Cycling art, energy, and locomotion

by Robert P. Scott

No doubt the old Kangaroo, as bad a failure as it was, led us up to endure more complacently the rear-driver in respect to the sprocket-chain; yet in no type of machine could the subject have been brought to our notice in a worse form. The tricycles using a single chain did away with one of the great evils which appertain to this system as found in the Kangaroo, in which we have two chains working entirely independently. The evil of such an arrangement is easily seen: no old Kangaroo rider, or rider of any other double-chain device, is ignorant of the annoyance caused by reversing the slack in each at every half-revolution of the pedal. Keep the chains ever so tight, this slack will be felt as the pedal crosses the dead-centre line at the top and the bottom. In spite of all this, some reputable makers persist in constructing rear-drivers having the double chain, and as a matter of course justly fail to meet with much approval from the riders thereof.

A word in regard to the nature of sprocket-wheels and chain. It is perhaps not generally understood how important it is that they should be well made, with especial view to resist stretching and alteration of pitch, any tightening device, no matter how deftly made, being an inconsistency in mechanics. To be sure, the spreading of the wheel-centres cannot do much harm, and it saves some annoyance, but it does not cure the real evil, nor is it any better to take a link out; it is the length of each and every link that is wrong, and it can only be cured by either changing each link or by altering the sizes of the sprocket wheels.

Two gear-wheels cannot run properly together unless they are proportional in size to the number of teeth. Now, the stretching of a sprocket-chain alters the pitch in a manner similar to that of retaining the same number of teeth in each of two intermeshing wheels, and then altering the size of one. A sprocket-chain acts substantially as an idle wheel; when it stretches we have, as it were, this idle wheel made larger while the size of the others and the number of teeth in each remain the same. Increasing the distance between the centres does not affect the size of the wheels, and when a sprocket-chain stretches or becomes longer by wear the wheels should either be larger or else the number of teeth diminished. It is a general idea among mechanics that chain gearing is about the most undesirable of all means of transmitting power we have. This is perhaps an exaggeration, and I think the cycle art has proved it to be so; but the idea no doubt is fostered by this constant tendency of the chain to stretch, and when this stretch takes place a very considerable amount of friction must result. There is another annoyance felt by patrons of the small wheel: the chains being low down and well oiled, as they should be, especially if once they become stretched, have a superlative capacity for accumulating and holding dirt, causing a grinding second only to that of a finely-set quartz-crusher. This feature is not so much to be deplored if the dirt can be kept out of the chain-link bearings, since it is not the wear of the link against the tooth of the wheel, but that within the link, which makes it longer, alters the pitch, and causes great friction.

We shall, however, have to accept this chain arrangement for the present in Safeties, as it cannot be helped. Some ingenious inventor will no doubt ere long come to our assistance; but until then we can tolerate it with a good grace, since it is a necessary concomitant of so valuable an acquisition to our assortment of mounts.

There is apparently little difference in the construction of the crank Rover Safeties, yet there is more than a cursory glance would lead us to suspect. To begin with, there is quite a variation in the slant of the neck or front fork, many makers giving a considerable curve to the fork, thus throwing the neck much straighter up. Then we have the telescope head, where the front fork revolves inside the tubular front extension of the main frame; and lastly, the swing-joint or Stanley head.

No very startling difference in the durability of these two heads has as yet developed itself. The telescope is often hung in balls, which makes it work as freely as the Stanley, if not more so; it has also a little advantage in appearance; still, a large majority of the makers have adopted the Stanley, probably because it is a little cheaper and quite as efficient. There seems to be less disadvantage in the slant of the front fork than might have been expected. According to an old theory in the Ordinary, the more nearly vertical the head, the less “sensitive” the steering; but experience demonstrates that by practice all machines are so easily steered that the point is really not so vital.

The original Rover machine as put upon the market has everything combined to give it a full slant in the neck; that is to say, it has a large thirty-six-inch front wheel and no curve to the fork, while in other machines of the same general pattern a thirty-inch front wheel is used with considerable curve to the fork, which taken together make the neck almost vertical; riders, however, are equally satisfied with either style.

It will be well to notice here that though I speak of the curve of the fork in relation to steering, it really has necessarily nothing to do with it, since a perfectly straight fork could have a more vertical head bearing than one much curved.

The slant of the pivotal line is the important feature, and this may be varied in either by bending the fork or, in the Stanley, by setting back the lower bearing.

The four drawings below show necks of equal slant and considerable variation in the curve or shape of the forks.