WHEEL WOBBLE

Evening Post, Volume CX, Issue 83, 4 October 1930, Page 24

WHEEL WOBBLE

GETTING AT THE FACTS

1" TESTING- APPARATUS

, Tie t)unlop Company has been trying to fathom tile mystery of front wheel wobble.. There are. .two "kinds of wobble, a low speed and' high speed. The former usually is* set up when a pot-holed road is being traversed, and it can be prevented or minimised by correct adjustment of the wheels. High apeed wobble is on another footing; the causes have yet to be revealed. The company reports having installed an ingenious apparatus to enable scientific! tests to be carried out. The plant consists of a large hollow ramp, on to which a ear suffering from wheel •wobble can be driven. The front wheels are run on. to. two separate large diameter drums oh a shaft driven by an electric motor. The vehicle is securod on the ramp, with the front tires at rest on the rollers, the jpoint of contact being/ carefully sat to correctly reproduce the conditions of road travel. When tho front wheels ate •in position, a spring-loaded pencil is attached to the centre of one of the hubs, j the pencil bearing on a paper strip, which is rotated. At the same time, a second pencil, operated from a special indicator, Tecords on the same ; strip of paper the equivalent, road speed of the vehicle. This apparatus, which gives a graph record of each ; test, clearly depicting the severity of the vibrations set up, has resulted already (it is stated) in much valuable data being obtained. Old and new cars have been tried out, and one interesting thing disclosed is the fact that wheel wobble has always been1 present in motoring, but in days gone by cars generally did not travel fast enough to reach the critical speeds at | which wobble would occur. Wobble is more apparent nowadays ; because tho I extra weight of front-wheel brakes ! and the use of low-pressure balloon tires produce the wobble in an intensified form, and within speeds that are fairly common on the better roads of to-day. ; : . Experiments proved that with a car equipped with a'plain axle ; and high-pressure 815 s 105 m.m. tires no wobble was apparent until a speed of 73 m.p.h. was reached. When 5.25 s 21 balloon tires were substituted on the same car the wobble appeared at 64 ni.p.hlj whilst with the weight of front-wheel brakes added,-the wobble started at 53 m.p.h. It was found that the weight of passengers in the car slightly reduced the severity of the wobble. . , Another point of interest is that a slight lack of balance in the front wheels has little apparent effect on setting up wobble. Balloon tire pressures On the ■ front wheels and tho tension of shock absorbers were found to have an important bearing; at 301b pressure, with absorbers slackened right off, a violent wobble set in at 55 m.p.h. The absorbers were then tightened up, with the result that wobble started at the same road speed, but its intensity was nofc-so severe. With the "'pressure at

401b the wobble did not appear until 67 m.p.h. was reached, but it was more severe, proving that high . inflation will not prevent wobble but. will defer the trouble until a considerably higher speed is reached. : Of course, all cars are not addicted to wheel; wobble under ordinary driving conditions. They may never reach tho critical period when tho trouble is apparent. Should it appear, however, the progress so far made in research, and as outlined above, may prove of benefit to the driver. Ho should avoid the speeds af which wobbie makes itself apparent.