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Cycling tech glossary
The bike tech terms in our guides and tools, in a sentence or two.
- 1x and 2x
A 1x drivetrain has one chainring up front, a 2x has two. The gear calculator compares a 2x and a 1x setup gear by gear.
- 20-minute test
An FTP test built on one 20-minute effort: TrainingPeaks puts FTP at 95% of the average power. 240 W for 20 minutes gives an FTP of 228 W.
- 700c and 650b
In ETRTO sizes, 700c is a 622 mm bead seat and 650b is 584 mm. The smaller rim leaves more room around the tire, so some frames list a wider 650b limit (Cervélo gives 700c x 40 mm or 650b x 49 mm for the Áspero).
- ANT+
An inter-brand wireless standard built on the ultra-low-power 2.4 GHz ANT protocol, which trainers and power meters list next to Bluetooth. Zwift says virtual shifting needs the trainer on Wi-Fi or Bluetooth, not ANT+, though ANT+ still works for standard trainer control.
- Big-big method
Sizing a chain on the bike: chain on the largest chainring and the largest cog, then add what your drivetrain maker says. SRAM road 2x adds one inner and one outer link, 1x adds two of each.
- Burping
A low-pressure tubeless problem: the bead briefly unseats and the tire loses air. If it happens on hard hits, add air.
Gravel tire pressure for 40mm tires, and what changes at 38 or 45mm
- Chain length
Park Tool's equation is L = 2C + F/4 + R/4 + 1 inch, with C the chainstay and F and R the teeth on the largest chainring and cog, rounded to the nearest inch. One inch is two links, so the count is always even.
- Chainstay length
The distance from the bottom bracket centre to the rear axle, the C in Park Tool's chain length equation. SRAM endorses Force XPLR AXS on chainstays of 415 mm and up with a 47.5 mm chainline.
Chain length calculatorUDH and SRAM Full Mount gravel frames
- Crank-arm power meter
A sensor bonded to the left crank arm (single-sided) or to both arms. It has to match your crankset model and arm length.
- Design rim width
The internal rim width a tire's stated width refers to (ETRTO, as Vittoria publishes it). On a different rim, the tire's width changes by about 0.4 mm for every 1 mm of difference.
Does rim width change tire width? Yes, and your pressure should follow
- Development
How far the bike travels per crank turn: gear ratio times wheel circumference. On 28 mm tires, 50x11 gives 9.68 m.
- Direct-drive trainer
A trainer that replaces your rear wheel: the bike mounts on a cassette or a single cog fitted to the trainer, so there is no tire contact. It needs a freehub body and axle adapters that match your bike.
Smart trainer buying guideSmart trainer compatibility for 12 and 13-speed drivetrains
- Dual-sided power meter
A dual-sided meter measures both legs, which gives real left/right balance. A single-sided meter measures one leg and doubles it, so uneven legs skew the total.
- ERG mode
A trainer mode in which the app sets the resistance, so there is no need to shift (TrainerRoad).
- ETRTO size
The tire size in width-bead seat format: 28-622 is a 28 mm tire on a 622 mm bead seat diameter. ETRTO also sets the hookless pressure limits that Schwalbe publishes.
Does rim width change tire width? Yes, and your pressure should followHookless-compatible road tires
- Flattop chain
SRAM's chain on Red, Force, Rival, Apex AXS and Eagle Transmission, as Wahoo lists them. SRAM's 13-speed XPLR Full Mount derailleur works only with XPLR 13-speed cassettes and road Flattop chains.
- Float
The freedom your foot has to rotate left and right while clipped in (Look). Shimano's yellow SPD-SL and SPD-SLR cleats give 6° (±3°), red is fixed, and Look's Keo cleats come in 0°, 4.5° and 9°.
- Frame clearance
The raw space in the frame, which is not a tire size. Cervélo's first Áspero lists a 43 mm maximum tire but 53 mm of frame clearance.
- Freehub body
The part of the rear hub the cassette fits on, on your wheel or on a direct-drive trainer. If it doesn't match your cassette, nothing else matters; most trainers ship with a Shimano HG-style body.
Smart trainer compatibility for 12 and 13-speed drivetrainsCompatibility at a glance
- FTMSBluetooth Fitness Machine Service
The Bluetooth standard that lets a fitness machine, such as a smart trainer, send training data to an app. Kinomap says any equipment using it is automatically compatible with Kinomap.
- FTPFunctional Threshold Power
Your power at threshold, which Andrew Coggan says is measured most directly by a time trial of about an hour (TrainingPeaks). The FTP calculator estimates it from a 20-minute or ramp test.
- Full Mount
SRAM's way of fitting a rear derailleur straight to the frame, over the drive-side dropout and centred on the rear axle, with no hanger. It needs a UDH frame; SRAM lists Eagle Transmission and RED, Force and Rival XPLR AXS as Full Mount.
UDH and SRAM Full Mount gravel framesCompatibility at a glance
- Gear ratio
Chainring teeth divided by cog teeth: 50x11 is 4.55 and 34x34 is 1.00. Below 1, as with 40x44, the wheel turns less than once per crank turn.
- Gross efficiency
The share of food energy that reaches the pedals, roughly 20 to 25% for riders. The calorie calculator defaults to 22.5%, and at 23.9% (1 ÷ 4.184) kJ of work and kcal burned are equal.
- HG freehubShimano Hyperglide
Shimano's Hyperglide freehub body, the style most trainers ship with. Shimano 12-speed road cassettes fit the 11-speed road HG body, and the Zwift Cog needs one.
- Hookless rim
A rim with no hook on the flange, so the tire is held only by its bead and friction against the flange (Continental). Use only tires approved for hookless, at no more than 5 bar for 25-29 mm tires and less for wider ones.
- Internal rim width
The width inside the rim, usually on the rim decal or in the manual. It sets the narrowest tire allowed on a hookless rim and moves a tire's real width by about 0.4 mm per mm.
Does rim width change tire width? Yes, and your pressure should followHookless-compatible road tires
- kJ (kilojoules)
Work done on the pedals: average watts times seconds, divided by 1000, so 200 W for an hour is 720 kJ. Riders turn roughly 20 to 25% of food energy into work, so 1 kJ of work is close to 1 kcal burned.
- Look Keo
Look's three-bolt road cleat standard, introduced in 2004, with cleats in 0°, 4.5° and 9° of float. Favero's Assioma and Look's Keo Blade Power power meter pedals both come in Keo versions.
Best-value power metersSource: Look
- Max cog
The largest cog a rear derailleur takes: SRAM AXS derailleurs are marked MAX 33T, MAX 36T or XPLR (MAX 44T), and no marking means 33T. Wahoo warns that a trainer cog bigger than your bike's largest can damage your drivetrain.
- Micro Spline
Shimano's freehub for 12-speed MTB and some GRX cassettes. Wahoo says no Micro Spline body is available for KICKR, CORE or MOVE, and the Zwift Cog does not fit one.
- N3W
Campagnolo's freehub body for Ekar and its other 13-speed systems, 4.4 mm shorter than the classic Campagnolo body. Wahoo has no N3W body for KICKR, CORE or MOVE; Garmin has a Tacx one.
- Nominal tire width
The width printed on the sidewall, true on the tire's design rim within tolerance (no more than 2 mm off since the 2023 ISO and ETRTO update, per Zipp). For the real width on your rim, measure across the widest point of the casing with calipers.
Does rim width change tire width? Yes, and your pressure should follow
- Pedal power meter
The sensor sits in the pedal spindle, so it moves to another bike with a pedal wrench, but you are tied to that pedal's cleat system. No brand listed an SPD-SLR power pedal when we checked on 28 September 2026.
- Pinch flatSnake bite
A tube flat from running too little pressure, which Frank Berto called a "snake bite". Tubeless avoids it, which is why the pressure calculator adds 5% when you pick inner tubes.
Road tire pressure for 28, 30 and 32mm tiresTire pressure calculator
- Power zones
Training intensities set as a share of FTP. Andrew Coggan's seven levels, as TrainingPeaks publishes them, run from Active Recovery (under 55%) and Endurance (56-75%) through Lactate Threshold (91-105%) to VO2 Max and beyond.
- QUICK-LINKMaster link
Shimano's name for its chain connecting link. Count it when you size the chain: Shimano's road 12-speed check is 2-3 links plus the QUICK-LINK, and Park Tool measures including the master link.
- Ramp test
An FTP test that TrainerRoad and Zwift score at 75% of your best 1-minute power. A best minute of 320 W gives an FTP of 240 W.
- Rolling resistance
The power a tire costs as it rolls, measured in watts per tire on a lab drum. In GRAN FONDO's 2026 gravel test, Schwalbe's G-One RX Pro measured 13.9 W at 20 km/h with 50 kg per tire.
- Sealant
The liquid in a tubeless tire that plugs small holes, "solid latex liquified by a high pH solvent" in SILCA's words, and it slowly dries out. Check every 2 to 3 months and top up when it is low.
- Simulated grade
The steepest gradient a smart trainer can mimic with resistance. Wahoo lists 16% for the KICKR CORE 2 and 20% up, -15% down for the KICKR BIKE SHIFT.
Wahoo KICKR CORE 2 vs Van Rysel D500Zwift Ride vs Wahoo KICKR BIKE SHIFT
- Smart bike
One machine with its own resistance unit, belt drive and shifters, like Wahoo's KICKR BIKE SHIFT. The Zwift Ride is a smart frame instead, mounted on a separate direct-drive trainer.
- SPD
Shimano's two-bolt clipless system for mountain, gravel, touring and indoor bikes. The small cleat sits inside the tread of a lugged shoe, so you can walk, and the stock SM-SH51 cleat gives 4° of float.
- SPD-SL
Shimano's three-bolt road system since 2003, with a larger plastic cleat that spreads load across the pedal but makes walking clumsier. The stock yellow SM-SH11 cleat gives 6° of float (±3°).
- SPD-SLR
Shimano's newer three-bolt road system, launched with Dura-Ace PD-R9300 and Ultegra PD-R8200, which Shimano says lowers the shoe-to-pedal interface by 2.3 mm. SPD-SL cleats don't fit SPD-SLR pedals, and Shimano says SPD-SLR cleats are not compatible with SPD-SL pedals.
- Spider power meter
The sensor sits between the crank and the chainrings and measures the combined output of both legs. It has to match your crank interface and chainring bolt pattern.
- Stack height
For pedals, the height of pedal and cleat under your shoe; Shimano says SPD-SLR lowers the shoe-to-pedal interface by 2.3 mm. Brands don't measure it on one basis (Look quotes pedal plus cleat), so compare figures with care.
SPD power meter pedals for gravelShimano SPD vs SPD-SL vs SPD-SLR
- Thru-axle
The axle type frames give as diameter and width, such as Specialized's "12x142mm thru-axle" on the Crux 5. On a trainer you need the matching adapter: Wahoo includes them with the KICKR CORE 2, Saris sells the M2's separately.
- Tire clearanceMax tire width
The widest tire the frame maker says you should fit, with the safety margin already taken off; it is the number to shop with. Use the smaller of frame and fork, and Cervélo recommends 4 mm between tire and frame.
- Tire drop
How much the tire compresses under the rider's load. Frank Berto put the optimum at about 15% of the tire's width, and the tire pressure calculator is built on his method.
Road tire pressure for 28, 30 and 32mm tiresTire pressure calculator
- TPIThreads per inch
The number of threads that cross one square inch of a single ply of the tire casing (Maxxis). Lower TPI resists punctures and cuts better but weighs more; higher TPI is lighter and conforms better to the terrain but is more fragile.
Best gravel tires by useSource: Maxxis
- TPU inner tube
A tube made of thermoplastic polyurethane that folds very small and weighs little. In BRR's drum test the better ones rolled about 1.4 to 3 W per tire faster than typical 100 g butyl tubes; latex is still slightly faster.
- TSS
Tubeless Straight Side, the official ETRTO name for a hookless tubeless rim (Schwalbe). In training apps, TSS is TrainingPeaks' Training Stress Score, which is calculated from your FTP.
- Tubeless
A tire run without an inner tube, with sealant inside that plugs small punctures as you ride and lets you run lower pressure without pinch flats. You still need a spare tube for the puncture sealant cannot fix.
How often should you top up tubeless sealant?Are TPU inner tubes worth it?
- UDHUniversal Derailleur Hanger
A standard derailleur hanger and the frame interface it fits, introduced by SRAM in 2019. A UDH frame takes a normal derailleur on a UDH hanger or a Full Mount derailleur, and the hangers are sold at SRAM dealers worldwide.
UDH and SRAM Full Mount gravel framesCompatibility at a glance
- Virtual shifting
Gears simulated by the app and trainer: you ride one cog and shift with a handlebar remote such as the Zwift Click. Zwift's version needs the trainer connected over Wi-Fi or Bluetooth, not ANT+.
Zwift Cog compatible trainersBest indoor cycling apps for winter
- Wheel-on trainer
A trainer that keeps your rear wheel in the bike and applies resistance through the tire. Saris lists its wheel-on M2 at ±5% power accuracy and its direct-drive H3 Plus at ±2%.
- W/kgWatts per kilo
FTP divided by body weight in kilograms: 228 W at 70 kg is 3.26 W/kg.
- XDRSRAM XD/XDR
SRAM's driver body for most AXS and eTap AXS cassettes, XPLR included. Elite's rule: if the smallest cog on your SRAM cassette has 10 teeth, you need XDR "regardless of the number of speeds."
Smart trainer compatibility for 12 and 13-speed drivetrainsCompatibility at a glance
- Zwift Cog
A single sprocket that goes on a Shimano Hyperglide freehub, on direct-drive trainers only, with virtual shifting doing the gear changes. Zwift sends a 14-tooth Cog for every compatible trainer except Elite, which gets an 18-tooth one.
Each definition comes from the linked guide or tool, where every claim links to its source, or from the source named with it. Missing a term? [email protected]