How to read an e-bike tire size
An ETRTO size is two numbers with a dash: 50-622 is a tire 50mm wide on a rim with a 622mm bead seat diameter. It is the only unambiguous system, and it is printed on almost every tire sold. If the two numbers match your wheel and your frame has the clearance, it fits. Everything else on the sidewall is an older name for the same thing.
Why there are three systems at all
Bicycle tire sizing grew up separately in Britain, France and America, and each country measured something slightly different. The result was that 26 inch meant at least four incompatible diameters depending on where the wheel was made.
ETRTO fixed it by measuring the one thing that decides whether a tire will physically go on: the diameter of the rim at the bead seat, in millimetres. There is no interpretation involved.
The numbers you will actually meet
622mm is the 700c and 29 inch rim. It is the most common size on trekking, commuter and larger e-MTB wheels.
584mm is 650b and 27.5 inch, the standard for most current trail and enduro mountain bikes and therefore most e-MTBs.
559mm is the older 26 inch mountain bike size, which survives on cargo bikes because a smaller wheel is stronger under load.
406mm is 20 inch, used on folding bikes, small cargo bikes and moped-style e-bikes.
The translations
700x47c is 47-622. 29x2.4 is about 61-622. 27.5x2.4 is about 61-584. 26x2.15 is 55-559. 20x4.0 is about 98-406.
Note the word about. The inch width is a nominal figure and the millimetre one is measured, so they do not convert exactly and two tires both marked 2.4 can measure several millimetres apart on the same rim.
Width, and the two things that limit it
The rim. A wide tire on a narrow rim takes a light bulb shape and squirms; a narrow tire on a wide rim is at risk of the bead unseating. Manufacturers publish a recommended rim width range for each tire.
The frame and the mudguards. On an e-bike this is usually the real limit, and it is worth measuring rather than guessing, because a tire that clears when new will not clear once it has picked up a winter's worth of grit.
Going wider generally means more comfort and more grip at lower pressure, and slightly more rolling resistance. On a heavy e-bike the comfort is usually worth having.
Common questions
- Where do I find the ETRTO size?
- Moulded into the sidewall, usually close to the inch size, as two numbers with a dash between them.
- Can I fit a 50-622 where a 47-622 was?
- If the frame and mudguards clear it, yes. The rim is identical; only the width changes.
- Is 29 inch the same as 700c?
- The rim is, at 622mm. The tires are usually much wider on a 29er, but they will physically fit the same wheel.
Last checked 2026-09-22. Where this page and your own vehicle disagree, the vehicle wins.