We have an upright frame provided with two cross pieces, b c and e f, a saddle at a, rests for the feet at b and c, and a roller, d, placed under e f. Sitting upon the saddle a, I was totally unable to move the roller d by any pressure upon either pedal b or c. The above I consider conclusive proof and the result unbiased by prejudice in trying the experiment, because I tested the matter before looking carefully into Mr. Stoney’s article and becoming convinced that in this he is right. The laws applying to internal forces or forces within a system are very often disregarded, and especially are internal confounded with external forces, as in this case. In any machine where the rider throws his weight on and vertically over the pedal, the formula given for the side-slip does represent a force acting to swing the machine out of perpendicular and to cause it to “wabble,” as Mr. Stoney calls it, but not to slip it on the surface of the roadway, as many would suppose. The rider rarely, however, throws his weight directly over the pedal sideways, as he does in raising upon it in a forward direction in order to get over the work. The lateral or wabbling strain in a cycle of the foot-pressure in one direction is balanced by the pull on the handle-bars and pressure of the leg against the saddle. The only feasible connection the formula theory can possibly have in this matter is that the thrust on the pedal is so sharp and violent that the inertia of the man and other heavy parts of the system are not perceptibly affected sideways; hence we might get an action against the slight weight in the lower part of the wheel. I cannot, however, detect any slipping action of this or any other kind in the roller experiment.
The futility of an effort to slip the machine sideways by a force upon the crank might be illustrated in this manner: Suppose the drive-wheel of an Ordinary is made rigidly fast to the front fork. Now, it would be impossible for the rider to slip the tire on the road-bed by pressure on the crank, as he can when the wheel is free to revolve in its bearings, no matter how long the crank may be; if the rider leans out over it, the machine could be rolled forward, but not slipped on the surface. Loosen the wheel so that it can revolve as usual, then it can be slipped, as every good rider well knows. Suppose now that the drive-wheel is rigidly fixed in the frame of the bicycle so far as any lateral motion is concerned, and the wheel cannot revolve within the system about any horizontal line at right angles to the axle of the wheel, as it would have to do in order to make it slip in the manner it would in the other case, then it is easy to see that the machine and rider might be rolled over sideways by throwing the weight on one crank; but it cannot be slipped: the only slipping that can occur is when the machine is allowed to get out of perpendicular, but the angle at which it would begin to slip would be the same regardless of width of tread. If the wide tread does affect the slipping, it is the result of other forces than those generally supposed.
I do not believe that the extra weight on the drive-wheel will relieve the trouble. I have a Rover pattern machine in which the weight is almost entirely in the rear, and I can conscientiously aver that it is the worst slipper I was ever on. Now, this is in spite of the fact that there was every reason to believe, and to desire, that it should not slip at all.
One of the Cyclist correspondents mentions the American Star, and justly says that it does not slip; yet that fact could be explained by our formula, since it is a tall machine with narrow tread. I cannot see, after all, that any theory of wide or narrow tread could be applied to the Rover type, even if it were found to be valid in other cases, because there seems to be complaint, and I have found it so in practice, that the machine will slip more than the old Ordinary, even when not pushing on the cranks at all. It seems to slip worse than any other in making a curve or in descending hills and upon cobble-stones, whether there is any pressure on the crank or not. This will apply against the Cyclist idea that the slanting fork breeds the mischief, since, if it slips in running a straight line, the slant of the fork could not possibly have anything to do with it.
In answer to the idea advanced that the fault is due to the mere size of the wheel,—that a large one has more surface exposed to contact, etc., and will hold better,—the writer has noticed very little difference in his thirty-eight-inch narrow-tread front-driving pattern as compared with a fifty-two-inch Ordinary; if there is any difference caused by the size of the wheel, this fourteen inches ought to have shown itself more than it did.
If the small wheel in a bicycle is a cause for slipping, we could naturally ask why it does not show itself more in the rear wheel of the Ordinary. It may be said, in answer to this, that there is but little weight on it, and that, not being a driver, whatever capers it might choose to cut are ignored by its regal, imperturbable leader; hence, if the rear wheel slips, it is immediately drawn up in line again. Another plea is that the lack of weight on the front wheel of the Safety makes it slip, and then it carries the rear wheel with it. To the last I can simply reply, as I would to the Cyclist’s notion of the slanting fork, that it is the rear wheel which slips first, last, and all the time, or else a large majority of riders are very much misled, and really can’t tell what is going on under them. Certainly we must say that if appearances and sensations of the riders are worth anything, the doctrine of the front wheel slipping first must go to the wall and carry several ingenious solutions with it. Still another bright speculation is, that the unusual bumping of the front wheel holds it back, and the rear pushing on, for the nonce, cannot go forward, hence it must go sideways.
If we admit that the American Star does not slip, then the theories of small weight on the front wheel, the slanting fork, and front bumper must all go for naught. There are some other qualifications, however, which would modify or exclude the Star as a reference. The fork is slanting to a greater extent than in any other machine, but the small front steerer is swung from a point directly above the centre, which, it is said, gives the wheel a better chance to caster. To our ingenious front-bumper friend, I would also suggest the trial of a first-class anti-vibrator to the fork, which will let it spring back a good way.
And again, it has been stated, in regard to the Rover slip, that the large rear wheel swings from side to side, or wabbles, humorously likened by some to the wagging of a duck’s tail. This feeling of disturbance in the rear part of the machine is felt in the Ordinary when supplied with the large rear wheel advocated by some, and it may have something to do with the slip, though it is hardly possible that it would in the well-built, steady machines of the present time.
As to the high-up saddle or centre of gravity, true, an inch side-slip at the ground, of a machine with a low-down centre of gravity, will cause it to assume a greater slant or angle from the vertical than a higher; hence our friend could well say that when the Safety starts to slip it will be more certain to go on down. It is to be noted, however, as against this idea, that other machines with low-down saddles do not slip.
Taking all the theories and experiences, pro and con, into consideration, I am inclined to believe that no one cause can account for the entire difficulty; it is probably a combination of smaller elements partly belonging to several of the theories advanced. The elements which have been most strongly urged are, first, the driver being small; second, the driver being in the rear; third, the weight being in the rear; fourth, the work being done between the wheels. All these seem to work to the same end. Again, any drive-wheel will slip worse than a non-driver, since a sliding force in any direction will tend to loosen the hold of the rubber tire from the surface of the road more than any rolling action. A short slide from a stone is felt more when the weight is upon the wheel, and the drop in rolling off so distinctly felt in connection with the small wheel is much sharper than a similar action of a large one. A rider can certainly manage himself better and more surely when he drives, steers, and leads with the same wheel and has his weight upon it. This is what he does on the Ordinary and just what he does not do on the rear-driver.