Know your enduro fork
AIR SPRING
Air-sprung forks support rider weight with a tuneable air cushion. Air pressure is added via a Schrader valve with a specific high-pressure shock pump to tune ride feel and adjust spring rate and support.
POSITIVE AND NEGATIVE SPRINGS
Within the air spring there are typically two separate elements balancing breakaway friction and small-bump sensitivity against support. A negative spring pushes back against the main positive spring, and either takes the form of a separate (automatically equalising) air chamber or a coil spring.
OFFSET
Fork rake or offset has evolved as an important design element. Most brands now offer two different offsets in each wheel size, ranging from 37mm up to 51mm. It’s complicated, but offset affects steering feel and tyre stabilising force, so shorter offsets offer more stability and a ride quality that emulates a slacker head angle, while still keeping the bike’s wheelbase shorter.
VOLUME SPACERS
These aren’t used on every fork, but tweaking the size of the (positive) air chamber by adding or removing volume spacers (or in-built systems to do the same) affects the spring curve. More spacers increases spring progression and helps prevent harsh bottom-outs, while fewer spacers (a larger internal volume) softens the end stroke. Öhlins uses a separate, third, ramp-up chamber to tune progressivity.
COMPRESSION DAMPING
Compression damping controls the rate at which displaced damper fluid is allowed to move during bump events. Low-speed controls low shaft-speed impacts like body weight shifts and rolling terrain, and highspeed damping absorbs harsh impacts like square bump faces and landings.
Forcing oil through ports or shim stacks generates damping resistance, with energy converted into heat.
EXTERNAL ADJUSTMENT
Dials on the top and bottom of the fork legs adjust parameters to tune support and control. Separate damping dials allow specific tuning options as to how much oil is allowed through ports and shims inside to absorb impacts, but more options also introduce more opportunities to mess up settings. Having said that, most suspension brands and bike companies now offer decent tuning guides according to body weight, and these will give you a good start point to work from.
CHASSIS
Stanchion diameter is an important metric for overall stiffness, with thicker fork legs generally adding weight. Bushing size and overlap, plus crown and brace construction also affect rigidity. Tapered steerer tubes are the norm – 1 1/8in to 1.5in at the base. Lower-leg assemblies use cast magnesium to save weight, and all forks here use a Boost 110mm axle spacing with quickrelease-style or Allen-key fixings.
REBOUND DAMPING
This is the damping circuit that controls the speed that the fork returns to sag after a bump event. Low-speed damping is the most common external adjustment. The damping circuit uses orifices and shim stacks to regulate the oil flow – ports can be opened or closed and shims made stiffer or softer. Some systems also act ‘dynamically’ and respond differently according to the shaft speeds (the speed the legs slide up or down).