MYSTERY TO OWNER

NZ Truth, Issue 1202, 13 December 1928, Page 22

MYSTERY TO OWNER

Simple To Mechanic WASTE OF PETROL Some strange cases come under the notice of a motor writer at times. Here's one instance. AN owner of a popular make of car who had covered some 2000 miles m the machine, asked "N.Z. Truth" for advice, as he was getting only 20 miles to the gallon, compared with 25 or more which he should get. A run m the car was suggested; and the writer took it out during 1 the week. After going a couple of m\les it was found that the owner, owing to some misunderstanding, had been running with the spark fully retarded instead of advanced. When the alteration was made the car was a very different machine to handle, its all-out speed toeing increased about ten miles an hour, and its petrol consumption rate should.' be nearer what the maker says it will do. There, is a moral m this for owners of "petrol eaters." They should make sure they are running with every bit of useful advance they can get. . The fitting of oversize tyres will cause the speedometer to register lower speed than the car is travelling at. The amount of error is determined by multiplying the speedometer registration by the. distance traversed by the new tyre m one revolution, and the dividing by the distance covered by the original tyre m one rev. Say the registration is 30 m.p.h., the two tyre distances 95 inches and 90 inches respectively, the true speed will be 30 multiplied by 95, divided by : 90,- which equals 31 2-3 m.p.h.