Suspension Forks – More Comfort and Performance for MTB's, Trekking & Gravel Bikes

Basically, a suspension fork on a bicycle always works the same way – regardless of whether it is a mountain bike or a trekking bike. Like at all bike forks basically they consist of two fork blades, but in detail these are divided in two lower legs (also called casting) and two stanchions tubes, that can dip into the lower part. The stanchions house the suspension on one side and the damping on the other. The suspension traditionally works with a steel spring or at modern types with an air chamber – if the bike hits the ground, the spring element of the fork will be compressed.

To ensure that the suspension does not uncontrollably spring back to its original position after this movement, and to avoid unnecessary bobbing at the slightest nudge, a suspension fork also has damping. This is usually a cartridge filled with oil inside the fork, in which the oil is pressed through valves during compression and extension. This slows down the speed of the compression and extension and increases comfort. With higher-quality suspension forks, the strength of the rebound damping can even be adjusted.

As a bicycle part developed in the early 1990s, steel springs were used in the first front fork suspensions in terms of the suspension element – that's why they were called suspension forks. The steel spring is compressed when the bike hits the ground. Springs of varying hardness were used to adapt the suspension to the rider's weight. Furthermore, at many current steel suspension forks, the spring can be more or less compressed using an adjuster to make the suspension harder or softer; this is also called preload. Steel suspension forks respond more sensitively as well as linearly, but they are a bit more heavy – today they are mainly used on MTB suspension forks for freeride and downhill cycling or on suspension forks in the very low price range.

Today, suspension forks with an air chamber based spring are commonly used. In the event of impacts, this air chamber is compressed – as with the steel spring. The advantages are their significantly lower weight and their much better adjustment possibilities. With an air suspension fork you can easily adjust the hardness of the air suspension to the rider's weight and personal requirements using an air pump.

Whether you are riding with steel or air suspension, the spring element can be adjusted to the rider's weight, but this changes the speed at which the suspension compresses and decompresses. In particular, a fork that rebounds too quickly can be problematic because it makes the front wheel difficult to control. To solve this problem, most suspension forks today have what’s known as a rebound damping system. This consists of a cartridge filled with oil in the fork. When the suspension springs back to its original position, this oil has to pass through valves and thus controls the speed of the rebound. This rebound damping thus controls how quickly the fork extends again – or rebounds – after it has been compressed, which is where its name comes from. Most suspension forks have this kind of rebound damping; higher-quality forks can be adjusted individually from the outside.

You can also find compression damping, particularly on higher-quality mountain bike suspension forks. This is also a cartridge filled with oil, but it controls the speed at which the suspension compresses and also prevents the suspension from bobbing in response to the rider’s movements, for example when riding out of the saddle. Compression damping therefore controls the speed at which a fork compresses under pressure. Adjustable compression damping is offered by higher-quality suspension mountain bike forks, and more rarely for trekking bike or touring bike suspension forks as well.

Modern suspension forks now offer many adjustment possibilities. We’ve put together a list of the most important functions of bicycle suspension forks below.

• Lockout: This allows you to lock the suspension so that the fork cannot bob, for example, when riding out of the saddle on level ground. The lockout is operated either by a lever at the top of the fork or, with higher-quality suspension forks, by a lever on the handlebar.
• Spring travel: The spring travel means how far the fork's immersion tubes dip into the standpipes – in other words, how far the fork can compress. The spring travel is always given in millimetres. With some suspension mountain bike forks, the spring travel can be adjusted. At BIKE24 you will always find this information in the respective product description.
• Rebound damping: This is the damping to determine the speed at which the fork extends. Rebound damping is built into every suspension fork, and the strength of this damping can be adjusted on high-quality forks.
• Compression: This is the damping that controls the speed at which the fork compresses. Compression damping is not common in every suspension fork, and it can only be adjusted in higher-quality mountain bike suspension forks.
• Platform damping: High-quality suspension forks feature what is known as platform damping. This ensures that slowly occurring impacts, such as rocking back and forth in the saddle, are damped and thus the riding behavior becomes smoother. Spring compression therefore only occurs at higher forces, where the suspension is really necessary.

Generally speaking, suspension forks can be divided into two broad categories: suspension forks for MTB's and hybrid, touring and gravel bike suspension forks. Front suspension originally invented for mountain biking, and almost every MTB today comes with a suspension fork. That’s why there is a huge selection of different forks for every cycling activity in this segment. Whether you’re after a classic suspension mountain bike fork, a downhill suspension fork or a high-end suspension fork for 29-inch bikes – mountain bike suspension forks offer plenty of spring travel, between 100 to around 200 millimetres depending on the cycling activity. Suspension MTB forks usually offer the widest range of adjustment options for suspension and damping in order to optimally adapt the suspension to the rider's weight, riding style and terrain. The spring travel can often be adjusted as well. Whenever there are innovations in bicycle suspension forks, they are most likely to be found in MTB suspension forks first.

Suspension forks for trekking, city and urban bikes offer less spring travel, normally around 45 to around 100 millimetres. They usually offer fewer adjustment options as well. But they don’t really need them, because the demands of the terrain on a classic trekking bike tour are not as extreme as those found on mountain bike adventures.

Most suspension forks consist of two lower legs and the stanchions that stand parallel to the left and right of the front wheel – like a rigid bicycle fork, but containing the suspension parts. However, a few suspension forks have two rigid fork blades, while the suspension is placed above the fork crown, directly under the frame’s head tube – these are known as ‘headshocks’. And just as exotic, if not more so, are the suspension forks with only one immersion tube and standpipe on one side – the so-called ‘lefty’ fork.

No matter which bike you need a suspension fork for, you must be aware of several key measurements to ensure the new suspension fork is the right fit for your bike. We have summarised the most important measurements to note when buying a bicycle suspension fork here:

• Wheel size: The suspension fork must fit the diameter of the wheels – there are suspension forks for wheels between 20 inches and 28/29 inches.
• Spring travel: The spring travel of the new fork should correspond to the spring travel of the previously mounted fork; a maximum of 10 millimetres more or less is tolerable if the fork’s installation length stays the same.
• Axle-to-crown height: This is the measurement between the axle and the upper edge of the fork crown – in other words, the length of the fork. If the suspension fork’s installation length deviates from the previous one, the handling of the bicycle may change for the worse, and if it deviates greatly then worse handling is inevitable.
• Steerer tube diameter: The steerer tube is the suspension fork’s upper tube that has to be inserted into the frame’s head tube. For non-offroad application the typical measurement is 1 1/8”, while MTB suspension forks have a tapered steerer tube measuring 1 ½” at the lower end and 1 1/8” at the upper end. Older 26 suspension forks have a steerer tube with a continuous 1 inch diameter. 
  Steerer tube length: The steerer tube must be as long as the frame’s head tube + headset + stem + spacer. If you want to replace an existing suspension fork, then use the old fork’s steerer tube length as a guide.
• Axle standard: The fork end must fit the front wheel’s hub and axle. The axle standard consists of two numbers: axle diameter x hub width. So, for example, an axle with a 12 mm diameter and a 100 mm wide hub would be: 12x100.
• Brake mounting: The brake also needs the right attachment to the suspension fork: on the one hand, you have the classic rim brake; on the other hand, there are also post-mount caliper standards (widespread) or IS2000 mount standards (nowadays only rare) for disc brakes.

Does an e-bike needs a special suspension fork? Some manufacturers have developed special suspension forks for e-bikes, because of the higher speeds and the greater forces that can impact them. These are very similar to solid mountain bike suspension forks, but featuring an even more stable chassis. In general, however, any solid suspension fork will also work on an e-bike. As with any bicycle, the suspension fork for an e-bike must fit all the dimensions described above. At BIKE24 you will accordingly find a large selection of e-bike suspension forks as well.

Please note: For speed pedelecs and electric bikes offering speeds up to 45 km/h, it is mandatory to pay attention to the type approval. According to this, replacement parts must explicitly correspond to the parts listed in the type approval of the fast electric bike. Depending on the manufacturer and model, there are lists of approved suspension forks.

To mount a suspension fork yourself, you need some special tools. Besides a well-stocked maintenance equipment in terms of bike tools, you will also find specific bike fork accessories for sprung version such as oil or seal kits in our range. A must for all mountain bike riders also is a shock pump to be able to adjust the air suspension.

• There is a huge selection of suspension forks for bicycles. They can be divided into suspension forks for city, hybrid and touring bikes with a maximum of 85 millimetres of spring travel, and mountain bike suspension forks with at least 100 millimetres travel.
• Most affordable suspension forks usually feature a steel spring; higher-quality suspension forks work with air suspension which reduces the overall weight.
• In order for the fork to fit the bicycle, the wheels and the brake system, various measurements must be taken into account. The most important measurements that should be taken into account when making a purchase decision are the corresponding wheel size as well as the spring travel and the axle-to-crown length, i.e. the height of the suspension fork.
• A suspension fork should always allow the spring rate to be adjusted to the rider's weight. With air suspension forks, this is easily done with an air pump; with steel suspension forks it is done with a rotary wheel.
• Higher-quality suspension forks offer further damping adjustment options – this allows the fork to be optimally adapted to the rider's weight and the terrain, but also requires a certain basic understanding of how a suspension fork works and what is expected of it.