For reasons that scarcely require elaboration, "lubricity" is one of my favorite words. It is, first of all, fun to say, all slippery with sibilance. Second, many fine things are lubricious in nature. Easy dinner conversation, for instance. The balanced slickness of a well-oiled pistol (caution: Avoid combining dinner conversation and pistols). In fact, lubricity might even be counted as one of the universal cues of quality. Whenever a thing has a heft and substance that nonetheless yields to effortless operation -- a Waterman pen, for instance, or the stout zipper on Prada boots, or the gliding drawers of a Pegaso desk -- that registers as a thing well made.

I propose Neil's Coefficient of Frictional Quality. In any object with moving parts, the ease of that moving is directly proportional to the quality thereto.

And that brings us to the 2008 Audi S5 Coupe. The S5 -- the performance variant of the A5 Coupe, with an extra 89 horsepower in the snout -- is another in a lengthening line of Ingolstadt's products that deliver crazy-great performance with a refinement and absence of stiction that makes them feel like they are lubricated with angels' tears. Or the fatty renderings of an enchanted ermine from some Russian folk tale. Or Astroglide. Whatever it is, these cars' moving parts seem to commune in a way that has banished friction to the dustbin of physics.

This quality -- which manifests itself as smoothness in operation, and absence of noise and vibration -- is even more notable because the S5 has so darn many moving parts. Obviously, there's the lump of recip- rocation under the hood, a slightly de-tuned version of the 4.2-liter direct-injection V8 found in the R8 sports car. With its super-stiff deck, counter-balance shafts, active engine mounts, lightened and micro- polished valve train assemblies and silicon-impregnated cylinder lin- ings, this dual-cammer revs with a lightness, a willingness, a zingy-ness (not, officially, a word) that makes it feel like it's topped off with 5 quarts of 0W-nothing-weight motor oil.

The S5 is fitted with a conventional six-speed manual transmission (automatics will come later, but there are no plans to offer the DSG "manumatic" gearbox so beloved by Audi-ence members). Not surprisingly, the S5's clutch pedal action is light and precise, but it's the way the clutch engages -- with no palpable vibration, or even a dry whisper as it meets the flywheel -- that is so uncanny. It's like the clutch is a felt-buffing wheel stolen from Harry Winston. This refinement is no minor feat, considering the S5 sings 354 hp at 6,800 rpm and 325 pound-feet of torque at 3,500 rpm. A Porsche 911 has roughly the same amount of power and torques, and when that clutch hits the flywheel it sounds like cattle getting romantic. Mooooooo.

Dump the clutch and the S5 digs for China. In less than five Mississippis (two shifts), you're at 60 mph. Third gear is passing-lane nirvana. Just nail the throttle and watch the tach needle dive for the 7,000 redline like it's being shot at. Keep the engine whirring away at high velocity and pretty soon you're crossing into three-digit territory, at which point you stand an excellent chance of being thrown in jail.

Compounding the engineering achievement, the S5 is also all-wheel drive, or Quattro, as the company's marketers would have it. This doubles, at least, the amount of parts rubbing against themselves, including gears, clutches, couplings and half-shafts. Gearheads will be interested to know that, in order to lengthen the wheel- base (over the A4 platform on which the A5/S5 is based), Audi sandwiched the front differential between the engine and the clutch assembly. Again, a fairly tricky bit of blacksmithing.

I could go on like this since the whole car (switch gear, doors, brakes) feels as if it were dipped in hot-buttered sin. But what I remember best from my time in the S5 ($50,500 base price) is its immaculate steering and handling. What a wonderful car to flog! For starters, the engineers moved the steering rack closer to the front wheel centerline, which frees up the steering, which is to say that it requires less hydraulic boost and transmits more live road feel to the driver's fingertips. Meanwhile, the car's redesigned front suspension -- aluminum five-link with an aluminum subframe -- locates the wheels with a heavily damped, battened-down security. No kickback in the steering, no pavement twitters, no jostling oscillations. To be sure, the ride on these 19-inch, 35-series gum- ball tires is crisp, but overall, the car feels like the fifth face carved in Mt. Rushmore. Solid gran- ite.

Lower and wider than the A4, and shod with the mighty Dunlop Sport Maxx tires, the S5 has road-holding grip for days. And, thanks to the 60/40 torque split of the Quattro system, it has the handling character of a proper rear-drive sport coupe. You can kick the rear end around with the throttle and not bog at the nose, which is more typical of all-wheel-drive cars. The hard-sprung suspension keeps the car level in steady-state cornering and damps out big, ugly weight transfers in transitional handling.

Perhaps the slickest bit of lubrication on the S5 is its shape. With the merciless technical beauty of that face, with the big chrome-streaked grille and the trapazoidal bumper intakes, the car should not cut through the air as easily, or quietly, as it does (wind noise in the cabin is barely there). Then again, this is a highly developed form we're talking about. Note the balance between the rake of the windshield and the complementary slope of the backlight. Also, the integrated, air-spoiling lip on the deck lid and the air-managing fascia under the rear bumper, between the double-barreled dual exhausts. That's pretty slick.

As a real-world, break-out-the-checkbook investment, the S5 is more accomplished than the Mercedes-Benz CLK, more affordable than the BMW M6, more practical than a Porsche Cayman.

But for me, as much as I admire the Audi, I could never, ever buy a car that gets 14/21 city/highway mileage. For all its lubricity, the S5 has that one major sticking point.

2008 Audi S5 Coupe Base price: $50,500

Price, as tested: $57,715

Powertrain: 4.2-liter, DOHC, 32-valve direct-injection V8 with variable-valve timing; six-speed manual transmission; all-wheel drive

Horsepower: 354 hp at 6,800 rpm

Torque: 325 foot-pounds at 3,500 rpm

0-60 mph: 5.0 seconds

Wheelbase: 108.3 inches

Overall length: 182.5 inches

EPA fuel economy: 14 miles per gallon city, 21 mpg highway

Final thoughts: Greased lightning