372 REPORT — 1903. 



He urges that the Committee take steps to ascertain — 



1 . The maximum ' useful ' width of tyre for heavy traffic oil average 

 roads. 



2. The ' limit ' of weight on each wheel (for various classes of road) up 

 to which road resistance increases in direct approximate proportion to 

 the increase of weight on each wheel. 



3. The rate of increased road resistance when that limit is moderately 

 exceeded. 



III. — Papers read at the International Congress on Antomohilism, 



Paris, 1903. 



By permission of the British Association Committee a paper was read 

 at the Congress by Professor Hele-Shaw on the work which has been 

 carried out during the past year. 



He gave a description of the British Association dynamometer, 

 recounting the reasons why it was decided to adopt the one-wheel trailer, 

 and then gave a rcsnvic of tlie experiments which have been made. The 

 paper was illustrated by photographs and diagrams. 



Abstract of Paper by M. Gerard Lavergne, on Tractional Resistance: — Tractive 

 Effort~SpriiH/s — Pffcct of Nature of Tyre — Air Resistance — Poiver required 

 by Antomohiles. 



Tractive Effort. 



In his paper M. Lavergne referred to the Report of this Committee 

 read at the Belfast meeeting last year, and gave some particulars of 

 similar experiments made in America. Ho stated that Professor Ira O. 

 Baker, of the Illinois tState University, is of opinion that the axle friction 

 is independent of the speed, but varies inversely as the square root of the 

 load supported. Wliere the vehicles carried only a light load, the 

 coetiicient of friction was about 002 ; heavy loads gave an average of not 

 more than 001 5, while with exceptionally heavy loads this coefficient fell 

 as low as 0-012. These values assume efficient lubrication ; with in- 

 different lubrication they rose to as much as six times the amount. 



Concerning rolling friction Professor Baker believes that the resist- 

 ance varies inversely as the square root of the diameter of the wheels. 



The values above given for axle friction i litter somewhat from those 

 given by M. Forestier, who gives 0-10 for an ordinary bearing lubricated 

 with cart grease, 0-01 with patent axle-lwx lubricated with oil, O'OOS with 

 lubricated ball-bearings, 0002r) with the lubricated ' Philippe ' bearings 

 (which last-named are ball-bearings having small balls between the larger 

 ones, thus obviating friction amongst the latter and ensuring an equal 

 distribution of pressure upon all the balls). 



To thoroughly understand the difference between these sets of figures 

 it would be necessary to know the exact conditions of lubrication and the 

 nature of the bearings employed by Professor Baker. 



M. Lavergne does not consider that the differences shown are very 

 surprising, as we know that the coefficient mentioned by M. Forestier 

 has reference to a patent journal, the wheel revolving evenly in a plane, 

 without lateral jerks, whilst a wheel revolving in less favourable condi- 

 tions — as, for instance, on a rough paved road — would give a higher figure. 

 The most important fact shown by Professor Baker's experiment is that 

 the friction of the journal varies with the load upon the axle. 



