AuGusx 1, 1911. 



THE INDIA RUBBER WORLD 



443 



ACCURATE TESTS OF TIRE EFFICIENCY. 



IN order to accurately define any strain or burden, tests of 

 uniform nature form an indispensable condition. These, 

 to be of utility, should as far as possible reproduce the in- 

 fluences to which the objects tested are subject in actual use. 

 The value of such tests is enhanced when the comparative effects 

 of an identical cause is shown with 

 reference to various forms of ma- 

 terial. 



The importance of this principle 

 as to the resistance of tires for 

 trucks, has been demonstrated by 

 The Michelin Tire Company. Solid 

 tires, they claim, do not seem to 

 have given the results expected 

 from them with commercial vehicles, 

 there having been a double sacrifice 

 of speed and lightness. An in- 

 crease of 5 per cent, in weight, in- 

 stead of reducing the wear, increas- 

 es it, it is stated, by about 14 per 

 cent. It is added, that while solid 

 tires have certain advantages in the 

 reduction of noise, they are hardly 

 more satisfactory than ordinary 

 iron tires in reducing vibration. If 

 nothing can be gained in speed, 

 horse traction, it is urged, becomes 

 far more economical. 



In the belief founded upon 

 the above facts, that car manu- 

 facturers can get no satisfaction 

 from solid tires, the Michelin com- 

 pany has refused to undertake 



their manufacture. This refusal was prompted by the results 

 of numerous experiments, conducted for the special purpose of 

 proving scientifically that solid rubber is incapable of allaying 

 vibration. Out of fifty experiments made, typical results 

 are quoted in re- 

 spect to eight, two 

 of these results be- 

 ing reproduced in 

 Figs. 2 and 3. 



A wheel (A fig. 

 1) loaded with a 

 weight of half a 

 ton, fitted first with 

 a solid rubber tire 

 2.46 inches tliick 

 and tlien with a 

 pneumatic tire, was 

 set revolving at a 

 speed of 16 miles an 

 hour on a fly-wheel 

 (B). The very 



broad rim of this 

 fly-wheel was ar- 

 ranged to accom- 

 modate various ob- 

 jects which would 



give it an uneven surface. The displacements of tlie hub of the 

 wheel (A) were registered by a pen attachment, which traced 

 the exact height of each rise and fall on a cylinder (C) revolving 

 at uniform speed. In this way the fly-wheel exactly represented 

 the uneven surface of a road, while the wheel (A) played the 

 part of a car wheel. A first examination of the curves shows 

 that in each instance the pen has traced the constant vibrations. 



Ovc 



uliich in tlie case of tlie solid tire measure from 0.23 to 0.27 

 inch, even when no object has been placed on the fly-wheel, 

 while they register only 0.02 inch with the air-filled tire. These 

 tracings came entirely from the fly-wheel and give some idea 

 of the work of solid as compared witli air-filled tires. 



RESULT WITH SOLID TIRE. (fIG. 2.) 



long half oval obstacle, 1.17 inches high, the solid 

 tire raises the wheel 2.30 inches. 

 kksult with pneum.atic tire, 

 (fig. 3.) 

 Over a long half oval obstacle, 

 1.17 inches high, the pneumatic tire 

 raises the wheel 0.44 inch. 



These diagrams, it is added, in- 

 dicate that the pneumatic tire ab- 

 sorbs tlie obstacle, the height to 

 which the hub is raised being less 

 than the height of the obstacle it- 

 self, while the solid rubber tire 

 does not prevent the wheel from 

 rising higher than the obstacle. 



TWIN TIRES. 



The natural advantages thus 

 connected with pneumatic tires are 

 accentuated by their use in the form 

 of 'Twin Tires," when two or 

 sometimes three pneumatic tires 

 are placed side by side on the same 

 wheel ; the pneumatic suspension 

 thus afforded ensuring speed with 

 comfort and increasing the weight- 

 carrying power. 



Fig. 1. Device for Registering Vibr.\tions of Tires 



Fig. 



Record of Vibr.xtion; 

 Tires. 



OF Solid 



In line with the above views, are 

 the opinions of ex-Lieut. Joseph A. 

 Webber, of the Boston Fire Department, in his paper read at the 

 annual meeting of the New York State Fire Chiefs. He con- 

 sidered that the choice between solid and peumatic tires for use 

 on fire engines should be decided by tlie wciglit of the car, which 



should be kept 

 below 3,000 11)S. 

 On such cars the 

 dual system of 

 pneumatic tires 

 had proved very 

 successful. Above 

 the weight named 

 either the dual 

 pneumatic system 

 should be used on 

 the rear or else 

 cushion or solid 

 tires. This rec- 

 ommendation o f 

 single and double 

 pneumatic tires 

 specially applied to 

 "first aid" cars, 

 such tires being 

 indispensable, at a 

 speed exceeding 18 

 of dual character. 



Fin. 3. 



Record of Vibrations of Pneu- 

 matic Tires. 



miles an hour ; those in the rear being 



The English are said to be using air instead of hydraulic 

 presses. In lieu of a ram a cylinder is made like a huge piece 

 of suction hose of fabric and rubber-armored and collapsible, the 

 pressure being secured by pumping air into this cylinder. 



