How to set up the suspension on your mountain bike

Air pressure, sag and damping adjustments demystified

Any good suspension product will have a range of adjustments to tune how the fork feels and performs. Getting these settings correct is essential to maintaining your suspension's performance and ensuring you have the most comfortable and controlled ride possible.

Suspension Controls

There are three main controls you’ll see on suspension: preload, rebound, and compression. Compression controls are also often split into low-speed and high-speed compression on high-end forks.

Preload

Preload adjustment alters the resistance the fork or shock gives against your weight. So the heavier you are, the more preload you’ll need. For a fork or shock with a coil spring, this would equate to having a stiffer spring, but for an air sprung shock it’s simply a case of pumping in more pressure.  

Compression damping

Compression damping comes from the internals of the fork and works by regulating the flow of oil through small holes. Compression damping only affects suspension when it is compressing – it doesn’t affect the preload but can appear to have a similar effect.

The more compression damping you dial in, the slower the fork or shock will move through its travel – this is good if you want a bike to pedal without bobbing for instance, but the negative effect will be the limitation of the suspension's movement when you hit a bump, making it feel a bit like it’s locked out. In fact, lockout is simply an extremely high amount of compression damping.

Rebound damping

Rebound damping is a similar internal system to compression and only affects the suspension when it is returning to its natural position after an impact.

The more rebound damping you dial in (+) the slower the fork or shock will return to its neutral position after an impact. 

A slower return, or more rebound compression is required if the bike feels as though it’s trying to buck you off, especially after corners or when you land a jump. 

If repeated hits are causing your suspension to feel like it’s ‘packing down’ and not returning to it’s neutral position, you’ll need less damping.

How to adjust a suspension fork

You will need:

  • Shock pump
  • Ruler
  • Full set of riding gear

It’s important to have your full riding kit to hand – as the weight of what you wear will need to be factored into the ‘rider weight’ and the suspension sag will need to be set accordingly. So it might be a good idea to make adjustments just before you ride, and take the shock pump with you so you can make further adjustments.

Step 1: Set preload sag

It’s a good idea to have someone to help, but it’s possible to set sag yourself by leaning against a wall or solid object.  

Start by measuring the stanchion of the fork, the shiny bit that moves inside the larger leg. Divide that length by four to calculate a 25 percent sag distance. Some more aggressive forks, such as those found on downhill bikes, can be set with up to 30 percent sag, but if you’re not sure, use 25 percent.

Get on the bike and assume the riding position. Most forks will have a small rubber ring on one of the legs which will allow you to see the amount of sag – if yours hasn’t, you can tie a rubber band around the leg.

Don’t be tempted to use a cable tie and don’t leave the rubber on the stanchion, as the it collects dirt, which can damage the stanchion.

Get on the bike and try not to bounce it as you mount it – you’re looking for a standing weight. Slowly get off the bike and measure the amount of sag.

Adjust the air pressure or preload dial and try again until the desired 25 percent is achieved. If you have an air fork, take it up or down by roughly 10psi at a time, or for coil forks, a full turn at a time should give the right increments.

It’s worth noting that for coil-sprung forks, you might need a heavier or lighter spring depending on your weight – these should be available to order from any good bike shop.

Step 2: Compression and rebound

Start by working out how many ‘clicks’ of adjustment you have with the compression and rebound – to do this, wind the dial in clockwise, then wind it back out. As you wind it out, count the clicks.

If you aren’t sure what you need, or have a new fork set the dials to the middle. You can then experiment by one or two clicks at a time until the desired setup is achieved.

Different trails and terrain will have difference setup requirements. So it’s a good idea to get a feel for what the dials are actually doing in terms of suspension action, so you can fine tune to your own preference.

Also, be aware that it’s quite rare that taking either compression or rebound to the extremes will have much benefit, so as a rule of thumb it’s usually better to stay near the centre of the available range

How to set up rear suspension

The steps involved are almost the same as setting up a fork, but for those of you that have jumped straight to this section, we've gone through them in detail again. 

1. Set preload

It’s a good idea to have someone to help, but it’s also possible to set sag yourself by leaning against a wall or solid object. 

Start by measuring the inner shock shaft – the shiny bit that moves inside the larger outer can. Divide that by four to get your ‘sag’ measurement.

You should aim for 25% sag, but some will adjust this to suit. 

Start by measuring the inner shock shaft – the shiny bit that moves inside the larger outer can. Divide that by four to get your ‘sag’ measurement
Start by measuring the inner shock shaft – the shiny bit that moves inside the larger outer can. Divide that by four to get your ‘sag’ measurement

Most shocks will have a small rubber ring or foam bump stopper to allow you to measure the amount of sag – if yours hasn’t, you can tie a rubber band around it. Don’t be tempted to use a cable tie and certainly don’t leave it on the shaft; the dirt it collects combined with the hard plastic will scratch the surface, something that won't be cheap to remedy.

Set the compression damping switch to its open position, reset the sag ring, gently mount the bike (wearing your riding kit, or at least with it in your backpack) and assume the standing riding position. Try not to bounce the bike – you’re looking for a standing weight.

Carefully dismount and check the sag distance – how far the small rubber ring has moved. For most people, you should be aiming for 25 percent sag, so adjust the pressure in the shock to suit. 

If you have no idea what pressure to run then pump in or release air until the gauge shows 150psi. then, add or subtract 25 to 50psi until you arrive at 25 percent sag
If you have no idea what pressure to run then pump in or release air until the gauge shows 150psi. then, add or subtract 25 to 50psi until you arrive at 25 percent sag

For coil sprung shocks, you can make minor adjustments using the preload dial, but might need a heavier or lighter spring depending on your weight – these should be available from any good bike shop.

2. Set compression and rebound damping

Start by working out how many ‘clicks’ of range you have in the dial. To do this, wind the dial fully in clockwise, then wind it back out. As you wind it out, count the clicks.

If you aren’t sure what you need, or have a new shock, you’d be well advised to set the dials to the middle of the range. You can then experiment by one or two clicks at a time, either way, until the desired setup is achieved.

It’s quite rare that taking either compression or rebound to the extremes will have much benefit, so most riders will want to stay near the midpoint.

Remember different trails and terrain will have difference setup requirements, so it’s a good idea to get a feel for what the dials are actually doing in terms of suspension action.  

Related Articles

Back to top