29-inch MTB forks

How to choose a 29-inch MTB fork

The fork is the component that transforms an MTB's handling the most. But your choice is limited: the frame dictates the compatible travel, the steerer tube type and the axle standard. Start with these constraints, and the selection narrows down naturally.

Travel, framed by your bike

• 100 to 120 mm : cross-country and marathon.
• 130 to 150 mm : trail and all-mountain, the broadest segment of the range.
• 160 to 180 mm : enduro, with 36 to 38 mm stanchions.
• 180 mm and above with dual crown : downhill and bike park.
• Do not exceed the frame manufacturer's recommended travel by more than 10 to 20 mm: beyond that, the head angle slackens, the bottom bracket height rises and the frame warranty is voided.

Mounting dimensions to check

• Steerer tube : tapered 1"1/8 – 1"1/2 on modern MTBs, straight 1"1/8 on older models. The two are not interchangeable without changing the headset.
• Steerer tube length : to be cut to the correct length during assembly, taking spacers and stem into account.
• Wheel axle : 15x110 mm Boost today, 15x100 mm or 20x110 mm on older forks and for downhill.
• Brake calliper mount : Post Mount, with a maximum rotor size specified by the manufacturer.

Offset, the hidden geometry adjustment

On 29-inch bikes, two values coexist: 51 mm, the traditional standard, and 44 mm, introduced with modern geometries. A shorter offset increases trail and makes the bike more stable at high speeds and on steep terrain, at the expense of a little low-speed agility. The frame manufacturer specifies the offset the geometry was designed around: sticking to it is safer than trying to compensate for it.

Air or coil

• Air : precisely adjustable to the rider's weight, ramp-up tuneable with volume spacers (tokens), and much lighter. It is standard on everything except downhill.
• Coil : superior small-bump sensitivity and consistent behaviour whatever the temperature. However, you need the right spring rate, and there is a weight penalty.

The damper, what explains the price difference

For the same amount of travel, what sets an entry-level fork apart from a high-end fork is the hydraulic damper cartridge: Motion Control, Charger, Charger 3, Grip or Grip2 depending on the brand and level. It determines the number of available adjustments and, above all, the quality of high-speed compression damping over sharp impacts. On a mid-range fork, upgrading the damper is often cheaper than replacing the entire fork.

To find out more: How to choose an MTB fork

See also: MTB rear shocks · Fork dampers and spare parts · MTB front wheel axles