Vintage Car and Motorcycle Speedometers and Tachometers We sell a range of original speedometers for veteran and vintage automobiles and motorcycles. The brands include Jaeger, Smith and Sons, Stewart, Ford, Stewart Warner, Jones, Johns Mansville and Corbin speedometers. The speedometers that we sell date from the early 1900s through to the 1930s and include those that operated with through a centrifugal mechanism such as the Jones speedometer and the magnetic type such as the Stewart speedometer. We specialise in the Ford Model T, Model A and early Ford flathead V8. We also sell the rare early tachometers. We also have a limited stock of the original speedometer cables, drives and brackets for the veteran and vintage cars and motorcycles. This consists of mainly early Stewart cables, drives and brackets but also some Corbin and Jones parts. Click here to view our vintage speedometers for sale on eBay History of the speedometer The earliest known design for a speed-measuring instrument was the design of Leonardo da Vinci dating from the beginning of the 16th century. However the need for an instrument that could provide an accurate measure of the instantaneous speed of a vehicle first became apparent in the early 1800s with the development of the railroad. During the 19th century a variety of speed measuring devices were invented including the so-called velocimeter patented by the Croation Josip Belusic in 1888.
The first automobiles that were developed in the late 1800s were generally slow and unwieldy and at first there was little perceived need for an instrument to measure the speed of these vehicles. However as the automobile manufacturers quickly developed more powerful automobiles and governments began to introduce laws to regulate the operation of these vehicles it became apparent that there was a need for a speedometer that could be utilised on an automobile. There were three main types of speedometer that were developed for the early automobile and motorcycles – the centrifugal, eddy current (magnetic) and chronometric type.
One of the most important developments was the invention of the so-called eddy current or magnetic speedometer. This was invented by Otto Schulze in the early 1900s. This approach used a flexible shaft to transmit the rotational speed of the wheel or transmission to the speedometer head, which has a driven shaft with a permanent magnet. Adjacent to the speedo magnet – but without direct contact – was a metal disc, or metal drum or cup that functioned as the speed indicator or pointer. As the magnet on the driven shaft rotates, the changing magnetic field produces eddy currents in the metal disc which then produces another magnetic field. This pulls the metal disc or drum in the direction of the rotating magnet. The metal disc or drum is held toward zero by a restraining spring. The torque on the metal disc or drum increases with the speed of rotation of the magnet. The restraining spring is calibrated such that a given revolution speed of the cable corresponds to a specific speed indication on the speedometer. This calibration must take into account several factors, including ratios of the gears that drive the flexible cable, and the diameter of the driven tyres.
The magnetic or eddy current speedometer proved to be very effective was adopted by a large number of early speedometer manufacturers including Stewart.
An alternative mechanism used on the some speedometers was based on centrifugal force. These were referred to as centrifugal speedometers and were sometimes called “governor” instruments due to their similarities to the mechanism seen on some steam engines. One such design incorporated a pair of weights carried around by a governor arm which was hinged to a rotating arbor. In response to the rotational input from a flexible shaft the weights are thrown outwards by centrifugal force against the constraint of a spring. The distance that the governor arm is displaced is proportional to the road speed of the vehicle as transmitted through the rotating shaft. The arm is linked to a sliding sleeve on the arbor which is linked to the instrument pointer which moves to indicate the speed as the sleeve slides up or down. The early speedometers manufactured by Jones are an example of a centrifugal speedometer. These speedometers were popular in the early part of the 20th century but were phased out in favor of the magnetic speedometers which came to dominate the market until the development of electronic speedometers.
The third type of speedometers used on the early automobiles and motorcycles are known as chronometric speedometers as they work out the mechanically the quotient of time into distance. In a typical setup the camshaft provides the time base and in addition to the cam carries the escape wheel which together with an escape lever and balance wheel constitutes a complete escapement. As the camshaft is driven through a slipping clutch it is constrained to run at a constant speed in the same manner as a timepiece and the cams will move the spring fingers in contact with them in a regular sequence at constant time intervals. Diagrams of chronometric mechanisms of the Smiths and Jaeger speedometers
