See Photos of the New 2019 McLaren 720S Spider

Open-topped supercars used to be inherently compromised. Sure, they would allow drivers to better enjoy their cars' exhaust notes and add a leathery sheen to their already tanned foreheads. But such cars were almost inevitably heavier, possessed less structural rigidity, and were considerably less athletic than their coupe equivalents. They were the variants chosen by buyers for whom showing off was higher on the priority list than driving.

Which, it turned out, was most of them. In this fashion-conscious part of the market, roadsters almost always outsell their fixed-roof counterparts, and supercar makers have been working hard to sharpen and improve them, minimizing their compromises.

McLaren boasts that the Spider has the fastest roof of all open-topped supercars; it can be raised or lowered in just 11 seconds, at speeds up to 31 mph, with a small rear window opening automatically in conjunction with the roof.

The active aerodynamics of the rear spoiler automatically adapt according to whether the roof is closed or open.

The retractable hard top's action is predictably fast, as it uses a pure electrical actuation system to improve speed and reduce mass compared to the more common electrohydraulic setup.

Apart from changes necessary to incorporate a rollover protection system, the Monocage II-S carbon tub is like that of the coupe and therefore offers identical torsional rigidity.

According to McLaren, the power-operated retractable hard top has added just 108 pounds of mass compared to the fixed-roof 720S.

The roof itself is made from carbon fiber with what the company describes as glazed flying buttresses intended to improve rear-quarter visibility.

The windshield is mounted within the same carbon-fiber frame as the coupe's with impressively thin A-pillars; the only changes necessary have been for the roof's latching mechanism.

When we put a coupe on our scales, they reported 3161 pounds, which means the Spider should come in with a sub-3300-pound real-world weight-that's remarkable given the potency of the 720S twin-turbocharged 4.0-liter V-8.

This is unchanged from the coupe, producing a peak of 710 horsepower and up to 568 lb-ft of torque, all delivered through a seven-speed twin-clutch transmission to the rear axle.

The use of a retractable hard top rather than a fabric roof has also allowed the option of a glazed electrochromic glass panel, which can be electrically dimmed.

The active aerodynamics of the rear spoiler automatically adapt according to whether the roof is closed or open.