Suspension school · Suspension Basics

Anatomy: The Jargon in Plain English

Stanchions, negative chambers, shim stacks and IFPs, translated

Suspension talk is thick with jargon, and most of it describes fairly simple parts. Here is what the words actually mean, so reviews, forum threads and service manuals stop reading like a foreign language. No need to memorise any of it. Come back whenever something puzzles you.

The fork, from the outside

• Stanchions: the polished upper tubes that slide in and out. Their diameter (32, 34, 35, 36 or 38mm) is shorthand for stiffness and intended use. Most full-power eMTBs come with 36 or 38mm forks because a heavier bike needs the stiffer chassis.
• Lowers: the one-piece cast lower legs the stanchions slide into, joined by the arch over the tyre.
• Crown: the clamp joining the stanchions to the steerer, which is the tube that runs through the frame's head tube.
• Wiper seals (dust seals): the rubber rings at the top of the lowers that scrape dirt off the stanchions and keep lubricating oil in.
• Sag O-ring: the small rubber ring on a stanchion that gets pushed along as the fork compresses, so you can see how much travel was used.

Inside the spring side

• Air spring: a piston in a sealed chamber. The air itself is the spring.
• Positive chamber: the side you pump up, the one that holds you up.
• Negative chamber: a second chamber pushing the opposite way, there to soften the very start of the travel so small bumps do not feel notchy.
• Transfer port: a tiny channel, sometimes just a dimple in the tube, that lets the two chambers equalise at one point in the travel. It is the reason you cycle the fork while airing it up.
• Volume spacers (RockShox calls them Bottomless Tokens): plastic blocks that shrink the air chamber. Smaller chamber, faster ramp-up at the end of travel, harder to bottom out. Fitting them takes minutes.
• Coil spring and spring rate: a wound steel spring rated in pounds per inch, so a 450lb spring takes 450 pounds to compress it one inch.
• Bottom-out bumper: a rubber cushion that softens the last few millimetres so full travel does not clang.

Inside the damper side

• Damper: the sealed oil cartridge that controls how fast the suspension moves in each direction. Springs decide how far, dampers decide how fast.
• Compression circuit: the valving that resists the suspension compressing.
• Rebound circuit: the valving that resists it re-extending after a hit.
• Shim stack: a stack of thin sprung-steel washers covering oil ports. They bend open under pressure, and their thicknesses and diameters are the real 'tune' of a damper. The external dials just trim around them.
• IFP (internal floating piston): a free-sliding piston separating the damper oil from a pocket of pressurised gas. It gives the shaft somewhere to displace oil to, and stops the oil frothing into foam, which would ruin the damping.
• Bladder: a flexible rubber reservoir that does the same job as an IFP in some dampers.
• Lockout or pedal switch: a lever that closes down the compression flow for smooth climbs and tarmac.

Rear shock words

• Eye to eye: the bolt-hole to bolt-hole length of the shock.
• Stroke: how far the shaft actually moves. A 230x65 shock is 230mm eye to eye with a 65mm stroke, and sag is measured against the stroke.
• Air can: the outer sleeve that forms the air chamber on an air shock.
• Piggyback (reservoir): the second cylinder on bigger shocks, holding extra oil and the IFP. More oil means more heat capacity and steadier damping on long descents.
• Leverage ratio: how much the rear wheel moves per millimetre of shock stroke, usually between 2 and 3 to 1. It is why a small shock change feels big at the wheel.
• Progression: how that leverage changes through the travel. A progressive frame gets harder to compress as it goes, which matters when choosing between coil and air.

Trailside vocabulary

• Small-bump sensitivity: how willingly the suspension moves on fine chatter. Good sensitivity reads as grip.
• Mid-stroke support: how well the middle third of the travel holds you up in berms and under braking.
• Packing: suspension that cannot re-extend fast enough between repeated hits, so it rides lower and harsher with each one.
• Brake dive: the fork compressing under hard braking.
• Stiction: static friction from seals and bushings, the tiny stickiness before the suspension starts moving.
• Wallowing: a vague, boaty feel that usually points to too little pressure or support.
• Bracketing: the tuning method of testing either side of a setting to find the middle. Covered properly in the setup order article.

That covers most of the vocabulary you will meet. Anything more exotic is usually a brand name for one of the parts above.