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Bicycle tire size explained: ETRTO, inch & 700C | TopTierParts

September 26 2025, by TJB Trading, 5 min reading time

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Bicycle Tire Sizes: How to Quickly Choose the Right Size (ETRTO, Inch, and French)

Choosing the right tire size seems simple until you encounter a mix of ETRTO numbers, inch sizes, and French sizes. In this guide, we'll explain bicycle tire sizes in plain language—including a step-by-step plan to check which size you need in under 2 minutes.

Tip: The most reliable measurement is almost always the ETRTO size on your tire.

Why the right tire size is important

With the right size, you:

your tire fits securely on your rim
prevent rubbing against the frame/fender
ride more comfortably (fewer flats) and efficiently

An incorrect size can lead to poor steering, more frequent punctures, or even a tire that doesn't "seat" properly on the rim.

1) Where to find the tire size on your bicycle tire?

Look at the sidewall of your tire. It usually says something like:

ETRTO: 37-622
Inch: 28 x 1.40 or 29 x 2.25
French: 700 x 35C

Often, multiple notations are listed on one tire.

2) ETRTO explained (the size you should trust)

ETRTO is the standard that causes the least confusion. Example:

`37-622`

37 = tire width in mm
622 = rim diameter (bead seat diameter) in mm

Important: the 622 must match exactly. If your tire is …-622, then your replacement tire must also be …-622.

3) 28 inch, 29 inch, 700C… what's the deal?

Much confusion stems from this:

28 inch and 700C often have the same rim diameter: 622 mm
29 inch (MTB) also often has 622 mm, but with wider tires

So:

700 x 25C ≈ 25-622 (road)
700 x 35C ≈ 35-622 (gravel/trekking)
29 x 2.25 ≈ 57-622 (MTB)

The "inch-name" doesn't tell the whole story — ETRTO does.

4) Common tire sizes by bike type

Road bike

often: 23-622, 25-622, 28-622
French: 700x23C / 700x25C / 700x28C

Gravel / all-road

often: 32-622 to 45-622
French: 700x32C to 700x45C

City bike / trekking (28 inch)

often: 37-622, 40-622, 42-622, 47-622

MTB 29”

often: 54-622, 57-622, 60-622 (e.g. 2.10–2.40)

MTB 27.5”

often: …-584 (e.g. 57-584)

MTB 26”

often: …-559

5) Does every width fit on your bike?

The diameter (e.g., 622) must match exactly. The width (e.g., 37 mm) is more flexible—but not unlimited.

Check 2 things:

Clearance in your frame and fork
Allow for mud/expansion: it's better to have some margin.
Suitable rim width
Too narrow/wide can make your tire "square" or unstable.

Rule of thumb: want to go wider? Check if your tire doesn't rub against the rear wheel (bridge) and fenders.

6) Step-by-step plan: determine your tire size in 2 minutes

Read the sidewall of your current tire
Look for xx-yyy (ETRTO).
Note the rim diameter (e.g., 622).
Choose the tire width that suits your usage:
- narrower = lighter/faster (but less comfort)
- wider = more comfortable/more grip (often fewer flats)
Check frame clearance and any fenders.
Order a tire with the same ETRTO diameter.

7) Frequently Asked Questions (FAQ)

What does 700x35C mean?

That's the French notation. In ETRTO, this is usually 35-622.

Can I go from 28 mm to 32 mm?

Often yes, if you have enough clearance in the frame/fork and under the fenders. The rim diameter remains the same (e.g., 622).

Is 28 inch the same as 29 inch?

They often have the same rim diameter (622 mm), but 29” is usually used for MTB tires (wider).

Which tire size is the most reliable?

ETRTO. Especially the second number (e.g., 622/584/559) must match exactly.