ELIMINATING THE SKID.

Auckland Star, Volume LVI, Issue 184, 6 August 1925, Page 13 (Supplement)

ELIMINATING THE SKID.

PRESSURE INFLATION. VARYING THE AMOUNTS. BALLOONS ON LIGHT CABS. Experiments recently made with a well-known light car equipped with 715 mm- by 115 mm. low-pressure tyres are interesting to motorists whose cars are equipped with balloon tyres. The mileage covered with these tyres was close on 6000, and the treads are absolutely untouched to all appearances, bo that as

k. regards durability the results are perfectly satisfactory, states lan English writer. Riding comfort is also very good, particularly on the type of road y surface which abounds in. numbers - of small pot-holes, or, for instance, granite ' setts in bad condition. The car being '' extremely light, however (the total i ■ weight with tanks filled, is slightly over ii llcwt), it does exhibit a tendency to , „ pitch fore and aft when negotiating rough surfaces. No shock absorbers are ' ' fitted. i M Another somewhat unpleasant feature 11 which must certainly be attributed to ( _ the tyres —at any rate, in some measure —is the liability to sliding on slippery 1 * surfaces such as wet macadam. The < ■ word sliding is used advisedly, because

the writer has never had a really bad skid. The effect is simply that the tail moves bodily sideways for perhaps 2ft or 3ft, but, given space, the movement can quite readily be controlled and corrected. It is, of course, most liable to occur when the road is wavy and corrugated, this setting up the pitching pre-' viously mentioned, and so reducing the adhesion of the tyre threads.

The springs of the car are perhaps more flexible' than those usually fitted, and after considerable • thought it was decided that these, acting in conjunction with the large, low-pressure tyres, were amplifying any motion once started. It was this combined action between the front and rear part of the suspension system which caused undue pitching in the first place, and lack ofwheel adhesion in 'the second place.

The obvious deduction \ras that if the periodicity of the tyres could be varied sufficiently to prevent them from acting in unison and with the springs, the problem -would, at any rate, be well on its way to solution. Owing to the low weight of the car, the running pressure recommended for the tyres was only 181b per sq. in. As a preliminary experiment the writer tried the effect of running with the front tyres inflated to 161b and the rear tyres to 201b. This proved to be a very slight improvement, but the pitching motion was certainly almost as bad as before. As a second experiment, the pressures were reversed; that is to say, 'the car was run with the rear tyres softer than those at the front, but," as

was almost to be expected, this did not improve the road holding. j Finally, it was decided to try the' effect of what might be termed diagonally equal inflation pressures. In order to do this, the off-side front tyre arioV near-side rear tijfre were inflated to 201b per square inch, whereas the other diagonal pair were inflated to 171b per square inch. This difference in pressure was only slight, but, nevertheless, was found to give remarkably good results. ■In fact, when trying the car with this ■system of pressures for the first time, one would almost have believed that shock absorbers had been fitted. Pitching would commence after negotiating a severe pot-hole or ridge, but would very rapidly be damped out because of the differing pressures with the corresponding differences in periodicity.

Furthermore, with the new system of pressure inflation, the liability to skidding on greasy roads was reduced to a very marked extent. Strange to say, this improvement could be noticed even on comparatively smooth roads. The difference was so marked that the average running time from home to 'business —a route over half of which consists of slippery London streets— was reduced in wet weather from half an hour to twenty-five minutes- Far more important than this, however, to the writer's mind, is the additional security, because nothing is more nerve-racking than the knowledge that if one should have to apply the brakes with rapidity a bad slide or skid is certain to result.