Page:Motors and motor-driving (1902).djvu/241

Rh desirable. A frame which has some diagonal stays or parts which act as diagonals is very desirable, though few car frames are so made. Diagonal staying prevents some of the injurious racking stresses, and with the longer distance between front and hind wheels now common there can be little difficulty about their use.

Wheel-base.—In the earlier designs of cars the wheel-base that is the distance between the axles was made short in accordance with ordinary carriage-makers' practice. This reduced the length of road covered, but its disadvantages are serious. A long wheel-base is desirable not only for steady running on straight roads, but for the greater security it gives in running on greasy and bad-surface roads, and on curves and downhill. It also gives greater certainty and definiteness to the steering. A very short wheel-base car is difficult to keep in a steady line, and it will easily turn quite round when side-slipping occurs. The farther the axles are apart the greater is the resistance to side movements and side-slip, the steadier and easier the steering. Long wheel-base lengthens the frame and makes extra care necessary in securing sufficient strength, partly because of the greater length unsupported between the front and back springs.

Springs.—The length and the number of plates in springs of the motor-cars of similar weight and power by different makers vary very much, and without much reason. More attention would no doubt be paid to this point were it not that the general use of pneumatic tyres hides imperfection in this respect as well as others. Springs of insufficient strength, and particularly of the front or steering wheels, are a source of great danger, and frequent careful examination should be given them; but springs are not necessarily of insufficient strength because they appear to be light. Short springs are generally undesirable, as being more liable to break with an ordinary range of flexure than the longer spring, the bending per unit of length being greater. Stiffness in short springs is avoided by lightness, which is likely to lead to breakage, especially when the hole for the pin through the centre is not made as p