If you follow the sidewall round with your finger you’ll notice that there will be words and numbers embossed. The three-digit number after the dash is the more important. This is the bead diameter at which the tyre fits onto the rim. The former is ‘fractional’, the latter ‘decimal’, and as a rule decimal and fractional tyre sizes that look the same are not.

The Dunlop valve, also known as a Woods is a variation of pneumatic valve that is rarely used on modern bikes. However they were once popular. They look like a cross between the two valves, with a wider lower section, like the Schrader, then a collar and a narrow top section, like the Presta. As the rim drilling is the same for both Woods and Schrader, it is easy to replace the older tubes with the more modern variety. How can I choose the right valve length? On the other hand, they’re much more fragile and more awkward to fit as they’re floppier than butyl tubes. The former are simpler to use, but add a dead space above the valve, making inflation harder, while with the latter you need to make sure that there’s a fully airtight seal to the inner tube’s valve stem, or your tube will leak air. Even worse, the same or very similar markings can sometimes be found on completely different sizes of tyre: 26×1½ and 26x1.5. It might be supposed that these two tyres are both notionally 26" diameter and one and a half inches in width, but 26×1½ is a whole inch bigger than 26×1.5. If you have carbon rims on a bike with rim brakes, you also need to be careful not to drag your brakes on long descents because overheating can cause latex tubes to fail. Some wheel makers recommend against using latex tubes with their rims.You must make sure you replace your inner tubes with a tube that is the right size according to the diameter and width for your tyre. The size is almost always written somewhere on the sidewall of the tyre. Inner tubes typically state a wheel diameter and width range for which they will work, e.g. 26 x 1.95-2.125", indicating that the tube is intended to fit a 26 inch tyre with a width of between 1.95 inches and 2.125 inches. Well, actually, they have and it’s the ISO system (which was previously known as ETRTO). It hasn’t been universally adopted though and you’ll see tires which have both ISO numbering and either metric or imperial. If you are unsure of your bicycle tire size, you can look into a bicycle tire table where you can easily and simply find just the tires that fit your bike. Most lists the tire size both English, French and German targets and rim circumference in millimeters. This means that you can easily find the right tire size, although it is a Danish number. If your wheels are even deeper than the longest valve you can find, you can buy valve extenders to add length to your valve. There’s a range of lengths available: Zipp for example makes extenders from 27mm up to 98mm long. Tire solutions for sport, touring and everyday life. Schwalbe is working to eradicate the puncture.

Lots of bike tubes and virtually all car tires will use Schrader valves. Presta valves are slimmer and longer than Schrader. How do you know what size tyres will fit your bike? It should be easy: buy exactly the same model of tyre as those already on the bike. Of course, this isn’t much help if identical tyres aren’t readily available, if you fancy something different or if you’re looking for replacements in unusual and hard-to-find sizes. If the rim is not marked with its bead diameter you can read this from the tyre – it’s the one dimension they have in common. If you crouch down by the side of one of your bike wheels and take a look at the sidewall you’ll be able to get all the information you need – simple as that.As far as possible, then, use these columns to convert to ISO dimensions and then have nothing more to do with those old markings! Bigger tyres naturally require bigger inner tubes. On the left is a 700×32-47C inner tube, while the right is a 700×18-28C. Simon Bromley/Immediate Media

The following list shows all common tire sizes. For virtually every tire size, you should be able to find a corresponding ETRTO-size in this list.

Continental Light Road Inner Tube

the first is the width of the tire in millimeters and the second is the diameter of the tire in millimeters. Another reason not to exceed the 2.2 limit on road is that a more bulbous tyre can deflect side ways with a noticeable effect on control and road holding. Conversely, fitting a tyre of less than 1.4 times the rim section will result in a harsh ride and more rolling drag than a larger tyre at the same pressure. Tubeless tyres These classifications originate from the time of tire brakes. In those days, the exact outer diameter of the tire was defined by the brake. Depending on tire width, various standards for the inner diameter applied. For even more weight saving, latex tubes are significantly lighter than butyl tubes, plus there’s less friction against the tyre, resulting in lower rolling resistance.

There is some overlap in sizes between 650b gravel and mountain bike tyres, but gravel tyres are usually sold in metric sizes as listed above. Whilst you need to use a replacement tire that is the exact same size as the existing one, you have a little more wiggle room when it comes to tubes. Valve extenders come in a range of sizes, types and even colours. These ones simply screw over the top of an open Presta valve, but you can also get ones that allow you to place the valve core at the top. Simon Bromley/Immediate Media These are inexpensive and super-simple to fit and use – you just screw them by hand and away you go. After that you’ll be able to use your pump with either Presta or Schrader tubes, so they’re very handy to have. You can get more details on the one I recommend here.Both indications are, however, very imprecise. A less wide 28 inch tire, e.g. with a tire width of 23 mm, which is usual for a road bike, has in fact only an outer diameter of something more like 26 inches. In the case of a tire width of 40 mm, The following sizes are common for mountain bike tyres, regardless of whether your bike has 26in, 27.5in (650b) or 29in wheels. One way to define it, popular in times past, was to measure the tyre’s outside diameter and its maximum width when inflated, but this can be misleading. For example, some tyres marked 28" are actually much less than 27 inches in diameter, while 26×1.5 and 26×1½ are two completely different sizes.