The short version: what a bike tire is made of
A bike tire looks like a single piece of rubber, but it is built from several parts that each do a different job. From the outside in, you have the tread, the sidewalls, the casing underneath, and the beads along each edge. Many tires also include a puncture protection layer beneath the tread. Inside the tire there is either an inner tube or, on tubeless setups, a layer of sealant and an airtight rim.
Knowing these parts makes it much easier to read a product listing, decide between two tires, and recognize what is wearing out when a tire starts to look tired.
Casing
The casing (sometimes called the carcass) is the fabric body of the tire. It is made of fine threads, commonly nylon, woven into a layer that is then coated with rubber. The casing holds the tire’s shape and carries the air pressure, so it largely determines how supple or tough the tire feels.
Casings are described by their thread density, called TPI (threads per inch). In general, a higher TPI means finer threads and a lighter, more flexible casing, while a lower TPI usually means thicker threads and a tougher, stiffer casing. Our guide to TPI and whether a higher thread count matters goes into the trade-offs.
Some tires use more than one layer of casing, or add reinforcement in the sidewalls, particularly for mountain biking. These choices affect weight, cut resistance and ride feel, which is why the TPI number alone does not tell the whole story.
Bead
The bead is the edge of the tire that locks onto the rim. Inside each bead is a strand that stops the tire from stretching and popping off the rim when it is inflated. There are two main types:
- Wire bead: a steel wire. It is usually less expensive and a bit heavier, and the tire stays in a fixed ring shape, so it does not fold compactly.
- Folding bead: made of a flexible fiber such as aramid. It is usually lighter and the tire can be folded, which is convenient for carrying a spare.
The bead has to match the rim it sits on. The tire’s size designation, covered below, includes the bead seat diameter for exactly this reason.
Tread
The tread is the rubber layer that touches the ground. Its pattern and rubber compound shape grip, rolling speed and how long the tire lasts.
- Pattern: road tires are often smooth or lightly textured in the center, while gravel and mountain bike tires add knobs (lugs) for traction on loose surfaces. Our article on mountain bike tire tread patterns explains how those knobs are arranged and matched to terrain.
- Compound: the rubber mix. Softer rubber generally grips better and wears faster, and harder rubber generally lasts longer. Some tires use a firmer center and softer shoulders to balance wear and cornering grip.
- Siping: small slits molded into the tread that are meant to help the rubber conform to wet surfaces.
Puncture protection layers
Many tires include an extra layer between the tread and the casing, often a woven or belt-like material, to resist thorns, glass and sharp stones. More protection typically adds some weight and can make the tire feel a little less lively, so the amount offered is a trade-off against speed and comfort. No layer makes a tire puncture-proof, so it is still worth carrying repair gear. If you keep getting flats anyway, read why your bike tire keeps going flat.
Sidewall and the markings on it
The sidewall is the part of the tire between the tread and the bead. It flexes constantly, so it is usually the thinnest part of the tire and the part that suffers if you ride at very low pressure or scrape a curb. Cracking or fraying here is a reason to inspect the tire closely.
The sidewall is also where you find the printed information:
- Size: for example 700x28c, 26x1.95 or 29x2.4. The first number is the approximate outer diameter, and the second is the approximate width. A 26x1.95 tire is therefore a tire for a 26 inch wheel, roughly 1.95 inches wide.
- ETRTO size: a metric format such as 50-559, giving the tire width in millimeters followed by the bead seat diameter in millimeters. It is the most precise way to confirm that a tire fits a rim.
- Pressure range: a minimum and maximum, usually in psi and bar or kPa. Treat the maximum as a limit, not a target.
- Direction arrow and other labels: some tires are directional and need to be mounted facing the correct way. Others carry tubeless-ready marks or a wear indicator.
If you need a tube for the size you read, see our guide to bike tube sizes.
Inner tube, valve or tubeless
Most bikes still use an inner tube inside the tire. The tube holds the air and has a valve that sticks out through a hole in the rim. The two most common valve types are Presta and Schrader, compared in our guide to Presta vs Schrader valve types.
Tubeless setups remove the tube. The tire seals directly against a compatible rim and liquid sealant fills small punctures. They need tubeless-ready tires and rims, a tubeless-specific valve and tape or a rim designed for the system.
Clincher, tubular and tubeless
- Clincher: the common type, with a bead that hooks into the rim and an inner tube inside.
- Tubular: the tube is sewn inside the casing and the whole tire is glued to a special rim. It is more common in racing and trickier to repair.
- Tubeless: a clincher-style tire designed to seal on the rim without a tube.
Which parts wear out first
The tread usually wears first, and the rear tire wears faster than the front. Visible casing threads through the tread are a sign the tire is done. Sidewall cracking and age-related hardening can also end a tire’s life even if the tread looks fine. Our article on how long road bike tires last lists the common warning signs.
Frequently asked questions
Where do I find my bike tire size?
Look at the sidewall of the tire. The size is printed there, often in more than one format. If it is worn off, check the rim, the bike’s documentation, or measure the tire and the rim (see how to find and measure your bike tire size) and confirm with a bike shop.
What does 26x1.95 mean?
It means a tire for a 26 inch diameter wheel with a width of about 1.95 inches. Inch-based sizes are loose approximations, so confirm fit with the ETRTO number where possible.
What are the components of a bicycle wheel?
A wheel typically consists of a rim, spokes, a hub, and the tire (with a tube or sealant) that sits on the rim. This article focuses on the tire itself; for the rest of the wheel, see anatomy of a bike wheel.
How do I put a tire on a bike?
In outline: deflate and remove the old tire, check the rim and the inside of the tire for debris, seat one bead on the rim, add the tube with a little air, work the second bead on, check that the tube is not pinched under the bead, then inflate gradually. Follow your tire and rim manufacturer’s instructions for details.