Sometimes 175 mph just isn't enough. That, at least, is the view of Jaguar North America, which reckons the limited-edition XKR-S sports coupe isn't quick enough for U.S. sports-car buyers. Knowing that AMG and Porsche specials make a big impact in the United States with sledgehammer power outputs, Jaguar NA probably has its customer radar pretty well tuned. But it means U.S. Jaguar fans will miss out on the sharpest incarnation yet of the handsome XK, created to appeal to the enthusiast leanings of two engineers. Mike Cross, Jaguar's handling guru, and Russ Varney, XK platform chief, worked out the XKR-S in spare moments as they road-tested the suspension on drives home, directing technicians to make changes during the working day."We developed an XK with the chassis we fancied as our everyday driver," says Cross, "a bit more focused than our typical customer would usually want but still comfortable and safe in all road conditions, including the wet."You notice the changes as soon as the XKR-S purrs away for the first time; the steering has a meatier feel, and the ride is firmer. The headline mechanical changes are the type that might be expected on casual examination: stiffer springs and dampers front and rear, 8 percent quickened steering rack, thicker rear antiroll bar, lighter 20-inch forged alloy wheels and wider rear tires.The forged wheels cut unsprung weight by 10 percent. The two-stage Bilstein dampers are completely revalved, the ride height dropped slightly and the variable ratio/assist ZF rack quickened by 10 percent. Jaguar also worked with Pirelli to develop bespoke tires for the XKR-S.