Road headsets and bearings

How to choose a headset

This is the range where it’s easiest to make a mistake, because the right choice depends neither on the bike brand nor on the type of riding: it depends on the exact shape of the frame’s head tube. There is a standardised code for describing it, and that’s what you need to check.

Understanding the SHIS code

Each specification has two parts, upper then lower, such as ZS44/ZS56 or IS42/IS52. The two letters tell you how the bearing fits into the frame; the number gives the housing diameter in millimetres. A frame can perfectly well be integrated at the top and semi-integrated at the bottom : read the two parts separately.

• IS (Integrated) : the bearing sits directly in the machined head tube, without a cup. The most common type on recent carbon frames.
• ZS (Zero Stack, semi-integrated) : a cup is pressed into the head tube, with the bearing sitting inside it.
• EC (External Cup) : the cup sits outside the head tube. This classic arrangement is still common on steel and aluminium frames.
• The threaded headsets are still found on older frames with threaded forks.

Steerer diameter

• 1" (25.4 mm) : older frames.
• 1"1/8 (28.6 mm) : the long-established standard, still very common.
• 1"1/4 (31.8 mm) and 1.5" (38.1 mm) : at the base of the steerer on tapered, which are narrow at the top and wider at the bottom — hence mixed specifications such as 1"1/8 – 1.5".
• A tapered fork will not fit a straight head tube, and vice versa.

Individual bearings

You rarely need to replace a complete headset: it’s the bearings that wear out. Order them by diameter and contact angle — a 41.8 mm with 45/45° contact angles is the most common size at the top of the headset. The diameter is often etched on the edge of the old bearing. The stainless steel hold up much better in winter conditions.

Headset cups and crown races

The crown race (crown race) is pressed onto the base of the steerer and provides the contact surface for the lower bearing. Choose it according to the diameter at the base of the steerer — 30 mm in ZS44, 40 mm for IS52 — and it often needs replacing on its own after a fork change. The cups are also sold individually.

Internal-routing headsets

The DCR (Deda), ACR (FSA), ID (Vision) route cables and hoses through the headset. They require a matching top cover, spacers and often a stem from the same system. You’ll also find thin adjustment shims from 0.25 to 1 mm, used to take up any remaining play — a part that’s hard to find elsewhere but essential for assembly.

Diagnosing the problem

To check for headset wear, hold the front wheel still: if the bike rocks back and forth with a clunk you can feel through your hands, the preload or bearings are at fault. A notch at the centre when you turn the handlebars means the bearings are worn — adjustment won’t fix them; they need replacing.

To find out more: How to choose a road bike fork

See also: Top caps and expanders · Headset spacers · Road bearings