Halda Tripmeter

Racing drivers who talk of finding their way around a circuit are refetring to the identification of braking and turn-in points, of discovering where the worst bumps are, and of assessing which kerbs you can take liberties with.

Finding your way around in rallying is a very different proposition. The rally's route book shows competitors the roads or tracks to follow by means of tulip diagrams; the co-driver's job is to convert that information into verbal instructions to the driver.

To do that reliably, you have to know precisely how far you are along the route; for that, a rally computer is essential.

Today's examples are electronic, of course, but in the 1950s, '60s and early 70s, that technology wasn't available. The rally computer then was a mechanical device and the most famous of all were made by Haldex AB in Halmstad, Sweden: the Halda Tripmaster, Twinmaster and Speedpilot. Pretentious as it might seem to describe these boxes of gears and (in the case of the Speedpilot) clockwork as computers, the term is justifiable. The first 'computers' were humans, not machines: people who did sums and put the results in navigational or mathematical tables. As mechanical equivalents the Haldas were limited to very basic arithmetic indeed all the Tripmaster and Twinmaster could do was continuously add or subtract but they nevertheless made the rally co-driver's task a great deal simpler.

Haldex became a maker of rally instruments via a curious path. Founded over 100 years ago and originally a manufacturer of typewriters, the company diversified into making mechanical taxi meters. A spin-off from this product line was a simple 'spy in the cab' odometer, used by suspicious bosses to check on employees' vehicle usage. From that it was a relatively small step to the specialist Tripmaster and Twinmaster rally odometers. The Speedpilot, which actually predates its simpler cousins, was a more complex (and historically less important) device to help the driver maintain a preset average speed.

Prior to the Halda Tripmaster being introduced in 1958, the only measure of distance available to most rally co-drivers was a standard car odometer.

BMC, for instance, had some special speedos built by Richfield which were essentially the conventional item minus speed needle. AT-gear inserted in the drive cable allowed this second unit to be positioned in front of the passenger seat, leaving the standard instrument for the driver.

Such arrangements had limitations. Tenth of a mile (or tenth of a kilometre) resolution wasn't really good enough; you couldn't rely on the odometer's accuracy; it couldn't easily be adjusted for different gearing or tyre sizes; and a conventional instrument simply couldn't do everything a co-driver would want of it, particularly if the car took a wrong turn. These shortcomings were all addressed by the Halda Tripmaster and Twinmaster the latter introduced in 1960 and essentially the same but with two odometers, one of which could be used to record cumulative distance while the other was reset for individual sections. Like a conventional odometer, they were designed to be driven from the speedo cable (via a T-gear with 8:1 reduction gearing) but there the similarity ended.

For a start, Haldas read in hundredths of a mile or kilometre, and their internal gearing could be changed in sufficiently small increments to ensure an accuracy of plus or minus 0.7 per cent BMC's competition department had Abingdon council mark out an accurate measured mile on a local road to check the calibration. This adjustability also meant they could accommodate different overall gearings and tyre sizes or any vagaries in the nominal mile or kilometre measures used by rally organisers. As the number of their control stalks indicates, a Halda also allowed the co-driver to do more than zero the read-out. Critically, one control allowed the odometer to operate in reverse, subtracting distance rather than adding it, so that an inadvertent detour could easily be corrected. As soon as the codriver realised the mistake and told the driver to turn around, the Halda could be set to subtract for the journey back to the wrong or missed turn.

Over the years, both designs were refined to improve shock resistance the gear wheels on early models could be knocked out of alignment on rough-and-tumble rallies like the Safari and keep dust out Even then they weren't perfect, though. Despite the brochure's proud claim of 'Large illuminated 6.2mm figures', digits less than a quarter-inch high could be difficult to read, particularly once the advent of fullharness restraint made it impossible to lean forward. What was difficult during daylight became impossible at night, so a solution was dreamt up by the BMC competition department: a dash-mounted magnifying glass and additional illumination, which made the figures much easier to see. For the iciest events some teams also contrived new ways to drive their Haldas.

Having them driven via the gearbox meant copious wheelspin would cause them to over-read, negating the high inherent accuracy. So means were contrived for gleaning distance information from the non-driven wheels. Strange drive mech anisms and cables began to sprout from wheel hubs to feed Haldas a more reliable input. But then a preponderance of left or right turns on any stage could again harm accuracy.

Halda introduced its first electronic rally computer in 1980 but continued to supply the Tripmaster and Twinmaster until 1989. By then it had sold 78,000 and 66,000 units of each, along with 56,000 examples of the Speedpilot (produced until 1978). Despite its previous hegemony, the company's electronic products proved less successful, however, suffering at the hands of competitors like Terratrip.

The Halda name survives but not on rally computers. In 1992, Trancometer System AB bought the Haldex taxi meter operation and continues to sell the Halda brand. In the end, calculating cab fares turned out to be a more lucrative business than counting off the stage miles. Thanks to Martin 7-Ialdaman'Jubb, Bill Price, Don Barrow and Gunnar Palmfor their help in preparing this article.