Home >> A-treatise-on-roads-and-pavements-1903 >> Sheet Asphalt to Work Of Maintenance Gravel >> Super Elevation_P1

Super-Elevation

track, banking, speed, mile, velocity and wheel

Page: 1 2

SUPER-ELEVATION. If a man attempts to ride a bicycle around a curve, the rider and the wheel must lean inward to bal ance the centrifugal force; and if the surface of the track is level transversely, the wheel will not be perpendicular to the surface and will tend to run in a curve, which may have a greater or a less radius than that of the track, and consequently increased attention and effort will be required in guiding the wheel. Further, if the in clination of the wheel is considerable, there is a tendency for it to slip on the surface. If the outside of the track is elevated on the curves so that the wheel is always perpendicular to the surface, then the wheel has a tendency to continue in a straight line, and only a minimum effort is required in guiding; and consequently the whole attention may be given to securing speed.

Equation (2), page 290, shows the relation that should exist be tween the super-elevation or banking, and the speed and the radius of the curve.* . Having the design of the ground plan, the radius of curvature will be known; but since the banking depends upon the velocity, the track must be designed for some particular speed. In deciding upon the velocity to be adopted, it is necessary to deter mine whether the maximum or mean velocity shall be employed. If the track is to be used chiefly for races ridden against time, the maximum velocity should be adopted; but if the track is to be used chiefly for miscellaneous racing, the super-elevation should be de signed for the average velocity. To determine the practice in this respect, the banking of the more noted tracks will be investigated.

In the early tracks high banking seems to have been avoided for two reasons: first, because of a baseless prejudice against it; and second, because many of the races ridden in competition were so slow as not to require high banking. Recently the speed has in creased, and motor pacing has become prevalent; and hence higher banking is more common.

The curves of the Louisville and of the Waltham tracks have a banking such that at a speed of a mile in 2 minutes and 53 seconds the wheel is normal to the surface. The super-elevation of the

Manhattan track was computed for a speed of a mile in 2 minutes and 32 seconds. Fig. 166, page 635, shows the banking of this track, expressed in degrees with the horizontal. The curves of the Racine track, which have the same radii as the Manhattan track, are banked for a speed of a mile in 2 minutes and 26 seconds—a trifle higher speed than for the Manhattan track. The banking of the Garfield Park track was computed for a speed of a mile in 2 minutes. The angles of the super-elevation of this track are shown in Fig. 167, page 636. It is stated that Johnson in 18% on this track. in making a world's record of a mile in 1 minute and 49 seconds, leaned slightly toward the inside of the track. Since the banking was figured for a 2-minute gait. the rider going at a speed of 1 minute and 49 seconds would be compelled to lean toward the center of the track to bal ance the centrifugal force, which shows in a crude way the agree ment of theory and practice.

Many short wooden tracks have been constructed with very high banking. Notable among these is a sixth of a mile track opened in Springfield. Mass., in July. 1900. The curves (appar ently semicircles) are banked for a speed of a mile in 1 minute and 20 seconds, the inclination of the surface on the curves being 48` and on the tangents 30°—the steepest track known. This track is pronounced by racing men to be the fastest in the world.

A summary of the speeds for which the various tracks were con structed is shown in Table 68.

It is obvious that the choice of the velocity to be used in computing the super-elevation depends upon experience and judg ment, and not upon mathematical relations. If the track is to be used for motor racing without competition, the velocity should be high, perhaps 66 feet per second, or a mile in 1 minute and 20 sec onds; but if the track is to be used for races of competition without motor pacing, this velocity should be about 44 feet per second, or a mile in 2 minutes.

Page: 1 2