right. The puncture that does not reseal must be plugged or patched.
Rubber plugs are made in all sizes; and rubber cement, liquid rubber, is
put up in collapsible metal tubes, like paint-tubes, with a pointed
spout to introduce the cement behind and through the puncture. There are
numberless convenient contrivances made to hold plugs, enlarge holes,
and to do the repair work neatly.
In mending a puncture, the tire remains on the wheel, and the work is
done from the outside of the tire. If the hole is very small, it must be
enlarged sufficiently to introduce the plug. The rubber of the plug is
very soft and compressible, and the hole should be considerably smaller
than the shank of the plug.
The plug must be held firmly, and forced through the hole, and held in
place while the nose of the cement-tube is introduced, and a plentiful
supply of liquid rubber smeared over the inside of the hole around and
on the plug, and enough extra cement added to flow all about the inside
of the tire around the puncture. Pull the plug back by the shank,
allowing the head to rest on the inside of the tire, and the shank to
come back through the hole. Pull the plug firmly into place by the
shank, which should fit the hole very tight. Cut off the projecting end
of the plug shank, and the repair is made. Turn the wheel until the plug
comes to the lowest point, and keep it there until the cement gets
around the plug. To smooth a ragged hole before introducing the plug,
when the proper tools are not to be had, a heated wire may be used to
make a round smooth hole. Rubber may be handled and cut while wet with
water, but must be dry and free from grease to take cement. Always wet
the knife-blade before cutting the end off the plug; this will ensure a
smooth, clean cut.
A puncture may be repaired by introducing almost any material on the
inner surface, and holding it in place; and it is well to know of a few
substitutes for the regular repair-kit for emergency use. Punctures
difficult to locate may be found by inflating the tire and wetting with
soapy water, when a bubble will form where the air escapes.
A puncture that goes all the way through the inner tube of the tire must
be repaired on the inside. The outer covering of the tire is porous, and
if the hole is plugged or patched on the outside, the air will escape in
other directions through the material of the tire. Failing the
repair-kit tools, a rubber plug, some liquid cement, a piece of string,
and a pair of pliers will do good work. Tie the string to the plug to
keep it from slipping, apply plenty of cement to the plug, then grasp it
with the pliers, and introduce it through the hole prepared for it in
the tire. Pull the string to pull the plug into place, see that there is
plenty of cement around and about it, inflate the tire, and the air will
hold the plug in place until the cement hardens.
The plugs that are supplied are disks of rubber of different sizes, with
stems attached to the centre, and a nice tool is made for the purpose of
punching the hole in the tire. When a hole is burned, the charred edges
should be removed, and if possible cleaned with benzine. A tire well
patched on the inside is almost as good as new, and very serviceable,
unless the brake is applied frequently and unevenly, when the plug is
almost sure to feel the push.
The commercial patch or plug makes the most satisfactory repair for a
puncture, although there are other things that may be used. Rubber bands
may be pressed into service, and sheet rubber also may be used. Repair
on the roadside is made in the same way as repair in the workshop, the
differences being in the conveniences for working and the permanency of
the patch. A rent may be repaired with plugs, it being first stitched
together, then the plugs introduced, and finally a patch cemented on the
outside over the rent to protect the stitches. A puncture may be
repaired with rubber bands held in place on a wire, covered with cement,
and forced into the hole made in the tire. A piece of wire flattened on
the end, a cross piece with a notch cut in it and twisted below, makes a
fair repair needle. The end of the projecting rubber cut off, a very
fair plug results.
Sheet rubber may be placed over the hole on the inside, though it is
difficult to keep it in place. Twisted up and tied into a plug, or
spread into place on the inside, the difficulty with this repair is that
the patch must be held in place until the cement hardens, and then is
liable to work out of place. Inner tube tires are repaired with patches
of soft rubber. After the puncture is located, the patch will retain its
place by being pressed against the inner surface of the tire when
inflated.
To do good work in repairing rubber, always clean the surface of the
rubber material thoroughly, washing with benzine when possible; and
always test a patch when finished by placing it in water or wetting it,
to ascertain that it is satisfactory. On the road a puncture may be
plugged in any time under five minutes when located. In the workshop, it
is more convenient to hang the wheel up while making a patch, as it is
more readily held in place when working from below.
There are many ways of doing makeshift repairs. Melted rosin may replace
the rubber cement, and rosin may be found at any tinsmith’s. Melt the
rosin, and dip the rubber in that to make it stick.
Tire tape may be used in a variety of ways. Find the puncture, cut
strips three or four inches long, and place them lengthwise on the tire,
lapping the edges at least half way over; then wrap the two thicknesses
of tape round and round the tire, and keep lapping the tape each time
over the last turn to hold the edge down, making it air-tight. Well put
on, tire tape will last for many miles. The tire should be partly
inflated while the tape is being put on, and fully inflated when it is
all on. Force more air into the tire to cause the tape to grip securely.
Such repair, though not permanent, may prove serviceable in emergency.
A simple and effective substitute for the rubber plug is absorbent
cotton or jeweller’s cotton, well dipped in cement, and the cement
worked into the cotton. Quite a large puncture may be repaired with
this, and the hole need not be enlarged or burnt to receive it, as the
soft mass of cotton fills the irregularities in the puncture. It may be
introduced into the puncture either with an ordinary repair tool or a
piece of twisted wire. The tire is held on the rim by cement made of
shellac or some other equally good cementing substance. Of course, in
using a cotton plug, the greatest mass of the cotton should be on the
inside of the tire, leaving a stem in the puncture, and then the outside
ends should be trimmed off.
The tire may be readily removed with the hands by pulling at right
angles with the wheel. Rubber cement may be made by dissolving perfectly
pure rubber in naphtha; but the commercial cement is usually found the
cheapest in the end.
If you should be so unfortunate as to break down, what are the problems
you must meet? The bicycle is made of different materials--iron, metal,
steel, wood, rubber, and leather, and each different material requires a
different kind of treatment. The general idea in any kind of repairs is
to effect the holding of the parts in position with a material that
will supply strength and stiffness. The use of glue or cement is merely
to hold parts in position, to replace the fractured pieces and keep them
in place, to enable the particular part to do its duty, and to keep the
piece in place while the cement hardens.
There is room for great ingenuity in handling repair work and in
estimating the available resources. The most common accident is a
puncture in a pneumatic tire. There are also repairs to be considered to
the wooden rims and the spokes and the tubing and lost or broken parts.
A great deal of damage could occur in a collision, and the bicycle be in
very poor shape, but it can be set right with a little assistance from a
mechanic, even though he does not understand the mechanism of a bicycle.
Suppose nothing to be injured except a piece of the supporting tubing;
or that the bicycle could be made to go if the rim were spliced or
strengthened at a place where it has been split. A temporary repair
usually takes considerable time, and should never be attempted unless
there is nothing else to be done. A blacksmith shop, unless the smith is
very ingenious, is not a very good place to look for assistance; a
plumber or tinsmith or locksmith, unless a bicyclist, can help but
little. For a broken rim I would betake me to a carpenter shop or
carriage maker’s. If the break is in a straight piece of tube, get the
carpenter to make a round stick, not as long as the broken tube, and fit
it to the inside, to slip in easily. Hardware stores keep round wooden
rods, and perhaps one of these would answer. Push the round stick up
into the tube, and, holding the parts in place, let it slip down into
the other part of the break; this will keep the ends of the break
together. Then get the carpenter to take two blocks of wood, hollow them
out to hold the tube, and screw them fast together, holding the tube
between them. If he has an auger-bit the size of the tubing, he can
easily bore a hole in a block the size of the tube; then have this block
cut in two with the saw, leaving the hole cut in half, and screw the
pieces together after they are placed on the broken part. The same kind
of a repair may be made on the angles of the frame if the blocks are
hollowed to fit. This makes an unsightly job, but can be recommended as
strong and safe when properly done.
A broken spoke may be repaired, if it cannot be replaced, by bending the
ends of the broken parts into loops; then, taking a piece of wire
through both loops, fasten it together, and tighten by screwing it up.
A wooden rim may be whipped or wound. The tire must be deflated first,
and removed from the rim at the broken place; then wind fine wire or
fish-line about the place, after filling the break with glue or shellac.
In wrapping, take care that the turns are made very smooth and even, and
close to each other. Then the tire may be cemented and inflated. Of
course, there will be a lumpy place on the rim, but it will do until the
rim can be replaced.
Any bolt that has lost its nut, when the nut cannot be replaced, may be
held by hammering a burr on the end. If the end is too long, a piece may
be cut or filed off, and a burr hammered down to hold.
A bicycle cannot travel easily if the frame has been bent out of true;
and to straighten a bent frame is an easy matter. Take out wheels,
saddle, and handle-bars, and use a piece of broom-handle to spring the
frame into true; or take a stout cord, fasten it to either end of the
part to be straightened, insert a stick, and wind the cord up tight.
There are three things to take into consideration when doing repair
work: First, finding out what is to be done, then doing it, then seeing
that it has been done right.
_CHAPTER XVIII._
_Mechanics of Bicycling._
All applied mechanical power is the application of lever movement (and
lever movement is but the effect of applied power), either simple,
compound, or complex.
In the bicycle propelled by human power, we have a series of lever
movements, initiated and executed by the highest and most effective
mechanism known--the human body, applied human power. There is the seat
of power, the point of application, and the object. The bicycle or
object is so constructed that it continues the application of power
applied.
The lever is described as “a bar or other rigid instrument having a
fixed point for the exercise of power and the application of power to
the object to be moved.” The series of lever movements in the human body
is the most wonderful known.
There are three varieties of levers, of three different degrees of
efficiency, known as levers of the first, second, and third classes, or
orders, of levers.
In the lever of the first class, the fulcrum is between the weight and
the power:
P F W.
In the lever of the second class the fulcrum is opposite to the power:
P W .
F
In the lever of the third class the fulcrum is opposite to the weight:
P W.
F
These different powers of levers are used in combination, and produce a
great variety of power effects and applications.
Other factors to note are:
That a body in motion persists in maintaining its direction unless other
forces intervene.
That the gyroscope overcomes the force of gravity while rapidly
revolving.
That a body set in motion tends to move in a straight line.
That the centre of gravity must be maintained by balance if disturbed or
shifted.
That force is the cause of a change in the velocity or direction of
motion of a body.
That all alterations of velocity take place gradually and continuously.
That centripetal force and centrifugal force are force directed by
radial action.
That the air offers resistance, which increases when the air is in
motion.
That friction offers resistance to power.
That the smaller the surface presented, the less friction there is to
resist.
That resistance must be overcome by power expended for the purpose.
That the base of the bicycle is practically without width, and is
usually about from forty-two to forty-four inches long.
That the direction of the base may be changed at will within certain
limits.
That the bicycle will fall unless prevented from doing so.
That to prevent a bicycle from falling, or to maintain a bicycle on its
base, it is necessary to balance it.
That the constant effort to maintain the bicycle upright upon its base
is on account of the motion of the different opposing forces.
The bicycle is constructed to overcome the resisting forces in different
ways, supplying as many forces as can be made available to accomplish a
particular purpose, permitting a certain choice and discrimination in
the matter.
The bicycle has one weight-carrying wheel and a frame and a pivoted
wheel. The driving power is applied to the weight-carrying wheel, and
the steering is done with the pivoted wheel. The bicycle remains upright
because several forces co-operate to enable it to maintain its plane,
change direction, and overcome certain resisting and opposing forces.
A bicyclist is propelled at a sufficient velocity to maintain the plane
of movement. By altering the centre of gravity, inclining one way or the
other, change of direction may be made.
The front or guiding wheel of the bicycle, being controlled by the
different angles of resistance it presents to the surface it rotates
upon, and not being immovably fixed, can pivot to a plane corresponding
to a plane of least resistance. After a little momentum is attained, a
bicycle will maintain its speed with but little assistance of power,
unless it is accidentally obstructed, or an increase of grade requires
an increase of power.
The frame of a bicycle is a compound lever, combining the second and
third orders. The wheels are a compound lever of the second and third
orders. The fork and handles a lever of the second order.
The forks and handle-bars are set at an angle with the front wheel, thus
conveying the touch on the ground or other surface to the pivot head and
the hands.
A moving body tends to pursue its direction. A wheel loses its power to
change its direction after passing the point of friction. With the forks
at this angle, the blow is felt, and change of direction caused by an
obstacle conveyed; but the wheel has still some power to maintain its
plane from friction, and is steadied by its head. The motion of swaying
is conveyed and overcome at the tire base. If the pivot were directly
over the tire base, the swing would be given to the wheel; and the tire,
having passed its point of friction, would continue to swing. If the
head were pivoted on a point, there would be no side friction on the
rim; because it is pivoted at an incline, the friction base is increased
in proportion, and the wheel, steadied in itself, is easily controlled
by an increased line of friction or by prolonging the time from the
point of contact.
A body in motion persists in maintaining its plane of motion unless
additional forces intervene. The occurrence of these forces is
detrimental and frequent, requiring a continuous swing of the guiding
wheel either by the hands or by balance. The direction of the base line
is continually changed, as it were, broadening the base line. The weight
must incline with the front wheel, and the front wheel will support it.
If inclined away from the direction of the front wheel, the weight
becomes the long arm of the lever, exerting weight against weight at the
base of the bicycle, there being no opposing force. The front wheel
being turned away, the bicycle falls or slips over.
With the fork at this angle the wheel is inclined, the frame held on the
wheel at this angle, as the wheel is turned sideways, it gradually
brings the centre directly over the axles, raising the front end of the
frame up. This pressure or leverage from the frame tends to keep the
wheel straight in the line of least resistance. In turning, the wheel
must lift the weight, and push it up; and this factor greatly adds to
the steadiness of direction.
A bicycle with the steering wheel held fast will maintain its plane so
long as its momentum is not overcome. With the steering wheel the plane
of movement may be regained after each opposition, provided the
proportionate amount of power is expended.
The radius of a wheel is the long arm of a lever; the pedal crank is the
short arm of the lever, though its length may exceed that of the radius
of the wheel.
Power and speed are interchangeable. The shorter the arm of the crank,
the greater the weight required to balance the long arm at the rim of
the wheel (an imaginary line). If the pedal crank is lengthened, it will
require less power to move it. At the same time the foot, following the
crank, describes a larger circle for the distance travelled by the rear
wheel. The crank lengthened, the power is diminished, demanding
increased exertion to follow it, the foot travelling at a rate
determined by the distance to be traversed.
When the hub rests on the axle of the wheel, there is considerable
friction to overcome in the entire length of the hub, the friction, or
ability of the wheel to turn, depending on the amount of axle surface.
The axle, therefore, becomes heated when the air cannot readily reach
the surface to convey away the heat generated by friction.
Weight may be balanced and supported on a point; when weight rests on a
sphere, only a point supports weight. By surrounding the axle with
balls, the weight is taken from point to point on each ball, and a
circulation of air allowed. The weight, carried from ball to ball, gives
the advantage of a larger cooling surface in a confined space, while the
weight and friction are applied directly to a very limited area. Each
ball is also an axle in itself, and carries the weight, and passes it on
to the next ball. The balls act as lubricators, preventing the moving
surfaces from contact.
The problem of speed produced by power means that speed is obtained at
the expense of power expended. The relative size of the sprocket-wheels
determines the relative speed of the cranks and rear wheel. To get the
greatest speed with the least power possible means diminished friction
and lessened weight. The band or chain complies mechanically with these
requirements, permitting a certain amount of play, which lessens the
danger of sudden strains and jars, and supplies the power to the rear
wheel with the least possible loss by friction.
Gear 63 72 76 80
6¹⁄₂ crank
proportion 4¹¹⁄₁₃ to 1 ⁵⁄₁₃ to 1 5¹¹⁄₁₃ to 1 6²⁄₁₃ to 1
8 crank
proportion 3¹⁵⁄₁₆ to 1 44¹⁄₂ to 1 33³⁄₄ to 1 5 to 1
6¹⁄₂ crank pressure 4.85 5.54 5.85 6.15
8 crank pressure 3.37 3.84 4.5 5.00
6¹⁄₂ crank ground
covered by large wheel 16 ft. 19 ft. 20 ft. 21 ft.
8 crank ground
covered by large wheel 16 ft. 19 ft. 20 ft. 21 ft.
6¹⁄₂ crank ground
covered by pedal 40.84 inches
8 crank ground
covered by pedal 50.26 inches
“_Scientific American Supplement, No. 1025_,” August 24, 1895.
Rating wheel by the amount of progression for each turn of the crank
(pedal), the following table, compiled by Henry Starkweather, will be
found of advantage:
No. teeth in 26 in. wheel.
large Sprocket. No. teeth in small sprocket.
6 7 8 9
18 20 ft 17 ft 15 ft 13 ft
19 21 ft 18 ft 16 ft 14 ft
20 22 ft 19 ft 17 ft 15 ft
28 inch wheel.
18 22 ft 19 ft 16 ft 14 ft
19 23 ft 20 ft 17 ft 15 ft
20 24 ft 21 ft 18 ft 16 ft
The following table, from the New York _Evening Post_, shows the gear
according to the number of teeth on large and small sprocket-wheels:
Sprockets 28 in. wheel
on pedal crank. Sprockets on rear wheel.
7 8 9
17 68 59¹⁄₂ 53
18 72 63 56
19 76 66¹⁄₂ 59
20 80 70 62
21 84 73¹⁄₂ 65
_CHAPTER XIX._
_Adjustment._
In bicycling, the word “adjustment” means much, for the movable parts of
the bicycle must be adjusted to suit the requirements of the individual
bicyclist, and the mechanical parts of the bicycle’s construction
adjusted so that they will work together properly.
In a machine properly adjusted, the chain and other gear should run
smoothly, the chain be neither too tight nor too loose, and the
sprocket-wheels exactly in line. The bicycle wheels should run true and
be exactly in line with the frame, and the rear wheel follow the
identical plane of the front wheel when in place. The frame should be
true and square at all points, and should be examined and tested always
after the machine has been travelling by rail or has had a fall. The
bearings in all parts of the machine should have their cone-caps in
place and so screwed and keyed that the balls run easily without
perceptible play. Nuts and washers should all be in place and screwed
home. The handle-bar should be tight and square with the front wheel,
but only tight enough to turn the wheel on a good surface, not so tight
as to prevent it from turning easily if the wheel is caught or held.
The proper adjustment for position has to do with the frame, wheel-base,
length of crank, height and position of saddle; the curve, width,
height, and general adjustment of the handle-bar; the size and number of
teeth on the sprocket-wheels, which determines the gear; and the weight,
construction, and inflation of the tire.
The saddle is one of the most important, if not the most important, part
of the bicycle to study, as it should provide the fulcrum to work from.
Any saddle may be adjusted to be comfortable, but saddles seldom remain
comfortable after being adjusted. The saddle should be hard enough to
act as a fulcrum and should not give or spring under work, for power is
lost on each stroke that presses down on a soft saddle; it should also
permit of change of position without readjustment, unless it is intended
for racing purposes, for the bicyclist should be able to speed, climb,
or coast on a saddle properly constructed for general purposes. Each of
these different kinds of bicycle work requires a different application
of muscular power, and the saddle should permit of a readjustment of
position that will at least accommodate the altered tendency caused by a
shifted centre of gravity in grade work.
Every individual is differently proportioned, with differing lever
lengths and lever power. If people differently proportioned find the
same adjustment possible, it would be for the reason, not that their
different requirements average the same, but that the average of their
different requirements is the same. A higher gear means greater
resistance; a lengthened crank causes the foot to travel in a larger
circle while gaining in increased leverage in the lengthened arm.
In determining the proper proportion of crank length and gear, it may be
calculated that the same amount of resistance may be overcome by using a
higher gear and longer crank as by using a lower gear and shorter crank,
the difference being in the rapidity of the stroke necessary to cover a
given distance in a certain length of time. This adjustment may be
considered equivalent to length of pace and rapidity of pace in walking.
It is well to have crank and gear selected by some one sufficiently
experienced to make an intelligent choice.