handbuch mountain bikes

The Wheels

Caution:

If you have a bicycle with tubular tyres, please read the instructions of the tyre/ rim manufacturer on the

STEVENS CD-ROM.

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7. The Wheels

The wheels of your bicycle create the contact to the road or track you are riding on. They are subject to considerable stress through the weight of rider, the luggage and through bumpy road surfaces or ground. Although the wheels are manufactured with great care and delivered accurately trued, this does not prevent the spokes from losing a little tension on the first kilometres. Ask your STEVENS dealer to true up the wheels after you have bedded them in over about 100 to 300 kilometres

(60 to 180 miles). Check the wheels regularly after you have run them in.

It will rarely be necessary to tighten the spokes.

The wheel consists of hub, spokes and rim. The tyre is mounted onto the rim so that it encases the inner tube. There is a rim tape running around the base of the rim to protect the sensitive inner tube against the spoke nipples and the edges of the rim base, which are often sharp.

7.1. Tyres, Tubes, Rim Tapes, Valves, Inflation

Pressure

The tyres provide grip and traction on the road which is absolutely necessary for braking, accelerating and taking turns.

In addition, they provide smooth running and riding comfort by absorbing inferior shocks. The cross-country mobility or the inclination of the road depends on the nature of the tyre carcass and the tyre tread. As some of the requirements are mutually exclusive, there are many different tyre types for different uses. Ask your STEVENS dealer to inform you about the best tyre for you.

If you want to replace a tyre, you need to consider the actual size of the old tyre. It is marked on the side of the tyre. There are two designations:

One of the sizes is the standardised size in millimetres which is more precise, the number sequence 50 - 559 means that the tyre is 50 mm wide when fully inflated and has an inner diameter of 559 millimetres.

The other designation for this tyre reads 26 x 1.90 which refers to inches. Tyres have to be inflated to the correct air pressure in order to work properly. Adequately inflated tyres are also more resistant to flats. An insufficiently inflated inner tube can easily get pinched (“snake-bitten”), when it goes over a sharp kerb.

The air pressure recommended by the manufacturer is given on the side of the tyre or on the type label. The lower of the two pressure specifications makes for better cushioning and is therefore best for off-road cycling. Rolling resistance decreases with growing pressure, but so does comfort. A high tyre pressure is therefore most suitable for riding on tarred roads. A higher pressure hardly means a lower resistance, it only makes the tyre harder.

Ask your STEVENS dealer for advice. Inflation pressure is often given in the old system of units, i.e. in psi (pounds per square inch). The table on the right gives the most common pressure values in terms of three systems. The tyre and rim alone are not able to hold the air. Therefore, an inner tube has to be placed inside the tyre to retain the air pressure.

The tube is pumped up via a valve.

An exception to this are the tubeless systems for mountain bikes. In this case, the rim and the tyre hold the air without inner tube. To find out whether or not you have tubeless tyres, look for the UST-marking. The valve is provided with a plastic cap to protect it from dirt. The tubelessready-tyres are not tubeless tyres. By adding a special sealing fluid they can however be converted to tubeless tyres.

The Wheels

There are three valve types in general use on today’s bicycles

• Dunlop or Woods valves, the usual valves

• Sclaverand or race valves: This type is nowadays used on almost all types of bicycles. It is designed to withstand extremely high pressures

• Schrader or car valve: This is an adapted car tyre valve which is mainly used on mountain bikes.

These three valve types are fitted with a plastic cap to protect them from dirt. The car valve can be inflated with a suitable pump directly after removing the protective cap.

With race valves you first have to undo the small knurled nut a little and press it in carefully until air starts to escape. With this valve type it may happen that the valve body is not screwed in properly and that air leaks out slowly. Check the seat of the valve body in its stem.

Tyres with car valves can conveniently be inflated at car filling stations with a compressed air dispenser. A compressed air dispenser must be used very carefully as you may otherwise overinflate the tyre. It might burst. To let out air press the needle in the centre of the valve by using e.g. a spanner/key.

Hand pumps are often unsuitable for inflating tyres to the necessary pressure. A better choice is a stand or foot operated pump equipped with a manometer which enables you to check the pressure at home.

Your STEVENS dealer has adapters for all valve types. They allow you to inflate any type of inner tube at the filling station.

Replace tyres with a worn tread or brittle or frayed sides. Dampness and dirt penetrating the tyre can cause damage to its inner structure. Replace spoilt rim tapes immediately. In the extreme case, the inner tube may suddenly burst!

Conversion table for tyre pressure psi in bar

psi

30 bar

2.1

psi

70 bar

4.8

40

50

60

2.8

3.5

4.1

80

90

100

5.5

6.2

6.9

psi

110

120

130

140 bar

7.6

8.3

9.0

9.7

Danger:

Treat your tyres well, in particular avoid sharp edges where possible! Never inflate your tyres beyond the maximum permissible pressure, otherwise they might burst or come off the rim during the ride. Risk of falling!

Danger:

Always ride your bicycle with the prescribed tyre pressure and check the pressure at regular intervals.

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