Why Does it Spin Backwards?

Posted September 15, 2017

History of the Legendary Smith's Reverse-Rotation Cobra Speedometer

by Randall Thomas

Photos by Dean Larson

The history of the legendary Smiths reverse-rotation speedometer that was installed in original Cobras has spawned a wide range of explanations over the decades, where some have reached near mythical proportions. Some of these theories include, but are certainly not limited to, the thought that the reverse sweep of the needle reduced confusion between the tachometer movement and the speedometer movement during racing. Of course, race cars rarely, if ever, have speedometers in them. Another popular theory was that with the sweep being reversed when used in the street cars, the driver could more easily see the needle movement from 0 to 60 mph, due to his hand on the steering wheel otherwise being in the way of a normal-sweep speedometer. Now, if they really thought this was a problem and wanted the driver to see the speedometer, it would have been moved up front where the tach is right over the steering wheel. And the list of theories and guesses goes on and on, ranging the gambit from the incredible, to the absurd.

For several months I sought out the real answer through many phone calls and email transactions, and even checking into some of the old English nursing homes looking for surviving Smiths employees from the 1960’s, was not at all out of the question. After months of searching and research, I found the final answer from the original Smiths employees in Europe on an otherwise quiet December morning.

Let's start with a brief history of Smiths from then to today. Samuel Smith Junior began selling clocks and watches in London in 1871 and later began to manufacture automotive speedometers. The automotive instrumentation side was sold to Lucas in 1984 and later renamed 'Caerbont Automotive Instruments Ltd. (CAI).

Smiths Gauge 1

After months and months of searching, here is the transcript of the phone interview with Neal Meakin and Ian John of Caerbont Automotive Instruments Ltd. in Abercraf, Swansea, on December 7, 2004 conducted and recorded verbatim as it occurred.

"...We have pursued a number of retired ex-Smiths employees to gain benefit of their knowledge. When the car [Cobra] was being designed, the engineers realized that the cable drive from the gearbox to the speedometer was anticlockwise rotation, instead of the more usual clockwise. The normal procedure for an anticlock drive was to fit a reversing gearbox on the rear of the speedo to convert the rotation to drive a conventional clockwise speedo. Between the Cobra engineers and Smiths Industries, it was decided to offer an anticlock speedo as a feature, and obviously cost reduce the speedo installation by not having a cable drive gearbox. None of the Smiths guys from that time are around here these days, so this summary is an educated guess at what happened at the time. Our part number originally fitted to AC Cobra was SN5346-00, first made at the end of 1965. This speedo was updated by us in Nov 1995, we still manufacture it as part no. SN5346-02. Also recently we've developed a full range of Cobra Instruments with black print on white dials..."

Neal and Ian were confident that the Smiths reverse-sweep speedometer was actually the result of a Shelby inspired cost savings measure due to the odd rotational gearbox that was used at the time. When asked, the legendary Peter Brock told me that “...this was usually the reason behind many of Carroll’s decisions, so it sounds about right...”.

Randall Thomas

January 07, 2004

Superformance Owners Association


Comments for: Why Does it Spin Backwards?

comments powered by Disqus

Related Stories You Might Like

Filed Under

Cobra Gauges