Bicycle Rim Types: Construction, Profiles and Differences in Depth and Cross-Section

Bicycle rim types differ in four main ways. The first is construction: single-wall or double-wall. The second is bead profile: hooked, hookless or tubular. The third is braking interface: rim-brake or disc-brake. The fourth is cross-sectional geometry, meaning internal width, external width and depth. The tire sidewall numbers tell you which rim diameter a tire fits and roughly how wide it is. The rim's own markings and type tell you whether that tire will seat safely and how it will take shape. To compare wheels, start with the sidewall code. Then check the rim's internal width and bead type. Treat any calculated diameter as an estimate, not a measurement.

How do you read the numbers on a bicycle tire sidewall?

The most reliable number on a bicycle tire sidewall is the ETRTO/ISO code. It is written as two numbers, such as 25-622 or 57-584. The first number is the nominal tire width in millimetres. The second is the bead seat diameter (BSD) of the rim in millimetres. Most tires also carry an older inch or French size, along with performance ratings such as a pressure range. These ratings describe limits and construction, not size.

The ETRTO/ISO code: width and bead seat diameter

In an ETRTO code such as 28-622, the tire is nominally 28 mm wide. It fits a rim whose bead seat measures 622 mm in diameter. The bead seat diameter decides compatibility. A tire fits only a rim with the same BSD, whatever name the wheel size goes by. Common bead seat diameters include:

• 622 mm: sold as 700C on road and gravel bikes, and as 29-inch on mountain bikes. These are the same rim diameter.
• 584 mm: sold as 650B or 27.5-inch.
• 559 mm: the common modern 26-inch mountain bike size.
• 571 mm and 590 mm: older 650C and 26 × 1 3/8 sizes. These do not interchange with 559 mm, even though some are also called 26-inch.
• 406 mm and 507 mm: common 20-inch and 24-inch sizes on children's, folding and BMX bikes.

Inch and French sizes: helpful labels, unreliable for fit

Inch sizes such as 29 × 2.4 or 26 × 1.95 give an approximate outer diameter and a width in inches. French sizes such as 700 × 25C give an approximate outer diameter in millimetres and a width in millimetres. Neither is precise enough on its own. The letter C in 700 × 25C is an old width-class letter. It does not refer to a hooked or crochet rim. Decimal and fractional inch widths are a common trap. A 26 × 1.95 tire (559 mm BSD) and a 26 × 1 3/8 tire (590 mm BSD) will not fit the same rim. When in doubt, compare the ETRTO numbers.

Pressure, TPI and other performance ratings

Performance ratings describe what a tire is built to handle, not how big it is. Pressure is usually printed as a range in both bar and psi. One bar equals about 14.5 psi, and 100 kPa equals 1 bar. So a maximum of 7 bar is about 101 psi, and 5 bar is about 72.5 psi. The tire's pressure limit is not the system limit. The rim also has a maximum pressure, and you must stay below whichever is lower. TPI (threads per inch) describes how fine the casing threads are. It is a construction detail, not a dimension. Markings such as TLR, Tubeless Ready or TL indicate tubeless compatibility. Some tires also show an e-bike rating or a hookless-compatible marking.

Sidewall marking	Category	What it means	What you can compare with it
28-622	Dimensions (mm)	Nominal width 28 mm, bead seat diameter 622 mm	Rim fit (BSD) and approximate width
700 × 28C	Dimensions (French system)	Approximate outer diameter class and nominal width	Rough size only; confirm with ETRTO
29 × 2.4	Dimensions (inches)	622 mm BSD class, about 61 mm nominal width	Rough size only; confirm with ETRTO 61-622
Max 5 bar / 73 psi	Performance rating (pressure)	Upper pressure limit for the tire	Compare against the rim's limit and use the lower one
120 TPI	Construction rating	Casing thread density	Casing suppleness between tires, not size
TLR / Tubeless Ready	Compatibility marking	Designed to run without an inner tube on a suitable rim	Whether the tire suits a tubeless-ready rim

How do tire width and rim diameter change overall wheel diameter and circumference?

The overall diameter of a bicycle wheel is roughly the bead seat diameter plus twice the tire's height above the bead. Circumference is that diameter multiplied by π (about 3.1416). Bicycle tires usually do not carry an aspect ratio the way car tires do. For a simple estimate, people often treat tire height as roughly equal to nominal width. Real tire height is often somewhat lower, so this estimate tends to run slightly high.

How to estimate diameter and circumference from the sidewall

1. Read the ETRTO code, for example 25-622.
2. Take the bead seat diameter: 622 mm.
3. Add twice the nominal width as an estimate of tire height: 622 + (2 × 25) = 672 mm.
4. Multiply by π for circumference: 672 × 3.1416 ≈ 2111 mm.
5. Compare against another size in the same way. Express the difference in millimetres or as a percentage.

Worked examples

Tire (ETRTO)	Common name	Estimated diameter (mm)	Estimated circumference (mm)
25-622	700 × 25C	672	≈ 2111
28-622	700 × 28C	678	≈ 2130
40-622	700 × 40C	702	≈ 2205
47-584	650B × 47	678	≈ 2130
54-559	26 × 2.1	667	≈ 2095
71-584	27.5 × 2.8	726	≈ 2281
61-622	29 × 2.4	744	≈ 2337

These examples show the practical logic. Going from a 25 mm to a 28 mm tire on a 622 mm rim adds about 6 mm of diameter and about 19 mm of circumference. That is under 1%. A 47-584 tire on a smaller 650B rim reaches roughly the same estimated diameter as a 28-622 road tire. That is why some frames accept both. A wider tire on a smaller rim can match the outer diameter of a narrower tire on a larger rim. For a bike computer, a 1% circumference difference produces about a 1% difference in displayed speed and distance.

Why calculated geometry differs from actual tire size and frame fit

A calculated diameter is an estimate based on nominal numbers. The real dimensions of a mounted tire depend on the rim, the pressure and the specific tire model. Three factors cause most of the gap:

• Internal rim width. The same tire measures wider on a wider rim and narrower on a narrower one. A commonly quoted rule of thumb is roughly half a millimetre of tire width per millimetre of internal rim width. The real change varies by tire.
• Casing shape and tread. Two tires labelled 40-622 can differ in measured width and height. Knobs, tread thickness and casing construction all play a part.
• Pressure and load. A tire grows slightly at higher pressure and compresses under a rider. Rolling circumference measured on the road is therefore usually a little smaller than the calculated figure.

Frame and fork fitment is a separate question from rim compatibility. A tire can match the rim's BSD perfectly and still rub the frame, fork crown, brake caliper or fender. Clearance depends on the frame's maximum tire size and the measured width and height of the mounted tire. Leave some margin for mud and wheel flex. Treat the calculation as a way to compare sizes, then confirm with the frame maker's stated clearance or a measurement.

What do the markings on a bicycle rim mean?

A bicycle rim is usually marked with its bead seat diameter and internal width, for example 622 × 19C or 584 × 25. The first number is the bead seat diameter in millimetres and must match the tire's ETRTO BSD. The second number is the internal width between the bead walls in millimetres. A letter suffix may show the bead profile. C indicates a crochet (hooked) rim. TC and TSS appear in tubeless standards for hooked and straight-side (hookless) rims. Many rims also state a maximum tire pressure and a range of approved tire widths.

What are the main bicycle rim types?

Bicycle rim types are best grouped by three questions. How is the rim body built? How does it hold the tire? How does the bike brake? One rim belongs to a category in each group. For example, a rim can be double-wall, hookless, tubeless-ready and disc-brake all at once.

Single-wall rims and double-wall rims

A single-wall rim has one horizontal wall between the tire bed and the spoke holes, giving it an open, U-like cross-section. Single-wall rims are simple and inexpensive. They are typically less stiff, so they mainly appear on children's bikes, basic utility bikes and some budget wheels. A double-wall rim adds a second wall, forming a closed box between the tire bed and the spoke bed. This box section makes the rim stiffer and stronger for its weight. It also spreads spoke tension more evenly. Most modern road, gravel and mountain bike rims are double-wall.

Hooked rims and hookless rims

Hooked rims have a small inward lip along the top of each sidewall, called the hook or crochet. The hook grips the tire bead and helps hold it at higher pressures. Hooked rims work with inner tubes, clincher tires and tubeless tires. Hookless rims, also called straight-side rims, have straight sidewalls without a lip. The tire stays on because of a tight bead seat and bead shelf geometry, held by air pressure. Current ETRTO and ISO guidance limits hookless road-type rims to 5 bar (about 72.5 psi). Hookless rims also require tires the manufacturer approves for hookless use, usually tubeless-type tires within a stated width range. Hookless designs can be simpler to manufacture in carbon and give a wider bead area. In return, they leave less room for error in tire choice and pressure.

Tubeless-ready rims

A tubeless-ready rim has a bead seat shaped to lock the tire bead airtight. It also has a central well (channel) that makes mounting easier, and a spoke bed that can be sealed with rim tape. On a tubeless-ready rim, a tubeless-ready tire runs without an inner tube, using sealant. Most tubeless-ready rims also accept a standard tire and inner tube. The term describes bead seat geometry and sealing. It can apply to both hooked and hookless rims.

Tubular rims

A tubular rim has a shallow, concave tire bed and no bead hooks or bead seat. It is made for tubular tires, in which the casing is sewn around an inner tube and glued or taped to the rim. Tubular rims do not accept clincher or tubeless tires. A tubular tire's marked width refers to the tire. Bead seat diameter does not apply in the same way, because the tire has no bead.

Rim-brake rims and disc-brake rims

A rim-brake rim has flat or slightly angled braking tracks on its outer sidewalls, where the brake pads press. These tracks wear over time. Many aluminium rim-brake rims have a wear indicator. Carbon rim-brake rims need a braking surface and pads designed for the heat of rim braking. A disc-brake rim has no braking track, because the brake acts on a rotor at the hub. Without a braking track, the rim shape is freed from pad-alignment constraints. This often allows wider, more rounded profiles. A rim-brake rim can sometimes be used with disc brakes if the hub suits. A disc-specific rim cannot be used with rim brakes, because it has no braking surface.

Rim type	Defining feature	Tire systems	Key limit or consideration
Single-wall	One wall, open cross-section	Usually tube-type clincher	Lower stiffness; mainly basic and children's bikes
Double-wall	Two walls forming a box section	Clincher, often tubeless-ready	Standard on most modern sport bikes
Hooked	Inward lip on each sidewall	Tube, clincher, tubeless	Follow rim and tire pressure limits
Hookless	Straight sidewalls without a lip	Approved tubeless tires	5 bar maximum under ETRTO/ISO guidance; approved tire list
Tubeless-ready	Sealing bead seat and central well	Tubeless with sealant, or tube	Needs proper rim tape and compatible tire
Tubular	Concave bed, no bead seat	Tubular tires only	Tire is glued or taped on
Rim-brake	Braking track on sidewalls	Depends on bead type	Track wears; heat matters on carbon
Disc-brake	No braking track	Depends on bead type	Cannot be used with rim brakes

How does rim depth affect a bicycle wheel?

Rim depth is the height of the rim cross-section, measured from the tire bed edge to the spoke bed, in millimetres. Rim depth does not change the bead seat diameter. A 25 mm deep rim and a 60 mm deep rim with the same 622 mm BSD take the same tires and give the same estimated overall wheel diameter. Depth changes how the wheel behaves, not the tire size.

• Shallow rims, often under about 30 mm. These are usually lighter and less affected by crosswinds. They are common for climbing, mountain biking and general riding.
• Mid-depth rims, often about 30–50 mm. These are a compromise between weight, stiffness and aerodynamic benefit. They are widely used on road and gravel wheels.
• Deep rims, often 50 mm and above. These are chosen mainly for aerodynamics at higher speeds. They can be stiffer radially but heavier, and more sensitive to crosswinds.

A deeper rim also allows shorter spokes and can raise radial stiffness. It may need longer valve stems, and on rim-brake bikes the braking track sits at the same outer edge regardless of depth. These category boundaries are common conventions, not fixed standards.

Cross-section profiles: box, V-shaped and U-shaped

The cross-section profile is the shape of the rim seen as if it were sliced through. A box-section rim has a roughly rectangular shape, common on shallow aluminium rims. A V-shaped rim tapers to a narrower spoke bed, an older aero shape. A U-shaped or toroidal rim has a wider, rounded spoke bed. Designers use it to manage airflow around a modern, wider tire. For aerodynamic profiles, a frequently cited guideline keeps the rim's external width slightly wider than the mounted tire. This helps the tire and rim act as one shape. It is a design guideline, not a fit requirement.

How does internal rim width shape the tire profile?

Internal rim width is the distance between the inner faces of the rim sidewalls at the bead seat, in millimetres. It controls how the tire casing spreads. A tire on a narrow internal width takes a rounder, taller, slightly narrower shape. The same tire on a wider internal width takes a broader, slightly flatter shape with more support at the sidewalls. This is why the same 28-622 tire can measure differently on a 17 mm and a 25 mm internal rim. It is also why rim makers publish minimum and maximum tire widths for each internal width, especially for hookless rims. External width matters for aerodynamics and frame clearance. Internal width is the figure that determines tire fit and shape.

How to check that a tire suits a rim

1. Match the bead seat diameter. The tire's ETRTO BSD, such as 622, must equal the rim's BSD.
2. Check the internal rim width against the tire width. Use the rim or tire maker's approved width range.
3. Match the bead system. Use tubular tires on tubular rims and clincher or tubeless tires on hooked or hookless rims. On hookless rims, use only tires approved for hookless use.
4. Find the lowest pressure limit. Compare the tire's maximum, the rim's maximum and, for hookless rims, the 5 bar limit, then stay below the lowest.
5. Confirm the braking interface. Rim brakes need a rim-brake rim with a usable braking track.
6. Estimate the outer diameter, then check actual frame and fork clearance with the mounted tire.

Taken together, the sidewall numbers give you the tire's diameter class and nominal width. The rim's markings and type tell you whether the tire will seat, hold pressure and take the intended shape. Calculations are useful for comparing sizes. Actual measurements and the manufacturers' stated limits decide what fits and what is safe.