Whilst cycling recently over some rough ground I realised that one of my tyres was slowly deflating. On closer inspection I realised that the end cap had been dislodged and that grit had got into the valve and was pressing on the spring loading causing the tube to go down. Luckily I managed to clean out the grit, inflate the tyre again and get home safely.

The next day I trawled the internet to look for some new caps ahead of my next outing. I was surprised to discover that as well as there being all sorts of other end caps available for bicycles, there are also different sizes of valves for the caps to fit on. Heres some of the information I found out about tyres, inner tubes and valves.

Since the advent of the pneumatic tyre at the end of the nineteenth century there has had to be a means of inflating the rubber inner tube contained within the hollow rubber tyre. An integral part of the inner tube is the valve which allows passage of the outside air into the tube via a bicycle pump. The valve opens as air is pumped in and then closes as the pump is removed so that air cannot escape again.

As valves and inner tubes are inextricably linked you may first want to consider the tube itself based on what sort of cycling you do. Some materials are thicker (and therefore heavier) than others making them more resistant to puncture. For competitions and time trials you may risk the possibility of puncture to give you a lighter weight thinner tube. If youre doing the daily commute you may wish to gain the extra protection against (time-consuming) punctures that a thicker tube would afford. The latter line of thinking would also apply when cycling over rough-ground or downhill.

The next thing of importance when replacing tubes is to make sure you get the right size to fit your wheel rim and tyre. To help with this, the diameter and width are generally embossed on the tyre wall itself. The tube packaging will then state the diameter of wheel it will fit along with the range of widths it will work with. For example a size of 26 x 1.95-2.125 means that the tube will fit a 26 diameter wheel and will work on widths of 1.95 to 2.125

Bicycle wheels have a hole drilled in them through which the valve is passed; there are different sizes of hole so it is important to match not only the size of the wheel but to match the right-sized valve as well. There are three main types of inner tube valves used on bicycles and here is just a short description of each:

Schraeder valves fit into the larger sized holes and are the same design as a standard car tyre valve. They are generally used on bikes that have low pressure tyres such as mountain bikes and childrens bikes, the inner part of the valve is kept closed by a spring mechanism.

Presta valves are more commonly used on high-pressure tyres such as those on racing bikes. The valve itself is more slender and often has a screw-on locking ring that keeps it in place against the wheel rim. These valves are kept closed by the air-pressure from the inside of the tube.

Woods (or Dunlop) valves have been superseded by the other two types and are now more or less obsolete. Looking like a cross between the two it fits the larger drill hole of the Schraeder valve.

Naturally once you have got your tube safely inside your tyre and inflated you will want to keep everything clean and protected from dirt and grit. Bike valve caps screw onto the ends of the valves, keeping them clean, dry and grit-free for when you need to carry out any maintenance on your tyres and tubes.