TF Tuned Glossary

Mountain Bike Suspension  - Jargon Buster

Here at TF Tuned, we spend loads of time chatting shop to our customers via phone, email or in person. No matter if its info on service kits, oil and consumables or advice on the best option for new product purchases, we're here happy to help!

One thing that we see on a daily basis is confusion on features or understanding technologies of the wide variety of products out there on the market. Often this confusion is made worse by different people or manufacturers using different language to describe the same thing.

In this ‘jargon buster’ we aim to give some clarification of some of the key terminology being used, as well as explaining some of the key principles which if understood can help make riding more pleasurable – this is the reason we ride after all!


Basic Terms

 

Spring: The component of the shock or fork that supports the combined mass of the rider and bike (sprung mass).

Damper: The component of the shock or fork that controls the spring or springs energy as it oscillates. 

Coil Spring:  A spring that wound from a wire and offers a resistance based on the angle of the wind and diameter of the wire. This resistance usually increases in a linear manor, is measured in a force over a distance and by the amount it will move before it goes coil bound or by the stroke of shock it is designed for. For more info click here.

Air Spring: A spring that supports the rider’s mass, by compressing a volume of air in a cylinder using a piston. 

Bottom Out: The harsh feeling when you run out of suspension travel, the spring is fully compressed. Can be avoided by having the right suspension, well maintained and correctly set up (air pressure or spring weight).

Top Out: The harsh feeling when the suspension un-loaded or fully extended at the ‘top’ of the travel. May feel like a knock or a bump as the suspension reaches its maximum extension. Again this can be avoided by having well maintained and correctly set up suspension.

Travel: This is the term used to describe the movement of the wheel allowed by the fork or frame.

With a fork, the travel will be expressed in terms of the maximum length (inches or mm) that the fork will compress under the rider weight.

Frames are usually described in terms of the rear-wheel travel they achieve. 

Shocks have their own travel described by how much the shaft can compress. This term is known as Shock Stroke.

Compression: The movement of the spring as it is ‘squeezed’, by riding over bumps, etc.

Rebound: The action of the shock/fork extending having been compressed.

 


Damping

 

Compression Damping: This controls how quickly the fork or shock are able to be compressed. This can be used by the rider to keep pedalling efficiency, control dive or to control the big hit capability of the suspension.

Rebound Damping: This controls how fast a fork or shock can extend after being compressed. Not enough rebound damping, the fork will extend too quickly, resulting in a lack of control and grip. Too much rebound damping, the suspension will have a tendency to compress and remain compressed over multiple bumps, resulting in a harsh, bumpy ride and a lack of travel or packing down.

 


Compression

 

High Speed Compression: This controls how easily the unit is compressed for large, fast movements, like drops or rock gardens.

Mid Speed Compression: This controls the unit once the initial compression damping has been used up.

Low Speed Compression: This controls how easily the unit is compressed for small movements. You should use it to keep the bike prepared for riding situations like berms, where the suspension is compressed but you might still need a little bit of travel in reserve.

Platform/lockout: A low speed choke or block of oil flow causing an immediate firm up of the fork or shock. This will usually have a threshold and will move when this threshold is overcome. The overall level of "Firmness" varies between manufacture and product. Sometimes it’s more of a lockout sometimes more like a platform. 

Compression Control: The control of compression/lockout or platform can be achieved with a set of dials or leaver-sometimes remotely mounted.


Rebound

 

Rebound; the movement of the spring as it extends having been compressed.

Low Speed Rebound; this controls the unit extending after hitting small bumps ridden at all speeds.

High Speed Rebound; this controls the unit extending after hitting a large obstacle at medium to high speeds.

Rebound Control; a dial or lever on a fork or shock that enables the rider to adjust the ease with which the suspension will rebound. This might be expressed as ‘Clicks from maximum/minimum’ or ‘Turns from maximum/minimum’ referring to the extent to which the rebound control lever is rotated from one or other position.


Technical Terms

 

Sag; this is the amount of travel used up by sitting on the bike when it is at rest, which allows the wheel to drop into bumps to give more grip and a more comfortable, controlled ride. A rider wants sag so that the suspension is active as soon as the bike's in motion rather than only when it is being compressed by bumps. This can be changed by adjusting the preload/air pressure. Depending on you, your riding style your bike manufacturers advice the suggested amount of sag will vary.

Linear Rate; this means that the unit's travel feels the same all the way through to bottoming out, and is common in spring suspension systems.

Progressive Rate; this means that the unit stiffens up towards the end of the travel, and is common in air suspension systems.

Falling Rate; this is the opposite of a progressive rate unit – it is difficult to compress at first, then resists less as you use up more travel.

Air Assist; this is a means of adding extra preload to a coil spring by adding air to the chamber as well. This is used as a cheap shortcut by some manufacturers to allow one fork to be suitable for all rider weights, in theory. It is also supposed to help ease the fork into its travel.

Air Volume adjustment; Can be achieved by introducing ‘Tokens’ into the air chamber to increase air spring progression. Alternatively some manufactures have a secondary air chamber that will reduce the main air chamber with a secondary ‘ramp up’ air chamber. In more modern systems air volume can be adjusted in both + & - chambers.

 

 


Componentry

 

Shim Stack; a series of thin shims which regulate the oil flow through ports in a piston. These can be orientated in many ways and can have quite dramatic effects. 

Damper Piston; this can come in many guises, but it is the doorway for oil to pass through separate rebound and compression sections. The piston has holes in it, called ports. On either side of the piston you can find shims or a variant of platform valving to slow down oil through these ports.

 

Shaft; this is the part of the shock that disappears into the main body of the shock under full compression.

Damper Body; this is similar to the shaft but is a term used for air shocks.

Air Can; this is the shroud/case for an air shock which holds the air that you pump in. This can be unscrewed on some shocks to carry out periodic maintenance.

Air Valve; this is the bit you attach your pump to when pressurising the shock unit.

Valve Cap; this is simply the cover for the air valve.

Eyelet; these are the loops at either end of a shock. They hold mount kits, and are part of the system which keeps the shock attached to the frame.

 

Shock Bush; this is the hula-hoop shaped item pressed into the eyelet of the shock. They are designed to wear instead of the eyelets of the shock, and are therefore replaceable. They may also be Top hat shaped and formed of two parts to make the bearing interface. materials for these include both metal backed but coated bushings and solid polymer depending on mount kit type.

Fork Bush; these are cylindrical rings in the lowers which the stanchions sliding smoothly up and down, and in line with each other- if they are too tight, they can make the fork feel sticky , but if they're too loose, the stanchions will have play.

Mount Kit; this is the assembly that presses into the shock eyelet. This adapts the shock to the frame They can come in a huge variety of dimensions to allow the fitment of any shock to any frame.

Heavy Duty Mount Kit; this is a variant of mount kit. They consist of a stainless steel axle, with a polymer bushing to reduce friction on the eyelet. This eyelet is surrounded by two rubber sealing rings to keep out dirt and grime. Aluminium spacers are placed on either end of the axle to keep everything tightly fitted. These kits spread the force of the shock over a greater area, therefore increasing durability.

 

Reducers; these are the aluminium ‘top hat’ spacers that press into the bushes on a standard shock mount kit. These are generally weak and tend to wear out fast.

High Volume Air Can; air shocks can ramp up excessively toward the end of the stroke as the air can runs out of volume. The result is a lack of travel and a harsh feeling at the end of the stroke. A high volume can literally has larger volume to squeeze a bit more travel out at the end. Side effects are less support mid-way through the stroke as the air wallows in a now much larger can.

Nitrogen Charge; this is used to fill a separate chamber to allow the oil chamber to expand when the shaft enters the shock displacing the oil. Nitrogen is used because it has no moisture, unlike the air we breathe or pump into our shocks. (Moisture contaminates oil and the two should be kept separate) Another advantage is that nitrogen will not expand when heated up; if it did, it would restrict travel and give the shock a gapped feeling.

CSU; stands for Crown/ Steerer/ Upper. The upper assembly on most forks, these are usually bonded together so individual parts can't be replaced.

Lowers; these are the lower assembly of the forks. They are thicker than the stanchions (upper legs), and are usually covered in manufacturer's stickers.

Stanchions; these are the upper legs which slide into the lowers. These are anodised for a harder wearing finish but can wear out if the fork is not correctly maintained. If the stanchion is allowed to wear, the fork will perform poorly as oil will be allowed out, and water and dirt will get in.

 

Steerer Tube; this is the long tube which extends from the top of the forks. It goes through the headset and the stem is clamped to it.

Triple Clamp Forks; these are downhill forks that are braced above and below the headset, allowing greater strength at the cost of increased weight.

Single Crown Forks; these are more common than triple crown forks – typically, they offer less travel, but are lighter. They can be used for almost all applications in one form or another, depending on their design, amount of travel etc.

Bolt-Through Axle; this is a type of fixture to secure the wheel to the lowers. 15mm and 20mm axles are common for this type of fixture, and can have pinch bolts or a wedge system to stop the axle rotating.

Quick-Release Axle; this is the other most common method of wheel attachment. The common sizes here are 9mm. Advantages include easy tightening and quick wheel removal, but it's important to make sure they're done up properly every ride.

Boost axle spacing; This is the latest industry standard for axle width allowing for stiffer wheel builds. Front are 110mm spacing’s in either 15mm or 20mm and rear 148mm for trail and up to 157mm for DH

 

Shock Reservoir or piggyback; this refers to the attachment of a reservoir to a shock. This gives more oil volume for the size of the shock.  These present on both air and coil shocks.

The shock reservoir allows for further adjustment to oil flow and dissipates more heat over long runs.

The Resi holds oil and a gas (usually nitrogen or air), and is separated by a piston (IFP) or bladder.

Travel Indicator O-ring; this is an o-ring on either the stanchion of a fork, or the shock shaft, which can be used to show how much travel you're using - as the suspension compresses, the o-ring is pushed along the stanchion/shaft.

Control valve or Boostvalve; This is a pneumatic piston which closes the oil ports during pedalling, this then opens when you hit bigger stuff. Again, this translates to more efficient pedalling, while still allowing full use of travel.

IFP; this stands for Internal Floating Piston. This piston separates the nitrogen from the oil inside the damper body. The reason for this is to allow the oil to expand when the shaft enters the shock (think of it like getting into a full bath, the water rises as you get in and spills over the top), this displacement is necessary to allow the shock to get full travel. Also, when oil gets hot, it can expand, so having a chamber that can take up this expansion is very important.

Bladder; This is another way of allowing for Displacement of shaft and compensation of heat in a fork or shock (same as the IFP). In this instance it is achieved by either extending a rubber oil filled bladder, or compressing a nitrogen filled bladder submerged in the shocks damper fluid.

Wiper Seal; this is the usual way of keeping dirt out of the fork lowers. As the forks are compressed, the wiper seal scrapes dirt from the stanchions, stopping it from contaminating the oil and damaging the internals of the fork. If these are allowed to degrade, the lowers will become contaminated with dirt and water.

Oil Seal; these keep the oil where it should be, in the shock/fork. Some forks can be run without these, which reduces stiction, but means the fork must be maintained more frequently.

Foam Ring; these are fitted between the oil seal and wiper. Sometimes there are only wiper seals and foam seals. The foam seals are soaked with oil, so that every time the forks are compressed, the stanchions receive lubrication, minimising wear.

 

Spiking; this occurs when the forks are compressed too fast for the oil to travel through the pistons and shim stacks. Imagine people walking through a door. One at a time, they can pass through okay, but when they all try to run through at once they jam up the doorway and shake the walls. The name 'spiking' refers to how this feels at the handlebars.

Ramping Up; this occurs towards the end of the stroke and is commonplace in air forks/ shocks. It is a feeling of increased resistance towards the very bottom of the suspension travel. This can also be an engineered bottom out resistance on some units to help with excessive bottom-out situations.

Fork Brace; this is the curved arch which connects the lower legs of the fork over the front wheel. It increases the stiffness of the fork.