Bicycles/Maintenance and Repair/Wheels and Tires/Inflating Tires

Bicycles

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Tire inflation is by far the most frequent task that the bicycle owner encounters. Fortunately, inflating tires is simple to learn.

Overview

Bicycle tires, for the most part, have an inner tube, and a protective rubber casing. Tire inner tubes are inflated with air using a pump. This is done via a one-way valve in the tube, that prevents the air from spilling out again.

Even when tires do not have punctures, manufacturing limitations cause small amounts of air to leak from them over a number of days. The resulting deflated tires make for heavier work pedalling. In addition, low tire pressures increase the number of punctures. See Repairing Punctures for details of such repairs.

Preliminaries

Although tires exist that do not use an inner tube, these comments apply to tires with tubes.
The manufacturer's recommended tire pressure is found written on the side of the tire. For adult-sized bikes it is usually a figure between 50 and 100 psi, (pounds per square inch), though figures vary greatly.
If you have no restrictions in choosing a pump, try to find one with a pressure gauge on it. It will help to get the tire pressures right each time.
If there is no pressure gauge on the pump then consider a separate gauge, sold as an accessory.
If no gauge is available at all then there is no alternative but experience of how hard the tires should feel.
Be careful not to over inflate tires when using compressed air lines as they can explode. Air lines used for inflating truck tires and narrow track bicycle tires are capable of supplying more pressure than a wider bicycle tire can withstand.

Valves, Connectors and Pumps

Valves

Tubes have one of two main valve types:

Schrader valves. These are similar to the kind found on motorcar tires.
Presta valves. These are thinner than Schraders and have a small locknut on the end of the valve body, and a nut on the rim.

Schrader valve types have springs inside them, so they do not need locknuts to seal them. After removing the dust cap, the pump can be applied directly or a pump-adaptor screwed into position.

Presta valves need the locknut on the end of the stem unscrewed as far as it will go before securing the pump or adaptor to the valve stem. Once the tube has been inflated, the locknut should be screwed closed again. The locknut only needs to be finger-tightened so that it is snug when opening or closing. Do not overtighten it.

It is unusual for valves to become blocked, except perhaps in the use of innertube sealants. If valves are blocked then pumping becomes difficult. Schrader valve cores can be removed for cleaning, but in general Presta valves cannot. (Bontrager and Schwalbe Presta valves are exceptions and do have removable cores). Before attaching a pump it is a good idea to press the end of the valve so that escaping air can unblock any debris.

Connectors

Both valve types have threads on their stems for connections, and hand pumps often need flexible adaptors to connect between the pump and the thread on the valve. These connections, although used on the cheaper pumps, are useful in that they avoid stress on the valve stems during pumping. Pumps of this kind can be used for both types of valve simply by changing the adaptor.
The Schrader and Presta flexible adaptors have different threads; the Schrader is wide and the Presta is thin, so it is important to get the right adaptor for the valves on the tires.
Other pumps do not use flexibles but are attached directly to the tops of the valves. Some of these have connection heads that can be interchanged in the same pump, but some others are made only for one kind of valve.
Some bicycle shops sell brass adaptors that allow any Schrader pump to convert to use with flexible adaptors of either kind, thus extending the use of the pump.
Track pumps, the kind that stand on the ground, use long flexible tubes and a choice of heads for direct attachment.

By far the most common connector is the threaded flexible tube that is screwed onto the valve and into the pump. Press-on plastic connectors also have a lever to switch the air-flow on and off. The fittings for press-on connectors differ for the two valve types also, though some pumps have fittings for both. The press-on fitting is faster to use so is found on most track pumps.

Some pumps with press-on fittings have serrated screws on each head. To get a proper, snug fitting with these, the screwed end can first be adjusted. However, when the valve stem is loose owing to a very flat tire, it is best to support the valve stem while attaching the head; this reduces the stress on the stem. For direct attachment pumps without a flexible connection, it is also a good idea to support the pump in use so that the stem remains in its usual position.

These pumps often require that an air switch be positioned correctly before pumping. In any case, when it feels that you are pumping against an unreasonable pressure, it usually means that the head of the pump is not properly seated on the valve or the switch is closed; stop pumping, check and re-seat the head.

If the tires have slime or other sealants in them, they can sometimes block the valve stems. If pumping seems blocked in this situation, then bleed air from the tube until there is a good flow, before adding air.

Instructions supplied on the packaging of such pumps tend to assume too much knowledge on the part of the user, and would benefit from a good deal of expansion.

Technical Note:

Pumps that use a flexible connection tube are said to place lower stresses on the valve stems than those that press onto the valve stem directly. (See the technical note box above). The Presta valve has a locknut to hold it onto the wheel rim and that is also said to reduce valve stress. This rim locknut should be finger-tight, and never over tightened.

Choosing a Pump

Use the points below for guidance in choosing pumps. For more information on pumps see Bicycle Pumps.

The pump must be suitable for inflating to the pressures intended. Some pumps cannot attain higher pressures.
The valve fitting must be the right kind for your tubes; Schrader or Presta; having both is best in case you can't find the right innertube.
Consider how much effort is needed to use the pump. Some lightweight riders might have trouble pumping to 100psi, even with a track pump. Narrow-tubed pumps need less effort than wide-tubed pumps but take slightly longer to complete the task.
Some pumps are small enough to take on the bike, and can often be clipped to the frame. In fact, some pumps are made to be the hidden part of the seat post.
Inflation of tires is easiest with a fairly bulky track pump. It is an upright pump that stands on the ground with a handle on top. Some have a pressure gauge and have fittings for both valve types. Since most tire inflation is done at home, the size of the pump is not a disadvantage.
Always ask the advice of the bike store, since they know what works best. Also, browse on the internet for comments on your intended purchase.
Ask at the store whether or not spares exist for the pump.

Gas Inflators

On the road it is often convenient to use a carbon dioxide gas canister to inflate tires. These disposables are only about three inches in length, and contain some sixteen grams of gas at sufficient pressure to inflate most tires. This assumes that any punctures are patched in the usual way.

The accessory consists of a tool to hold the gas cylinder in place and a control valve to adjust the rate of inflation. The tool with its cylinder is hand-sized so is small enough to carry on the bike or in a back-pack.

Another method uses a puncture repair fluid combined with air pressure and manufacturers claim that it makes internal repairs to punctures and inflates the tire at the same time. The repair fluid is retained for the life of the tire. Such treatments are supplied in a container comparable in size to a deodorant aerosol.

Separate containers of internal repair fluid, (Slime), without gas inflation are also available, and these are usually poured into the tube after removing the valve core. A connection tube as a pourer and a valve stem remover for Schrader valves is supplied with the bottle. All Schrader valve cores can be removed, but only Bontrager and Schwalbe tubes have removable Presta valve cores. In any case Slime products are not supplied with removal tools for Presta valves, and because the Presta valve stems are thinner, the filling tubes would not fit. Presta valve users, and for that matter Shrader users, are best to purchase inner tubes that are pre-filled with sealant by the manufacturer; they are not much more expensive than the plain tubes.

Inflating the Tire

If the tire is completely flat: for example, when a puncture has been repaired

Add just enough air to the inner tube to give the tire some structure.
Work around the tire with your fingers, pressing in the sides to make sure that the edges are properly seated.
Then, inflate the tire in accordance with the usual methods given below.

Inflating with the Presta valve:

First rotate the bike's wheel to a convenient valve position.
Remove the valve's plastic dust cap and place it somewhere safe.
Unscrew the small nut on the valve stem all the way to the end.
Depress the valve end briefly to air blast any debris from the valve
Attach the pump to the valve.
Inflate with the pump to the required pressure. If the pump feels pressure-blocked, rather than forcing it, check again for the proper fitting of the head, (see the technical note above), and try again. This will usually correct the problem.
Remove the pump from the tire and retighten the small nut on the valve stem. If much pressure is lost in removing the pump then consider a slight overpressure during the pumping process.
Replace the valve's plastic dust cap, and make sure that the nut at the tire's rim is only finger-tight.

Inflating with the Schrader valve:

First rotate the bike's wheel to a convenient valve position.
Remove the valve's plastic dust cap and place it somewhere safe.
Depress the pin in the end of the valve briefly to air blast any debris from the valve.
Attach the pump to the valve.
Inflate with the pump to the required pressure. If the pump feels pressure-blocked, rather than forcing it, check again for the proper fitting of the head, (see the technical note above), and try again. This will usually correct the problem.
Remove the pump from the tire. If much pressure is lost in removing the pump then consider a slight overpressure during the pumping process.
Replace the valve's plastic dust cap.