CHAPTER XIII.
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 connectedtherewith. 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 amplitudethrough 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 bemore 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 youhave 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.