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Fork tuning for beginners

09:59 14th October 2008 by Bikemagic
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So you’ve got a new bike complete with shiny new suspension forks. Or you’ve got some shiny new suspension forks on your old bike. Either way, there’s a fair chance you’re looking at the fork and all the knobs, dials and valves thereupon and feeling ever-so-slightly lost. If that’s you, quickly scan through our guide to fork anatomy and then pop back here and we’ll run through Setting Up Forks For Beginners…

The idea of suspension is twofold. First, it’s intended to absorb shocks from the ground before they reach the rider, improving comfort. Second, it keeps the wheels in contact with the ground for more of the time, improving grip and control. The key to achieving both of these is sag and damping.

fork_setup_tools (11K)

We’re working just with the adjustments available outside the fork here, so you won’t need many tools. Some zip ties and a tape measure are essential, and you’ll need a shock pump if you’ve got air-sprung forks.

Setting sag

fork_setup_ziptie (8K)

1. Forks work best when they’re allowed to settle slightly into their travel under the rider’s weight, giving them some reserve extension so the wheel can drop into holes and down small drops without the rest of the bike dropping too. To achieve correct sag, start with a simple zip tie around one leg.

fork_setup_measure (8K)

2. Zip tie in place, push it down until it’s resting on the fork seal at the top of the slider. Then get on to the bike and adopt the “attack position” – slightly off the saddle, weight balanced between hands and feet, centred over the bike. You’ll need either really good balance, a helper or something to gently lean on to achieve this. Make sure the zip tie is right down on the fork seal and gently get off.

Now measure the distance between the zip tie and the fork seal. Optimum sag is somewhere between a quarter and a third of the total fork travel – on a 100mm travel you’ll want around 25-35mm of sag. Run more sag if you like a soft, plush ride, less if you like things firmer. If it’s wildly out, you’ll need to make some spring adjustments…

fork_setup_preload (8K)

3. If you’ve got 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 it’s right. 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 (if you’re light) or heavier (if you’re 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.

fork_setup_posspring (8K)

4. Owners of air-sprung forks don’t have to worry about preload or spring changes. Just get your shock pump (often supplied with the forks) and add or remove air until the sag is correct. Like preload dials, there’ll be an air valve under a cap on one or both legs. If there’s air in both legs, try to have the same air pressure in both. Don’t over-tighten shock pumps – do them up until the gauge registers and just a touch more. Try the manufacturer’s recommended pressure first and fine-tune until sag is right – we’ve knocked up a fork pressure gizmo with recommendations for some current forks.

fork_setup_negspring (9K)

5. Some air forks have a negative air spring as well as the main (positive) spring. This is designed to counteract the positive spring to overcome the initial “stiction” often found in air forks and help them to move more easily over smaller bumps. At this stage, set the negative spring to the same pressure as the positive spring. Later on you can use the negative spring to fine-tune the feel of the fork; adding air will make it more supple over small bumps, releasing some air will make it stiffer over small bumps but it’ll bob less.

Damping

Springs sorted, it’s time to turn your attention to damping. A fork with just springs in it tends to 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. Some budget forks don’t have hydraulic damping, relying instead on friction or the little bit of damping inherent in elastomer springs. But if you have damping and there’s a handy adjuster for it, here’s what to do with it:

fork_setup_rebound (9K)

1. Rebound damping keeps the fork from bouncing back too quickly after a hit. RockShox, Manitou and Pace put their rebound adjusters at the bottom of the right-hand fork leg, Marzocchi and Fox put them at the top. To get in the ballpark, stand astride the bike, put your hands flat on the bars and 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. If they drift sluggishly upwards, reduce the damping.

You may also have a compression damping adjuster. Leave this on minimum for now.

Go ride

After that little lot, your fork should be in the performance ballpark. But the only way to get it spot on is to go out and ride. Leave the zip tie in place and go and ride a familiar route as you usually would. You should get full travel over the biggest hits you encounter. If you never bottom the forks out you can get away with softer springs/less air. If you’re bottoming out all the time you’ll need a stiffer spring or more air.

Trickier is damping. It can take a while before you’re tuned in to what the fork is doing. A simple test is to find a sequence of closely-spaced medium sized bumps – tree roots, rocks, a shallow flight of steps or even an old ladder on the ground. Ride at them at a reasonably speed and concentrate on what the fork’s doing. If it all feels bouncy and sketchy, add some rebound damping. If it feels as if the fork’s getting gradually shorter, reduce damping; too much damping prevents the fork from fully re-extending after each hit, so it gradually “packs down”.

You’ll probably find you keep making small adjustments for quite a few rides. As you get more familiar with the feel of the suspension, start to play with the negative spring and compression damping to get the feel you want. We usually run no or very little compression damping, but if you want to reduce fork bob and brake dive at the expense of small-bump plushness, wind a bit more on. There are really no hard and fast rules – if it feels right to you, it probably is.

More maintenance

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  1. mark

    Well hi there. I have been looking for someone to explain how positive-negative air works since I bought my forks, 2 years ago. They were bought OE, so all you got was the forks and nowt else! I have been faffing about with them ever since.Thanks to you folks, I have just found out how its done. You are my heroes! Gonna do a bit of fettling, and go give the bike a beasting. Computing is new to me, and I have quickly learnt that the internet knows everything. Scary! Thanks. Mark B.

  2. Ken Edwards

    My rockshox Reba RL 29 forks go flat after and sometimes during a ride,Is that normal? The dust seal on the left side also moves about, often not staying in its correct place, I have tried to reseat it but it will not stay in place. Could this have something to do with the air loss?

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