286 EXPERIMENT STATIOlSr EECOKD. [Vol.43 



the motor-cooling system, carburetion and carburetors, ignition systems, gov- 

 ernors and speed controlling devices, the clutch and transmisssiou, universal 

 joint and propeller shaft, the differential, the final drive, front and 4-wheel 

 drives, motor-truck brakes, the front axle, steering gears and fundamental 

 principles of steering mechanisms, motor-truck frames, power-plant mount- 

 ings, springs and spring suspensions, the fuel-supply system, control, and mufOer, 

 motor-truck wheels, motor-truck tires and rims, and electric lighting and start- 

 ing on commei'cial vehicles. 



Relation of solid and pneumatic tires to motor-truck efficiency, S. V. 

 NoKTON (Jour. Soc. Automotive Enf/in., 6 (1920), No. 4, pp. 208-2/4).— The 

 author presents and analyzes considerable data on the use of solid and pneu- 

 matic tires on motor trucks, and suggests that in the present state of develop- 

 ment the field for each type of tire may be separated into three classifications, 

 namely, the imperative field, the economic field, and the optional field. 



" The factors that would bring a truck within the first classification for solid 

 tires are (1) if it travels over pavements not necessarily good, but having a 

 reasonably hard road surface to provide traction, (2) if the delivery nmst 

 positively reach its destination without fail at a promised time, (3) if the 

 delivery must be made regularly on a given schedule in which the regularity 

 is a more important factor than either speed or cost of delivery, and (4) if it 

 carries heavy loads with frequent overloads beyond the rated capacity of the 

 tii'es. Similarly the factors that would bring a truck within the imperative 

 field for pneumatic tires are some combination of the following: (1) If it 

 travels over surfaces on which traction can not be obtained by solid tires, and 

 when the need for traction is such as to outweight the item of cost, (2) if the 

 need for speed of delivery is more important than its cost, and (3) if the mer- 

 chandise carried is so perishalile or fragile that it must be protected from road 

 shocks, even at high cost. 



" The factors that would bring a truck within the economic field for solid 

 tires are (1) short hauls in cities where speed is relatively unimportant, (2) 

 heavy loads with a tendency to overload, (8) traffic congestion which reduces 

 average speed, (4) loading and unloading delays, and (5) need for low delivery 

 cost. Similarly the factors that would bring a truck within the economic field 

 for pneumatic tires are (1) road conditions which will not prematurely destroy 

 the tires, (2) long hauls, (3) high average speed, (4) relatively light loads 

 with no overloads, (5) good tire-service conditions, and (6) low cost sub- 

 ordinated to quick service." 



Tests reveal relative values of pneumatic and solid tires, A. F. Masuky 

 (Engin. News-Rec, 84 (1920), No. U, pp. 66S-670, figs. 2).— Tests of different 

 types and sizes of motor trucks subjected to different kinds and amounts of 

 shock in excess of probable service shock, and observations of the effect of road 

 impact on spring and tire equipment, as well -as the effect of unsprung weight 

 upon road impact, are reported. The trucks were operated at speeds of from 

 15 to 18 miles per hour. 



The conclusions di-awn are that the impact of a truck striking the ground 

 after bounding over an obstruction is increased approximately as the square of 

 the speed and as the weight, but inversely as the resiliency of the springs and 

 tires. A further conclusion is drawTi that a 7i-ton truck on pneumatic tires 

 will do less damage to a road than a 5-ton truck on solid tires operating over 

 the same route and at the same speeds. 



Thirteen years of tractor development work, J. H. McCollough, jr. 

 (Agrimotor, 2 (1919), No. 12. pp. 5-10, figs. 12). — An account is given of the 

 trials encountered for 13 years in tractor development. 



