Bike Wheel and Tire Glossary: Rims, Spokes, Tubeless and Valves

The hub, spokes and rim, not counting the tire. It's one of the parts that most changes how a bike rides, because its weight spins and has to be accelerated every time you start.

See also: rim, hub, spoke

The outer hoop of the wheel that the tire mounts on. It can be aluminum or carbon, with a brake track (for rim brakes) or without one (for disc brakes).

See also: internal rim width, rim depth, hookless rim, effective rim diameter (ERD)

The center of the wheel, which spins on bearings around the axle. The rear hub includes the freehub body for the cassette. Standard widths are 100/142 mm on thru-axle road bikes and 110/148 mm (Boost) on mountain bikes.

See also: freehub body, Boost, thru axle, spoke Spoke Length

A rod, almost always stainless steel, that connects the hub to the rim and works under tension. Wheels usually have 24-32 spokes, 2.0 mm thick or thinner in the middle (butted) to save weight.

See also: spoke nipple, spoke tension, spoke lacing (crosses), effective rim diameter (ERD) Spoke Length

The long nut that threads onto the end of the spoke from the rim. Turning it with a spoke wrench changes spoke tension, which is how you true a wheel. They come in brass (stronger) and aluminum (lighter).

See also: spoke, wheel truing, spoke tension Spoke Length

The rim diameter measured where the spokes end inside the nipples. It's the key number for calculating spoke length: a 2 mm error in ERD gives spokes 1 mm too long or too short.

See also: rim, spoke, spoke lacing (crosses) Spoke Length

Adjusting spoke tension so the rim spins without wobbling side to side or up and down. A wheel that's out of true rubs the brake pads or the frame and loses strength.

See also: spoke nipple, spoke tension

How hard each spoke is pulled, measured with a tension meter in kgf or newtons. The rim maker sets the maximum, often between 100 and 130 kgf on the tighter side of a rear wheel.

See also: spoke, wheel truing, spoke lacing (crosses) Spoke Length

How many other spokes each spoke crosses between hub and rim: radial (0 cross), 2-cross or 3-cross. More crosses make the spoke longer and transfer pedaling and braking torque better.

See also: spoke, effective rim diameter (ERD) Spoke Length

The outer tire mounted on the rim. You choose it by diameter, width and riding style, and it can run with a tube, tubeless, or be a tubular sewn around its own tube.

See also: inner tube, tubeless, ETRTO, tire pressure Tire Size

The rubber tube with a valve that sits inside the tire and holds the air. A butyl road tube weighs about 100 g (3.5 oz); TPU tubes weigh less than half that.

See also: tire, Presta valve, flat tire (puncture)

A tube-free system: the tire seals against the rim and liquid sealant plugs small punctures. It lets you run lower pressure without risking pinch flats; rim and tire must both be compatible (tubeless ready).

See also: tire sealant, tubeless repair plug, rim tape, pinch flat (snakebite) Tire Pressure

A liquid with latex or particles that goes inside a tubeless tire and seals small punctures, a few millimeters across, on its own. It dries out: top it up every few months, sooner in summer.

See also: tubeless, tubeless repair plug

A sticky rubber strip you push into a cut that's too big for the sealant, using an insertion tool. It lets you keep riding without removing the tire; check the repair once you get home.

See also: tubeless, tire sealant, flat tire (puncture)

A slim 6 mm valve with a small nut on the tip that you loosen before inflating. It's standard on road, gravel and mountain bikes; tubeless setups use a version that bolts to the rim.

See also: Schrader valve, inner tube

A thick valve, about 8 mm, the same as on cars, so you can fill it at a gas station. You see it on kids' bikes, city bikes and some entry-level mountain bikes.

See also: Presta valve, inner tube

The standardized tire and rim size (ISO 5775) that gives width and bead seat diameter in millimeters: 28-622 is a 28 mm tire for a 700c wheel. It's the only size that can't be misread.

See also: 700c, 29-inch wheel (29er), tire Tire Size

The name of the road and gravel wheel size, with a 622 mm bead seat diameter. It's the same diameter as a 29-inch mountain bike wheel and the 28-inch wheel of European city bikes.

See also: ETRTO, 29-inch wheel (29er) Tire Size

A mountain bike wheel size with a 622 mm rim, the same as 700c, but with tires 2.2 to 2.6 in wide. It rolls over obstacles better; the 27.5-inch wheel (584 mm, also called 650b) is more agile.

See also: 700c, ETRTO Tire Size

The distance between the inner walls of the rim, where the tire bead sits. It changes the tire's real width: a 28 mm tire on a 21 mm internal width rim usually measures 29-30 mm.

See also: rim, tire, hookless rim Tire Pressure

The height of the rim from the tire seat to the inner edge. A deep rim (40-60 mm) is more aerodynamic but heavier and more affected by crosswinds.

See also: rim, CdA (drag area)

A rim with straight walls, without the hook that holds the tire bead. It only takes compatible tires and limits pressure to 5 bar (72.5 psi) under the ETRTO standard.

See also: rim, tubeless, tire pressure Tire Pressure

The edge of the tire that sits on the rim. It can be wire, which is rigid and heavier, or aramid (Kevlar) fiber, which lets the tire fold and saves weight.

See also: tire, tire levers

The raised rubber blocks on mountain and gravel tires. Tall, widely spaced knobs grip in mud and loose dirt; low, tightly packed knobs roll faster on dry hardpack.

See also: tire, rolling resistance

Loss of air from an object going through the tire or from a pinched tube. You fix it with a patch, a plug if you run tubeless, or by swapping the tube.

See also: pinch flat (snakebite), inner tube, tubeless repair plug, tire levers

A flat that happens when the tube gets trapped between the rim and an obstacle; it leaves two parallel slits, like a snake bite. Avoid it with more pressure or by going tubeless.

See also: flat tire (puncture), tire pressure, tubeless Tire Pressure

Plastic levers for prying the tire bead over the rim. Use two or three, and never screwdrivers, which damage the rim and the tube.

See also: bead, flat tire (puncture)

Tape that covers the spoke holes inside the rim so they don't damage the tube. On tubeless setups it's adhesive and airtight, and should be slightly wider than the internal rim width.

See also: rim, tubeless, internal rim width

The air inside the tire, in psi or bar (1 bar = 14.5 psi). It depends on weight, tire width and surface: a 165 lb (75 kg) rider on 28 mm tires on pavement is usually comfortable and fast at around 73 psi (5 bar).

See also: tire, pinch flat (snakebite), hookless rim Tire Pressure

The distance the wheel travels in one turn, in millimeters. It's what bike computers without GPS ask for and the basis of rollout: a 700 × 28 wheel measures about 2,136 mm (84.1 in).

See also: rollout (gear development), bike computer, speed sensor Tire Size