What size of wheel and tyre is used on my bicycle ? Choosing the right size of tyres for your bike can be difficult due to competing methods of measurement.

47-406: A "20 inch" tyre.
47 mm wide, mounts on a 406 mm rim

Bicycle tyres come in a bewildering array of different sizes. It's absolutely vital to buy the correct size for your bike.

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).

ETRTO 40-559 = 40 mm wide 559 mm
diameter rim. Also labeled 26x1.50 but
you are best off ignoring this old "size"

This system would work just fine if each size of wheel was described by a different number. However, that was not so. As an example, the "26 inch" wheel size used on traditional British bicycles is a lot larger than the "26 inch" wheel size used on traditional American bikes. British bikes were for many years imported to the USA, and when Mountain Bikes became popular, they brought the American wheel size to the UK. What's more, there are more "26 inch" wheel sizes than just these two.

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

The most common size for Dutch town bikes and many touring
bikes. A 622 mm diameter rim with a 37 mm wide tyre

In 1964, the European Tyre and Rim Technical Organisation was formed. They're an organisation that few people have heard of, and I know little of what they've been doing for the last 50 years except that they've given cyclists a great gift in the form of a system for identifying tyre and wheel sizes which guarantees compatibility. This has been standardized internationally in the form of ISO 5775, but most people still refer to these figures as "ETRTO numbers".

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.

Top to bottom. Speed & good grip: Kojak
Everyday use and touring: Marathon
Ice and Snow: Marathon Winter

When on a hard surface (concrete, asphalt), grip comes from the tyre deforming over small sharp edges in the surface, not from the surface deforming to fit the tyre, for this reason, a complete slick tyre provides all the grip you need on such a surface. What's more, a tyre which has a tread pattern will generally have a higher rolling resistance due to deforming of the tyre as you ride along. For this reason, a completely slick tyre (like the Kojak) would serve most people well most of the time.

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.

Racing bike tyre with "French" 700x23C
description alongside ETRTO

Narrower tyres need higher pressure than wider tyres. The racing bike tyre on the left has a recommended pressure between 6 and 10 bar (85 to 145 psi), while a wider mountain bike tyre may need just 2 to 3 bar (30 to 45 psi).

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.

Choosing between inner tubes and pumps

Few people pay much attention to inner tubes. They're a bit boring. You can't see them as you ride. Actually, it is quite reasonable that most people pay little attention to them, as most of the time the differences between quality inner tubes are slight, and for most people they don't matter.

However, there is a difference in the construction, and some are better for some purposes than others. I've currently got three different inner tubes in stock which are suitable for relatively narrow 20" (ETRTO 406) tyres. This is how they differ:

The lightest of the bunch is the Schwalbe SV6A. These have a claimed weight on the packet of 65 g, and that's exactly what my kitchen scales say they weigh.

This inner tube is the lightest of the three, and also feels most supple. I have not tested rolling resistance with this inner tube, but if there's a difference you can expect this will be the best performer.

It will probably also lose pressure faster than the other options, so you'll need to pump up your tyres more often with this inner tube. Also, maybe it's less damage resistant too.

Reflecting its special status, the SV6A costs an extra €2.38 over the price of normal Schwalbe inner tubes.

The second lightest is also a Schwalbe - the SV6. It says nothing on the box about the weight, I found it to be 95 g.

This is a standard grade inner tube from a quality manufacturer. It's still actually quite a nice supple inner tube, and it's what I have in the front tyres of my Mango at the moment.

Either this or the Continental are a good choice for everyday use.

The heaviest of the three is the Continental Compact 20 inner tube. Continental make extra thin high performance inner tubes (akin to the SV6A) in other sizes, but not for 20" wheels.

This is again a standard inner tube from a quality manufacturer, which again means it is actually of good quality. According to my scales, it weighs 100 g, which is an irrelevant difference over the weight of the Schwalbe equivalent.

The construction of this inner tube is a bit different. The rubber feels thicker than the Schwalbe SV6, though given that they're about the same weight it obviously can't really be so different.

What is a little different is that the Continental is wider than the Schwalbes, even though it's only rates as being suitable for tyres up to 32 mm wide, while the Schwalbes are for tyres up to 40 mm wide. This makes it a little more difficult to fit into a narrow tyre. Continental also specify that their inner tube will also fit 451 size wheels, while Schwalbe suggest theirs will not.

Either this or the Schwalbe SV6 are a good choice for everyday use.

In practice, I find the Continental is a slightly awkward fit even within Continental's own 28mm wide tyres. It's just a bit too wide, and makes it more difficult to fit the tyres. As a result, I'm using the Schwalbe SV6 in those tyres at the moment. If I were racing, I'd use the SV6A as it is slightly lighter, and more importantly it is reckoned that due to its flexibility it will roll a little better. I'm using a Continental inner tube in my rear tyre, which is a bit wider than they recommend, but here it seems a good fit. I also carry a Continental as one of my spares spare (I have two for personal use).

I also weighed a few no-name inner tubes for the same wheel size. Most weighed about 130 g, but one was 200 g - a surprising difference. There is almost certainly a difference in performance between such an inner tube and those from the better manufacturers.

Valve types

Presta / French / HP valve

Another difference between tubes on offer is the type of valve in use. Some people have very strong feelings one way or another. It can be nearly a religious issue. However, I think each has its place

For racing, when you might actually care whether the pressure in your tyres is up to the maximum and want to measure them, there is an advantage with the Presta ("French") valve rather than the Schrader (car type) or Dunlop (also known as Dutch or English) valves. Also, as everyone else will be using these, if you borrow a pump it will already be set up to fit these valves.

Dunlop / Woods / Dutch valve

However, unless there is a special reason to choose, all three types keep the air in equally well, so most of the time it's best to use what's convenient and what you're used to.

In the Netherlands, there are sometimes publicly accessible pumps designed to accommodate the Dunlop valve, and you can buy very well priced floor-standing pumps which make pumping these up very easy indeed. The perfect choice for everyday cycling.

Schrader / Car valve

I use Presta valves for sportier bikes and Dunlop valves for our town bikes.

As much as possible, I avoid the Schrader type as they're most difficult to push the pump on and off, and due to the larger area of pressure they're the type which most often gives problems with keeping the pump head on the valve while pumping.

However, I might feel differently if this was the most commonly used valve type where I lived as the convenience would then be on the side of the Schrader. In the US, these seem to be the most popular valves in use so they perhaps make sense for everyday cycling.

Fitting Presta valves in Schrader rims

Adaptor to use presta valves in
schrader rims

For many people, including myself, the Presta valve is the best choice for higher performance bikes. However many wheel rims come ready drilled for the larger Dunlop and Schrader valves. It's common for people to use Presta valves in such rims and despite the difference in diameter it usually doesn't cause a problem, but inner tubes are sometimes damaged when abused in this way. For this reason, we now sell an adaptor to convert between valve sizes. This fills the larger hole in the rim and makes it safe to use Presta valves.

Pumps
Some of you might have noticed that for a long time now we've had a bike parts and accessories shop which didn't sell any bicycle pumps. I've now added two floor-standing pumps to the shop website, including one which is light enough to take along with you, if a little bulky. However we still don't have a truly portable small pump.

They seem an obvious thing to have, so why not ? The problem is finding a product which we can trust ourselves. We said from the beginning that we'd only list things that we either already use ourselves, or that we'd happily use ourselves. This is what we're sticking to.

One pump which we don't recommend and won't be selling is the SKS Airboy.

SKS Airboy. Don't buy this, even for just £1.

I bought my "Airboy" at the Mildenhall Rally, probably ten years ago. It cost me the grand sum of one pound. At the time I thought this was a bargain. However, it's too flawed to be useful. It has a double headed design with one side for Presta or Dunlop valves and the other side for Schrader. The pump relies on air pressure to keep a small rubber ball in a position to block the pump head that you're not using.

There are a number of problems with this idea. Usually, this means you can only pump upwards as initially gravity has to put the rubber ball in place. That may not sound like a big issue, but it becomes one as soon as you try pumping up tyres on a bike with laden panniers or a coat guard. However, the problems go beyond this issue. The heads don't fit well on valve stems for any of the three types of valve, and it's impossible to pump tyres up to an adequate pressure without the pump popping off the stem.

This problem hit me a few weeks ago when I got a puncture on a ride. Before leaving I'd picked up a pump to take with me, but not until I got the puncture did I discover it was this pump. At first I thought it would be OK, as in the past, I'd managed to get just enough air into a tyre with this to at least ride to a bike shop, but not this time. I had to walk a distance and ended up buying a working pump at a bike shop.

Anyway, I bought it ten years ago, so why am I writing about it now ? You can still buy these ! I've seen the exact same model for sale this year. To double the insult, in the last few days I accidentally bought another pump with exactly the same problems. We need something sensible and usable in the shop, so I added what seemed to be a well speced, but also well priced pump to an order from one of our suppliers. When it arrived, it turned out to be an SKS under a different name, with a variation on the same kind of head. It has exactly the same issues as the older one, plus a new problem: A spring works against you for almost half the stroke, making it difficult to achieve much pressure even if the pump would stay on the valve.

SKS used to be a very good name for pumps. I've a few old ones which work very well, and I'm sure they also still produce good models. However, I'm currently waiting for a different manufacturer's pump to turn up from a supplier. It's not fancy and expensive, because portable pumps tend to get damaged or lost. But if it works well it will appear on the shop website in a few days.