ACU – Auto-Cycle Union, UK governing body for off-road competition (licences, rules, noise limits).
A-licence / A2 / A1 / CBT – UK motorcycle licence tiers. Required if you ride road-legal bikes on green lanes.
Air filter (oiled foam) – Traps dust/mud. Clean and re-oil often; it’s critical for engine life.
Anti-bottoming / bottoming-out – Suspension hitting end of travel. Add compression, spring rate, or technique fix (preload/unweight).
Arm pump – Forearm tightness from over-gripping/poor setup. Loosen grip, sort lever/bar angles, build endurance.
Attack position – Neutral standing stance: balls of feet on pegs, hips back/forward as needed, elbows up, head over triple clamps.
Bash plate (skid plate) – Sump/frame guard against rocks/logs.
Berm – Banked corner that supports higher speed; push into it, look through the exit.
BOAT – Byway Open to All Traffic (legal green lane for road-legal bikes).
Braking bumps – Chattery whoops before corners. Stand neutral, light hands, let suspension work.
Carb jetting – Main/pilot jets and needle that meter fuel on 2T/older 4T. Tune for temp/altitude; wrong jetting = bog/smoke/spooge.
Case saver – Sprocket guard that protects engine cases if the chain derails.
Casing a jump – Landing on the tabletop “deck” or the upramp of the landing. Build speed/technique gradually.
Chain guide/slider – Keeps chain aligned; slider stops swingarm wear.
Chain slack – Correct free play prevents binding and shock damage. Check at the manual’s reference point.
Clickers – External adjusters for compression/rebound damping (count clicks from fully closed).
Clutch slip/feathering – Partial clutch engagement to smooth power or maintain revs at low speed.
Compression damping – Controls speed of suspension compressing (impacts, landings). Too firm = harsh/deflects; too soft = blows through.
Counter-steer (MX) – A quick bar input to initiate lean; at low speed you steer into the turn with body/peg weighting more than bars.
Dabbing – Touching a foot down to save a tip-over. Keep feet near pegs to avoid catching ruts.
Double / tabletop / step-up / step-down – Common jump shapes. Start with tabletops; progress under coaching.
ECU/map switch – Fuel/ignition settings on EFI bikes. Softer map helps in slick conditions.
Enduro – Longer off-road loops with liaison sections; UK formats include time-card enduro and Hare & Hounds (multi-lap mass start).
Engine braking – Deceleration from closed throttle, stronger on 4T; stabilises descents.
FIM tyre – Enduro tyre meeting FIM rules (knob height/spacing); legal on road links.
Final drive (gearing) – Front/rear sprocket tooth counts. Bigger rear/smaller front = more snap, less top speed.
Fork oil height – Affects end-stroke support. Higher oil = more ramp-up.
Gearing up/down – Taller (up) for speed/road links; shorter (down) for tight woods.
Glazing (brakes/clutch) – Overheated, shiny friction surfaces → reduced bite. Roughen or replace.
Green-laning – Riding legal rights-of-way (BOATs/UCRs) on road-legal bikes (MOT, tax, insurance, correct plate).
Hardpack / loam / clay / sand – Common surfaces. Tyre choice and pressures vary accordingly.
Head shake – Front-end wobble at speed. Check sag, steering head, tyre pressure; move weight forward, relax grip.
Highside / lowside – Crash types: highside = rear regains grip violently; lowside = slides out. Smooth inputs prevent both.
Holeshot – Lead into turn one off the start. Managed with body position and traction, sometimes launch control.
Jetting “spooge” – Oily black residue at 2T silencer from rich jetting or short runs.
Kickstart / electric start – Starting systems. E-start is common; kick is lighter/simpler.
Kill switch – Handlebar engine stop—learn location for emergencies.
Launch control – ECU feature reducing wheelspin off the gate (MX).
Levers (angle/reach) – Set so, standing, your wrists are straight; reduces arm pump and improves control.
LHRB – Left-hand rear brake kit (clutch-side lever operates rear brake). Useful for technical climbs; advanced mod.
Linkage (shock) – Rear suspension linkage. Keep pivots greased; play causes harshness/kicks.
Log hop / wheelie-bump – Unweight front with throttle/preload to roll a log or square edge.
Mousse – Foam tyre insert; no punctures, “low-pressure” feel. Not for long road sections (heat).
MX (motocross) – Closed-course racing on jumps/berms/whoops. Short motos, high intensity.
Nacelle/number plate – Front plate (MX) or headlight mask (enduro).
Noise test (dB) – Track scrutineering check. Keep packing fresh and exhausts compliant.
Off-camber – Slope falling away from the turn. Weight outside peg, gentle throttle.
Pilot jet / main jet / needle – Carb circuits: pilot = idle/low; needle = mid; main = wide-open.
Pinch flat – Tube pinched between rim/tyre at low pressure or hard impact. Use UHD tubes, rim locks, or mousses.
Powerband – RPM range where a 2T makes strong power. Manage with clutch/throttle.
Preload (spring) – Initial spring compression to set ride height. Adjust sag; don’t use preload to fix wrong spring rates.
Premix ratio – Oil:petrol mix for 2T (e.g., 50:1). Follow oil/bike guidance; measure accurately.
Rebound damping – Controls return speed of suspension. Too fast = pogo; too slow = packs down.
Reeds / reed valve – 2T intake valves that improve low-end response.
Rim lock – Clamps tyre bead to rim so it won’t spin at low pressure.
Roost / roost guard – Dirt/stone spray from the rear tyre; a roost guard is a chest/back protector.
Sag (static/rider) – How much the bike settles under its own weight (static) and with you in kit (rider). Target ~30–35% of travel at the rear.
Scrub (jump) – Advanced technique flattening trajectory by leaning over the lip; reduces airtime.
Seat bounce – Using seat compression on the upramp to gain pop (advanced, timing-critical).
Shim stack – Internal suspension shims setting damping. Revalving is a suspension-shop job.
Singletrack – Narrow trail, one bike wide. Look ahead, light hands, elbows up.
Sprocket wear (hooking) – Teeth curve like hooks; replace chain and both sprockets together.
Stall / hot-start – Engine stops at low speed; on some 4T carbs a hot-start lever helps clearing a flooded engine.
Step-through / triangle stand – Paddock stands for MX; don’t rely on side-stands off-road.
Tear-offs / roll-offs – Goggle film systems to clear mud. Roll-offs are better in heavy mud days.
Throttle roll-on – Smooth application to maintain traction; spikes cause spin.
Time-card enduro – You ride liaison stages to time checks and race “special tests”; penalties for early/late times.
TRO (Traffic Regulation Order) – Legal order restricting access to a lane. Respect signage; check council/TRF resources.
TRF – Trail Riders Fellowship; route info, access advocacy, group rides.
Triple clamps – Fork yokes. Bar position/offset changes steering feel.
Tubliss – High-pressure inner bladder locks the tyre bead; run very low pressures without pinch flats.
UCR – Unclassified County Road; many are legal vehicular routes (check locally).
Whip – Styling the bike sideways in the air; for show/line adjustment (advanced).
Whoops – Repeating rollers. Stay balanced, light hands, and let the bike plane; advanced riders skim or double-double.