MTB Suspensions Jargon for Beginners

Mountain Bike Shock Jargon (Explained Simply)

Here's a beginner-friendly breakdown of the terms you'll hear when rebuilding or talking about mountain bike suspension, divided into coil shocks, air shocks, and forks.

Β Damper vs. Spring

Every shock or fork has two main systems: a spring (stores energy, like a trampoline) and a damper (controls how fast it compresses and rebounds). Without damping, you'd just bounce uncontrollably.

Rear Shock Terms

  • Damper Tube: Where the main piston slides into and where the spring preload ring threads on (for Coil shocks), on air shocks, it's polished.
  • Inner Damper Tube (twin tube shocks only): A secondary cylinder inside the damper tube where the main piston slides, instead of sliding directly in the damper tube like in a monotube shock.
  • Damper Body: The main body that holds the piggyback reservoir, base valve, and adjusters. The damper tube threads into this. The Eyelet is on there.
  • Damper shaft or main shaft: The damper shaft is usually quite small (around 10Β mm in diameter) and is the shaft you see entering the damper body on a coil shock. One end is connected to the eyelet; the other is attached to the mid-valve/main piston inside the damper. Most monotube shocks use a bigger coaxial shaft with a smaller rod running inside it, which controls low-speed rebound. In contrast,Β twin-tube shocks typically use a solid, smaller, non-coaxial shaft since all the damping (compression and rebound) happens inside the damper body itself, not ar the Mid-Valve. An exception is the FOX X2 with VVC, which places the high-speed rebound adjuster at the eyelet, but this is a unique case among twin-tube designs.
  • Main Seal Head / Bearing Assembly: Guides and seals the damper shaft from the outside world, prevents oil leaks, and houses a bushing and one O-ring or U-cup seal (coil shocks). This part is located on the end of the damper tube. It is also the air piston on air shocks.
  • Adjusters: What you use to externally increase or decrease damping. They are located on the damper body and for some shocks, a rebound adjuster can be found on the the eyelet (Mostly LSR on monotube shocks)
  • Eyelets: Connect the shock to the frame or linkage. Most use standard 0.5" hardware (only boutique brands with spherical bearings are different).Β 
  • Trunnion mounts: use two small M10 bolts into the damper body instead of a two eyelets standard eyelets arangement.
  • Piggyback Reservoir: A small reservoir on the side of your shock β€” usually parallel to the body, sometimes perpendicular (e.g., Γ–hlins TTX22m, new fox X2 lineup). Increases oil volume and houses the IFP or bladder to pressurize the system and prevent cavitation.
  • IFP: The internal floating piston located in the piggyback reservoir or in the damper tube if your shock doesn't have a piggy back (Fox DPS or Rockshox Deluxe). Set at a precise depth after bleeding so it doesn’t hit the reservoir cap when the shock is bottomed out and oil is displaced.
  • Bladder: Some shocks use a bladder instead of an IFP. It does the same job: maintaining pressure and absorbing oil displacement by the main shaft volume variations while keeping the shock airtight and bled.
  • Base Valve: Controls compression damping via oil displaced by the damper shaft entering the shock. Located in the damper body. Has more effect with larger-diameter damper shafts (monotube shocks) because their volume is very large. May use a preloaded poppet valve or shim stack.
  • Mid Valve: Located on the main piston inside the damper tube and is on the end of the Damper Shaft inside the shock. Contains shims that control oil flow in both directions. Factory-tuned: rebound valving on top, compression valving underneath.
  • Main Piston Nut: Secures the main piston on the damper shaft. Must be torqued precisely to allow the shim stack to flex properly. On HBO shocks, the Main piston Nut is a Small piston.
  • HBO (Hydraulic Bottom-Out): A secondary piston that slows the last portion of travel to prevent harsh bottoming. Replaces the main piston nut and acts as a piston itself.

Β Air Shock Terms

  • Air Piston: Bolted to (Cane Creek) or part of the seal head. Compresses air inside the inner air can. Makes the seal head wider than the damper tube, with seals around it.
  • Inner Air Can: Contains the air piston’s movement and is part of the main structure, the cylinder of the air piston.
  • Negative Chamber Seal Head:Β 

    This part contains a dust wiper to keep dirt out of the shock and seals off the negative air chamber. It slides directly on the polished surface of the damper body, just behind the main air piston.

    The size of the negative chamber plays a major role in how your shock feels. A larger negative chamber makes the spring curve more linear, it softens the initial travel and improves small bump sensitivity. However, it also means you'll need to run higher air pressure to reach the same sag. In return, you get more ramp-up at the end of the stroke when the negative spring becomes weak, which often lets you run fewer volume spacers while still maintaining bottom-out resistance.

  • Eyelets (larger than coil shocks): Large structural ends of the air can, threaded into the inner air can AND the damper shaft, unlike coil shocks which are threaded only on the damper shaft.
  • Outer Air Sleeve: Covers the inner air can and is usually secured with a circlip. Holds volume spacers for tuning the spring curve.
  • Volume Spacers: Found inside the outer air sleeve or special chambers (e.g., FloatX/DPX2). Make the spring curve more progressive.
    • Greasing Seals: Always apply Slickoleum or SRAM Butter to all seals and O-rings to prevent damage and improve feel.

⚠️ Coil shocks use threaded damper tubes for spring preload. Air shocks use polished tubes for airtight, low-friction sealing with the negative seal head Q-ring.

Big air shocks like the Float X2 and Vivid have multi-part Bigger air cans like explained earlier. Others like the Super Deluxe Air, Float X, and DPX2 use a one-piece can that threads into the damper body and is easier to open.

Β IFP/Reservoir Filling Systems

  • Schrader Valve Style: Used on DVO and older Fox designs.
  • IFP Fill Adapter: Required for newer RockShox and FOX designs. Screws into the fill port. Air fill Adapter
  • Needle Fill: Common on high-end or compact designs (DPX2, Bomber CR, EXT, Push, Γ–hlins, Fast, Formula). Uses a needle through a rubber pellet. Shop Needle Fill Kit

Β Fork Suspension Terms

  • Left Side Stanchion: Typically houses the air or coil spring assembly. Has a cap on top to adjust air pressure or coil preload.
  • Right Side Stanchion: Typically holds the damper assembly. Just check which leg has the compression and rebound adjuster, that’s the damper side.
    • Reverse on ΓΆhlins and for some other high end brands I think but for most forks (Fox, Rockshox, DVO) it’s the standard left=Air, Right=Damper.
  • Lower Legs: The outer section of the fork that slides over the stanchions. It contains the arch, dropout mounts, and is where the oil bath and dust wipers live. In inverted forks, this orientation is reversed. It also contains the stanchion bushings, which take a lot of the force when the fork is working.
  • Foot nuts/screw: Basically what secures the damper shaft and the air shaft to the lower legs. They are mostly nuts (Fox) but some brands use screw (rockshox). They have to be removed to push the shafts into the lower legs for opening a fork. For forks with Foot Bolts, we can almost always use the bolts to push the shafts into the lowers for service.
  • Rebound Adjuster: Almost Always situated on the bottom of the lower leg's damper side. It adjusts the rebound of the fork. This adjuster is almost always Low Speed Rebound but fox also had High Speed Rebound for their GRIP2 and GRIP X2. You can almost always remove them by un-doing a small allen screw on the side.
  • Damper & Air Shafts: Internal shafts (usually 8–10 mm) that drive the air piston and damper piston inside the fork. They’re only visible when the lowers are removed and can be 200mm or more in length.
  • Seal Head: Similar to rear shocks. Most fork dampers include a seal head with a built-in wiper and spring. It keeps damper oil isolated from the lower leg oil. Some designs like the Fox GRIP damper allow a small amount of lower leg oil to pass through a one-way valve for lubrication and auto-bleeding.
  • Air Shaft: Holds the air piston and defines the spring curve. Travel changes typically require swapping the air shaft. Fox and RockShox use circlip-retained shafts accessible from the bottom of the fork, while Γ–hlins air shafts come as a complete cartridge-like assembly that threads out from the top.
  • Air Piston: A small internal piston located inside the left fork leg. As the fork compresses, it moves through the positive air chamber, compressing air to store energy and generate spring force. This is what absorbs impacts. Its size, shape, and seals play a major role in spring rate, ramp-up, and mid-stroke feel.
  • Rebound Assembly: Located at the end of the damper shaft, accessed from the bottom of the lower legs. This is where the rebound knob is installed and rebound adjusters are housed and linked to the mid-valve.
  • Air Cap Assembly: Located at the top of the left stanchion. Used to pressurize the air spring and to install or remove volume spacers.
  • Base Valve: Sits at the top of the damper. Controls the oil displaced by the main damper shaft during compression and contains many compression adjustment circuits.
  • Open Bath vs. Closed Damper:
    • Open Bath: Found in many entry-level forks. These use unpressurized oil baths and gravity-fed damping. Performance is lower, and cavitation occurs easily during repeated fast hits.Β 
    • Closed Damper: Sealed systems using a bladder or IFP (Internal Floating Piston) to separate air from oil. Nearly all modern forks use IFPs now, including RockShox Charger 3, Charger 3.1, and all Fox GRIP dampers. Bladders are becoming rare due to long-term reliability issues, if overfilled, they can rupture as lower leg oil enters the damper.
    • Auto-Bleeding Systems: Many IFP-based dampers like Fox GRIP are self-bleeding. They purge air and small amounts of excess oil automatically, keeping the damper topped off and bled even after hard riding.
  • Air Shaft Variants:
    • Fox 38 Factory: Uses a unique larger-volume air shaft assembly that reduces ramp-up by increasing lower leg volume. The piston is smaller to avoid creating too much force in the tight 180 mm travel configuration with very low positive air volume possible (I recommend running 1 spacer MAX on fox 38 180mm).Β 
    • Fox 40: Uses a custom cup shaped piston located inside the stanchion, similar in shape to a Vorsprung Luftkappe. Requires a special pin wrench to remove. Due to the double crown design, the positive air chamber is much larger, allowing the piston to sit directly inside the stanchion without over-compression even for a 200mm fork.
    • DVO OTT: Uses a negative spring that needs to be greased with Marine Grease on reassembly. Also, their air piston is not bolted on the air shaft, it's kind of an IFP and just sits on the air shaft tip.Β 
    • Γ–hlins/EXT/(High end brands): They use dual air chambers to control the ramp up of the air spring and add mid stroke support. It's basically, for most of them, a secondary chamber with a floating piston that increases the air chamber volume as the suspension compresses.
πŸ’‘ Need Help Choosing Fork Dust Wipers?
Use the S4 Suspension Dust Wiper Finder to select the correct size for your fork.

Β What Are Shims?

Shims are thin steel washers that bend to control oil flow. Found in base and mid valves, they’re the core of suspension tuning. Fox’s VVC (Variable Valve Control) is a tunable shim substitute, complex, finicky, and sometimes unreliable. ⚠️ Never unscrew the VVC bolts in the 2021–2025 X2 shocks, NEVER. They require extreme precision and you might have zero rebound control because your high speed rebound will be fully open all the time. You can remove the piston to slide the seal head, just don’t touch the two small VVC nuts PLEASE DO NUT TOUCH THEM. On forks, you can kind of open it but, let's be real, do you want to revalve your damper? No. So don't open the valving parts if not necessary, just change the dynamic seals and do a good bleed.

⚠️ Tips and Warnings

  • Always grease seals with Slickoleum or SRAM Butter during reassembly.
  • Check your mounting type : eyelet vs. trunnion matters for hardware and tools.
  • Use the right tool for damper pressurization: needle, Schrader, or adapter.
  • Fork dampers can be annoying to bleed. Most of the time, you can just insert a hose into the bleed hole and it will seal well enough for a basic bleed. I also use kitchen funnels sometimes with tape around the sealing area.
  • Shocks and forks contain pressurized air. Always fully depressurize the damper and air spring before opening. Failure to do so can result in serious injury or even death (you have no idea of the amount of energy stored in air springs or dampers unless you understand how strong pressure is on large surfaces). Most fork dampers are not pressurized but I think push forks are, anyway you probably won't be playing in that if you have a 3000$ fork.
  • Some IFP chambers are pre-pressurized to 350+ psi. (Mostly Fox DPS shocks) Use a 600+ psi shock pump to adjust these : a standard shock pump will not work and the seals will explode.
  • Always use a shaft clamp when removing or installing seal heads. Clamping the shaft improperly can ruin it. How to Use Shaft Clamps
  • Don't forget to check out our Essential Tools Starter Pack if you're starting out.