Bike Jargon Glossary: UK Cycling Terms Explained

How to use this glossary

Bike listings are written in shorthand, and the shorthand carries most of the information about what a bike is worth. A listing that says "Ultegra Di2, 11-speed, 56cm, tubeless-ready, 2021" has told an informed reader almost everything. The same listing tells an uninformed reader nothing at all.

This page defines the terms that appear most often in UK used bike listings, grouped by what they describe. Each definition says what the term means and why it matters when you are buying or selling. Where a term needs more than a paragraph, there is a link to the guide that covers it properly.

Frame and sizing

Frame size is the manufacturer's stated size for a frame, given in centimetres on road bikes, in inches on some mountain bikes, or as S, M and L. Sizing is not consistent between brands, so a 56cm from one manufacturer will not match a 56cm from another. Use the geometry chart rather than the label. See our bike size guide.

Geometry chart is the table of frame measurements a manufacturer publishes for each size of each model. It is the only reliable way to compare frames across brands, and it is normally still available on the maker's website years after a bike was sold.

Stack is the vertical distance from the centre of the bottom bracket to the top of the head tube. More stack means a more upright riding position.

Reach is the horizontal distance from the centre of the bottom bracket to the top of the head tube. More reach means a longer, more stretched-out position. Stack and reach together describe a frame's fit more accurately than any other pair of numbers. See reach and stack explained.

Standover height is the height of the top tube where you straddle it. It matters for whether you can stand over the bike safely, and almost nothing else.

Head angle is the angle of the fork relative to the ground. A slacker, lower-numbered angle gives more stable steering at speed. A steeper one gives quicker handling.

Bottom bracket is the bearing assembly that the cranks turn in, sitting in the shell at the bottom of the frame. There are many incompatible standards, which matters when a bike needs one replaced.

Frame number, also called a serial number, is the unique number stamped into the frame, usually underneath the bottom bracket. It is how a bike is identified if it is stolen, and it is the single most important thing to record about a bike you own. You can check a frame number against a stolen-bike registry and rider-filed theft reports, and register your own free.

Dropouts are the slots or fittings at the ends of the frame and fork where the wheel axles sit.

Derailleur hanger is a small replaceable aluminium bracket that the rear derailleur bolts to. It is designed to bend or break in a crash so the frame does not. It is a cheap part and a bent one is the most common cause of shifting that will not adjust.

Materials

Aluminium is the most common frame material at mid-market prices. It is light, stiff, does not rust, and cannot practically be repaired if cracked.

Carbon fibre is lighter still and can be shaped precisely, so it dominates at higher prices. It can be repaired professionally, but impact damage is not always visible, which is why crash history matters more on a carbon bike than on any other.

Steel is heavier, comfortable to ride, repairable by any framebuilder, and rusts if neglected. Common on touring bikes, older bikes and custom frames.

Titanium does not rust, lasts effectively forever, and is expensive. Titanium frames hold their value better than most.

Our guide to frame materials covers the trade-offs in full.

Drivetrain

Groupset is the matched set of shifting and braking components sold together by a manufacturer: shifters, derailleurs, chainset, cassette, chain and brakes. The groupset is usually the strongest single indicator of what a bike cost new. See the groupset hierarchy guide.

Speed, as in 11-speed, is the number of sprockets on the rear cassette. More speeds usually means a newer and higher-specification drivetrain, and parts are generally not interchangeable between different speeds.

Cassette is the cluster of sprockets on the rear wheel. Its range is written as smallest to largest, for example 11-34, and a bigger largest sprocket means an easier climbing gear.

Chainset or crankset is the cranks and the front chainrings.

1x, said "one by", means a single front chainring and no front derailleur. Simpler, lighter and quieter, with a slightly narrower gear range. Standard on modern mountain bikes and common on gravel bikes.

2x means two front chainrings, giving a wider range with smaller steps between gears. Still standard on road bikes.

Compact, semi-compact and standard describe the size of a road chainset's chainrings. Compact, typically 50-34, gives the easiest gearing and is the most common on modern bikes.

Derailleur is the mechanism that moves the chain between sprockets or chainrings.

Di2, AXS and EPS are the electronic shifting systems from Shimano, SRAM and Campagnolo. They shift by wire or wirelessly instead of by cable, are more precise and need charging. See Di2 versus mechanical.

Chain wear is the elongation of a chain as its pins and rollers wear. Measured with a chain checker. Replacing a chain before it passes the wear limit protects the cassette and chainrings, which cost far more.

Chainline, cross-chaining and chain slap describe, in order, the alignment of the chain between front and rear, the noisy inefficiency of running the biggest front ring with the biggest rear sprocket, and the chain hitting the frame over bumps.

Wheels and tyres

Rim is the outer hoop of the wheel. Hub is the centre. Spokes connect the two, and spoke count matters more than most listings suggest, particularly for heavier riders or loaded touring.

700c is the standard road and gravel wheel size, also called 622mm. 650b, also called 27.5 inch, is smaller and allows wider tyres. 29er describes a mountain bike using 700c-diameter wheels with wide tyres. See our 650b versus 700c and 29 versus 27.5 answers.

Tyre width is given in millimetres on road and gravel bikes, in inches on mountain bikes. Wider tyres run at lower pressure, ride more comfortably and are usually no slower on real roads. See wider tyres, lower pressure.

Clincher is a conventional tyre with a separate inner tube. Tubeless runs without a tube, using sealant to make the tyre airtight and to seal small punctures as you ride. Tubeless-ready means the rim and tyre can be set up tubeless but may currently have tubes fitted. See the tubeless setup guide.

Rim depth is how tall the rim section is. Deeper rims are more aerodynamic and more affected by crosswinds.

Quick release is the older lever-operated wheel fastening with a thin skewer. Thru-axle is the newer, stiffer system using a thicker axle that threads into the frame. They are not interchangeable, which matters when buying wheels for an older bike.

True describes a wheel that runs straight. A wheel with a visible side-to-side wobble is out of true and can usually be corrected by adjusting spoke tension.

Brakes

Rim brakes grip the wheel rim. Caliper brakes are the compact road type, V-brakes the longer-armed type on hybrids and older mountain bikes, and cantilever brakes an older design found on cyclocross and touring bikes.

Disc brakes grip a rotor bolted to the hub. They perform better in the wet and do not wear the rim. Hydraulic disc brakes use fluid in a sealed hose and self-adjust for pad wear. Mechanical or cable disc brakes use a cable and need adjusting by hand.

Rotor is the steel disc. Common sizes are 140mm, 160mm and 180mm, with larger rotors giving more braking power and better heat management.

Bleeding is the process of replacing the fluid in a hydraulic brake to remove air. A brake lever that feels spongy usually needs bleeding.

See disc versus rim brakes on used bikes and our guide to changing brake pads.

Suspension

Hardtail is a mountain bike with front suspension only. Full suspension, or full-sus, has both front and rear. Rigid has neither.

Travel is how far the suspension can compress, in millimetres. More travel suits rougher terrain and is heavier and less efficient on smooth ground.

Sag is how far the suspension settles under the rider's static weight, set as a percentage of travel. Setting sag correctly is the single most useful suspension adjustment.

Lockout is a switch that stops the suspension moving, for climbing or road sections.

Dropper post is a seatpost that lowers at the push of a lever, letting a rider drop the saddle for descents. Now standard on mountain bikes and increasingly common on gravel bikes.

See hardtail versus full suspension.

Electric bikes

EAPC, meaning Electrically Assisted Pedal Cycle, is the UK legal category for an electric bike that can be ridden without registration, tax, insurance or a licence. To qualify, the motor must be no more than 250 watts continuous rated power, assistance must cut out at 15.5mph, and assistance must only be provided while the rider is pedalling. Anything outside those limits is legally a motor vehicle. See UK e-bike law explained.

Hub motor sits in the centre of a wheel. Cheaper, simpler, and less balanced in feel. Mid-drive motor sits at the bottom bracket and drives through the bike's own gears, which handles hills better and rides more naturally.

Watt-hours (Wh) is the capacity of the battery and the number that predicts range. Range claims in advertising are less useful, because they depend on rider weight, terrain, assistance level and temperature.

Charge cycles count how many times a battery has been through a full charge, and battery health declines with them. On a used e-bike the battery is the most expensive component and the hardest to assess. See the used e-bike battery guide.

Torque sensor measures how hard you are pedalling and assists proportionally, which feels natural. A cadence sensor only detects that you are pedalling and delivers a fixed level of assistance, which feels more like a switch.

Bike types

Road bike has drop handlebars and narrow tyres, built for tarmac. Endurance road bikes have a more upright position than race bikes.

Gravel bike has drop bars with wider tyres and clearance for rough surfaces. Cyclocross bikes look similar but are built for hour-long races with different geometry. See gravel versus cyclocross versus adventure.

Hybrid combines a flat handlebar with road-style wheels, aimed at commuting and leisure. Touring bikes carry luggage over long distances. Cargo bikes carry loads or children.

Mountain bike splits into cross-country for speed and climbing, trail as the all-round option, enduro for aggressive descending, and downhill for lifts and uplift only.

Folding bike folds for storage and public transport. Fixed gear, or fixie, has no freewheel, so the pedals turn whenever the wheels do. Single speed has one gear and a normal freewheel.

Condition and listing shorthand

NOS means new old stock, an unused item from a previous model year.

Sold as seen signals that a private seller is offering no assurance about condition. It reflects the real legal position on a private sale rather than removing a right you would otherwise have. See our guide to warranties and used bikes.

Serviced should be backed by a date and ideally a receipt. Without either it is an opinion.

Upgraded means components have been changed from the original specification. Upgrades rarely return their cost at resale, and a listing that names them is more credible than one that just claims them.

Original spec means the bike is as it left the factory, which is what makes a model-year comparison reliable.

Crash damage and frame repair must both be disclosed. A repaired carbon frame is not automatically a bad buy, but an undisclosed one is a misdescription.

RRP is the recommended retail price when the bike was new. It is a starting point for valuation, not a substitute for one. What a bike is worth now depends on age, condition, specification and what similar bikes are actually selling for. Our free valuation and sold bike prices cover both sides of that.

For what these terms are worth in money, see what specs affect resale value and bike depreciation in the UK.

Common questions

What does groupset mean on a bike?

A groupset is the matched set of shifting and braking components sold together by one manufacturer: shifters, front and rear derailleurs, chainset, cassette, chain and brakes. Manufacturers sell them in tiers, and the groupset is usually the strongest single indicator of what a bike cost when new.

What does 1x mean on a bike?

1x, said "one by", means the bike has a single front chainring and no front derailleur. It is simpler, lighter and quieter than a 2x setup, with a slightly narrower overall gear range. It is standard on modern mountain bikes and common on gravel bikes.

What is the difference between stack and reach?

Stack is the vertical distance from the bottom bracket to the top of the head tube, and reach is the horizontal distance between the same two points. Together they describe how a frame will fit more accurately than the stated frame size, which is not consistent between manufacturers.

What does tubeless-ready mean?

Tubeless-ready means the rim and tyre are designed to be set up without an inner tube, using sealant to make the tyre airtight, but that the bike may currently have inner tubes fitted. Converting to tubeless then needs rim tape, valves and sealant rather than new wheels or tyres.

What is an EAPC?

EAPC stands for Electrically Assisted Pedal Cycle, the UK legal category for an electric bike that needs no registration, tax, insurance or licence. The motor must be no more than 250 watts continuous rated power, assistance must cut out at 15.5mph, and assistance must only be given while the rider is pedalling.

Where is the frame number on a bike?

The frame number, or serial number, is usually stamped into the underside of the bottom bracket shell, where the cranks pass through the frame. It can also be found on the head tube, the rear dropout or under the down tube. It is the number used to identify a bike if it is stolen.