Bike
MTB
Get to know your MTB suspension with this guide
Sag, compression damping, lockout?! What does all this mean? We break down all the weird suspension-specific terms you'll hear in the bike shop so you won't look like a total idiot.
When it comes to mountain bike geekery, perhaps no other area of the bike contains such a deep and mystifying vocabulary as the suspension.
While you probably shouldn’t get too hung up on the ups and downs (sorry) of mountain biking’s fiercely competitive jargon scene, it will certainly help to understand the basic terminology deployed in reference to the suspension.
In order to help, we’ve compiled a glossary of some common MTB suspension references.
Getting the right suspension settings is a fine art
© Bartek Woliński
Arch: The arch connecting the two legs of a suspension fork.
Axle: The axle holding the front wheel in place on a set of forks.
Axle path: The direction the rear axle moves as the suspension is compressed.
Bottom-out: When the suspension unit reaches the limit of its travel. As a very general rule of thumb, a fork or shock shouldn’t be regularly hitting the end of its travel harshly (too soft) but should be getting there occasionally (otherwise it’s probably too hard).
Bottom-out bumper: A rubber bumper that stops the suspension being damaged if it bottoms-out harshly.
Bushing: A lining used at the interface between shock eyelet and hardware (rear), and between stanchion and lower (fork). Reduces friction and wear.
Compression damping: Adjusts the feel of the suspension as it compresses. More compression damping means more hydraulic resistance, so the shock or fork will feel firmer.
Fox Racing Shox' redesigned 40 fork
© Bartek Woliński
Crown: The brace that holds a fork’s stanchions in place. Single crown forks are found on most mountain bikes. Dual-crown forks, which are stiffer and more suited to longer-travel bikes, are mostly found on downhill bikes.
Damping circuits: A reference to the internal damping system (compression or rebound).
Eyelet: Hole at end of rear shock through which the mounting bolt passes.
Eye-to-eye length: The length of a rear shock, measured from the centre of the bolt holding it in place at each end.
Ohlins work closely with Specialized on all their suspension products
© Miles Holden
Footnuts: Bolts holding the fork lowers in place, found at the bottom (foot) of the fork.
Fork: Front suspension. Holds the front wheel in place.
Hardware: Refers to the components used to mount the rear shock in the frame (via the eyelet bushing). Measured in terms of bolt diameter and width (e.g. 8mm x 20mm). Also referred to as a ‘mount kit’.
Internals: The working insides of a fork or shock.
Linear compression: Suspension’s resistance to compression varies in equal increments through its cycle.
Anton's RockShox Argyle suspension fork
© Bartek Wolinski/Red Bull Content Pool
Lockout: A setting that blocks (stops it moving) the suspension partially or completely, usually to make uphills and pedalling easier.
Lower and upper: Usually refers to the lower and upper parts of a fork.
Metric sizing: Introduced to several major companies’ 2017 (and beyond) shock ranges, standard shock measurements (eye-to-eye length and stroke, as well as hardware) were changed from the Imperial to Metric measurement systems, while for simplicity’s sake also reducing the number of available sizing options for eye-to-eye length, stroke, and hardware.
For example, a shock’s eye-to-eye and stroke might now be 230mm and 65mm. (An example hardware size might now be 8mm x 20mm, one of just 18 possible combinations, whereas previously there were 80.) RockShox was a major player in this movement, but Fox already offered Metric options. Both companies currently continue to produce both options.
Pinch bolts: Small bolts that help secure the axle of a bolt-up fork and stop it from spinning/working loose.
Preload: On a coil shock, a preload ring is turned to pre-compress (load) the spring. With added preload, the bike will feel firmer at the start of its travel.
Keeping your suspension seals lubed will help
© Bartek Woliński
Progressive compression: Suspension’s resistance to compression fluctuates through its cycle, taking increasingly greater force to compress nearer the end of its travel.
Ramp up: In reference to a fork or shock firming up as it moves from fully extended to fully compressed.
Rebound damping: Controls the rate at which a suspension unit can rebound (return to its original position) after compression by hydraulic restriction.
Sag: The amount suspension moves through its travel under the weight of a rider while stationary.
Seals: Rubber rings that keep air or fluid in the right place.
Shaft: Central shaft the suspension unit moves along.
Shock: Rear suspension unit. Attached to the frame.
Öhlins TTX rear shock
© Miles Holden
Shock absorber: Another name for a rear suspension unit.
Shim: A metal disc that is used internally in suspension units to control the flow of damping fluid through compression and rebound circuits.
Spring: There are two types of spring: coil, and air. Coil-sprung suspension uses a metal spring (usually steel or Titanium) to absorb impacts. Air-sprung suspension uses air (which compresses in a closed canister) as its spring.
Gwin runs an air-sprung fork and rear shock combo
© Bartek Woliński
Stanchion: The smaller round tube(s), visible externally, in a fork’s telescopic construction.
Steerer: Tube that attaches fork to handlebar stem. Available in alloy or carbon, though the latter is rare.
Stroke: The range of movement through a suspension unit’s travel. E.g. ‘At the end of its stroke, the rear shock bottoms out.’
Supple: Soft, smooth, silky action.
Top-out: When the suspension unit returns to its full extension. Usually in reference to a harsh top-out – the fork or shock rebounding too fast or uncontrollably and making a noticeable clunk as it hits the end of travel.
A separate room to work on the iconic Lefty fork
© Bartek Woliński/Red Bull Content Pool
Trunnion mount: A trunnion-mount shock is mounted directly onto a set of bearings in the bike’s frame via two bolts that bolt directly into either side of the shock. Under compression, the shock then pivots on the bearings (instead of a bushing).
Upside-down fork: The fork is reversed compared to most typical mountain bike offerings, with the stanchion at the bottom.
Volume spacers/tokens: Adding volume spacers, or ‘tokens’, decreases the volume of an air-sprung fork or shock’s spring, affecting its characteristics. These ‘tokens’ are easily added by the user with minimal technical know-how.
Wiper seal: A tight seal to minimise dirt entering the suspension unit.
