Jamis Bicycle Owner's Manual - page 21
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CAUTION: Pencil type automotive tire gauges can be inaccurate and should not be relied upon for consistent, accurate pressure
readings. Instead, use a high quality dial gauge.
Ask your dealer to recommend the best tire pressure for the kind of riding you will most often do, and have the dealer inflate your tires to that
pressure. Then, check inflation as described in Section 1.C so you’ll know how correctly inflated tires should look and feel when you don’t have
access to a gauge. Some tires may need to be brought up to pressure every week or two, so it is important to check your tire pressures before
every ride.
Some special high-performance tires have unidirectional treads: their tread pattern is designed to work better in one direction than in the
other. The sidewall marking of a unidirectional tire will have an arrow showing the correct rotation direction. If your bike has unidirectional tires,
be sure that they are mounted to rotate in the correct direction.
2. Tire Valves
There are primarily two kinds of bicycle tube valves: The Schraeder Valve and the Presta Valve. The bicycle pump you use must have the fitting
appropriate to the valve stems on your bicycle.
The Schraeder valve (fig. 18a) is like the valve on a car tire. To inflate a Schraeder valve tube, remove the valve cap and clamp the
pump fitting onto the end of the valve stem. To let air out of a Schraeder valve, depress the pin in the end of the valve stem with the
end of a key or other appropriate object.
The Presta valve (fig. 18b) has a narrower diameter and is only found on bicycle tires. To inflate a Presta valve tube using a Presta
headed bicycle pump, remove the valve cap; unscrew (counterclockwise) the valve stem lock nut; and push down on the valve stem to
free it up. Then push the pump head on to the valve head, and inflate. To inflate a Presta valve with a Schraeder pump fitting, you’ll
need a Presta adapter (available at your bike shop) which screws on to the valve stem once you’ve freed up the valve. The adapter fits
into the Schraeder pump fitting. Close the valve after inflation. To let air out of a Presta valve, open up the valve stem lock nut and
depress the valve stem.
WARNING: We highly recommend that you carry a spare inner tube when you ride your bike.
Patching a tube is an emergency
repair. If you do not apply the patch correctly or apply several patches, the tube can fail, resulting in possible tube failure, which
could cause you to loose control and fall. Replace a patched tube as soon as possible.
G. Tires and Tubes
1. Tires
Bicycle tires are available in many designs and specifications, ranging from general-purpose
designs to tires designed to perform best under very specific weather or terrain conditions.
If, once you’ve gained experience with your new bike, you feel that a different tire might
better suit your riding needs, your dealer can help you select the most appropriate design.
The size, pressure rating, and on some high-performance tires the specific recommended
use, are marked on the sidewall of the tire (see fig. 17). The part of this information which is
most important to you is Tire Pressure.
WARNING: Never inflate a tire beyond the maximum pressure marked on the
tire’s sidewall. Exceeding the recommended maximum pressure may blow the
tire off the rim, which could cause damage to the bike and injury to the rider
and bystanders.
The best and safest way to inflate a bicycle tire to the correct pressure is with a bicycle pump
which has a built-in pressure gauge.
WARNING: There is a safety risk in using gas station air hoses or other air compressors. They are not made for bicycle tires.
They move a large volume of air very rapidly, and will raise the pressure in your tire very rapidly, which could cause the tube
to explode.
Tire pressure is given either as maximum pressure or as a pressure range. How a tire performs under different terrain or weather conditions
depends largely on tire pressure. Inflating the tire to near its maximum recommended pressure gives the lowest rolling resistance; but also
produces the harshest ride. High pressures work best on smooth, dry pavement.
Very low pressures, at the bottom of the recommended pressure range, give the best performance on smooth, slick terrain such as hard-packed
clay, and on deep, loose surfaces such as deep, dry sand.
Tire pressure that is too low for your weight and the riding conditions can cause a puncture of the tube by allowing the tire to deform
sufficiently to pinch the inner tube between the rim and the riding surface.