Jaguar's XK120 changed the car industry and, along with the MG, put sports cars on the map in the U.S. market which was key to Britain's postwar export drive. A lot of this success was due to the engine design, which equalled the power of the new Cadillac V8 for 1949. The first thing Americans noticed, though, was that roadster body design. Like the British who first viewed the car at the Earl's Court show in 1948, they were pretty much hypnotized by it (Clark Gable was the first customer). Most people aren't aware, however, that the impetus for the whole design can be traced back to decisions made in Germany by others...
In 1937, BMW aimed to increase the race-winning abilities of their 328 roadster, and asked (ordered, really) their design department to come up with a lightweight, aerodynamic roadster. Designer Wilhelm Kaiser (you can't get much less British than that) sketched out a body to be formed in alloy over a tubular frame. The resulting Buegelfalte (named for the "trouser crease" at the fender tops*) and its Italian-bodied sister cars were light enough and slippery enough that BMW took 1st, 3rd, 5th and 6th places in the Mille Miglia for 1940, a year when most people were thinking about other things...
Things like the Luftwaffe's bombing of England, for example. Soon the industrial center of Coventry was bombed, and Jaguar chief William Lyons did fire-spotting duty on the roof of the factory (by then in use for storing aircraft fuselages) with some of his team, which included stellar engineers: William Heynes, Harry Weslake, Claude Bailey and Walter Hassan. Apparently when they ran out of generic topics like the survival of Western civilization, their conversation turned to engine design, and the idea of replacing Jaguar's line of engines, which had most recently consisted of inline units manufactured by Standard Motors (postwar Standard Triumph of TR fame) with Jaguar-designed OHV heads. The engineers wanted something with hemispherical combustion chambers and twin overhead cams (like an Alfa Romeo) and Lyons wanted something beautiful to look upon, and (with an eye towards the future American market) with ample reserves of effortless power.
You'll note that the engine in the photo is a 4-cylinder unit*. Right after the war, the Jaguar crew began experimenting with various head and block designs, running through prototypes XA through XK, a 2 liter twin-cam with those hemispherical combustion chambers. It's helpful to remember that Jaguar's domestic competition consisted of somewhat fusty outfits like Alvis, Lea Francis and Riley, and not-so-fusty Aston Martin, all of whom offered four cylinder engines in the 2 to 2.5 liter range. Also, fuel rationing made gas consumption important. But the little four was too rough-running to satisfy Lyons, and the team informed him that it would be no more expensive to tool up for a six. In a move that proved decisive, Lyons decided to produce a 3.4 liter twin-cam six (XK) offering about a third more power than a Bentley, for about one-third the price. The first destination for the new engine was to be a luxury sedan, but Lyons decided to build a couple hundred 2-seater roadsters to showcase it. After that first 1948 showing, demand far outstripped supply, and in the scramble to make roadsters, the new sedan was delayed. Several sources of inspiration for the XK120 body design have been suggested, including French and German ones. The year before the XK debut, the Frazer Nash people (see our posting for 1-27-17) had brought over one of the two post-Buegelfalte BMW roadsters built by Touring of Milan (they'd erased those fender creases) and displayed it with a Frazer Nash grille. With the BMW-derived 2 liter Bristol engine, they'd suggested this for sporting drivers, but at a Bentley price...
Specialist builders like Alvis and AFN didn't yet realize it, but Jaguar would soon have them in checkmate. Using racing success to garner publicity (Jaguar won at Le Mans in '51, '53, '55, '56 & '57) and making cars with Bentley levels of style at Cadillac prices, Jaguar took over a lion's share of the home market for performance cars (including sedans) while it established a firm foothold in America. It's hard to imagine today, but the most popular import in California by 1956 was not VW, it was Jaguar. On the home front, Jaguar bought out competitor Daimler in 1960 (the year Armstrong-Siddeley folded its automotive tent) and Alvis was extinct by 1967, with Bristol turning out tiny handfuls of overpriced, obsolete chassis designs powered by Chrysler V8s after 1961.
The first 242 XK roadsters were bodied in aluminum over ash framing; after that, construction switched to steel bodies with alloy doors, bonnet and boot lids. During these years, Jaguar regularly updated and expanded the line, including a "fixed-head coupe" version of XK120 in 1951, the year after they introduced the Mark VII luxury sedan. Both cars featured generous amounts of polished wood and leather inside, and a curved rear roof form which seductively followed the side window shape and nearly mirror-imaged the rear fender shape. No BMW influence here; it was a bit like the prewar teardrop Figoni-bodied Talbot in red below...
Upgrades to engine power came along too, and are summarized in the footnotes.* A drophead (convertible to Americans) followed in 1953 with a similar interior featuring a standard heater, padded top and roll-up windows, unlike the side-curtained roadster which was usually driven with the top down anyway. You just drove a bit faster to keep the rain off...
When it became apparent that a lighter, more rigid frame than the 120's modified Mark V ladder layout would be needed to keep the car competitive in road racing, the engineering team and aerodynamicist Malcom Sayer came up with the XK120C in 1951, giving it 4 wheel disc brakes during 1953. The new car adapted the independent front suspension by torsion bars from the XK120, but substituted a torsion bar trailing link system at the rear for the 120's leaf springs.
The compact, lightweight car gave Jaguar its first wins at Le Mans, but it was almost as far from an XK120 production car as the contemporary Mercedes 300SL was from a standard 300 sedan. Maybe as a result, it quickly became known as the C-Type, and it was produced in 54 examples, while the standard XK120 concluded production in 1954 after well over 12,000 cars had been sold*, mostly to Americans.
The XK120 wasn't a perfect car, of course, and by 1954 even diehard Jaguar fans (especially tall ones) were wishing for more space, better ergonomics (though nobody used that word then) and more efficient cooling for both the engine (sometimes a victim of that narrow grille opening) and the cabin. Road race fans were aware, too, that the C-Types often won because they stopped better than other cars, and they were wondering when the road cars would get those disc brakes. Maybe because a good number of Jaguar owners raced their cars on weekends, the complaints made it back to Coventry and provided food for thought in the engineering section. In Part 2 of our Jaguar saga, we'll see where those thoughts went.
*Footnotes: The four-cylinder prototype engine is in the Collier Collection at the Revs Institute in Naples, Florida. It was intended for a possible junior version of the roadster called the XK100, but the project was cancelled. According to the Revs Institute, some 4-cylinder engines were sent to dealers for display. One 4-cylinder engine was released to Goldie Gardner for a record run in the MG Ex135 streamliner, and it achieved 176 mph.
Engine & performance notes: Power from the 3.4 liter XK-120 was increased during the car's production life from 160 bhp at model introduction to 220 for a Weber-carbureted C-type. All engines featured a cast-iron block with 7 main bearings, and an aluminum head. Tallies of total XK120 production range from 12,055 (Wikipedia) to 12,078 (Consumer Guide to Collectible Cars), counting the 242 alloy-bodied cars produced in 1948-49. In their road test of an XK 120M coupe (180 bhp, 3,100 lb.) in February 1953, Road & Track achieved a 0-60 time of 8.5 seconds and a one-way top speed of 123.3 mph. In their test of Masten Gregory's Golden Gate Road Race-winning C-Type (210 bhp, 2,550 lb.) that same month, Road & Track achieved 0-60 in 6.6 seconds and a one-way top speed of 134.3 mph. The car's final drive ratio of 3.92 to one was well-suited to the Golden Gate course, but not to the best top speed run, and R & T noted that with the standard 3.31 ratio the top speed would rise to above 140. Road & Track also noted that it was the fastest-accelerating car they'd tested to date.
German to English translation: Christa Rosza notes that the buegel (iron) makes the falte (crease); the English translated the name loosely as "trouser crease". But subsequent interpreters of the Buegelfalte idea thought these creases were a pain to make in aluminum and got rid of them. Here are the creased fenders in plan view; note the tight seating area front to back, a feature also of the XK120:
Photo credits:
Top: Wikimedia
2nd and bottom (12th): bmwblog.com
3rd: the author
4rd: AFN Ltd.
5th: The author thanks Dennis Varni for showing his XK120 and D-Type (to be featured soon).
6th: carstyling.ru
7th: britishmotoringjournal.com
8th: fantasyjunction.com
9th & 10th: Wikimedia
11th: Jaguar Heritage Trust
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