Mountain bike suspension forks vary massively when it comes to travel, shock damping ability, stiffness and weight – and that’s before we even get onto price, which can run into hundreds or even thousands of pounds.
That means it’s important to know what to look for when buying a new fork.
What to think about when buying a fork
Mountain biking is a very diverse sport and there are suspension forks designed for every type of bike: cross-country bikes generally offer 80 to 120mm of suspension travel, trail bikes range from 120 to 140mm, enduro and all-mountain bikes have between 150 to 170mm, and gravity/downhill rigs go from 180 to 210mm.
The first question is, how much travel will work best for you? All other things being equal, the further your fork can move, the more smoothly it can absorb impacts. But longer-legged forks have to be heavier to cope with the extra leverage and bigger impacts.
An extra 10mm of travel will tip head and seat angles back by roughly one degree, which makes steering slower and more stable. Running too long a fork can also overstress your frame and void the warranty, so always check what the recommended travel is for your bike before upgrading. In general, it’s best to replace your existing suspension fork with one with that offers a similar amount of suspension.
That said, many forks have travel-adjust features. These either let you drop the travel in small steps to tweak the bike’s geometry and handling to taste, or crush it down dramatically to give a shorter, stiffer fork.
The next question is budget. Sadly, there aren’t many budget forks that deliver a smooth suspension stroke and stiff, screw-through axle structure without weighing a ton. Damping circuits are also simpler on cheaper models, which means less control in high impact or multiple-hit situations.
There’s a clear progression in standards of control and consistency up to around £400 / US$670, but after that the waters get a lot murkier and it’s time to be honest about yourself and your riding. The overall performance and reliability of basic forks has definitely improved though.
The more travel you have, the harder it is to control – which makes damping control paramount. You should at least get adjustable rebound damping so the fork returns smoothly to its natural ride height, rather than bouncing back up with a clang. More advanced forks also have compression damping to help the spring slow down and absorb the impacts.
Top-end forks split compression damping into two separate circuits – low speed for controlling loads such as braking, cornering or movement under pedalling, or high speed for controlling sudden large loads such as square-edged rocks or landings. Having lots of damping adjustment is only useful if you know what you’re doing with it and have the time to tune it correctly though, so be honest rather than pretending that you’ll become a pro suspension fork tuner overnight.
If you’re likely to plug the fork in, do the minimum setup tweaking and then ride it day in, day out without servicing it then you’ll want a simple but totally reliable unit. If you clean and care as much as you ride, then you can get something a bit more needy. If you’re a real fork fettler who’ll spend hours with a shock pump and a safe cracker’s level of dial turning dexterity to find your suspension sweet spot then it’s worth having a full range of adjustments to exploit.
As well as travel and tuning, you need to think about how much strength you really need, or you’ll just be carrying extra weight you’ll never use. Light, tight forks will suit climbers and other cross-country riders, while super-plush traction Hoovers are worth the extra weight for progressive envelope pushers. Getting the right balance is really important. Fork strength is hard to gauge though, so go by the manufacturer’s recommendations.
Most modern suspension forks use tapered steerer tubes which measure 1.5in at the crown and 1.125in at the stem.
There are also three different axle standards to consider: 9mm quick-releases can still be found on some lower end forks, though the majority of cross-country and trail forks now use 15mm thru-axles. Longer travel suspensions forks for enduro and downhill frequently use 20mm thru-axles.
Anatomy of a fork
- Crown – Most mountain bike forks are single-crown models, with just one cross brace (the crown) holding the two legs together below the head tube of your frame. Long-travel downhill bikes often have double-crown forks, with a second cross brace at the top of the head tube for added stiffness. Materials vary and some crowns are hollow for increased stiffness-to-weight performance.
- Steerer tube – This is the upper tube of the fork that slides into the head tube. Most are alloy but steel (cheap) and carbon fibre (super-light but also super-expensive) steerers appear on some forks. Most forks use conventional 1 1/8in steerers but some use tapered or oversized versions for extra stiffness; these will only work with appropriately sized head tubes. We’d thoroughly recommend you use a tapered steerer if your bike is compatible.
- Spring – Air springs (essentially pressurized air chambers) are light and easy to adjust for different rider/ride preferences just by changing pressure, but resistance will always increase as they reach full compression. Metal coil springs are significantly heavier and less adjustable, but are invariably cheaper and they feel super-smooth, particularly over small bumps. Some forks use a primary air spring backed up by a coil spring or elastomer block used as a secondary negative spring or bottom-out bumper.
- Legs – The telescopic legs are the moving structure of the fork. The lower legs are joined together by at least one brace to stop them moving independently. The upper legs (stanchions) have increased in sized dramatically in recent years, with up to 40mm diameters used to boost stiffness, especially on longer-travel forks. Lengths, wall thicknesses and external finishes vary. Seal heads are used to keep the internals clean. The stanchions house the spring on one side (usually left) and the damping on the other.
- Damping – Without damping, forks would just bounce up and down on their springs. Fork movement is controlled by pushing oil through a series of valves and/or shims. By altering the size of the holes and the speed of the oil flowing from one side to the other, it’s possible to control, or ‘damp’, the impact. Compression damping controls the impact strike, while rebound controls the post-impact speed of the fork as it returns to its static length. High-speed damping deals with big, blunt trauma like boulders and landings from jumps. Low-speed damping controls smaller, slower-applied forces like pedalling bob or cornering/braking loads. Basic forks just have rebound damping, while advanced forks have separate damping circuits to handle different shaft and impact speeds.
- Axle – Forks are increasingly being offered with 15mm or 20mm axles that slide right through the hub and screw or clamp into the fork leg. These increase fork tip stiffness and steering accuracy dramatically compared to traditional quick-release skewers, and they’re more secure, too. Cam systems like RockShox’s Maxle setup mean they’re just as quick to tighten/undo. You’ll need a compatible front wheel, but we’d still recommend a through-axle to anyone thinking of upgrading their fork.
- Air spring – Fork using compressed air to act as the spring.
- Air assist – Air added to increase the effective spring rate of a coil spring.
- Anodised – Alloy electrically coated with a hard wearing, coloured surface finish.
- Bladder – A flexible ‘bag’ containing damping oil.
- Blow-off – A valve that only opens when a preset impact load is exceeded.
- Bottom-out – Full compression of the suspension.
- Brace (or Arch) – The linking bridge between the two lower legs.
- Bushings – The slippery bearing blocks inside the lower legs that the stanchions slide up and down on.
- Cartridge – A self contained chamber. Generally used in forks to keep the damping oil isolated from lubricating oil and minimise contamination from muck or air, improving overall control consistency.
- Cavitation – An air pocket or void in the oil causing a sudden loss of damping.
- Circuit – The routing of damping oil through valves and holes.
- Coil spring – A coil wound metal spring.
- Compression – The shortening of the fork as it absorbs an impact.
- Damping – The valve circuit that hydraulic oil is pushed through as the fork compresses and rebounds. This dissipates impact force into heat energy.
- Dive – Under-damped suspension that rushes down through the compression stroke without absorbing much energy. Makes steering, braking and cornering feel very unpredictable.
- Handlebar remote – A switch that sits on the handlebar and is linked to the fork by a cable.
- High-speed forces: Impacts from blunt, square-edged objects or drop-offs that push the suspension through its stroke very quickly.
- Knock – Any looseness or wobble found in the fork.
- Linear – A very consistent resistance all through the travel.
- Load – The force transmitted into the suspension by rocks, landings, etc.
- Lockout – Compression damping cut-off that locks the fork at full height for more efficient climbing/sprinting on smooth surfaces.
- Lockdown – Compression damping cut-off that locks the fork at either a partially or fully compressed height.
- Low-speed forces – Small, slowly-applied suspension loads caused by weight shift, cornering pressure and pedalling.
- Open bath – Damping system using free flowing oil that also acts as a lubricant for the bushings and stanchions. Harder to control consistently than cartridge oil flow, but more tolerant or oil leaks or other issues and therefore generally more reliable.
- Platform – Low-speed compression damping that uses a preset ‘blow off’ load to control when it starts working.
- Preload – Additional pressure applied to a coil or air spring to increase the load needed to start it moving.
- Position sensitive damping – Damping that changes as the fork goes through its stroke.
- Post Mount – Easily adjusted disc brake mount using twin threaded posts perpendicular to the brake rotor.
- Progressive – Spring rate that increases as the fork compresses to full travel.
- Ramp-up – When a spring offers increased resistance as it compresses.
- Rebound – The return part of the fork stroke.
- Screw-through – Hollow oversize axle that screws into the fork leg and is then secured with a tool-free cam mechanism.
- Shaft speed – The speed at which the fork – and the damping piston shaft inside it – compresses.
- Speed sensitive damping – Damping that changes depending on stroke speed during impact.
- Spike – Sudden violent stop when the compression damping is unable to cope with high shaft speeds.
- Spring rate – Load needed to compress the fork.
- Square edge – A blunt-edged obstacle (like a boulder or big kerb) that pushes the fork through its travel fast.
- Stanchion – The upper fork tubes that the lower legs slide up and down on. Different manufacturers use different surface treatments to increase smoothness and reduce stiction.
- Stiction – Friction between the upper and lower legs of the fork which makes it reluctant to move over bumps.
- Top-out – The behaviour of the fork when it’s unloaded and extends to the very top of its stroke.
- Travel – The maximum vertical distance the fork can compress to absorb an impact.
- Travel-adjustable – Fork whose compression stroke can be adjusted externally.