Ascertaining Legal Overhang
Page 49
If you've noticed an error in this article please click here to report it so we can fix it.
ONE of the problems which has proved troublesome to vehicle operators, purchasers and makers has been that of legal permissible overhang. With the aid of the tables accompanying this article any question concerning this dimension for any particular chassis can be solved in a very short space of time.
First it is necessary to grasp the meaning of the term "overall length." This means the length of the vehicle, exclusive of the starting handle and hood (if any), when down. The maximum overhang permissible under the Construction and Use Regulations is 7-24 of the overall length.
The following points are important in measuring the overhang :—Dealing first with conventional fourwheelers with a front steering axle, the overhang (dimension B in the appropriate illustration) is measured horizontally from the centre point of the rear axle to a vertical line which denotes the rearmost limit of vehicle length, exclusive of the hood (if any).
Next, in the case of a rigid six-wheeler the first step is to measure the distance between the hub-cap centres of the axles of the bogie and to note the midway point along that line. The overhang is not, however, measured from here, but from a point 4 ins, to the rear thereof. This is clearly set forth in one of the accompanying diagrams.
In each of the two illustrations the term "dimension A" equals the 17-24 portion of the vehicle, whilst dimension B equals the overhang-7-24 of the overall length.
Having thus elucidated the meaning of the term • "overhang," the next question to consider is the maximum amount permissible for any particular chassis or vehicle. By the use of the two tables published herewith the problem can be solved in a few moments. Table X gives the overhang in feet and inches for any chassis, the 17-24 portion of which is an exact number of feet. Table Y is used in conjunction with table X, and gives the overhang in inches for each inch in excess of the number of feet in dimension A. Thus tables X and Y together can be used to give the maximum dimension B, or overhang, for any vehicle.
Let us take an example to illustrate the method of working. Assume that it is desired to find dimension B in respect of a cha;sis having a dimension A of 13 ft. 7 ins. Turning to table X we find that 13 ft. (A) has a corresponding dimension B of 5 ft. 4.23 ins. In table Y 7 ins. (A) has a corresponding dimension B of 2.88 ins. Adding together the results we find that the maximum permissible overhang of the vehicle in question may be 5 ft. 7.11 ins.
These tables operate correctly whether the chassis be a four-wheeler or a rigid six-wheeler ; in the latter case, however, it is necessary to remember the difference in the method of measuring dimension A.