OBSERVATIONS ON THE SIX DAYS' TRIAL

OBSERVATIONS ON THE SIX DAYS’ TRIAL.

Extracts from the Official Report on the Results of the Recent International Test.

TN their introduction to the official report, the A.C.U. I stewards state that, in their opinion, the course

as a whole was more strenuous than in any previous trial of the series, and that although the number of retirements was considerably less, the route was well chosen and a severe test for both the vehicles and their drivers. They record the fact that the condition of the machines which finished was generally much better than in previous years, and that the standard of driving also showed a considerable improvement. A great deal of tyre trouble was experienced, and it would certainly appear that the tyres are the least reliable part of the modern motor cycle.

From a Technical Point of View.

The salient features of the report by the Chief Technical Observer, Prof. A. M. Low, M.I.A.E., are as follows :

Although the total distance covered was approximately 800 miles, that distance was probably equivalent to 5,000 miles of average touring. The surfaces encountered were rough, and the average hill gradient was approximately 40 per cent. higher than would have been encountered on ordinary main roads. The road holding capabilities and frame strength of the modern machine were demonstrated by the ability of over 70 per cent, to complete the course without damage to frames or working cycle parts. On account of the tortuous nature of the route the riding conditions subjected every control and accessory to a searching test, which the high standard of driving maintained by the riders could not counteract.

Few Departures from Standard.

Although the use of standard machines was not called for by the regulations, examples of departure from commercial design and equipment were in the minority. There was a noticeable tendency towards the lowering of the centre of gravity by improved methods of cradling the engine and by the use of duplex frames, with a general improvement in the necessary degree of rigidity. In most cases frames were so designed that flexing could not produce an increase of vibration or lack of steadiness. It is worthy of mention and was observable upon several occasions that road holding capabilities were not always secured by low engine position. The ground

clearances of some machines were rather low for use over rough country, but the adoption of a unit system of construction is providing a satisfactory compromise.

Engine Details.

It is only possible to indicate briefly the many technical details in which engines have improved during the year. More care would appear to have been devoted to the arrangement of cooling fins. That an engine may be capable of operation without loss of power for long periods on low gear was amply demonstrated, and it was most noticeable that those engines which could maintain a low temperature were more reliable, clean, and silent. These qualities are of the utmost importance, and it is unfortunate that such minor points of design as the provision of extra heavy engine lugs, the enclosure of sprockets, and overhead gear lubrication, should have been largely confined to the heavier classes. Proper enclosure of all working parts can undoubtedly be achieved, and with the increase of power-weight ratio some slight consequent sacrifice of efficiency is of less importance than general comfort. Lubrication systems are now satisfactory, but more positive methods for transmission lubrication are becoming desirable on all machines. The increasing popularity of the motor cycle amongst all classes or unskilled riders, renders it necessary that direct control of lubrication should be removed from the hands of the driver.

Silence.

Although there is a general improvement in the degree of silence of most motor cycles, increased engine efficiency renders this quality more difficult to attain. As has been consistently urged in these reports, it is essential for a further improvement in the degree of silence to be accomplished, only the relatively small number of motor cycles at present on the road has rendered their noise in any way tolerable. Mechanical noise has been reduced. All exposed working parts lead to noise, which is objectionable, unnecessary and inefficient. Much more attention might be given to the incorporation of silencers as a normal part of the engine design, as it is practicable to reduce the silencer capacity to convenient limits by breaking the wave frontage of the exhaust discharge.