27 Apr 2022

How to set up your suspension sag in six easy steps

If your Merida bike has suspension, the correct setup is key to getting the best performance from it – and having the right amount of sag is a vital part of that.

What is sag?

Sag is the amount of travel of the bike that is used up just with the weight of you, the bike and your kit. It’s hugely important as having sag allows the wheel to maintain contact with the ground by extending into dips as well as compressing over bumps, maintaining grip and control as you ride down the trail.

Having your tyre in contact with the ground for as much of the time as possible is the entire point of suspension in the first place, so you can see why this is vital. In an ideal scenario, your suspension would work to absorb bumps at the wheel without passing them on to you at the frame – though, in the real world, that’s not really possible.

How much sag should you run?

Well, all of our suspension equipped bikes are designed around a specific sag figure – it’s usually 30% at the rear and anywhere from 15 or 30% at the fork, depending on personal preference. If you do have rear suspension, it’s really important that your sag figure is within the range specified by the designer, because the suspension is designed to optimise pedalling performance with the sag as a starting point. This is related to anti-squat, but it’s a fairly complex topic in itself. Sag is also the point that the suspension will be designed to ramp up from to give support throughout the travel – so if you start off with too much or too little sag, you’ll throw everything from the suspension to the geometry out of whack and the handling will be badly flawed.

Setting sag is a balancing act of adjusting how much the spring in your suspension pushes back against the weight of you, your bike and kit. 

If you have too much sag, your suspension will be too soft for your weight. You’re likely to run out of suspension travel on bumps and bottom out all the time, meaning you will have really poor control on big hits, plus poor pedalling performance and soggy feeling reactions the rest of the time. 

If you don’t have enough sag the suspension will be too stiff. The bike’s suspension won’t be able to extend into dips, so it’s really important to get this correct as it’s the starting point for all other suspension adjustments, such as rebound and compression damping. 

On full suspension bikes, you also need to get the sag balanced from the front of the bike to the rear, as having one end too soft will negatively impact the dynamic geometry of the bike. Too soft on the front and too hard on the rear and the bike will dive heavily under braking or on steep sections, giving a steep and sketchy head angle that might have you over the bars.

Go the other way around and you’ll end up with a bike that suddenly becomes very slack under compressions, making the handling unpredictable when you need control the most.

Like many suspension settings, it’s always best to start using the guideline figures, but you should feel free to fine tune your sag settings to your tastes and the terrain you ride. Be methodical and ride the same piece of trail, making small individual adjustments – you’ll soon start to feel the differences and find out what you prefer. There’s no definitive right way, though there definitely are plenty of wrong ways.

Anyway, now we’ve covered the why, let’s do the how!

How to set up your sag

The tools you’re going to need are:

  • Tape measure or ruler
  • Shock pump
  • Calculator or some good mental math abilities
  • A clean bike

1.    Remove the air valve caps and set o-rings 

To adjust the air in the shocks, you need to remove the protective valve caps. Simply thread them off and place them somewhere safe. Most forks and shocks have a rubber O-ring on the shaft to indicate travel – push this all the way to the seal. If you fork or shock doesn’t have an o-ring, put on a zip tie, but thread it backwards so it can be easily removed.

2.    Sit on bike

Pick whether you’re going to do the front or rear suspension first – you should only adjust one end at a time. You now need to sit on your bike in order to compress the suspension underneath your own weight. need to wear your usual riding kit plus your pack, if you ride with one. It’s best to get leant against a wall or get a friend to help stabilise the bike. If you’re doing the rear suspension, adjust the saddle to your normal riding height and sit gently down. If you are doing the fork, get into the standing up position you would use when going downhill. Bounce the suspension once and allow it to stop.

3.    Measure sag

Move the o-ring on the shock or fork down until it contacts the seals. It might be easier to get a friend to do this so that you don’t disturb the position you are in. You now need to get off the bike gently, so that you don’t cimpress the suspension any more. Using the tape measure or ruler and measure the distance between the o-ring and the seals. Make a note of this. 

4.    Add or remove air

You now need to calculate what the optimum sag should be – for a fork this is easy. Just time the sag percentage by the overall travel and this will give you what the sag should be. For example, a fork with 160mm of travel that you want 20% sag with would be 160 times 0.2 – which equals 32 mm of sag. 

A shock is a tiny bit more involved as you need to know the stroke length of the shock. It’s often written on the shock or given with a code that can be looked up on the manufacturer website, but if you don’t know it or can’t find it, you’ll have to fully deflate the shock, compress it to bottom it out, then reinflate it, then measure the distance from the seal to the o-ring. It’s worth noting the stroke of the shock isn’t always the same as the exposed length of the shaft so double check – precision is needed here, even if it take a bit longer. Now you just need to repeat the calculation as with the fork. A shock with a 65mm stroke running 30 % sag would be 65 times 0.3, giving 19.5mm of sag.

Compare this target figure to the sag figure you measured earlier. If it’s bigger, you need to remove air and if lower, add it. Do this using the shock pump, but make sure that the valve and pump are clean and free from grit as it’ll really mess things up if you get dirt inside your shocks. Add or remove air in proportion to how far out your measured figure is from your target, but be aware that 5-10psi will make quite a large difference.

5.    Measure again, repeat until ready!

You now need to remove the shock pump and repeat the sag measuring step again. Taking the pump off is important, as even the relatively small air volume inside it will throw our your measurement. Some pumps have a special valve, so you can leave the pump attached but isolated from the air chamber.

Keep repeating steps 2-5 until you get the sag figures correct. To do the other end of the bike, just repeat this process.

6.    Replace valve caps and ride!

This one is easy – just pop the valve caps or covers back on and get out there. When you do have the setup right, make a note of the pressure you’ve put in both fork and shock so you can get set up faster next time if you have to deflate them for any reason.