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| 47-406: A "20 inch" tyre. 47 mm wide, mounts on a 406 mm rim |
While tyres are mostly made of rubber, the most important dimension when fitting is that of the bead of the tyre, and this is reinforced either with steel wire (for most tyres) or with glass or other fibres (for folding tyres) so that the tyre won't stretch and come off the rim when fully inflated.
For this reason, bicycle tyres do not stretch and even sizes which are very close in size are not interchangeable.
Old fashioned ways of labeling tyres
In the past, wheel sizes were usually described as the outer diameter of the size of the wheel including a nominal inflated tyre. In countries which used imperial units these would be expressed as a size in inches (e.g. "26 inch" or "28 inch") while in metric countries the size was expressed in millimetres (e.g. 700 C or 650 A).
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| ETRTO 40-559 = 40 mm wide 559 mm diameter rim. Also labeled 26x1.50 but you are best off ignoring this old "size" |
There are also two different sizes of "28 inch" wheel, one of which is larger and the other smaller than the "27 inch" size. "29 inch" wheeled mountain bikes actually use the same diameter rim as the smaller "28 inch" size, so these two use smaller wheels than "27 inch".
The same problems arise with smaller wheels as well. The two most commonly used "16 inch" wheel sizes are both considerably smaller than 16 inches in diameter. The largest of the two measures just over 13.5 inches in diameter, while the smaller is nearly 2 inches smaller than this. There are also several different wheel sizes referred to "20 inch".
The metric versions of these measurements also cause confusion. A 700 C wheel is not the same size as a 700 B wheel but it is the same as one of the "28 inch" sizes, even though it's neither 700 mm nor 28 inch in diameter.
Inevitably, there is much confusion about wheel sizes.
The solution: ETRTO numbers
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| The most common size for Dutch town bikes and many touring bikes. A 622 mm diameter rim with a 37 mm wide tyre |
The "ETRTO number" consists of two numbers separated by a dash. The first gives the width of the tyre, while the second gives the diameter of the rim which it fits. For instance, 37-622 indicates that a tyre has a width of 37 mm and is to be mounted on a rim of 622 mm diameter. This is the most common size for Dutch town bikes, and is also a common size for touring bikes everywhere.
Buying a replacement tyre
Before buying a replacement tyre, inner tube or wheel, first check the writing on the side of your existing tyre and find the ETRTO number. To help you find an exact match which will work on your bike, all the tyres and inner tube as well as the wheels in our web shop are listed with their available ETRTO sizes.
You do not always have to buy the same width of tyre as you had before. While it is not a good idea to fit a very wide tyre onto a very narrow rim, nor a very narrow tyre onto a very wide rim, in principle any tyre of any width will fit on any rim which is the correct size. In practice we suggest not going too far from what the manufacturer of your bicycle fitted. For example, if you currently have 32 mm wide tyres, then fitting a 37 mm wide tyre instead will likely give a bit more comfort. However, make sure you have enough clearance in the frame and under mudguards for a larger tyre size.
Recommended tyres and sizes for different types of bikes
Below we make some recommendations for some types of bikes. We supply a much wider range of tyres than this, so if you need a different size, please check all of what we have, and contact us if you need a size which isn't listed
You should always make reference to the ETRTO number on the side of your existing tyres before buying any tyre. Please take our recommendation, but confirm that these are the exact tyres you want by checking your tyre size yourself before ordering. If you are changing the width of the tyre that you use, make sure you have a new width that will work on your rims and in your frame:
| Type of bike | Tyre size | Old size | Recommendation with link to where to buy |
|---|---|---|---|
| British Three Speed | 37-590 | 26" | Marathon Plus, Marathon, Delta Cruiser |
| New Dutch town bike | 37-622 | 28x1 3/8 | Marathon, Marathon Plus, Delta Cruiser |
| "Old" Dutch town bike | 40-635 | 28x1 1/2 | Marathon, Marathon Plus, Delta Cruiser |
| Modern touring bike | 28-622 to 37-622 | 28" / 700C | Marathon Plus, Marathon, Marathon Supreme |
| Racing bike | 20-622 to 28-622 | 28" / 700C | Durano / Durano S, Contact Speed, Grand Prix |
| Old racing bike | 20-630 to 32-630 | 27x1 1/4 | Marathon |
| Mountain bike | 47-559 to 55-559 | 26" | Furious Fred, Marathon Winter, Big Apple |
| Mountain bike used on road | 32-559 to 50-559 | 26" | Big Apple, Contact Speed, Kojak, Marathon, Marathon Plus |
| 20" wheel folding bike | 28-406 to 47-406 | 20" | Kojak, Marathon, Marathon Plus |
| 16" wheel folding bike | 28-305 to 47-305 | 16" | Marathon, Marathon Plus |
| Brompton / Moulton | 35-349 | 16" | Marathon, Marathon Plus |
| Kronan | 54-584 or 47-622 | 26" / 28" | Kronan tyres (Kronan men's and women's frames are different) |
Profile
It is not possible for a bicycle tyre to "aquaplane" because speeds are too low, and pressures are too high. Therefore, a profile is not needed on bicycle tyres to increase grip in the wet.
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| Top to bottom. Speed & good grip: Kojak Everyday use and touring: Marathon Ice and Snow: Marathon Winter |
However, tread on a tyre is useful in some circumstances. If you sometimes ride on unfinished paths, mud, sand and snow, then a slight tread pattern is useful because the surface will then deform around the tread and provide extra grip. It is for this reason (as well as that new tread patterns look good in marketing materials) that most general purpose tyres have a slight tread.
A more extreme tread pattern is needed for more extreme circumstances. Those who do cross country riding or mountain biking on rough paths benefit from an aggressive tread, and of course this becomes more extreme in examples such as the Marathon Winter which go as far as having metal studs to pierce through ice.
Tyre Pressures
It is important to maintain correct tyre pressures. While it can be It is more common that people run their tyres at too low a pressure than too high. If the pressure is too low then too much of your energy goes into deforming the tyre as you cycle, and this makes cycling considerable less efficient.
If you can easily deform a tyre with your fingers then it is almost certainly under-inflated. All bicycle tyres run at higher pressures than car tyres, and car pumps are often not capable of achieving high enough pressures for a bicycle.
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| Racing bike tyre with "French" 700x23C description alongside ETRTO |
Narrow tyres may damaged quite quickly by too low a pressure, while some tyres (notably the Schwalbe Marathon) have been reformulated to make them more resistant to damage due to low pressure.
For everyday use, a thumb test (if you can deform the side-wall of the tyre with your thumb, pump it up) is enough for most people. However, we also stock the very good Schwalbe digital air pressure tester for people who want to make sure their tyres are at a suitable pressure. We also sell a range of pumps suitable for getting your tyres to a suitable pressure.
Note that with tyres with puncture resistant layers, like the Marathon Plus, if you try to test the pressure by squeezing the running surface of the tyre, all you'll "test" is how soft the anti-puncture layer is. It's important to do this on the sides of the tyre, squeezing between thumb and forefinger.
