

BMX headset spacers: setting bar height to the millimetre

Between the top of the headset and the stem, the spacer stack fixes handlebar height and, indirectly, how much weight sits over the front wheel. Two millimetres either way changes the feel out of the gate; it is the simplest setting to test, and the cheapest.

Materials and thicknesses available

• CNC-machined 6061 or 7075 aluminium, colour anodised: the standard, tough and light
• Carbon: a few grams less and a finish that matches carbon bars and stems
• Common thicknesses of 1, 2, 2.5, 3, 5, 10, 15 and 20 mm, sold singly or as a kit
• Conical spacers and head tube covers, which make the joint with the headset

The standard: a 1"1/8 (28.6 mm) steerer

BMX Race uses a 1"1/8 fork steerer almost exclusively, 28.6 mm outside diameter, so every spacer in this category is bored to that size. Tapered frames and forks change nothing here: the lower bearing moves to 1.5", but the upper part of the steerer, the section carrying the spacers and the stem, stays 1"1/8. The only variation comes from the first piece in the stack, often a conical cover specific to the model of headset.

Building the stack without getting it wrong

The rule to remember: the top of the steerer must sit two to three millimetres below the top of the stem. Without that gap the top cap presses on the steerer instead of compressing the stack, and the headset will never take up. Conversely, if the stem sits above the steerer, the clamp tightens on nothing. Leftover spacers go above the stem: that is the clean way to keep the option of raising the bars later, before considering cutting the steerer.

Compatibility with stem and handlebars

A top load stem already gains height by its construction, a front load stays low: with an identical stack the two do not put the bar in the same place. Count total height as the sum of the spacer stack, the stem height and the bar rise. Watch carbon steerers too: a tall stack lengthens the lever arm on the steerer, and the stem must be tightened to the recommended torque.

Setting up by rider category

In Micro and Mini, start with a generous stack under the stem and remove it gradually as the rider grows: cheaper than buying a new bar every season. In Junior and Expert the stack shrinks and adjustment shifts to bar rise. In Pro, the stem often sits almost directly on the headset, with a tall bar providing the height.

The BMX RACING advice

Change one variable at a time — a single 5 mm spacer, for instance — and ride two sessions before drawing conclusions. If you are unsure, send us your current total cockpit height and the rider's height, and we will tell you which kit to order. Dispatched within 24 to 72 hours and you can spread the cost over 2 or 3 payments with Alma.