Choosing a Bike Headset External or Semi-Internal

Headset selection is one of the few component decisions where preference does not come into it. The head tube has already made the choice, and the only question is whether you have read it correctly.

Look at the head tube first

An external cup headset needs a plain head tube, faced and reamed. A semi-internal headset needs a head tube bored and machined to accept a 44 mm cup inside it. You cannot fit a semi-internal headset to a plain head tube, and fitting an external headset to a frame designed for internal cups wastes the design intent and raises the front end.

The stack height difference is large

Our external headset VH-01 carries a 33 mm stack, made of 21 mm above and 12 mm below. The semi-internal headset carries 9.5 mm, made of 7.5 mm above and 2 mm below. That is a 23.5 mm difference, which is more than most riders' entire spacer stack. It changes the steerer length you cut and the bar height you end up with.

Weight is the smaller difference

110 grams against 98 grams. Twelve grams is not the reason to choose one over the other. Anyone telling you to pick a headset on weight is selling, not advising.

What they share

Both are fully CNC machined from 6061AL-T6 rather than cast, both run two sealed cartridge bearings rather than loose balls, both take a 28.6 mm steerer, and both are available anodised in red, gold, titanium, blue and black. The sealed cartridge point matters most: a loose ball headset needs stripping and regreasing every season, and a cartridge headset does not.

Do not forget the star nut

Both headsets are preloaded by a top cap bolt pulling against a star nut in the steerer. Our AL7075 star nut weighs 7 grams and fits steerers from 22.8 mm to 25.2 mm internal diameter. In a carbon steerer do not use a star nut at all - use an expander plug.

Measure twice before cutting

Steerer length is the one irreversible step in a headset fit. Add the stack height, the head tube length, any spacers and the stem clamp height, then leave 3 mm of steerer below the top of the stem so the top cap can still preload the stack.