GEARING UP AND DOWN.
This familiar phrase means simply that the number of revolutions made
by the drive-wheel in proportion to the number made by the cranks is
greater or less. Broadly, it varies the relative amount of motion of
the pedals, and consequently of the feet of the rider in travelling
over a given distance. In the simple crank device no change can be
made in this respect except in the length of the cranks, but in all of
the sprocket-chain devices it is also possible to change the amount of
motion in the pedals by altering the size of one or the other of the
sprocket-wheels. In lever machines and in those which have the sun and
planet connection, either with an oscillating lever or full revolving
crank, it is generally possible, by some alteration, to produce the
same effect as that of changing a sprocket-wheel as mentioned. The
variation in the length of crank produces an effect comparable to the
change of gearing in so far as the distance through which the feet
travel in covering a certain distance is concerned, but the difference
lies in this, that altering the crank means a given number of
revolutions in a circle of varying radius, while altering the gearing
means a variable number of revolutions in a circle of given radius, in
order to cover a given length of road.
In popular language, if a rider wishes more power, he must lengthen
the crank or decrease the size of the sprocket-wheel on the crank-axle;
_vice versa_, if he desires greater speed and less power, he must
shorten the crank or enlarge the sprocket-wheel connected therewith.
It is needless to say that enlarging the gear-wheel on the crank-axle
produces the same effect as decreasing the size of that on the
drive-wheel.
In a sprocket-crank machine the real question of gearing is whether
to change the length of crank or proportion of the sizes of the
gear-wheels; but you can’t by any combination get power and speed both
with the same amount of work done by the rider.
Simple as all this matter of gearing is, it is probable that there is
no feature in cycles so indefinitely understood, or, we might say, so
persistently distorted. The only trouble is that riders will not stop
to apply a most fundamental law of nature. If we gain speed, we lose
power; if we gain power, we must lose speed. To apply this particularly
to cycles, if you gear up for speed, you must push harder; if we gear
down, we need not push so hard, but must kick faster or go more slowly,
provided in each case the length of crank is the same. We cannot go
fast and push easy unless we increase the strength of the man. To
go over the same distance of given road, the same amount of work is
required, no matter how the machine is arranged through which it is
done.
This subject was better understood when no element but the length of
the crank was to be considered; but now, since bicycles have appeared
that are capable of being changed to a high or low gear, some riders
persist in treating it as an entirely new problem. It has in one
respect a new feature in that greater or less speed can be had without
decreasing or increasing the length of the crank; that is, since the
comparative speed of the pedal and rim of the wheel in space can be
varied either by the length of the crank or the number of revolutions
of the same, we can make one turn of a six-inch crank do the same work
at the same foot-pressure as two turns of a three-inch crank at the
same pressure. Now, this is a valuable feature, because it allows us to
increase the vertical amplitude through which to transmit power without
change in the velocity of the pedal through space.
A convenient standard has been adopted in gearing cycles by comparing
the speed of the driver to that of a wheel and crank connected and
revolving together, as in the Ordinary; that is to say, a thirty-inch
wheel geared to sixty means that one turn of the crank will drive the
thirty-inch wheel twice around, as it must do in order to cover the
same distance as one turn of a sixty-inch wheel. To find how high the
machine is geared, divide the number of teeth in the sprocket-wheel
on the crank by the number in the sprocket-wheel on the driver, then
multiply the result by the diameter in inches of the drive-wheel. In
short, the speed indicated by the size of the drive-wheel of the geared
machine is to the real speed as the number of teeth in the gear upon
the wheel is to the number of teeth in the gear on the crank-axle.
When tricycles first appeared in which the power was transmitted
through sprocket-wheels and chain, there was quite a cry for
“high-geared” machines; but the mistake was soon discovered, and buyers
eventually found that moderate gearing was best, and in fact many
adopted a level gearing (equal-sized sprocket-wheels) with thirty-six-
to forty-two-inch drivers. Notwithstanding this experience, when the
geared bicycles came in there was still a great cry for fancied high
speed. An English maker in 1885 complained to the writer that it was
the bane of his existence,—this howl for high gears,—when it was well
known to him that buyers would eventually be dissatisfied. It was of no
use to make, said he, what is really needed; customers will not even
try the machines, so sure are they that by their scheme “they can fly
through the air with the greatest of ease,” which expression, when used
by the ordinary man, means something like pulling a ten-horse load with
one mule.
In the early days of gearing, few riders could be more easily
offended than by intimating that they wanted a low-geared machine,
say fifty to fifty-two; no less than sixty or seventy would satisfy
their cravings for great speed, and in fact the writer has been asked
seriously, “Why not gear her up to about a hundred?” But now that the
idol of so many riders has been shattered, they will too complacently
accept the word of the maker as to what they need, and hence there is
a real substantial reason for investigating this matter. The advent
of the gearing process has developed a new point, as a result of
conditions spoken of, which is to make the machine suit the rider’s
strength and physical peculiarities as well as to fit him in the
length of leg,—a point to which insufficient attention has been paid.
If one man wants a machine geared to fifty-six or sixty, there is no
conceivable reason why another who happens to have the same length of
inseam of his trousers should want the same; nor is it a matter simply
of strength: if two men can make the same number of miles in a day,
it is fair to presume that they are of nearly equal riding capacity,
yet each may accomplish the work most easily on machines geared quite
differently. An instance of this kind has occurred to the writer,
in riding day after day on a machine geared to about forty-eight,
with a man who preferred and could do his best work on a sixty. This
difference held good on smooth or rough roads, and as a matter of my
own experience it is a pleasure to ride a low gear, and distressing
toil to use a higher. There are others whose experience is just the
reverse, and it is useless to try to guess at what is wanted; it is
best not to go to either extreme in buying unless you have proved
the necessity by extended experience on the road. It would be well
for all riders to avail themselves of any good opportunity to make a
thorough trial of machines geared differently from each other, for it
is possible to be unsuited and never know it. Even if you have been
able to lead the van when you have been out on a run, you do not know
but that you could have led it much easier on something else than that
which you rode. The physical system in man may easily become adapted
to a wheel which at first was not suitable, but there are those to
whom certain gearing will always be wrong. It is safe to say that the
prevailing mistake in the past has been the use of too high gears,
though this has been much improved of late by the use of long cranks.
There is one subject which should be touched upon with great caution,
since the prospects of some very worthy inventors might be unjustly
interfered with; it is that of multiple or two speed-gears. I have
tried to impress upon the reader the importance of gearing to suit his
strength, yet when once suited it is extremely doubtful if he should
ever change it; at least it is doubtful if he should do so on the same
trip or even during the same season. When a rider transfers his base of
operations from a level to a hilly country permanently, a change in his
gear may not be out of the way; but to fix the machine for more or less
power alternately as hills and levels are met with is, in the light of
my experience, more tiresome than the necessary variation in the effort
of the man.