Overshadowed by its successor, the 1955 Jaguar 2.4 was the most significant car in Jaguar’s evolution as a serious carmaker.
In 1955, Jaguar committed their most ambitious act up to that point with the introduction of the 2.4, an all-new, compact saloon of a sporting mien – every inch a Jaguar, but no hand-down version of its larger sibling. Far from it, because despite the announcement the same year of the revolutionary Citroen DS19, the compact Jaguar was probably as advanced a product as could reasonably be envisaged from what was then a low-volume, specialist carmaker.
Initiated around 1953/4, the Utah (in Jaguar parlance) compact saloon programme would mark their first departure from traditional body-on-frame construction to a stressed unitary bodyshell. Owing to uncertainty over its strength, two stout chassis legs ran the length of the floorpan, rearmost of which (beneath the rear seatpan) would house the mountings for the unusual, inverted cantilever semi-elliptic springs, so devised to avoid feeding stresses into the rear of the floorpan. Additionally, a detachable steel subframe, carefully mounted using rubber vee-shaped blocks supported engine, front suspension and steering.
However, Jaguar were neophytes in this area and were faced with a whole slew of seemingly intractable NVH issues. Fortunately, engineering chief, Bill Heynes had an ace in the pack in the form of Robert J. Knight, upon whose shoulders the task of refining the Utah bodyshell fell. Knight was technically gifted, having studied and absorbed Maurice Olley’s pioneering papers on chassis dynamics originally published in the US in 1934.
But moreover, not even the mathematically impenetrable vehicle stability papers presented at the I mech E in 1956 by Milliken and his Cornell team were beyond Knight’s comprehension, making him uniquely qualified at the time.
Knight outlined the issues to chroniclers in 1992, saying, “the noise and vibration from the engine, transmission and road surface was worse than a van’s. It was this car which forced me to treat [these] as a major issue.” His findings, coupled to his understanding of dynamics theory saw Knight make early forays into the hitherto arcane science of longitudinal suspension compliance, which was applied to both front and rear suspension mounting systems.
By early unitary construction standards then, the 2.4 was a refined car. But Mr Knight was not an individual who believed any design within his purview was fully signed off until he had arrived at a conclusion, and in the case of Utah, this was a matter best described as ongoing. With the car already on sale in 1956, and still dissatisfied; especially with the transmission of noise from the rear of the gearbox mounting into the central floor tunnel, Knight devised a new mounting system which incorporated a very soft helical spring, “to convince the body floor that it was not connected to an engine”.
Further investigations saw the front engine mountings carefully retuned to provide a pitch resonance in opposition to inputs arising from wheel bounce, thus attenuating its effects. Sir William drove the prototype, asked why it felt like it was worth £500 more and insisted the changes be incorporated in production immediately. From that point, all Jaguar engines would be mounted this way.
Bob Knight codified the essential philosophy of Jaguar’s NVH pre-eminence with this car, principles which both he and his successor would consistently refine in the years that followed. “Attempts to stiffen or detune the structure are of limited value. What you’ve got to do is stop the forces ever getting into the bodyshell.”
Originally intended to employ a four-cylinder version of the twin-cam XK engine, a short-stroke 2483cc version of the existing unit was ultimately developed, partially owing to a lack of refinement from the in-line four, but largely because it proved cheaper for Jaguar to produce a smaller six from existing tooling. Furthermore, thus equipped, Utah could also be sold at a higher price. The 2.4 developed a mildly tuned 112 bhp on twin Solex carburettors, giving a top speed of just over 100 mph – impressive for the time, and dismaying for rivals.
William Lyons was a canny businessman and something of a stylistic genius, but his approach to Utah almost derailed the programme entirely. Having carried out his styling experiments in seclusion, he presented the completed design to Heynes with strict instructions that it must not be altered. The streamlined teardrop shape was undoubtedly elegant, and it would appear, smoother through the air than its 1959 successor, but an imposed rear track width some 4” narrower than the front compromised the car’s roadholding, especially given the relatively unsophisticated live rear axle layout chosen.
Furthermore, the 2.4’s tight packaging dictated a nose-heavy layout with the longer six-cylinder engine mounted forward of the front axle, placing over 50% of the car’s weight ahead of the driver, with malign effects on steering and handling. This was no way to go about developing a car and the 2.4 would mark a watershed at Browns Lane, Heynes insisting that Lyons never do anything like this again. But it meant that the car was to all intents and purposes, reverse-engineered, engineers having to work around issues dictated by the body hard-points.
The 1957 introduction of the larger 3.4 litre engined version placed these matters into sharper relief, with the 120-mph car now at the outer envelope of roadholding and most notably, braking. The advent of disc brakes, co-developed with Dunlop at MIRA and Le Sarthe salved the latter issue, and prototypes running with a wider rear track (and broader wings to house them), demonstrated what was required to at least mitigate the former. Utah Mark 2 was by then in gestation, but this would prove far from straightforward either.
With the Mark 2 in production, the retrospectively termed Mark 1 was quickly forgotten amid the flood of accolades lavished upon its successor. They also rusted with alarming alacrity, decimating their numbers. Comparatively few have survived.
But it was a vitally important car for Jaguar and the lessons learned from it underpinned everything which followed. Indeed, without these learnings, it is questionable whether Jaguar would have made such strides over the decades that followed. For a small cat, the 2.4 represented very a big leap.
Sources/ quotes : The Automobile – June 2008/ Motor – August 1979/ Developing the Legend – Paul Skilleter.