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The perfect setup - this is how you set up your mountain bike chassis correctly

Do you let your spring rate jump to the ceiling? Do you feel like your rebound is not fast enough? Then it's time to allow an hour or two to adjust the suspension of your mountain bike with this basic guide.

Why do I even have to bother looking at the chassis?

Correctly tuned suspension can make a good bike feel great, but bad setup will make a great bike feel terrible. We accompany you through the essential steps to optimize your bike, tailored to your riding style and the trails you love. If you spend a few hours optimizing your chassis, it will pay off: you ride more effectively, your self-confidence on the bike increases, you are prepared for more situations - and the right tuning can also be a lot of fun.

You are not just a number!

This tuning guide should help you to find a suspension setting that is optimized for you alone. The setup of a chassis is highly dynamic and you have to take many variables into account: your weight, where you ride, what you ride and how you ride. This is exactly why it will end up in a suboptimal performance if you just copy the attitudes of your buddies - or even worse: those of a pro. While most manufacturers now offer printed guide values ​​that allow you a solid basic setting, you can personalize this setup with the help of our guide.

A chassis is always a compromise

There is no such thing as “the” perfect suspension setting. If you optimize your chassis so that it offers you support with heavy impacts, the sensitivity to small impacts will suffer. The setup of a chassis is always a compromise; it's about the perfect balance between sensitivity and support. It is therefore important to find the right chassis balance that suits your riding style and your trails.

Before you start

Before you invest time in optimizing your chassis, you have to make sure that your suspension fork and damper are in working order. Of course, it doesn't make sense to spend time setting up if your suspension components just gasp and hiss on their way downhill. Most chassis component manufacturers recommend an oil service every 50 hours of driving and a full damping service every 100–200 hours. Be honest, when was the last time you had your landing gear checked? If you are setting up a new bike, you don't have to worry about it, but if your bike has already been through a lot, it is essential to have your chassis components serviced by professionals first - that will turn the performance of your bike upside down!

To tune your chassis, you need your normal bike clothes as well as your helmet and backpack. So that you can optimize the performance of your bike effectively, you need a short section of your favorite technical trail, a shock pump, a ruler, a calculator and a buddy to help you.

Step 1: Set SAG

In order for your chassis to work as well as possible, it must be able to react to every bump in the trail. When you hit an obstacle, your suspension fork and damper compress and absorb the energy of the shock. This in turn is released again by the subsequent rebound. In order for you to maintain traction, suspension forks and dampers not only have to absorb shock, they also need to expand to plunge into holes and keep your tires on the ground. So that the chassis can both compress and rebound, we pre-tension the chassis with our own body weight. This amount of preload is known as SAG and describes the amount by which the suspension sags in its suspension travel when you are sitting on the bike. If there is too little SAG, the bike lacks grip because it cannot “stretch out”, if too much SAG it feels spongy and reacts poorly to repeated hits.

The measure of how much the spring elements compress in their travel when we are sitting on the bike is known as SAG. This value largely determines how your bike rides.

Adjust the SAG of your damper

Before you begin, make sure your shock is in fully open mode. If it has an adjusting wheel for the low-speed compression stage, turn it completely in the (-) direction. Ask your assistant to secure the bike from tipping over on level ground while you are stepping on.

  1. Vigorously springs in and out again to fill the negative air chamber and free the spring deflection.
  2. Take your normal sitting position and allow the bike to "sit down" for at least 5 seconds. Then let your assistant push the rubber O-ring on the piston rod towards the damper and up to the dust scraper.
  3. Carefully shift your weight forward and get off the bike without moving the O-ring.
  4. Measures the distance between the O-ring and the dust wiper in mm.
  5. Now divide this number by the stroke (often less than the total length of the damper shaft, check your bike manual) and multiply the whole by 100 to get the percentage SAG, e.g. E.g .: (15 mm: 50 mm) x 100 = 30%.
  6. In order to achieve the correct SAG, depending on your needs, pump air into the air spring or let it off and repeat the aforementioned procedure.

Many manufacturers recommend a certain SAG setting, but if not, we recommend a basic setting of 30%. If you want less SAG, just pump some air into the damper and if you want more SAG, let some air out. Add air in 10 psi increments and repeat this process until you have the required sag.

Pro tip: Just keep the front brake pulled while you set the SAG, not both - otherwise you will get incorrect readings.

SAG adjust your fork

Once your shock is set correctly, it's time for the suspension fork. Make sure that the damping of your fork is completely open and adjust the pressure in the air spring according to the manufacturer's recommendation. Your assistant can again hold the bike while you get on.

  1. Vigorously pushes in and out to fill the negative air chamber and loosen the seals.
  2. Take your normal standing downhill position, give the bike at least 5 seconds to "sit down" and ask your assistant to push the rubber O-ring on the fork tube down to the dust scraper.
  3. Now lean back carefully and get off the bike without moving the O-ring.
  4. Measure the distance between the O-ring and the dust scraper in mm. Divide this number by the total spring travel (e.g. 160 mm) and then multiply the whole by 100 to get the percentage SAG again.
  5. In order to achieve the correct SAG, depending on your needs, pump air into the air spring or let it off and repeat the above procedure.

Starts with the manufacturer's recommendation. If there is none, then start with 20% SAG. If you want less SAG, just pump more air into the fork. If you want more SAG, then let off some air. Add the air in 10 psi increments and repeat this process until you have achieved the desired SAG.

Advanced tuning

Now it's time to tweak your basic settings. Pick a short and typical section of a trail that you regularly ride on. Rocks, drops, jumps, berms and compressions, whatever you like to put under your tunnels - the more of them, the better. Find a trail that you feel comfortable on, with at least one section that you expect to use your full suspension travel there, and where you can take the same lines over and over again. Before you start tuning, make sure that all external rebound and compression settings are set according to the specifications recommended by the manufacturer. This gives you a solid basic setting for your weight.

If a rider is out on a trail every week and knows it very well, then he should use his entire suspension travel on certain occasions. It often happens that a rider drives a new or relatively unknown trail and does not use the entire suspension travel. That's absolutely okay, after all, it doesn't go as fast there as on familiar trails.
Mark Fitzsimmons, FOX Suspension Program Manager

Step 2: Optimization of the air spring rate

Although 20% SAG on the suspension fork and 30% on the damper are a good basic setup, this is probably not ideal for your riding style and the rear triangle design of your bike. The spring rate - i.e. the force that is required to compress the spring - is always a balance between support for large impacts and sensitivity for small bumps. The perfect setting for you depends on your riding style and the trails you are on.

After a few descents to get used to, you push the O-rings on the fork and damper up to the dust scraper and drive the trail. Concentrate on what big hits and drops feel like: Do you experience severe punctures on your bike? Does it feel too insensitive to small hits? Do you get the full travel where you expect it to be?

If the rear of your bike feels spongy and as if it was stuck to the ground and easily broken through:
The spring rate of your damper is too low. Increase the air pressure on the shock by 10 psi and ride the trail again. Still does not fit? Increase the spring rate in 10 psi increments until the setting works. If the bike feels good and if the worst comes to the worst, it still provides all the travel, then the air pressure is correct. Make a note of the optimized pressure.

If the rear of your bike feels too hard with small impacts and does not provide the entire suspension travel where you want it:
The spring rate of your damper is too high. Decreases the air pressure on the shock by 10 psi and rides the trail again.Still does not fit? Decreases the spring rate in 10 psi increments until the setting works. If the bike feels good on small bumps and offers reasonable traction, then leave it at that. Make a note of the optimized pressure.

If your suspension fork dips too deeply when braking or on very steep trails:
The spring rate of your fork is too low. Increases the air pressure in the suspension fork by 5 psi and repeats the trail. Still does not fit? Keep increasing the spring rate in 5 psi increments until the setting works. If the fork is less immersed and guarantees good support, the procedure stops and you make a note of the optimized pressure.

If your suspension fork feels too insensitive to small impacts and lacks grip:
The spring rate of your fork is too high. Decrease the pressure in the fork by 5 psi and ride the trail again. Still does not fit? Decreases the spring rate in 5 psi increments until the setting works. If the fork feels sensitive to small hits, but still offers good support, then you are on the right track. Again, make a note of the optimized pressure.

Pro tip: Can you only prevent regular punctures on your suspension fork and your damper by using a high air pressure in the spring? And do the suspension fork and damper feel extremely insensitive to small impacts? Then maybe you should increase the progression of your spring rate, see step 3.

Step 3: Progression of the spring rate

Now we have to take a closer look at how powerful you are as a rider and how demanding your trails are. If you are strong and regularly have the feeling that your rear triangle is bottoming out or your suspension fork is low in travel when braking hard and in fast corners, even though the bike does not generally feel too soft when riding, then you may have to follow the progression of the Adjust spring rate. For a more progressive spring rate, you'll need to add volume spacers (or remove them if you can't use enough travel). Adding volume spacers makes the final piece of travel tighter, as more force is needed for a punch.

If you have the feeling that your suspension is subject to bottoming out too often, even though the air springs are at the correct pressure:
Reduces the volume of the air chamber in the suspension fork or the air spring chamber of the damper with one or two additional volume spacers.

If you have trouble using the full suspension travel in some situations:
Increase the volume in the air chamber of the suspension fork or in the air spring chamber of the damper by removing one or two volume spacers.

Pro tip: If you make profound changes to the setup of your suspension fork, such as setting a tighter spring rate or adding volume tokens, then the spring rate and progressivity of the damper adjust accordingly. Presumably, with more self-confidence at the front, you'll ride more powerfully - that's why you should configure your damper accordingly. So get back on the test track and start over!

Step 4: Adjust rebound

The rebound damping controls the speed at which a compressed chassis element rebounds after an impact.

If the rebound damping is too low (-), the suspension components rebound too quickly. It then feels like a spring and like it's out of control. However, if the rebound damping is too strong (+), the chassis components do not recover quickly enough after repeated impacts, and as a result compress more and more or sink deeper and deeper into the suspension travel and simply work poorly.

Adjusting the rebound damping on your damper:

  1. Start by activating full rebound damping (+) on the damper.
  2. Select a small drop from which you slowly descend and concentrate on how the damper rebounds after a blow.
  3. Repeat the test, reducing the rebound damping by one click (-) each time, and watching the damper begin to rebound faster and faster.
  4. Stops the procedure when the damper rebounds a little too quickly and bobs slightly. That should be a solid mindset. Now repeat a complete section of the trail with this setting. Experiment for two more runs with two more clicks in each direction and then decide which setting feels most controlled with good grip.

Adjusting the rebound damping on your suspension fork:

  1. To set a basic setup of the rebound stage on the suspension fork, you start with a completely closed rebound stage (+). Stand over your bike and compress the fork with your body weight. Then suddenly let go of the fork to let it snap back.
  2. Change the rebound until the fork rebounds as quickly as possible without causing the front wheel to "jump" off the ground.
  3. As soon as the basic setting is established, a complete section of the trail repeats with this setup. Experiment two more times with two clicks in each direction and decide for yourself which setting feels most controlled with good grip.

But what about the high-speed rebound? Most suspension forks and dampers have a single rebound adjuster, which is basically the low-speed rebound setting. Some of the absolute high-end chassis components have an additional adjuster for the high-speed rebound stage, which controls the rebound speed at high piston speeds. However, we have found that high and low-speed rebound damping overlap a lot - any adjustment on one side has a direct effect on the other. If you have an adjuster for the high-speed rebound stage, we therefore recommend that you set it according to the manufacturer's recommendation and then adjust the low-speed rebound stage as described above.

Pro tip: If you travel a lot in moderate terrain or drive more leisurely, a slower rebound stage will initially seem more comfortable to you. However, if you move in faster terrain, for example on a holiday in the Alps, then a slower rebound stage leads to painful arms and legs, as your bike cannot recover from the bumps quickly enough and thus "wastes" travel. Ride for maximum performance with as fast a rebound adjustment as is just comfortable.

Step 5: Low-speed compression damping

The low-speed compression damping (LSC) influences the behavior of your chassis at low piston speeds (not the speed of the bike), mainly at the beginning and in the middle of the suspension travel.

You probably now have the feeling that you have achieved a good spring rate, with great performance in small impacts and decent protection against punctures. Nevertheless, you are of the opinion that the bike lacks support in the mid-travel range, because on many occasions it immerses too much in its travel: for example when braking hard, even on steep trails or when you push the bike into bends or forward Jumps pulls the trigger. The solution: You need to add more low-speed compression damping. This reduces the sensitivity of the chassis components, as you only want to increase the minimum level in order to achieve enough support. Starts with the fully open setting (without additional damping).

If you think that your bike is rustling too quickly through its mean suspension travel:

  1. Starts without additional low-speed compression damping on the damper, drives the test trail and increases the low-speed compression by two clicks (+) each time.
  2. Focus on how the bike behaves when there is a large shift in weight, such as braking, cornering or jumping. Stop adjusting when the bike offers good support in the middle of its suspension travel.
  3. Repeat the whole thing with your fork.

Pro tip: Try to keep your low-speed compression damping settings balanced. For example, if you are riding with a very high low-speed compression on the fork and completely without the shock, then the bike will tend to put more weight on the rear wheel while riding, and vice versa. A balanced setup is the key to success.

Step 6: High-speed compression damping

The most expensive suspension forks and dampers have a setting option for high-speed compression damping (HSC), which controls the damping when the chassis is compressed at high piston or stanchion tube speeds (strong, fast impacts).

If you have the feeling that your suspension fork or your damper still hits too easily, and if you have a high-end damper or a suspension fork with this option, then you can adjust the high-speed compression damping there. More high-speed compression damping reduces the amount of spring travel that the fork uses during high-speed impacts (again, it's about the compression speed of the damper piston or stanchion tube, not the speed of the bike). A low level of high-speed compression causes degressive damping. This quickly releases the entire suspension travel in response to large, fast impacts, whereas a high level of high-speed compression leads to progressive damping - the available suspension travel for large, fast impacts is therefore reduced.

If you have the feeling that your bike needs more support at the end of its travel in high-speed hits:

  1. Ride the test trail and start completely without added high-speed compression damping on the damper. Then increase it by one or two clicks each time (if the adjustment range is very wide).
  2. Focus on how the bike feels when you hit fast hits, e.g. B. when landing after jumps or when hitting large obstacles when you are really fast. Stops when the bike offers good support at the end of its travel.
  3. Repeat the whole thing with your suspension fork.

Step 7: Controls the balance

As far as suspension and damping are concerned, a balanced chassis setting is essential for optimal performance in almost all cases.

As a final check, find a level surface and slowly roll forward on your bike. Now pump up and down from a standing riding position - a few times and as hard as you can. The bike should feel supportive and the rebound speed should seem balanced front and rear, both at the front and rear. If the bike feels unbalanced, find out where the mismatch is coming from and make corrections.

A balanced setting of your suspension is very important. Traction comes not only from the tires and the surface of the terrain, but also from the amount of force with which the driver acts on the front and rear wheels. A balanced setup is important for this component of traction.
Mark Fitzsimmons, FOX Suspension Program Manager

If you follow this tuning guide, then it will not only help you to a suspension setting that is optimized for your driving style and your preferred terrain. You will also get a deeper understanding of how the properties of your chassis work and how they affect each other. Good chassis performance is always a balance, rather a compromise between countless different factors. If you make major changes to one setting of your suspension, you also have to adjust the other settings so that the interaction continues to work.


Text: Trev Worsey Photos: Finlay Anderson