Some say the XK 150 proves that Jaguar's first postwar sports cars hung on too long. They may be right, but the 150 was also the most thoroughly developed of the early XKs, if arguably the least sporting. This final variation on the original XK 120 theme was Jaguar's response to recently introduced rivals such as the BMW 507 and Mercedes-Benz 300SL, which bettered the XK 140 in catering to American demands for more comfort and refinement.
The 150 was thus roomier, plusher, and more civilized than any previous XK. And the bodyshell was restyled, losing some pouncing-cat contours and gaining a wider grille and one-piece windshield. Critics bemoaned the heavier appearance, especially since it was matched by higher curb weight. Fortunately, the extra heft didn't spoil overall handling balance. And Jaguar scored a production first by replacing fade-prone drum brakes with four servo-assisted Dunlop discs that easily compensated for the extra weight. The discs had demonstrated their value on Jaguar's LeMans winners.
Initially, the XK 150 was offered as a coupe and convertible. The roadster returned after nine months, but now with wind-up windows. Engine specs were the same as the 140, but the 150's extra weight prompted more buyers to pop for the 210-hp option, which now produced peak torque at 3000 rpm, not 4000. Not coincidentally, the extra-cost automatic transmission also garnered more orders, a sure sign of change in the sports-car world.
Inevitably, the first XK 150s were slower than their predecessors, but the deficit was corrected in the spring of 1958 with a 3.4-liter "S" engine rated at 250 hp. For 1960, Jaguar bored its 3.4 to 3.8 liters, rating this option at 220 hp in standard tune or 265 in "S" form. A 3.8- liter 150S could top 135 mph and sprint from 0-60 mph in around 7.0 seconds, thus restoring whatever verve the XK had been missing.
Though not the longest-lived, the 150 proved the most profitable of the original XK series. Tellingly, where roadsters had been the best-selling XK 120 and 140 body styles, the coupe was by far the most popular 150, accounting for 52 percent of sales. The roadster was the least popular, at just 13 percent. William Lyons had correctly read the evolving market and, with the XK 150's successor, he'd do it again.