THE INDIA RUBBER WORLD 



Motor -Truck Efficiency as Related to Solid and Pneumatic Tires. 



By S. V. Norto 



THERE are two ways of viewing tlie problem of pneumatics 

 on motor trucks. One is to consider it in the light of 

 future changes and improvements in truck design which 

 may become possible through the use of air tires, and the other 

 is 10 look at it from the position of the present-day operator 

 who wants to know whether he can safely avail himself of the 

 advantages claimed for them. In the one case it is Hke throwing 

 the spotlight on the theoretical side of truck design to see what 

 it may be like ten or fifteen years from now. In the other it is 

 like asking an experienced business man or a banker whether, 

 by making certain investments, you can save or earn some money. 

 While future improvements in truck design are highly impor- 

 tant, they are of perhaps more interest to the designing engineer 

 than to the operator of a truck built for present-day service. 

 Hence, I have sought information from sources which would 

 throw light on the problem of whether trucks as built to-day 

 should use solid or pneumatic tires. The results of a nation-wide 

 canvass of truck manufacturers, truck salesmen, and operators 

 as well as tire dealers and those on whose local service the 

 truck depends are set forth in this article. 



WHY PNEUMATICS ARE USED. 

 At present, the accepted field for pneumatics appears to be on 

 trucks up to 1^ tons capacity, and that for solids on trucks of 

 3}4 tons or over. Between these two capacities the choice should 

 be made only after a careful study of the important factors in- 

 volved in each case. In order to ascertain why pneumatics were 

 used, I asked several hundred motor-truck and tire salesmen as 

 well as truck operators throughout the United States to state 

 what they considered was their chief advantage in this debatable 

 field. The following reasons were given, with the percentage of 

 replies for each : 



Advantage. Percent. 



Greater traction 40 



More cushioning 28 



Higher speed 21 



Lower repair bills 5 



Saving in gasoline 4 



More work possible 2 



100 



Other reasons were given for the use of pneumatic tires but 

 they were thought to be of secondary importance. They were : 

 less breakage of load, reduced fatigue of driver, less depreciation 

 of truck, reduced depreciation of roads, adaptability of truck to 

 farm use. lighter weight trucks possible, and increased earning 

 power. 



DEPENDABIX INFORMATION LACKING. 



The replies to my questions show a surprising lack of depend- 

 able information, as the following quotations will indicate : 



"This question is one that comes up very frequently," said a 

 large Eastern city truck agent, "and a complete discussion of the 

 merits of the two types would be advantageous to us." 



A tire salesman who has made many inquiries writes, "Some 

 operators who have kept fairly complete records on gas, oil, and 

 repairs say they have nothing they consider convincing as to com- 

 parative savings effected by pneumatics." 



An exceptionally well-informed publisher in Chicago says, 

 "Operators of large size pneumatics haven't had them long enough 

 to decide as to their relative value. Moreover, it is surprising 

 to find how few operators keep accurate cost records." 



A Seattle tire agent says, "Operators using pneumatics have 

 been entirely sold from a theoretical standpoint due to the mis- 



'The B. F. Goodrich Rubber Company, Akron, Ohio. 



sionary work of the advertiser, with no analysis of conditions." 

 These remarks and many others of a similar nature indicate 

 that a careful study should be made before deciding which type 

 of tire should be used. The factors bearing on the problem may 

 be divided into : (1) the engineering aspects involved; (2) the 

 practical operating features encountered by the driver, and (3) 

 the features of tire service in the community in which the truck 

 is running. 



In taking up the engineering aspects I speak frankly as a lay- 

 man and not as a truck engineer. 



DISADVANTAGES IN CHANGING TIRE EQUIPMENT. 



Before changing tire equipment from solids to pneumatics the 

 operator should realize that, in order to gain certain possible 

 advantages, he must face other definite disadvantages. In the 

 first place he will have to cut down the wheels of the truck, 

 which will prove a considerable item of expense. Moreover, 

 proper allowance must be made for both body and fender clear- 

 ance. It should also be remembered that the larger sectional 

 diameter of the pneumatic tires will affect the steering clearance, 

 and that the truck will be unable to turn in as short a radius as it 

 did on solid tires. 



-As the larger diameter of pneumatic tires will affect the gear 

 reduction, if substituted for soHds, the mechanical ability of the 

 truck will be affected. If the change is made, will the truck be 

 able to "make the grade?" Will it materially affect the pay- 

 load capacity of the truck? Will it reduce the ability to operate 

 trailers? What will the effect be on the engine? 



The increased maximuin speed due to the larger diameter of 

 the pneumatic tires will be relatively slight provided the engine 

 is governed to run at the same speed as formerly. If the change 

 is made to get more speed out of the machine, the gear ratio 

 must be reduced, which reduces the ability of the truck, or the 

 governor must be opened and the engine speed increased. There 

 is danger here, however, as speed induces extra vibration, joints 

 begin to loosen, and before long the engine may be literally racked 

 to pieces. 



Additional speed calls for greater braking ability. Brakes de- 

 signed for slower speeds but used under more severe circum- 

 stances will inevitably require more frequent renewal. The ques- 

 tion for the truck owner to decide before making the change is 

 whether the truck can be equipped with brakes having much 

 larger capacity, and if not whether it will pay to take the chance. 



Of no less moment than the features mentioned above, so far 

 as the dependability of the truck is concerned, is the question of 

 air supply. Since pneumatic tires require from 90 to 160 pounds 



