Inaccurate Speedometers

Sir,

I have read with interest your account of a visit to Smith’s speedometer factory, entitled “How Fast.” You referred to the happy workers making precision instruments to an extremely high standard, and wearing overalls of varying colours. I am prepared to accept the happiness of the workers and the colour of their overalls, but as to the precision of their instruments I am somewhat more doubtful.

I have recently become the fortunate owner of a Jaguar XK150 (a really splendid car once its somewhat ephemeral shock absorbers are replaced by Koni’s, and one which is giving me the utmost satisfaction and enjoyment) which is of course fitted with Smith’s instruments. As delivered it read 120 m.p.h. at an indicated 100 m.p.h. by the rev.-counter. I sent it back for adjustment. The car was returned ostensibly with a new speedometer—at any rate the mileage indicator read zero. It still read 120 m.p.h. at 100. I sent it back again. This time it came back reading only 116 at 100. I sent it back again. It was then returned with a letter from Smith’s stating that the instruments “were found to he within the limits laid down by our engineers and the Jaguar Car Company.” They therefore had “no option but to refit the instruments.” Despite this I was amused to note that the speedometer now read only 110 at 100 by the rev.-counter; in fact the limits laid down by Jaguar are 2½% for the rev.-counter at about 4,000 r,p.m. and 5% for the speedometer. Therefore, assuming the rev.-counter is slow by the maximum permitted and the speedometer is fast by the maximum permitted, and that increased radius of the tyres at 100 m.p.h. may account for as much as 3%, I have now, after three attempts, got a speedometer which may, possibly, be just within the maximum limits of inaccuracy laid down by the makers.

Evidently, therefore, it is not always the wicked motor manufacturer demanding “flatter” from Smith’s. So far as I am concerned, I am not in the slightest degree impressed.

I am, Yours, etc.,  Cecil Clutton. Westminster.