Mountain Bike Inner Tube Size Chart: Reading the Numbers on Your Tire Sidewall

To find the right mountain bike inner tube, read two numbers on the tire sidewall. The first is the wheel diameter: 26, 27.5 or 29 inches, which correspond to ETRTO bead seat diameters of 559, 584 or 622 mm. This number must match the tube exactly. The second is the tire width, for example 2.35 inches or 60 mm. This number must fall inside the width range printed on the tube box. After that, choose a valve type that fits the rim's valve hole and a valve length that reaches through the rim.

Which inner tube fits my mountain bike tire?

A mountain bike inner tube fits when its diameter matches the tire's bead seat diameter and its width range covers the tire's width. A tire marked 29 x 2.40 and 61-622 needs a 29-inch (622 mm) tube whose width range includes 2.4 inches or 61 mm, such as a tube labelled 29 x 2.1–2.5. The diameter has no tolerance. A 27.5-inch tube will not work in a 29-inch tire. The width has a range because a tube is elastic and stretches to fill the tire.

Mountain bike tube size chart

This mountain bike tube size chart pairs each common MTB wheel size with its ETRTO bead seat diameter (BSD), its typical tire widths and the kind of width ranges tubes are sold in. Tube width ranges differ between manufacturers. Always check the range printed on the specific tube.

Wheel size (inch label)	Other names	ETRTO bead seat diameter	Common MTB tire widths	Typical tube label patterns
26	26-inch MTB	559 mm	1.9–2.5 in (about 48–64 mm)	26 x 1.75–2.125, 26 x 1.9–2.35, 26 x 2.2–2.6
27.5	650B	584 mm	2.1–2.6 in (about 53–66 mm); plus sizes 2.8–3.0 in	27.5 x 1.9–2.35, 27.5 x 2.2–2.6, 27.5 x 2.6–3.0
29	29er, shares BSD with 700c	622 mm	2.1–2.6 in (about 53–66 mm); plus sizes 2.8–3.0 in	29 x 1.9–2.35, 29 x 2.1–2.5, 29 x 2.6–3.0

The bead seat diameter is the diameter of the rim at the point where the tire bead sits. It is the most reliable number to compare. Inch labels are nominal names, not measured dimensions.

How to read mountain bike tire sidewall markings

Mountain bike tire sidewall markings include size information and performance information. Only the size information decides which tube fits. A typical sidewall carries an inch size, an ETRTO size, a pressure range, and often a casing rating and other labels.

The inch size: diameter x width

The inch size, such as 27.5 x 2.35, gives the nominal wheel diameter followed by the nominal tire width in inches. The first number names a wheel standard. It is not the tire's measured outside diameter. The second number is the manufacturer's stated width. The width you measure on your own rim can differ from it.

The ETRTO size: width-bead seat diameter

The ETRTO size, such as 60-584, gives the nominal tire width in millimetres, then a hyphen, then the bead seat diameter in millimetres. ETRTO stands for the European Tyre and Rim Technical Organisation, whose system removes the confusion of inch naming. A tire marked 60-584 is about 60 mm wide and fits a 584 mm (27.5-inch) rim. Tube packaging often uses a related format such as 54/62-622. This means the tube suits tires from 54 to 62 mm wide on a 622 mm rim.

Units: converting inch widths to millimetres

To convert a tire width from inches to millimetres, multiply it by 25.4. Manufacturers round the ETRTO width in their own way. A 2.4-inch tire might be marked 61 or 62, for example. If the two markings seem slightly inconsistent, trust the ETRTO code for diameter and use either number for width.

Width in inches	Calculated width in mm
2.10	53.3
2.25	57.2
2.35	59.7
2.40	61.0
2.50	63.5
2.60	66.0
2.80	71.1
3.00	76.2

Markings that are not sizes

Several common sidewall markings describe performance or use rather than dimensions. They do not affect which tube size you need.

• Pressure range (for example, 25–50 PSI or 1.7–3.5 bar): the inflation limits the tire manufacturer allows. PSI and bar are both units of pressure; 1 bar is about 14.5 PSI.
• TPI (threads per inch, for example 60 TPI or 120 TPI): the thread density of the casing fabric. It describes how the casing is built, not how big the tire is.
• E-bike ratings (for example, E-25 or E-50): the manufacturer's statement that the tire is rated for e-bikes with assisted speeds up to 25 or 50 km/h.
• Tubeless Ready or TLR: the tire can be run without a tube using sealant. These tires still accept an inner tube of the correct size.
• Rotation arrows: the direction the tire should turn when mounted.

How does the tube width range work?

The tube width range is the span of tire widths a tube is designed to fill. A 29 x 2.1–2.5 tube, for instance, suits any 622 mm tire from roughly 53 to 64 mm wide. Inside that range the rubber stretches evenly. A tube that is too narrow for the tire has to stretch further than intended, which leaves thinner rubber. A tube that is too wide for the tire can fold or crease inside the casing, which makes mounting harder and can trap the tube under the bead. If your tire width sits right at the edge of two ranges, either tube will usually work. The tube whose range centres closer to your width is the more comfortable fit.

Which valve type and length do I need?

The valve type must match the hole drilled in your rim, and the valve must be long enough to pass through the rim and still engage a pump head. Mountain bike tubes come with three valve types:

• Presta (also called French or SV): slim, with a locknut on the tip. It is common on modern MTB rims.
• Schrader (also called American or AV): wider, the same type used on car tires. It needs a larger rim hole.
• Dunlop (also called Woods or DV): found mainly on some city and European bikes. It is less common on mountain bikes.

A Presta valve fitted in a hole drilled for Schrader can rock in the oversized hole. A Schrader valve will not pass through a hole drilled for Presta unless the rim is drilled out. Valve length is listed in millimetres on the packaging. Choose a length that leaves enough threaded valve exposed above the rim for your pump to grip. Deeper rims need longer valves.

How do tire width and rim diameter change sidewall height, diameter and circumference?

A mountain bike tire's overall diameter is roughly the bead seat diameter plus twice the tire's section height. Its circumference is that diameter multiplied by π (about 3.1416). Section height is the distance from the bead seat to the top of the tread. It grows as the tire gets wider. The rim diameter sets the starting point.

What about aspect ratio on bike tires?

Aspect ratio is the section height expressed as a percentage of section width. Car tires print it on the sidewall, as in 205/55 R16. Bicycle tires do not print an aspect ratio. For a rough estimate, people often treat an MTB tire's height as about equal to its width, which is a ratio near 100 percent. The real ratio depends on the casing, the rim's internal width and the inflation pressure. Treat any calculated height as an approximation.

Simple calculation steps

1. Convert the tire width to millimetres (inches x 25.4), or read the ETRTO width.
2. Estimate section height. Using the 1:1 approximation, height ≈ width.
3. Calculate overall diameter: bead seat diameter + (2 x section height).
4. Calculate circumference: overall diameter x π.

Worked examples

The table below applies these steps with the 1:1 height approximation. The figures are calculated geometry, not measurements of any particular tire.

Tire	BSD (mm)	Width ≈ height (mm)	Calculated diameter (mm)	Calculated circumference (mm)
26 x 2.25	559	57	673	about 2114
27.5 x 2.6	584	66	716	about 2249
27.5 x 2.8	584	71	726	about 2281
29 x 2.3	622	58	738	about 2318
29 x 2.4	622	61	744	about 2337

These examples support some practical comparisons:

• Rim diameter dominates. The 29 x 2.4 tire is calculated at 744 mm overall, and the 27.5 x 2.8 tire at 726 mm. That is a difference of 18 mm in diameter and 9 mm in radius, which works out to about 56 mm of circumference per wheel revolution (18 x π). Although the 27.5 tire is much wider, the larger rim still produces the larger wheel.
• Width narrows the gap. A wide 27.5-inch plus tire comes closer to the overall diameter of a standard 29-inch tire than a narrow 27.5-inch tire would.
• Small width changes matter little. Going from 29 x 2.3 to 29 x 2.4 adds about 2.5 mm of width. That adds roughly 5 mm to calculated diameter, or 2.5 mm per side.

The height assumption also matters. If the 29 x 2.4 tire's real height were 90 percent of its width (about 55 mm), its diameter would come out near 732 mm instead of 744 mm. This sensitivity is the reason calculated figures should be used for comparison, not as exact specifications.

Calculated geometry vs actual dimensions vs fitment

Calculated geometry, actual tire dimensions and bike fitment are three different things:

• Calculated geometry comes from the sidewall numbers and an assumed height. It is useful for comparing sizes.
• Actual dimensions are what a tape measure shows once the tire is mounted and inflated. Rim internal width, casing construction, pressure and wear all change them. A tire on a wider rim usually measures wider than on a narrow rim.
• Fitment compatibility depends on your frame and fork: clearance at the chainstays, seatstays and fork crown, plus room for mud. The sidewall numbers alone cannot confirm fitment. Your frame or fork manufacturer's stated maximum tire size is the reference.

The inner tube only has to match the tire's diameter and width range. Whether that tire fits the bike is a separate question.

Common sizing mistakes to avoid

Most tube sizing errors come from inch labels that look similar but describe different rims. The bead seat diameter is the most reliable way to catch them.

• Decimal vs fractional inch sizes: mountain bike sizes use decimals, such as 26 x 2.125. A fractional size such as 26 x 1 3/8 refers to an older 590 mm rim standard, not the 559 mm MTB rim. Check the ETRTO number to confirm.
• 27.5 and 650B: these are the same 584 mm diameter, so tubes labelled either way are interchangeable if the width range fits.
• 29 and 700c: both share the 622 mm bead seat diameter. Many 700c tubes, however, are made for narrow road or hybrid tires. A 700c tube fits a 29-inch MTB tire only if its width range covers the tire's width.

How to choose an inner tube from your tire sidewall

1. Find the ETRTO code on the sidewall (for example, 61-622) and note the bead seat diameter, the number after the hyphen.
2. Choose a tube with the same diameter: 559 mm for 26-inch, 584 mm for 27.5-inch, or 622 mm for 29-inch.
3. Note the tire width in inches or millimetres and check that it falls within the tube's printed width range.
4. Look at the rim's valve hole to confirm whether you need a Presta or Schrader valve.
5. Check the rim depth and choose a valve length long enough to leave usable thread above the rim.
6. Confirm the tube suits your setup. If you use a tire insert designed to work with a tube, follow the insert maker's tube size guidance.

What do the same sidewall numbers mean for tire inserts and mousse sizing?

The sidewall numbers that select an inner tube also select a tire insert or mousse. The wheel diameter must match the bead seat diameter, and the product's tire width range must cover your tire. Inserts and mousses are usually listed by wheel size (26, 27.5 or 29 inches) and a tire width range. Many also list a recommended rim internal width range in millimetres, because the insert sits in the rim channel. Most mountain bike inserts are made for tubeless setups. Some are designed to sit between an inner tube and the tire, and these usually specify which tube size to pair with them. As with tubes, an insert sized for the wrong diameter cannot be made to fit. Choosing a width range that is too narrow or too wide for your tire affects how the insert seats and supports the casing.