How to setup rear suspension

Rear suspension setup is dynamic and specific to the bike and rider. A lot of factors affect it’s performance and is key to making your trail-riding fun and exciting. Here we talk about the different types of shocks available and guide you on how to setup and tune your rear suspension to get the most out of it.

What Is A Coil Shock?

Coil shocks use a metal coil spring to provide resistance.  Coil shocks have a linear spring rate. This means that the force required to compress the spring remains the same as the shock compresses. Coil shocks are generally more sensitive (easier for it to compress and rebound) than air shocks because there are fewer seals in the system, therefore there is less force required to get the shock moving. Because of this, coil shocks tend to provide more traction and a unique feel.

To adjust the spring rate of a coil shock, you can swap out the coils for stiffer or softer options. You can set the sag by turning a dial on top of the stanchions. This changes the preload on the springs by compressing or decompressing them. Increasing the preload compresses the spring, which makes the shock stiffer and reduces sag. Most coil shocks also have a lockout function to prevent them from compressing.

Coli Spring Rear Shock

What Is An Air Shock?

Air shocks use compressed air resistance for shock absorption.  Unlike coil shocks, the spring rate is progressive which means more force is required to compress the shock as it compresses. The spring is provided by compressed air that is sealed in an airtight chamber inside of the shock. As the shock compresses, air is compressed and resists further compression. Air shocks are used for all types of mountain biking including trail riding, downhill, cross country, enduro, and freeride.

The spring rate of an air shock can be adjusted by changing the air pressure. Increasing the pressure increases the spring rate and makes the shock stiffer. Decreasing the pressure makes the shock softer. Adjusting the pressure of an air shock requires a special high-pressure pump called a shock pump. You simply attach the pump to a Schrader valve on the unit and add or remove air. You can also adjust the shock preload and sag by changing the pressure.  Most air shocks can also be locked out so they do not compress

On more expensive air shocks you can also adjust the progression by changing the volume in the air chamber. This is achieved by adding or removing spacers inside. Adding spacers decreases the volume inside of the air chamber. Reducing the volume makes the shock more progressive or harder to compress earlier in the range. This function makes air shocks more tuneable than it’s coli counterpart.

Air shocks also have a damping system to smooth out your ride over bumps and compressions. Most models allow you to adjust the compression and rebound damping.

Fox Float Rear Shock

Why Bother Setting Rear Suspension Up?

Good rear suspension can make a good bike feel great, but a poor setup can make a great bike feel terrible. Here are some steps to help you optimize your bike for your weight, your trails  and your style. Investing time setting up your suspension will transform your ride and you!

Be Prepared To Compromise

A perfect rear suspension setup does not exist. Suspension setup is always a compromise, finding a balance between sensitivity on trails and support for bigger impacts. Your suspension is unique to you, your trails and your style of riding them. While most shock manufacturers now offer printed guidelines that will give you a setup normally based on weight of the rider, following this guide will help you to personalise it.

Be Ready

Before you start to play with your shock, you need to ensure that it is in good working order.  Check your rear suspension manufacturers recommended service intervals and make sure you have the work done. Rear shocks are expensive so look after them. If you’re setting up a new bike you don’t have to worry, but if your bike has seen action it is essential to get your shock serviced by professionals – it will transform the performance of your bike and you!

To follow this guide you will need your normal riding clothes, helmet and backpack on. To best optimize your bike’s performance you will need a short section of your favourite technical trail, a shock pump, a measuring device (ruler or tape), a calculator and someone to help you.

A rider on a full suspension mtb rising uphill offroad

#1: Setting Your Shock Sag

Before you start make sure your rear shock is in ‘fully open’ mode (if you have a low-speed compression adjuster wind it fully in the [-] direction). Have your assistant support the bike on level ground as you climb on.

  1. Bounce firmly up and down to get your shock ready.
  2. Assume your normal seated position and after allowing the bike to settle for a few seconds have your assistant push the rubber O-ring on the shock stanchion up (or down) to the rubber wiper seal.
  3. Carefully dismount from the bike without disturbing the O-ring.
  4. Measure the distance the O-ring has been pushed up from the wiper seal in mm.
  5. Divide this number by the total shock stroke (often less than the physical shock shaft length, check in your bike manual) and then multiply by 100 to get the percentage sag, e.g. (15 mm / 50 mm) x 100 = 30%.
  6. To achieve the correct sag, add or remove air from the air-spring as needed with a shock pump and repeat.

Many manufacturers will have a suggested sag setting, but if not, we recommend a base setting of 25-30%. If you require less sag simply add air to the shock, if you require more sag lower the air pressure. Add air in 10 psi increments and each time repeat the process until you reach the required sag.

Pro-Tip: While setting the sag, hold just one brake, not both or you will cause incorrect readings.

#2: Optimising Your Spring Rate

While 30% sag in your shock is a good base setting, it may not be optimal for your riding style. Remember, your spring rate is always a compromise between the big hits and small bumps. The optimum settings for you will depend on your riding style and the trails you ride.

Now you need to find a trail you use regularly that offers as many features as possible. Jumps, bumps, berms, compressions, rocks, drops. Whatever you ride the most. After a few runs to warm up, push the O-ring down to the wiper seal and ride the trail. Concentrate on how big impacts and drops feel. Is your fork bottoming out? Does it feel harsh on singletrack? Are you getting full travel?

If the rear of your bike feels wallowy and stuck to the ground, bottoming out easily
Your shock spring rate is too low. Add pressure to the rear shock, 10 psi at a time, and repeat the trail. Stop adding air when the bike feels good, while still giving full travel when required. Make a note of the optimised pressure.

If the rear of your bike feels harsh over small bumps and does not give you full travel where you desire
Your shock spring rate is too high. Remove pressure from the rear shock 10 psi at a time and repeat the trail. Stop when the bike feels good over small bumps and maintains traction. Make a note of the optimised pressure.

Pro-Tip: If you find that the only way to stop frequently bottoming out your shock is to use a high spring pressure that feels very harsh over small impacts, you may need to increase your spring rate progression, see Step 3.

#3: Consider Your Spring Rate Progression

We now have to consider you as a rider and what trails you are riding. If your shock is frequently bottoming out even though the bike feels good on general trails, you may need to reduce the air volume in your shock. For a more progressive spring rate you need to add spacers to reduce the air volume in the chamber.  Adding these will make the final part of the suspension compression firmer, requiring more force to bottom out.

If you feel that you are bottoming out your rear suspension too frequently, despite running the correct air-spring pressure
Reduce the volume of air in the shock with the addition of 1-2 volume spacers.

If you feel that you struggle to achieve full travel where you expect to
Increase the volume of air in the shock by removing 1-2 volume spacers.

Pro-Tip: If you make big changes to the setup of your shock, such as a firmer spring rate or the addition of volume spacers, tune your fork to match. With more confidence from your new rear setup you will inevitably ride harder and your fork will need to be adjusted to your style of riding again

#4: Rebound Damping

Rebound damping controls the speed at which compressed rear suspension returns after a bump.

If rebound damping is too low (-) your fork will extend too fast and feel spring-like and out of control. If the rebound damping is too high (+) the suspension will not return fast enough after repeated bumps sinking lower into its travel and performing poorly.

  1. Start by adding full rebound damping (+) to the shock.
  2. Choose a small drop to ride off slowly and focus on how the rear suspension springs back after impact.
  3. Repeat the test, each time reduce rebound damping by one click (-) and see how the shock starts to recover faster.
  4. Stop when the rear shock recovers so fast it overshoots a tiny amount. This is a good base setting. Now repeat a full section of trail at this setting. Experiment a few times with two clicks either side and see which feels the most controlled with good grip.

But what about high-speed damping? Most shocks have a single rebound adjuster, which really is a low-speed rebound adjuster. Some very high-end shocks also have  high-speed rebound adjustment too. There is a lot of crossover between high and low-speed rebound, any adjustment of one will influence the other. If you do have high-speed rebound adjustment on your shock, we recommend setting it to the manufacturer’s recommendation and then adjust as above. High speed damping effectively keeps shock travel in reserve for bigger hits on the trail. The more you add the harsher the bike will feel and is generally set and forget unlike low-speed damping adjustment which is much more tuneable between trails and where most of your tuning and tweaking should be focussed.

Pro-Tip: If you ride slowly or on easy trails, a slower rebound may feel more comfortable. However, if you move to harsher, faster trails you may experience sore arms and legs as your suspension cannot recover fast enough from the bigger hits. Run as fast a rebound setting as you can for best performance.

#5: Get The Balance Right

In nearly all cases a balanced rear suspension setup is essential for optimal performance.

As a final check, find some level ground and ride slowly across it on your bike. From a standing, attack position jump repeatedly up and down as hard as you can. The bike should feel supportive and the rebound speed should feel good. If the bike feels unbalanced, identify where it is coming from and make some adjustments.

Traction not only comes from the tyres and terrain surface, but the amount of force the rider is placing on the tyres too. A balanced shock setup is important for this element of traction. 

If you follow this guide, you will have gained a deeper understanding of how each element of your rear suspension works. Good rear suspension setup is a balance between many different factors which we have talked about. If you make any big changes to one setting of your suspension, you need to balance the other settings to match.


Further Reading


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