Road forks

How to choose a road bike fork

You might replace a road bike fork after a crash, when switching from rim brakes to disc brakes, or as part of a build from a bare frame. Three measurements determine whether it will fit your bike, and none can be guessed.

The steerer

• Straight 1"1/8 (28.6 mm) : the traditional size, still the most common on rim-brake frames.
• Straight 1"1/4 (31.8 mm) : on some recent frames.
• Tapered : narrow at the top, wide at the bottom (usually 1"1/8 – 1.5"). It is standard on disc-brake frames because braking places greater loads on the front end.
• A tapered steerer will not fit a straight head tube, or vice versa. The SHIS code for your frame provides the answer: check it before buying.

Fork offset (rake)

It is how far forward the wheel axle sits relative to the steering axis, between 40 and 50 mm in this range. Combined with the frame’s head tube angle, it determines the trail, and therefore the handling: more offset makes the steering more responsive and the bike’s line easier to correct; less offset improves stability at high speed. Match the offset of the original fork — a 5 mm difference changes how the bike handles, and the frame manufacturer designed its geometry around a specific value.

The braking system

A fork is designed for one or the other. A disc-brake fork has a Flat Mount or Post Mount fitting and structural reinforcement on the left side; a rim-brake fork has a drilled fork crown. You cannot convert one into the other — and changing the front brake type also requires a compatible wheel and brake lever.

Tyre clearance

Check the maximum permitted width, as specified by the manufacturer. Recent road forks generally accommodate 30 to 34 mm tyres, while all-road models allow more. Always allow a few millimetres of clearance on each side: a tyre fitted to a wide rim measures wider than its stated width, and mud needs room to clear.

Cutting the steerer

A new fork comes with a long steerer, which must be cut to the desired height. This is an irreversible : first fit it with the full stack of spacers, ride for a few weeks, then cut it. And with a carbon steerer, only a expander plug is suitable — never a star nut, which can split the tube.

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

See also: Road bike headsets and bearings · Top caps and expanders · Road bike framesets