There are two basic types of tyre: wired-on, found on most mass-produced bicycles, and tubular (often wrongly called tubeless), found on specialist racing or touring machines. With wired-on tyres the inner tube is held in place by the rim sides and by wired beads running round the edges of the tyre; with tubular tyres the tube is sewn into the tyre which is secured to the rim, usually with tubular cement.
Tubes for wired-on tyres are fitted with Presta, Woods or Schrader valves; the Schrader is relatively new to the bicycle and is the kind commonly found on cars, although the strong rebound spring has been removed or shortened to make inflating with a bicycle pump easier. All tubular tyres are fitted with Presta type valves. Each type of valve requires a particular pump connector, so make sure you use the right one. Sizes and air pressures Most mass-produced bicycles will be fitted with the correct tyres for the machine’s intended use (general purpose, touring and racing for example), with a tread pattern to match the performance. If you have to replace a tyre, make sure the new one is exactly the same size to suit the rim and tube; using parts which are incompatible can be dangerous. Except in one or two very specialist situations, tubular. Tyres are sold as 27in. All wired-on tyres have the size of rim, tube and tyre moulded or stamped onto them; but if you are in any doubt about what size to buy, go to a specialist bicycle shop for advice.
Many manufacturers also put the recommended tyre pressure on the sides of the outer covers (as wired-on tyres are often called); these pressures should be observed for maximum safety, comfort and tyre life.
In time you may be able to judge what pressure is in the tyre simply by feeling it; but far accuracy you should use a tyre pressure gauge (available from bicycle shops).
Careful riding and regular inspection of tyres can help to keep punctures to a minimum. You should avoid riding over rough ground whenever possible and be wary of pot-holes and raised road markers such as cat’s-eyes; also resist the temptation to bump up and down kerbs. When pumping air into your tyres look for small stones or other objects between the tread patterns and remove them with an old thin-bladed screwdriver.
Tiny punctures can be repaired without taking the wheel, tyre or tube off the machine; this can save a lot of work if, for example, you have a complicated front or rear wheel with a dyno-hub installed or a machine with a chain guard or rod brakes. You will need a tube repair kit containing patches, adhesive and abrasive paper. You will also need tyre levers; always use properly hardened levers and not screwdrivers, since these may damage the tube and rim.
Detecting a puncture is a process of elimination. If it is not immediately obvious, first check the base of the valve; twist the valve and listen for the hiss of escaping air. Run a little saliva round the air inlet of the valve; if it bubbles up, the valve is loose and needs tightening. If the valve is sound, inflate the tyre a little and immerse the lower part in a container of cool, clean water; slowly rotate the wheel and look for bubbles rising to the surface — these will indicate the punctured area. Dry out the tyre, holding the puncture with your finger, and mark the spot with chalk or a ball point pen.
If you still cannot locate the puncture, you will have to remove the inner tube from the tyre and inspect it. An old repair patch could be lifting and expelling air; the puncture could also be a very tiny pin-hole which will reveal itself when the tube is pumped up and expanded over its normal size. Another fault could be a percussion puncture caused by running over a stone or similar object with the tyre under-inflated; this bruises the tube without cutting the tyre and can make locating a puncture very difficult.
To remove a wired-on tyre, deflate the tube and push as much of the beads of the tyre as possible into the well of the rim. Remove the knurled ring, if fitted, from the valve stem and push the stem down into its hole in the rim. Then use two or three tyre levers to ease the tyre over the rim, taking care not to pinch the tube.
Remove the tube from the tyre and locate the air leak by immersing the tube in water as before. Dry the tube thoroughly and draw a circle, about the size of the patch you will be using, round the puncture. Rough up this area with glasspaper or emery cloth until the finish is matt and apply a coat of rubber solution. Allow this to become tacky then apply a second coat; when this is tacky, remove the protective backing from the patch and press it firmly in place, squeezing it between your thumb and forefinger for a few minutes. Dust the patched area with French chalk or talcum powder.
Before refitting the tube, inspect the inside of the tyre for any objects and remove them. If the hole in the outer cover is very small, use tyre canvas and rubber solution to repair it in the same way as you repaired the tube and fill the hole from the outside with rubber compound. If the tyre is badly cut, you should replace it as soon as possible.
Now inspect the well of the rim to see if any spokes are protruding above the nipple heads — this can cause punctures; if necessary, file the spokes flush with the nipple heads. Ensure the rim tape is in good condition and is sitting neatly in the well of the rim.
Dust the whole of the tube and the inside of the tyre with French chalk or talcum powder, paying particular attention to the beads; this will allow the tyre to settle onto the shoulders in the well of the rim and also eliminate the risk of ‘Webbing’ (lines of bubbles which develop into splits). Inflate the tube a little until it just assumes its shape and insert the valve stem into the rim, feeding the inner tube evenly into the cover all the way round.
Now push the other side of the tyre into the well of the rim, starting near the valve and ensuring it is pushed well down into the hole in the rim; this will allow the beads of the tyre to settle under the rim and eliminate the risk of bulges or blow-outs. Work the tyre into the rim with your hands until the final portion is roughly opposite the valve. Now ease the tyre onto the rim; start at the valve and work round the tyre, easing the last portion on very carefully. Never use tyre levers to fit the tyre since they are likely to nip the inner tube. Once the. Tyre is fitted, ensure the tube is not trapped under the tyre bead. Inflate to about half pressure and, pushing the wall of the tyre outwards, ensure the small moulding line is an equal distance from the rim all the way round. Spin the wheel to check the tyre does not jump and inflate to full pressure. Refit the knurled ring to the valve.
Repairing this type of tyre can be difficult and is probably best left to a specialist. There are, however, repair kits available; if you want to do the repair yourself, make sure you follow the instructions very carefully. Removing a tubular tyre is simply a case of working it off the rim with your hands; start on a 100mm (4in) area and push on each side to free the tubular. Never use tyre levers since these can damage the rim and the base tape.
Fitting tubular tyres is more difficult, however. When you are attaching the tyre to an old rim, use a wire brush to remove any loose cement from the rim bed. If the base tape of the tyre is loose, use latex-based adhesive to secure it; don’t use rubber solution or rim cement. Apply an even coat of cement to the bed of the rim and leave this to dry overnight. Apply a second coat and, when this is tacky, put a little air into the tube and push the valve through its hole in the rim. With the valve uppermost and the rim on a clean, dry surface, push the tyre evenly onto the rim; ensure it is centrally positioned by using the base tape as a guide. Inflate to half pressure and spin the wheel to make sure the tubular runs true; if wobbling occurs, adjust the tubular on the rim. Then, holding the ends of the spindle, roll the wheel along the ground to bed the tubular onto the rim. Leave the rim and tubular to dry overnight for good adhesion and pump up the tyre to half pressure before use.
Alternatively tubulars can be secured with double-sided adhesive rim tape.