Suspension Buyer's Guide
Author: Darren Mallard Date Posted:9 March 2022
Today, mountain bike suspension is the most reliable and offers the best performance ever known to riders. While the suspension may be better than ever, it can still be quite a minefield to navigate your way to what will suit your riding the best. That is why we have created this guide to ensure you are on the best equipment for you.
Sag is the percentage that suspension sits in its travel when a rider is on the bike. Sag is required to ensure optimum traction as often as possible. The suspension likes to push the wheel into these holes because the terrain will usually go down away from the rider as much as it comes up at the rider.
Most bikes work best with 25-30% of sag in the rear suspension and 20-25% in the front. It is integral to try and keep your bike balanced in sag and as it moves through its travel to retain the geometry and ride characteristics.
Damping refers to the oil circuits that control the suspension's speed and resistance as it moves through the travel. Using needle valves or pistons composed of shim stacks to control oil flow, Damping can add precise control to your suspension. It is used to prevent your fork from compressing too easily or rebounding too fast.
Compression damping controls the force required to compress your suspension, irrespective of the spring rate. A lockout is a form of compression damping; it completely closes the compression oil circuit to prevent the fork from compressing.
If your fork is at the correct sag percentage, but it is diving through its travel under braking or in corners, then you may want to add low-speed compression demeaning to keep it riding high. If at the correct sag in your suspension and it feels harsh, you might have too much compression.
Rebound damping controls the speed that your suspension returns to its sag point after it is compressed. If there is too much Damping, your suspension won't get back to full extension. This will cause the suspension to pack down and decrease ineffectiveness. If it is too fast, your suspension will extend past sag and cause oscillation. When riding, this will cause the bucking sensation through rough terrain.
Ideally, after a compression, you want your suspension to return the bag to its sag point as fast but as controlled as possible.
High-speed dampening controls your suspension's dampening when compressing or rebounding at a high velocity. It is irrelevant how fast your bike is moving over the ground. It is all relative to how fast your suspension moves up or down.
Some instances where high-speed compression or rebound are used and come into play are Rock Gardens, Roots or landing a drop to a flatter landing.
Low-speed damping adjustments are used to control your suspension when travelling at a low velocity. These adjustments are used to control your fork in corners, G-Outs or jump takeoffs.
The term "Spring Rate" refers to the amount of force required to compress a spring by 1 inch. To achieve the correct sag, you need to ensure that your spring rate is correct.
You can adjust their spring rate by either adding or removing air. Steel coil springs are available in 50lb increments but can be slightly adjusted by adding preload.
Suspension kinematics refer to how the rear suspension acts at different points throughout its travel. These figures determine how the bike operates under pedalling braking and its support as it goes through the travel.
Learning about kinematics and how it determines how your shock works can help riders decide what style (air or coil) of suspension will suit them best.
There are always two air campers in air suspension, one above the piston that compresses when the suspension moves through the travel. To combat the extra friction from the seals in air suspension, the negative air chamber adds pressure to the back of the piston to overcome the friction and reduce the breakaway force required.
Token /Volume reducer
Volume reducers reduce the size of a positive air chamber and tune how much the suspension chamber ramps up. It helps achieve a soft off the top feel without blowing through the travel.
Suspension forks come with different diameter stanchions (the tubes your lowers slide on) sizes and lower designs. These two parts are the determining factors for your fork's stiffness and weight
Cross Country forks often use 32mm stanchions and lowers with lots of recesses to optimise weight reduction. They are usually limited to having 80-120mm of travel. A lighter fork lets the rider pick up over technical obstacles and change direction easily through tight switchbacks. A more lightweight fork will also contribute to a lighter overall weight of the bike and enable it to climb quickly.
The downside to thinner stanchions and lighter lowers is they allow the wheel to flex laterally and twist horizontally. While this might seem more forgiving, it can lead to the rider's input being less direct and cause the bike to wander.
Trail and All-Mountain bikes use bigger 34-36 mm stanchions with 120-150mm of travel, and there lowers are built with more bulk to reduce flex. This may add a little weight, but the improved control and ride feel on the descents far outweigh any cons on the way up. Larger stanchion diameters can also allow larger air springs for more subtle suspension.
Downhill and Enduro bikes are built to descend at top speed. Because they are changing direction and hitting trail features at high speed, stiffness is paramount. 36-40 mm stanchions are ideal in this scenario as they reduce any front wheel wandering and optimises the suspension's performance. These forks often have 170mm to 200mm of travel to accommodate the big hits.
While most folks only use one crown to hold the legs to the steerer tube and the bike. Downhill bikes will often use a Dual Crown fork to increase stiffness. The two clamps lock the stanchions in 2 places and keep the stanchions stiff while dramatically reducing fore and aft wheel movement.
Rear shocks pack a lot of technology into a small package. XC bikes often use smaller air shocks with small damping circuits to control the motion. They are designed to provide traction on the downs while optimising pedal efficiency on the climbs. These shocks will often feature a remote lockout mounted to the bars for ultimate power transfer.
While the XC shocks are light and efficient, they offer minimal performance on long high stress descents. They heat up extremely fast, and you will notice a loss of damping control on descents. Trail shocks will employ bigger air cans with an increased negative chamber for increased small bump sensitivity. The shocks are bigger overall to increase the amount of oil in the dampening circuit. Both the larger air chamber and increased oil capacity reduce the effects of heat on the shock.
Enduro and Downhill bikes use Big shocks with massive air cans or steel coil springs. Their shocks also often have a remote oil reservoir that increases the oil capacity and dramatically reduces the effects of heat. These shocks are optimised for small bump sensitivity and supreme traction. While manufacturers try to reduce pedal bob, the end goal is always to have them active, and the rear wheel is tracking the ground.
Air vs. Coil
The Air vs. Coil sprung debate is as old as time. Air suspension uses air pressure against a piston to provide resistance against the suspension moving through its travel. Coil sprung suspension is much like what you are used to seeing on a motorbike or on your cars. It uses a steel spring to suspend the bike in its travel.
Air sprung suspension is extremely popular due to its lighter weight and infinite adjustability. Adding or removing the amount of spring resistance to achieve the correct sag is a simple matter of adjusting the air pressure. Once you have a shock pump, you can adjust the spring rate 1000's of times for free.
As the air spring compresses through the bike's travel, it increases the force required to move progressively. This means it is much harder to make the shock move deeper in the travel than when it is at the beginning. You can tune the spring curve and how the shock feels as it compresses using volume reducers/tokens. People who want small bump compliance but support deeper into the travel love air shocks.
Because the shock has to hold a considerable amount of air, there are numerous seals in the shock. Every seal increases friction and, in turn, increases the initial breakaway force. This means that if you were to compress an air sock compared to the coil shock and they both had no spring resistance, the air shock would be harder to move. The extra friction also increases excess heat, and riders will notice diminishing performance on longer descents as the oil heats up.
Coil sprung suspension is famous because of the fantastic small bump compliance and low breakaway force required to move the shock. Supreme traction on all terrains, but most noticed on loose surfaces. Because there is no air for the spring, there are fewer seals, resulting in less heat generation. The steel spring is also not affected by different air pressure at different altitudes. Coils have equal consistency.
Coils are available in different weights, and riders need to switch out the coil to the correct size to achieve the proper sag. Each spring will cost money, which can be a slightly costly experience. Coils are also heavier and can add extra weight to your bike.
Coil springs are very linear in their spring rate progression. This means the coil spring is very predictable throughout its travel, and riders will always understand how the bike will behave. The downside is that if your bike's kinematics are not progressive enough, then a coil shock will blow through its travel too quickly, creating an unsupportive ride and excessive bottom outs.
Deciding which is best for you comes down to your frame's kinematics, riding style and how you like your bike to feel. If you want supreme traction on a progressive bike, it is often best to go for a coil spring. If your bike's suspension kinematics are linear and you want a supportive spring, the air is the way to go.
If you want to find out more about what mountain bike will suit you best, check out our full guide HERE