Hypnotized by the sea-blue BMW that slipped into my parking space a few weeks ago, I stopped wondering about how fast this test car would go or whether it could stop at all.

You should do the same.

But if you insist on details and are given to using words like downforce and stoichiometry, be assured that the 2010 edition of the Z4 is plenty fast and halts like a drill instructor.

Will it describe an asphalt arc as mathematically as the Porsche Boxster? No. But here’s the dirty little secret of luxury convertibles: Most buyers don’t do math.

For those who would consider dropping $50,000 or even $60,000 on a two-seat driveway ornament, this is what matters: The BMW is beautiful, inside and out. It’s the most luxurious convertible this side of a $100,000 Jaguar XKR or Mercedes-Benz SL550. The exterior makes the Porsche Boxster seem a bit played out; the interior makes a Corvette’s look like recycled duct tape.

If you don’t believe me, ask my wife. She drove the Z4 to the corner store and pronounced it her new favorite car, even before she shifted out of second gear. Add her to the week’s worth of women and men who flirted with the BMW, smitten by its milelong hood and sophisticated creases and cavities.

The new Z4 is undoubtedly one of the best do-overs in recent years, a confident, muscular reinvention by Juliane Blasi and Nadya Arnaout of BMW’s Munich design studio. The previous generation of the Z4 was cloyingly overstyled, arguably the least successful design by Chris Bangle, who has stepped down as BMW’s design chief. And with an exception for the brilliant M Coupe version, that earlier Z4 also fell short in arousing passion for many drivers.

The new car, now with a retractable metal roof rather than a soft top, soothes rather than strains the eye. And it is more engaging to drive, especially with the twin-turbo in-line 6 as was the case in the sDrive35i version I tested. BMW also slid the Z4 toward the decadent end of the two-seat spectrum.

The new car is nearly a half-foot longer and roughly an inch wider, but drivers are likely to show a greater appreciation for the richness of its cabin appointments, a first-class upgrade from the barren surroundings of the previous Z4. The glove box and interior storage accommodations are reasonable, and an optional center pass-through to the trunk lets owners carry two sets of skis or a full-size golf bag.

With its top down and midriff exposed, my Z4 test car looked ready for a South Beach summer, its paint hue contrasting smartly with the resort-ready ivory leather on the seats, dashboard and door panels.

On a run through the horse country of Dutchess County, N.Y., I dropped the top to feel the sun and hear that playful engine along the rolling two-lane roads. With 300 horsepower and 300 pound-feet of torque, the twin-turbo power plant has become BMW’s well-bred workhorse, powering everything from the 1 Series coupe and 3 Series sedan to the X6 crossover.

BMW cites a 5.1-second 0-60 mph time for the stick-shift 35i. That seemed conservative; Car and Driver magazine managed a brisk 4.8-second run. Even the lesser sDrive30i, equipped with a naturally aspirated 255-horsepower in-line 6, runs the 0-60 dash in 5.6 seconds.

In the tricky balancing act for any expensive convertible, the new BMW definitely leans toward luxury — but not so far that it loses touch with its sporting principles.