Suspension forks – they are like sliced bread for mountain bikes. And they just keep getting better and more adjustable.
But all the levers and adjustments can lead to confusion. High-speed compression, low-speed compression, sag, air pressure, low-speed rebound, high-speed rebound air volume and volume spacers… Get all of those right and your mountain bike will be a dream to ride. Mess them up and your arms will ache, your tyres will skid and you may find yourself under a bush. How do you get the best out of your forks?
WHAT ARE YOUR FORKS MEANT TO DO?
First, your suspension, including your forks, is intended to absorb any shocks and bumps from the ground before they reach you, the rider, which improves comfort. Second, it keeps your bike’s wheels in contact with the ground for more of the time, which improves grip and control. The key controls to achieving this are suspension sag and fork damping.
All of the adjustment are available outside the fork. The only tools you will need are some zip ties (if your fork doesn’t come with an o-ring) a measuring tape and a shock pump for air-sprung forks and some coil forks. Some forks (e.g. Rockshox) come with a handy scale printed on the fork stanchion which means you won’t need the tape measure.
HOW TO SET SAG
1. Your forks will work best if they’re allowed to settle slightly under your weight. This gives them some reserve so the wheel can drop into holes and down small drops without the rest of the bike dropping too. If your forks don’t come with a handy o-ring around one of the stanchions, simply attach a zip tie around one leg – carefully so as not to scratch the finish.
2. Push the ring (or zip tie) down until it’s resting on the fork seal at the very bottom of the stanchion. Now get on the bike and adopt the “attack position” – slightly off the saddle, weight balanced between hands and feet, centred over the bike. Ideally, you’ll be in your regular riding gear including a pack if you normally ride with one. Balance, get a helper or gently lean on a wall to hold you up. Make sure the ring is right down on the fork seal and gently get off, careful not to bounce the fork and move the o-ring. Now measure the distance between the zip tie and the fork seal. This measurement is your sag. The recommended sag is somewhere between a 25% to 35% of the fork’s total travel. E.g. on a 100mm travel you’ll want around 25-35mm of sag, on a 160mm fork between 40-53mm.
3. If you have a coil-sprung fork, your first stop should be the preload adjuster. This usually lives at the top of at least one fork leg – some forks will only have one, some (usually budget models) will have two. If you haven’t got enough sag, turn the adjuster(s) anticlockwise. If you’ve got too much sag, turn them clockwise. Remeasure until you reach the correct amount of sag. If you’re considerably lighter or heavier than average you might not be able to set sag just with the preload adjusters. If you’re light you may still have insufficient sag with zero preload; if you’re heavy you may have too much with maximum preload. In either case you’ll need to change the actual spring for a lighter or heavier one. Usually this is just a case of undoing the cap at the top of the leg, pulling the old spring out and dropping a new one in.
4. If you have an air-sprung fork get your shock pump and add or remove air until the sag is correct. Ther will be an air valve under a cap on one of the fork legs. Don’t over-tighten shock pumps – do them up until the gauge registers and just a touch more. Start with the manufacturer’s recommended pressure and fine-tune until sag is right. If your fork sags too much, add some air, if it is too stiff release some air.
HOW TO ADJUST THE DAMPING
Sag set, it is time to look at damping. A fork with no damping will keep bouncing long after a bump has passed. Damping keeps things in check, usually by means of oil being forced through small holes in pistons. There are two types of damping: rebound damping and compression damping. Basically, compression damping controls how fast the fork compresses or absorbs bumps, and rebound damping controls how fast it returns to fully extended after absorbing bumps.
1. Rebound damping keeps the fork from bouncing back too quickly after a hit. Most forks have their rebound adjusters at the bottom of one of the fork legs. To start, stand astride the bike, put your hands flat on the bars, quickly push down and then lift up. The rebounding forks should just about keep up with your hands. If they hit them, add more damping, slowing down the rebound usually by turning the adjuster clockwise. If they drift sluggishly upwards, reduce the damping, speeding up the rebound usually by turning the adjuster anti-clockwise.
2. Your fork may also have one or more compression damping adjusters. Leave these on minimum for now.
GO RIDE YOUR BIKE
Your forks should now roughly be in the right setup area. The only way to get it spot on is to go out and ride. If you’ve used a zip tie, leave this in place for now. Move the o-ring or zip tie to the bottom of your fork stanchion. Go ride a trail you would ride frequently, one that represents the most common type of riding you do. You should get full travel over the biggest hits on the trail, moving the o-ring right up, or very close, to the top of your fork. If you never bottom the forks out, or use the full amount of travel in your fork, you can get away with more sag by letting some air out. If you’re bottoming out too often on smaller bumps or drops you will need more air, or a stiffer spring on a coil fork.
Tweaking the damping is trickier. It can take a while before you’re tuned in to what the fork is doing. The simplest test is to find a sequence of closely-spaced medium sized bumps – tree roots, rocks or a shallow flight of steps. Ride at them at a reasonable speed and concentrate on what your forks are doing. If they feel bouncy, add some rebound damping. If it feels as if the fork is getting gradually shorter, reduce the rebound damping; too much damping will prevent the fork from fully re-extending after each hit, so it gradually “packs down”.
You’ll probably keep making small adjustments over a few rides. As you get more familiar with the feel of the suspension, start to play with the compression damping to get the feel you want. If you want to reduce fork bob or brake dive at the expense of small-bump plushness, wind a bit more on. If it feels right to you then it probably is.