Christoph and Georg from bc ride their bc original Podsol bikes over a trail in the forest.
Christoph and Georg from bc ride their bc original Podsol bikes over a trail in the forest.

How Does Suspension on a Mountain Bike Work? Springs and Shocks Explained!

Modern MTB suspension systems consist of a spring and a shock. We explain the differences so that you can find your perfect suspension setup more easily.

It sounds like a question from a quiz show: "What is the difference between a spring and a shock on a mountain bike?" Although there is a lot more going on in MTB suspension components, colloquial language clearly indicates the main function: it bounces! The spring is only one part of the chassis and has a very specific task. It is complemented by an additional shock absorber. If you read our text, you will not automatically be a millionaire – but hopefully you’ll gain a better understanding of what is happening in your chassis and how you can optimally tune it.

Christian from bc Product Management rides his RAAW Madonna down a stony slope.
Christian from bc Product Management rides his RAAW Madonna down a stony slope.

Shocks and suspension forks have a decisive influence on your riding experience.

Christian drifts through a bend with his YETI MTB on a forest path.
Christian drifts through a bend with his YETI MTB on a forest path.

Find out how the suspension elements of your mountain bike work here!

Hardtail versus Full-Suspension: One or Two Suspension Elements?

Mountain bikes usually have one or two suspension elements. If there’s only front wheel suspension, and the rear frame is rigid, this bike is called a "hardtail". If both the front and rear wheels have suspension components, the term "full-suspension bike" is used. A suspension fork is used for the front wheel, which connects it directly to the frame. For rear wheel suspension, a rear shock strut is used, which connects the rear wheel to the main frame via one or more deflection(s). The shock strut is usually called a "shock", also in our shop. Due to the risk of confusion with the functional damping within the suspension element, allow us a brief aside: We are speaking here about the MTB shock when we mean the material suspension element. When we speak of damping, we mean the damping capability of the part... Why install suspension at all? Suspension improves driving dynamics as well as comfort. It allows the wheels to traverse the ground without losing contact. This is why motorbikes or cars without suspension systems are inconceivable. Road bikes, cyclocross bikes or gravel bikes, on the other hand, often do without real suspension systems and are thus probably the fastest means of transport without them.

The MTB Spring: Energy Storage on the Trail

Physically speaking, the spring element isolates you from vibrations caused by riding across uneven ground. Your spring element, whether it’s a suspension fork or MTB shock, connects the front or rear wheel with the rest of the bike and you as the rider. This means that the front wheel or wheels can move up and down without the ensuing vibrations transferring to you or your bike. To do this, the spring is first compressed and later expands again. The spring therefore absorbs energy and releases it again. Of course, this also applies to landings after jumps, where the spring absorbs some of the kinetic and potential energy and returns it later. Both energy absorption and release are "controlled" by the shock. Air, steel or titanium are the main spring media used on mountain bikes and E-mountain bikes. We outline the advantages and disadvantages of individual materials and concepts here.

The MTB Shock: Control Freak on Off-Road Terrain

Imagine you compress a coil from a ballpoint pen and abruptly release it. It will probably fly straight into your eye. A non-damped suspension component on a mountain bike would behave in the same way. This is where the shock comes into play. Its function is to control the speed of the inward and outward spring movement. This allows you to precisely adjust the behaviour of your spring system to parameters such as suspension travel, body or system weight, track conditions or ambient temperature. The damping medium in almost every modern suspension component used on a mountain bike or E-MTB is suspension fluid – either in an open oil bath or a closed cartridge, depending on the quality level. High-end components often contain cartridges with a membrane, also known as a "bladder". The great advantage of the closed design is that air and suspension fluid are hermetically separated from one another. One of the benefits of this is that it prevents the suspension fluid from foaming. Foaming fluid leads to undesirable changes in the damping characteristics.

A bc mechanic fills a suspension fork with new fork oil.
A bc mechanic fills a suspension fork with new fork oil.

Regular servicing prolongs the life of your suspension elements and ensures particularly high performance when biking. © bc GmbH

The MTB Suspension Setup: The Right Setting is Crucial

Both the spring and shock side of your suspension can usually be adjusted externally. External means without opening the fork or the shock. An air spring allows you to adjust the suspension stiffness and thus the important negative spring travel with a special suspension fork or suspension pump. If a steel or titanium coil (more precisely: a helical compression spring) is used in your shock, you can achieve the appropriate suspension stiffness with various coils. In the case of damping, a distinction is made between rebound and compression. Higher-quality spring components allow you to adjust both directions separately, sometimes even individually for low and high speed. You can learn here what this means exactly and how you can find your optimal suspension set-up.

A bc mechanic optimises the suspension stiffness on an MTB using a suspension fork and shock pump.
A bc mechanic optimises the suspension stiffness on an MTB using a suspension fork and shock pump.

With a suspension fork & shock pump you can adjust your setup to your weight, riding style and terrain. © bc GmbH

Effects of Sprung and Unsprung Mass: Light and Heavy

Your suspension element connects a wheel to the rest of the bike. So when this wheel compresses, a smaller mass moves against a stable larger one. This is not only a law of physics, but also a stroke of genius. It ensures that impacts from the ground do not reach the steering components, bike and your body. The small mass that moves is called unsprung mass and consists of, among other things, the wheels, tyres, brake rotors, possibly the cassette and so on. The larger stable part "behind the suspension" that doesn't move is mainly your body, the main frame of your bike and most drivetrain parts such as derailleurs or cranksets. The smaller the unsprung mass is in comparison to the sprung mass, the better your suspension’s response. This is just one of the reasons why lightweight wheels have such a positive effect on the riding dynamics of your mountain bike. We have put together a guide to assembling your dream wheelset yourself here.

What About the Tyres? Self-Damping, etc.

Strictly speaking, all possible components of a mountain bike "spring" and "absorb shocks". First of all are the tyres, which flex as they roll, so they constantly deform while in motion and then return to their original shape. The deformation itself counts as a spring function, while the so-called self-damping of the material slows down the movement in both directions. When frames or handlebars bend under load (often called "flexing"), this is basically also a spring function. Nevertheless, one usually only speaks of suspension in the case of suspension forks and shock absorbers. There are good reasons for this: Firstly, the "pseudo-travel" of the components results from their respective material properties and can hardly be controlled and adjusted externally. Secondly, the "travel" that tyres, wheels, frames or handlebars can provide is extremely limited. If the material deforms beyond a certain limit, it fails. Nevertheless, on a road bike or gravel bike, the deformation of the tyre and carbon fork or frame is often already the entire suspension travel. However, that’s a different topic altogether.