Reading bicycle tyre sizes: ETRTO instead of confusing inches

The bicycle tire size can be read most reliably from the ETRTO marking on the tire sidewall. A marking such as 50-622 is more informative for purchasing a replacement than “28 × 2.00 inches.” It describes two measurements in millimeters and prevents many mix-ups caused by traditional inch designations. However, the rim, frame clearance, load, and vehicle approval must still be checked together to ensure the tire is suitable.

What 50-622 Means on a Bicycle Tire

With an ETRTO size, the first number indicates the nominal tire width and the second number indicates the rim seat diameter. 50-622 therefore stands for a tire approximately 50 millimeters wide whose bead sits on a rim seat with a diameter of 622 millimeters. The second value is particularly important for technical compatibility: a tire with a 584-millimeter rim seat will not fit a 622 rim.

The actual width may vary slightly depending on the rim’s internal width, tire pressure, and construction. Therefore, the number 50 alone does not prove that the tire will have enough clearance between the fork, rear triangle, and mudguard. It is a starting point for comparison, not a guarantee of fit.

Why Inch Designations Can Be Misleading

Traditional designations are historically based on different external measurements and naming conventions. The same inch name may be used for technically different diameters; conversely, different inch designations may refer to the same rim seat diameter. Tire manufacturer Schwalbe explains these differences in its overview of size designations.

Terms such as 26, 27.5, 28, or 29 inches are useful for a rough category, but they are not precise enough for placing an order. Always note the complete ETRTO number of the mounted tire and compare it with the bicycle documentation. An online filter for “28 inches” must not replace a technical comparison.

Finding the Marking on the Tire Sidewall

Turn the wheel slowly and look on both tire sidewalls for a combination of two numbers, a hyphen, and three digits. The marking may be embossed, printed, or part of a longer line. Clean the sidewall with a damp cloth instead of scraping it with a tool. Photograph the complete marking in good lighting.

Also note the model name, version, permitted pressure range, direction of rotation, and any load or speed specifications. The front and rear tires do not necessarily have to be the same width. Therefore, check both wheels separately. If the lettering is illegible or the tire is missing, the rim marking and bicycle documentation can help; simply measuring with a tape measure is not a reliable way to determine the rim seat diameter.

How to Choose a Replacement Tire in Five Steps

1. Photograph the complete ETRTO size of the existing tire.
2. Check the permitted tire dimensions in the manual, data sheet, or manufacturer approval.
3. Compare the rim’s internal width and tire-rim compatibility using the relevant tables.
4. Check clearance to the frame, fork, mudguards, kickstand, and cables.
5. Check the load, intended use, puncture protection, and, for motor vehicles, the approval requirements.

If several widths are approved, the choice should suit the intended use. A narrower tire may be lighter and provide more clearance. A wider tire may offer greater air volume and comfort with a suitable rim. Neither “wider is always better” nor “narrower is always faster” is a reliable purchasing rule for every bicycle.

The Tire and Rim Must Match

The same rim seat diameter is necessary but not sufficient. The tire width must match the rim’s internal width and design. A very wide tire on a narrow rim may sit unstably; a very narrow tire on a wide rim may lose its intended shape. Use the compatibility tables provided by the tire and rim manufacturers or the current recommendations of the European Tyre and Rim Technical Organisation.

Hooked rims, hookless rims, tubeless systems, and the maximum permitted pressure must also be taken into account. Do not transfer a pressure specification from another wheel. The lowest permitted limit among the tire, rim, rim tape, and any tubeless components is decisive.

Assessing Frame Clearance Realistically

There needs to be clearance between the tire and bicycle, not just when the bicycle is stationary and unloaded. Wheels can move slightly under load, dirt can cling to the tread, and mudguards require their own space. Check both sides of the fork, the chainstays and seatstays, brake components, mudguard stays, and cables.

A tire that barely does not rub in the workshop may have too little clearance outdoors. Extra clearance is particularly important with aggressive tread, snow, or mud. Do not rely on the nominal width: mounted tires from different models may vary in actual width despite having the same ETRTO width marking. If clearance is tight, have a specialist measure it.

Choosing the Right Inner Tube Size

A bicycle inner tube is usually offered for a range of tire widths and one specific rim seat diameter. The diameter must match exactly; the tire width must fall within the specified tube range. The Schwalbe inner tube finder shows by example how manufacturers document this allocation.

The valve must also match the rim hole, rim height, and pump. However, the valve is a separate compatibility check and does not change the tire size. With tubeless setups, the compatible tire, suitable rim, valve, rim tape, and sealant must be considered as one system.

E-Bikes and Pedelecs: Consider Weight and Approval

A Pedelec 25 is legally a bicycle, but it often has a higher system weight and greater drive forces than an unpowered everyday bicycle. Therefore, do not choose a replacement based solely on dimensions and tread. Check the permitted load, manufacturer recommendation, and pressure range for the actual total weight of the bicycle, battery, rider, and luggage.

For an S-Pedelec, a suitable ETRTO dimension alone is not sufficient. As a motor vehicle, it may require tires with the appropriate approval, load capacity, or speed rating. The operating permit and vehicle documents take precedence over a general shop description. Any unclear modifications should be clarified with the manufacturer or a specialist before installation.

Reading Direction-of-Rotation and Installation Instructions

Some tires have an arrow indicating the direction of rotation; others distinguish between front- and rear-wheel installation. Follow the instructions for the specific model. With a symmetrical tread pattern, the manufacturer may not specify a direction. In that case, there is no need to infer one from the tread design.

After installation, the inspection line above the rim must run evenly all the way around. Inflate the tire gradually, check that the bead is seated correctly, and stay within all pressure limits. If the wheel does not rotate freely, the tire is seated unevenly, or a bulge appears, do not ride. Tire levers must not damage the inner tube, bead, or rim.

Avoid Common Purchasing Mistakes

• Filtering in the shop only by the inch designation or wheel diameter.
• Confusing the first ETRTO number with the rim diameter.
• Ordering a wider tire without checking the frame and mudguard.
• Transferring tire approval for a Pedelec to an S-Pedelec without checking.
• Assuming that the choice of inner tube and valve proves that the tire dimension is suitable.
• Using the maximum tire pressure without considering the lower rim limit.

Frequently Asked Questions

Is 50-622 the same as 28 inches?

The 622 refers to a rim seat diameter commonly designated as 28 or 29 inches. For purchasing, however, the complete ETRTO specification 50-622 is decisive because it also includes the nominal width.

Can I install a 55-622 instead of a 50-622?

Only if the bicycle, rim, and all clearances allow this width. The same diameter alone is not sufficient.

How do I know which inner tube size is correct?

The inner tube must match the rim seat diameter and cover a width range that includes your tire size. Also consider the valve type and valve length.

Does an e-bike tire need special markings?

For a Pedelec 25, the manufacturer’s approvals, load, and system requirements are relevant. For an S-Pedelec, the operating permit and motor-vehicle tire requirements must also be checked.

As of: September 6, 2026. The current documentation from the bicycle, rim, and tire manufacturers and, for motor vehicles, the vehicle documents are authoritative.