Tune It Up: How to adjust your Front Suspension

From the Tune It Up: Front Suspension article in Issue #016, we divulged our secrets to getting our suspension set up perfectly. From dialing your sag to tuning your compression damping, we’ve got you covered, so read on and get ready to shred, because your bike will feel incredible!

Correctly set­up suspension can make a good bike feel amazing, but get it wrong and you can make an amazing bike feel terrible. Do you know how much sag you are running? Do you know what the red rebound control on your fork does? If not, then it’s time to give your suspension some love. Mountain bike suspension is better than ever, but in order to function properly it needs to be set up correctly. In this article, we will take you through the essential steps to optimize your fork for the trail. Spending a couple of hours setting up your suspension will transform your riding enjoyment, and can also be a lot of fun.

You’re Not a Number

The purpose of this tuning guide is to help you discover a suspension fork setting that is optimum for you personally. There are so many variables when it comes to correct suspension fork setup – such as where you ride, what you ride, and how you ride – that simply following manufacturers’ generic setup guides (or copying your mates) will result in a poorly performing fork. Following this field guide will allow you to first obtain a solid base setting before hitting the trails and tuning for optimum performance.

Get Prepared

Before you optimize your suspension, you need to ensure that your fork is in good working order. There is no point in optimising your suspension if your fork is creaking and wheezing its way down the hill. If you’re setting up a new bike you don’t have to worry, but if your bike has seen some action it’s essential to first check that your servicing is up to date. If your fork is clunking and feels rough, we would advise sending it off to a service centre for an overhaul.

Before you start you will need to dress in your normal riding clothes, right down to your helmet and backpack (full of tools and water if you carry them). Correct setup is dependent upon weight, so there’s no point in getting a perfect tune before strapping on a 5kg backpack. You will need to choose a short section of your favourite technical trail, and bring a shock pump, a measuring device (ruler or tape), a calculator, and a willing assistant.

“A balanced suspension setup is very important. Traction not only comes from the tires and terrain surface, but the amount of force the rider is placing on the front and rear tire. A balanced setup is important to this element of traction. At the very basic level, setting up sag is the first step in a balanced setup. We recommend 15­20% in the front.” ­Mark Fitzsimmons [Fox Suspension Program Manager]

What is SAG?

For your suspension fork to perform correctly, it must be able to respond to every contour of the trail. When you hit an object your fork compresses, and the energy from the impact is released
by extending back out again or through damping. To maintain traction, suspension forks not only have to absorb impacts, but also extend to fill holes, keeping the tyres on the ground.

In order to let the suspension both compress and extend, we have to preload the suspension with our own body weight. When we sit on the bike, the amount the suspension compresses is known as sag – and it defines the way the bike performs.

The Essentials – Getting Your SAG dialled

Before you start, make sure your suspension fork is in fully open mode (if you have a low-speed compression adjuster, wind it fully to the negative direction, and if you have a three-
position compression adjuster turn it to ‘descend’ or ‘soft’). Unscrew the air spring valve cap on the suspension fork and place it somewhere safe. Have your assistant support the bike as you while holding one brake (not both, or you will cause an incorrect reading), bounce firmly up and down to charge the negative spring and free up any stiction. Assume your normal standing attack position, then after allowing the bike to settle for at least twenty seconds, have your assistant push the rubber O­ring on the fork stanchion down to the rubber wiper seal.

Carefully rock your weight back and dismount from the bike without disturbing the position of the O­ring. Measure the distance the O­ring has been pushed up from the wiper seal in mm. Divide this number by the total travel (e.g. 160mm) and then multiply by 100 to get the percentage of sag. We recommend a base setting of 15% for aggressive riders, and 20% for those looking for more comfort. Using a shock pump you can now set the sag.

If you require less sag, simply add air to the fork, and if you require more sag, let some air escape from the fork. Add air in ten­psi increments, and repeat the measuring process each time until you reach the desired sag.

Now that the sag is set to 20% (or 15% for aggressive riders), we can start to optimize the bike for personal riding style and terrain. Set the rebound to the manufacturer’s recommended setting (or halfway) to get a good base setting. From this point forward it is important to adjust only one setting at a time ­ it’s now time to hit the trail!

The Fun Begins – Time To Tune

It’s now time to optimize your base setting. Find a short section of local trail that includes features that you regularly ride, rocks, drops, jumps, berms and G­outs – the more features the better. Choose a trail that you are comfortable with and can hit the same lines again and again.

“If a rider has a trail they ride weekly and know very well, they should be using all of their travel on occasion. What often happens is a rider will go to a new trail, or one that they don’t know as well, and won’t achieve full travel. This is OK, as they won’t be riding as fast as they would on familiar trails.” ­Mark Fitzsimmons [Fox Suspension Program Manager]

Tuning Air Spring Pressure

What to focus on:

• How does the fork respond to big impacts?
• Is the fork bottoming out frequently
• Are you getting full travel on the big hits?

At the end of the trail, check the amount of travel used. If you’re a long way off reaching full travel, you should reduce the main air spring pressure in your fork (if your fork has an additional negative air spring please check the user manual for guidance). However, if you feel like your suspension is bottoming out (running out of travel, resulting in a harsh impact) on the bigger impacts, you need to add air to the fork. Add or remove air in 5 psi increments and repeat the process until you are reaching almost full travel on the biggest impacts. If you find you have to add a lot of air to stop bottoming out and the fork now feels harsh over small bumps you may need to adjust your spring rate (see later in guide). When happy make a note of your optimized sag settings / air pressure.

“Beyond sag, making sure rebound is fast enough is the second most important aspect in making sure the bike is balanced.” ­Mark Fitzsimmons [Fox Suspension Program Manager]

Tuning Rebound Damping

What to focus on

• How does the fork respond to fast repeated impacts?
• Do you feel like the bike is pushing back at you after a big impact?
• Does the bike feel like it’s skipping or gripping?

Next it’s time to fine­tune the rebound damping. Rebound damping controls the speed at which
a compressed suspension fork re­extends after an impact; the more (+) damping added the slower the suspension fork extends. If rebound damping is too low (­), the fork will extend too fast and feel bouncy and out of control. If the rebound damping is too high (+), the fork will not recover fast enough after repeated impacts and will “pack down,” getting low into its travel.

You want the fork to rebound as fast as possible without losing grip and control. To set the correct rebound damping start by adding full rebound damping (+). Ride your trail and focus on how the fork springs back after impacts, and how it feels over repeated hits. The bike will feel harsh at first, as the wheel cannot follow the ground fast enough. Repeat again, but reduce rebound damping two clicks (­). Repeat this process, reducing two clicks at a time until the bike becomes too bouncy and lively on the trail, and you feel that you are losing grip and control. Now repeat, each time adding (+) one click of rebound damping until the bike feels controlled with good grip – boom! your rebound is dialled! When happy record the setting.

“It’s a good idea to ‘bracket’ on your local trail and find your personal limits. Add damping and spring rate until it is unrideable, and repeat the exercise by decreasing spring rate and damping until it feels unrideable again. You will most likely find yourself liking one end of the spectrum or the other. This will be your starting point and tuning range.” ­Mark Fitzsimmons [Fox Suspension Program Manager]

Tuning Compression Damping

What to focus on:

• Does the fork dive through it’s travel on hard braking or bermed corners?
• Does the fork feel harsh over small bumps

Your fork will either have a Low Speed Compression (LSC) control or a simple three­way firm/medium/soft adjustment. If you have LSC control the quickest and best way to tune it is through bracketing. Ride your test trail and focus on how the fork feels under hard braking and
weight shifts – does the fork dive excessively under braking or in G­out corners?

Start with minimum LSC (fully ­), ride the trail, then repeat while increasing the LSC (+) until the fork feels harsh over small bumps; these are now your tuning extremes. To bracket adjust the LSC to the middle point between these extremes and ride the trail again. You are looking for a setting that minimises fork diving, while remaining plush over small bumps. Compare the feel of the new setting with the previous two and choose the two settings that felt best, then adjust the LSC halfway between them again and repeat continuously until you find the setting that works best for you. When happy record the setting

Tuning High Speed Compression Damping

What to focus on:

• Does the fork bottom out too easily on moderate impacts?
• Does the fork feel harsh and lacking in travel?

Some forks have an external High Speed Compression damping control (HSC), controlling the rate at which the suspension compresses at high shaft speeds (big, fast impacts). If you find that your fork is bottoming out too easily, or lacks mid­stroke support, it’s time to tailor HSC. Not enough HSC results in a fork that blows through its travel easily during moderate hits. Too much
HSC makes the fork overly harsh, not absorbing impacts properly. To set the high speed compression, ride the test trail again and focus on how the fork responds to big impacts. Use the same bracketing technique as for LSC until the fork offers support without feeling overly.

Tuning The Air Spring Volume

What to focus on:

• Are you having to run minimal sag to stop bottom outs?
• Are you running lots of LSC and HSC?
• Does your fork feel harsh over small bumps?

If you have followed the guide this far your fork should be feeling pretty good. However, if you are a very aggressive or heavier rider, you may find you have to run very high pressures and lots of HSC to avoid bottoming out and are therefore sacrificing small bump absorption. If this is the case your fork can be improved by decreasing the air spring volume. As the fork moves through its travel initially the pressure in the air spring is low and the fork is plush, as the fork nears the end of its travel the air pressure in the spring rises and the suspension gets firmer (called ramping up). The lower the volume of the air spring, the faster the pressure increases (ramps up) during an impact. This means aggressive or heavier riders require a lower air spring volume to keep the small bump performance while reducing harsh bottom­outs.

Many forks now have methods for easily increasing the spring progression, such as Rockshox’s screw in Bottomless Tokens, Fox’s volume reducers, and the MRP Ramp Control ­ to name just a few. Other forks can be tuned by adding small quantities of oil to the air chamber (please consult your manufacturer). The addition of 1­2 volume reducers or Bottomless Tokens can have a huge impact on your fork’s performance. If your fork supports volume reducers, follow the manufacturer’s fitting guidelines. Then re­set the sag, rebound compression, and LSC and you should find the fork less prone to bottoming out.

Should I Not Just Copy The Pros?

We all know that pro riders run really firm setups, but it is important to optimise the suspension fork’s travel for your style and speed of riding. “I like to think of this in terms of speed. Unless you are capable of riding the trail at the same speed at which your racing hero is, then you don’t need the same setup as them. While a stiffer setup does allow you to stay on top of the bumps and generally carry more speed through sections, it doesn’t necessarily mean that it works for everyone.

Set your suspension for your trails and riding abilities, and adjust as your skill and speed increase.” ­Jon Cancellier [RockShox Product Manager] “In racing, a stiff/firm suspension setup equals efficiency. Whether it be DH race or enduro, a pro rider’s setup is tuned for that single run at maximum effort. The only limit of how firm they can go is speed and body fatigue. Most of the top riders in the world don’t even train or ride for fun on their ‘race settings.’ It’s just too firm for the body to handle.” ­Mark Fitzsimmons [Fox Suspension Program Manager]

It’s Time To Shred

Your fork should now be dialled in to how you ride, offering maximum performance on the trails you enjoy the most. In Issue #017, we will take you through rear suspension and how to set the perfect balance.

Words & Photos: Trevor Worsey