Formula One Trend of Design

Tachometers

TO THE racing driver in full action the most important instrument is the one that indicates what speed his engine is doing. He knows, for example, that his Cosworth DFV develops maximum horsepower at 10,800 revolutions per minute, so it is up to him to use the gearbox to keep the engine at this figure for maximum performance. The intelligent drivers will also know the r.p.m. at which maximum torque is developed by the engine and will have studied the brake horsepower curves and the torque curves of the engine to get a “feel” for when the engine is working at its best for any conditions. The r.p.m. figures are all important. The instrument used to indicate the speed at which the crankshaft is revolving is the tachometer, often loosely called a rev-counter. In fact, a rev-counter, or counter, is something else altogether and is an instrument used in experimental work to literally count the number revolutions of a shaft and this instrument used with a stop-watch to measure a time interval will give you the revolutions per minute of the shaft. An instrument that records revolutions and time, with a read out in the resultant numbers is a tachometer, and it is these instruments that we are looking at in Formula One, as seen at the recent Austrian Grand Prix. I mention the actual occasion because the pace of developrnent in Formula One is so strong at the moment that details change from week to week.

At one time tachometers were driven by a flexible cable off the end of a camshaft, or any similar convenient place, with the necessary reduction correction in the instrument so that your reading was the crankshaft r.p.m. Nowadays there are electrical instruments and impulses can be taken from the ignition system. But the most popularly used instrument is a cable-driven one by Smiths Industries, which is no longer in production. These are serviced by Thos. Richfields and feature a black dial with white figures. The dial is numbered from 1 to 12 with five divisions marked between the numbers. At the bottom of the dial is the important legend RPM x 1,000, so that a reading of 8 on the dial means 8,000 r.p.m. and each division between the large numbers represents 200 r.p.m. This type of instrument is used by McLaren, ATS, Lotus, Ensign, Fittipaldi. Arrows and Osella. Some of them have a red line on the dial to indicate maximum rp.m., others have a second needle that is moved by the main needle so that it stays at the maximum figure reached. These “tell-tale” needles used to be almost universal but now only McLaren. Ensign and Arrows use them. ATS have a fixed red line at 10,800 and Lotus and Fittipaldi have their red lines at 11,200. Naturally, the only part of the dial that interests the driver is the segment between 9 and 12, so most of them have the instrument rotated in the panel so that the vital segment is uppermost. Most drivers view the instrument through the steering wheel and the top end of the scale is all they really see.

Tyrrell, Renault and Williams all used an electrical instrument made in Germany called Contactless, which is fed from the ignition system and has a black dial with yellow figures reading from 4 to 12 and the important legend x 1,000 r.p.m. The Tyrrell cars have their instruments red-lined at 11,100, while the Williams are red-lined at 10,800 (at least Alan Jones’ race-car is). The Renaults have no red line. On the Jones car there is a thin red segment on the glass pointing at 10,800, so that if the engine is taken beyond that the yellow needle will disappear from view. Jones drives with the needle always in view, but only just! Again instruments are rotated in the panel to suit individual drivers’ taste, but mostly they like to see the all-important needle pointing straight upwards at maximum r.p.m.

Ferrari, Brabharn and Alfa Romeo all use identical cable-driven instruments made by Veglia and these are marked off in very large, white figures on a black background, from 4 to 14, accompanied by the legend Giri x 1,000 (Giri being the Italian equivalent of r.p.m.). On Scheckter’s Ferrari there is a yellow segment at 12,000 and a red segment at 12,600, while Villeneuve has the red segment at 12,500 and no yellow segment. Brabham have no maximum indicator and neither do Alfa Romeo. On the latest Lotus S1B there is a Veglia instrument. rather than the Smiths used on the other Team Lotus cars, and this one has figures from 2 to 12 (Giri x 1,000) with a tell-tale needle and the figures covered over from 10,800 onwards.

Alone on the instrument scene are the Ligier team, all their cars using black faced cable-driven MATRA instruments reading from I to 14 with the red line at 11,200 — D.S. J.