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Reference

Inner Tube Sizes and Valve Types

More tubes are bought in the wrong size than in the right one, and it is almost never carelessness. It happens because the inch names on the side of a tire were never a standard, and several completely different rims have been sold under the same name for decades. There is one number that is unambiguous, it is printed on nearly every tire made in the last thirty years, and once you know how to read it this stops being a problem.

Start here

Reading the marking on your tire

Look along the sidewall for two numbers separated by a dash, something like 37-622. That is the ISO marking, also called the ETRTO marking. The first number is the width of the tire in millimeters. The second number is the bead seat diameter of the rim it is built for, also in millimeters, and it is the number that decides whether a tube belongs on your wheel.

Beside it you will usually find an inch or French name such as 700 x 35C or 26 x 1.5. Those are nicknames. They are useful in a shop conversation and unreliable as a specification, because more than one rim diameter has been sold under several of them. Where a tire carries both, buy from the ISO number.

A tube is sold for a diameter and a range of widths. The diameter has to match exactly. The width only has to fall somewhere inside the range printed on the box, because a tube stretches to fill the tire it is put in.

The number that matters

Bead seat diameters and the names they hide behind

ISO bead seat diameter, in millimeters
ISOAlso calledFound onWhat to watch for
622700C, 29 in, 28 inRoad, gravel, hybrid, most modern mountain bikes and most e-bikesThe same rim diameter is called 700C on a road bike and 29 inch on a mountain bike. A tube for one fits the other if the width is right.
63027 inOlder ten-speed road bikes, mostly pre-1990Larger than 700C despite the smaller-sounding name. A 700C tube will not seat properly on a 27 inch wheel and the tires are not interchangeable.
584650B, 27.5 inTrail mountain bikes, gravel bikes, some touring bikes650B and 27.5 inch are the same rim. Widths on this diameter span everything from narrow gravel tires to wide trail tires.
571650COlder small-frame road bikes and some triathlon bikesNot interchangeable with 650B despite the similar name. Check the number on the tire, not the name.
55926 inOlder mountain bikes, many folding bikes, many hub-motor e-bikesThe most common 26 inch standard by a wide margin, but not the only one. Confirm the ISO number before buying.
59026 x 1 3/8, 650AOlder three-speed roadsters and some city bikesA different 26 inch. A 559 tube does not fit a 590 rim. This is the classic reason a replacement tube bought by inch size does not work.
50724 inYouth bikes, some cargo bikes, some folding bikesStandard on most 24 inch wheels sold today.
40620 inBMX, most folding bikes, many cargo bikes and kids bikesThe common 20 inch size. A few folding bikes use 451 instead, which is also called 20 inch and is not compatible.
45120 in (large)Some folding bikes and juvenile racing bikesAlso sold as 20 inch. Measure or read the ISO number, because 406 and 451 look similar on a shelf and do not interchange.
34916 in (large)Certain folding bikesOne of several 16 inch standards. This is a case where buying by inch size alone reliably produces the wrong tube.
30516 inKids bikes and some folding bikesThe common 16 inch size on childrens bikes.
20312 in, 12 1/2 inFirst bikes and balance bikesWidths and tire profiles vary a lot at this size, so match the width as well as the diameter.

Two rows on this table are worth reading twice. The 559 and 590 pair are both called 26 inch and do not interchange, and the 406 and 451 pair are both called 20 inch and do not interchange either.

Valve types

Schrader

Also called American valve, car valve

Short, wide, and identical in principle to the valve on a car tire, with a spring-loaded pin down the middle of the stem. Found on kids bikes, most hybrids and mountain bikes, and a large share of e-bikes.

Using it

Take off the dust cap and push the pump head straight on. There is nothing to unscrew. Any gas station or car pump fits, though a car air line delivers air far too fast to be safe on a bicycle tire.

And the rim

A Schrader valve needs the larger rim hole. A rim drilled for Schrader can carry a Presta tube with a grommet or adapter to stop the narrow valve moving around in the oversized hole.

Presta

Also called French valve, Sclaverand valve

Narrow, usually longer, with a small knurled nut at the tip that has to be unscrewed before air will go in. Standard on road bikes, gravel bikes and most performance-oriented wheels, because the narrower hole takes less material out of the rim.

Using it

Unscrew the small nut at the tip until it stops, press it briefly to release a puff of air and free the seal, then push the pump head on square. Screw the nut shut afterward and replace the dust cap.

And the rim

A Presta valve does not fill a Schrader-sized rim hole. Drilling a Presta rim out to take Schrader removes material from the rim bed and is not something to do at home.

Presta valve length

A valve has to project far enough past the rim for a pump head to grip it properly, not merely far enough to be visible. Deep rims need long valves, and a valve that is just barely long enough is the one that leaks air every time you take the pump off.

A starting point, not a specification
Rim depthValve lengthNotes
Shallow box-section rim, roughly under 25 mm deep32 mm to 40 mmThe everyday case: city bikes, hybrids, mountain bikes and older road wheels.
Mid-depth rim, roughly 25 mm to 45 mm48 mm to 60 mmCommon on modern road and gravel wheels. A 42 mm valve often works and often does not, which is why this is the size people end up owning twice.
Deep-section rim, roughly 45 mm and deeper60 mm to 80 mm, or a valve extenderEnough valve has to project past the rim for the pump head to grip properly, not merely enough to reach the surface.

Where the data runs out

  • This page does not hold a width chart for every tire model. Tube packaging states a width range, and the only reliable check is that your tire width falls inside the range printed on the box.
  • Inch markings are not standardized across eras or manufacturers. A tire marked 26 x 1 3/8 and a tire marked 26 x 1.375 are not necessarily the same size, which is the exact reason the ISO number exists.
  • There is no general rule for converting a fractional inch marking to a decimal one. Where a tire carries both an inch marking and an ISO number, the ISO number is the one to buy from.
  • Valve length that works on a given rim depends on the rim, the rim tape and the tire, and manufacturers do not publish a combined figure. Measure the valve you removed, or measure rim depth and add margin.

Tube and valve questions

Look on the sidewall for a pair of numbers separated by a dash, such as 37-622. The first number is the tire width in millimeters and the second is the bead seat diameter of the rim it fits. That second number is the one that has to match. The inch marking printed beside it is a nickname and is not always reliable.

Within the width range printed on the tube packaging, yes, because tubes stretch. Outside it, a tube stretched far past its range gets thin and punctures easily, and a tube too wide for the tire folds on itself and pinches. The range on the box is the answer.

Schrader is the wide car-style valve you push a pump straight onto. Presta is the narrow one with a knurled nut you unscrew first. The rim hole is drilled for one or the other, so the tube you buy has to match the wheel you own, not the pump you own.

Most modern pump heads take both, either by flipping an internal rubber grommet or through a dual head. Small adapters that screw onto a Presta valve to accept a Schrader pump head cost very little and live permanently in a saddle bag. An adapter does not change the rim hole, only the fitting.

They seal small punctures from thorns and glass slivers without you noticing, which is genuinely useful on a commuter that lives outdoors. They are heavier than a plain butyl tube, they do nothing for a sidewall cut or a pinch flat, and they are harder to patch afterward. Whether that trade is worth it depends on what is puncturing your tires.

Because more than one rim diameter has been sold under the same inch name. There are several different 26 inch standards and at least two different 20 inch and 16 inch standards. The ISO number on the tire sidewall is unambiguous where the inch name is not.

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