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70 years Lotus 70 years Lotus

Among Friends – Part 1

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Seventy years ago, racing icon, and notorious perfectionist, Colin Chapman, founded Lotus Cars. Early on, Chapman relied on ZF products. His successes in racing are still legendary. Over the years, ZF and Lotus developed a special relationship.
Janine Vogler,
Janine Vogler Vintage cars related to ZF-products have been at the heart of the journalist. Outside of work, she enjoys to ride motor bike or to be accompanied in nature by her dog.
In the 1950s, ZF had gained a fabulous international reputation as a transmission specialist with reliable and efficient transmissions. In the automotive market, ZF was able to position itself well as a precision manufacturer of chassis and driveline technology, and with the series production of a revolutionary transmission principle, which was introduced in the DKW Junior, ZF once again made a name for itself.

Here, the classic front-engine-rear-drive principle - flange-mounted transmission, cardan shaft, differential, rear axle, drive to the rear wheels - was reimagined and a new principle, in which the differential was integrated in the transmission housing, was implemented very successfully for the first time. In this application, a cardan shaft was no longer required and the differential, which was normally installed in the rear axle, could be omitted.

On the one hand, this applied principle made the handling more stable and safer; on the other hand, the concept was also more economical and efficient in terms of production technology, as it made production of the rear axle simpler and less expensive. Only the steering behavior in the curves was more challenging. The concept of the DS gearbox was quite interesting for the resurgent motorsport and especially for Formula 1, where the engine was directly behind the driver. This shifted the weight of the engine to the rear axle and brought more traction directly to the drive of the rear wheels via the differential integrated in the transmission.

In the early 1960s, a perfection-obsessed gentleman from England approached ZF and asked for a small, reliable, and lightweight five-speed transmission for his Formula 1 operation. Colin Chapman had been aware of the transmission specialist on Lake Constance for some time. His Elite sports car model was equipped with ZF S 4-12 four-speed transmissions, and he also used ZF self-locking differentials. On top of that, Chapman was already experimenting with ZF gears and transmission components in the Type 12 Formula 2 car. He ordered individual parts, which were then assembled in England to form a sequential manual transmission, known as the Lotus Queerbox.

Ingenious technician and tinkerer: Colin Chapman.

Chapman had a special interest in transmission development, and since he had just entered Formula 1 with the converted Type 12, he needed a highly effective driveline solution. He had already implemented some revolutionary innovations with the extremely slim, first Formula 1 monoposto, such as the lightweight construction of the trellis frame and double triangular wishbones at the front. Most likely, he already had his later sensational monocoque design in mind when something caught his eye in Friedrichshafen during one of his visits. Chapman, who was described as very alert and attentive, discovered a small, fully synchronized four-speed transmission in ZF's testing department - just such a DS transmission with an integrated differential in the housing. It was intended for front-wheel-drive, light commercial vehicles and was to go into series production in 1961. Since it had, among other things, an aluminum housing, Chapman felt it was suitable for racing. He provided some design changes which were subsequently made.

Chapman negotiated an exclusive right with ZF for a new racing five-speed transmission, which was then developed jointly on the DS principle. The production transmission was originally designed with the driveshaft above the differential, which would have moved the engine too far up. ZF engineers had to practically reverse their design so that the shaft could enter at the bottom of the transmission, and the extended gear also necessitated a new housing.

The innovative 5 DS10 transmission was then used in May 1961 by Innes Ireland at the Monaco Grand Prix in the Type 21, which was also new, and was described as still experimental. Jim Clark, on the other hand, had already won the Grand Prix de Pau on April 3 with a new ZF transmission. Nevertheless, Chapman was still experimenting with two ZF driveline variants: a four-speed and a five-speed transmission. This would ultimately prove difficult, as Ireland did not have an opportunity to practice with the right-hand gearshift. In addition, the gears were shifted in a different direction than usual, from the rear to the front, like a four-speed commercial vehicle transmission.

Sectional drawing of the ZF 5 DS 10.

Sectional drawing of the ZF 5 DS 10.

Doing the whole thing with an unfamiliar five gears didn't make it any easier - especially when things had to go rapidly in a race environment. Clark, who was known to have a talent for adjusting to vehicles very quickly, had fewer problems. Ireland, on the other hand, apparently shifted gears when accelerating due to the unfamiliar shifting environment, confusing second and fourth gear during the race and causing a serious accident in practice. Within a very short time, ZF engineers adjusted the shifting diagram onsite to a more familiar layout.

Success came quickly. Both Jim Clark and Innes Ireland had already won a total of seven races in 1961, including three Grand Prix titles. Colin Chapman raved about the new, fabulous synchronization with the fast, smooth shifting. Accordingly, in the event of clutch problems, the gears could simply be shifted through without using the clutch, although this was not advantageous for the synchronizer rings. The only drawback to the transmission had been that changing the wheel components would be more like a doctor's thesis than a quick change on the track.

ZF produced ten of the 5 DS10s for Colin Chapman. In 1962, the transmission was subsequently used in the Lotus Type 24 and Type 25 and later in the Type 33. In the extremely successful Type 25, Chapman, the well-studied aeronautical engineer, had replaced the lattice tube frame with a monocoque shell construction similar to aircraft construction. This reduced the weight by around 20 kg and increased the torsional stiffness, which is important for road holding and handling. The pioneer of Formula 1 racing, Chapman, who had contributed significantly to the further development of the Grand Prix racing car during his career, changed the rear suspension by omitting the rigid axle.

Graham Hill became Formula 1 world champion in 1968 with Lotus. In 1962 he won the title with B.R.M.

Graham Hill became Formula 1 world champion in 1968 with Lotus. In 1962 he won the title with B.R.M.

Longitudinal control arms remained, the drive shafts acted as wishbones, and in addition there were long, sloping wheel-guiding struts and very filigree wheel suspensions. This type of suspension was later given the name "Chapman axle" because Chapman used it in other models as well. His competitors sometimes criticized him for using "undersized" components with which he would disregard elementary safety rules in favor of advanced technology.

Nevertheless, the 5 DS 10 brought success to the Lotus team, with Chapman winning a total of 49 times from 1961 to 1965. Most of the time Jim Clark drove and went on to become the Formula 1 World Champion twice — in 1963 with Lotus Type 25 and in 1965 with Lotus Type 33, both race cars were powered by the 5 DS10 from ZF.

Chapman achieved a total of
from 1961 - 1965.

With the Lotus 25 and a ZF 5 DS 10 transmission, Jim Clark became world champion for the first time.

Jim Clark was an exceptional driver of the time. The two-time world champion won with Lotus and ZF.

An open gear ZF 5 DS 12 for application in Lotus 1967.

ZF was always clearly visible on the delicate Lotus racing cars. That a vehicle can still be driven with an original ZF unit after more than 50 years is rather rare.

Colin Chapman also revolutionized the axle suspension...

Colin Chapman had first replaced the lattice tube frame with a monocoque shell construction familiar from aircraft construction.

Colin Chapman was himself an ingenious technician and tinkerer. When he came to visit Friedrichshafen, engineers, designers and fitters would coordinate their work together.