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Valve types
We can distinguish between three
valve types.
1. Woods or English valve
These are still the most commonly
used valve type. They are mainly
used on entry-level models and on
children's bicycles. With the English valve, the air has to be pumped
through a simple shut-off valve with the correct pressure. This valve
type is not recommended for use with high tire pressure.
2. Car valve
These are most commonly used on mountain bikes. Air can be
pumped into the tire after opening a threaded valve core. The valve
core is released by a wedge located in the pump head when the
pump is placed onto the valve. To ensure that the valve core is
opened correctly, the pump must be pressed sufficiently onto the
valve stem. It is also important to position the rubber sealing ring
inside the pump head in such a way that it prevents the escape of
air from between the valve and the pump head.
3. Presta valve
Presta valves were once used only on racing bikes. Nowadays,
however, they have become common on light mountain bikes, as
well. To be able to inflate the inner tube, the small brass cap on the
valve stem must be unscrewed and raised to its top. Test: when you
press down on the top of the valve, air should escape from the inner
tube. The head of the pump must be placed precisely onto the
valve, without touching the valve stem if possible.
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Figure 30
1. 2. 3.
8
Rubber tire, inner tube, and air pressure
The ideal tire must efficiently reduce the impact of an uneven road
surface, be protected against punctures, and possess low rolling
resistance. The tire provides the traction and road holding necessary
for braking, taking bends, and accelerating. If you reduce the tire
pressure, you lose the benefit of low rolling resistance; on the other
hand, the following improve:
· ride comfort
· traction on wet or uneven roads or terrain
However, if the tire pressure is too low, the inner tube may burst when
passing over kerbs. The tire will only operate correctly and resist a
possible puncture if its pressure is correct. This also takes the strain
off both the rider and the bicycle. Tires are available in a great variety
of designs, sizes, and qualities. When replacing a tire, pay attention to
its size. The size of the tire is usually indicated on it with two values: in
millimetres, according to the metric system, and in inches.
Accordingly, the size of a tire can be for example 26 x 1.75, if given in
inches, and 47-559 mm, if using the metric system. 47 mm indicates
the width of the tire, 559 mm its diameter.
Most tire manufacturers indicate the optimal and maximum tire
pressure values. On one side of the tire, the optimal pressure range is
indicated by giving its minimum and maximum limits. Since pressure is
often indicated in PSI, you will find a conversion chart from PSI to bar
in the chapter on Technical Data. Most modern tires also contain an
inner tube. The use of tires without an inner tube is also becoming
increasingly widespread, at least among mountain bikes. This tire
type, which has long been used on cars and motorbikes, greatly
reduces the risk of punctures.
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