Imagine, gentle reader, a cardboard box. Picture this box fresh and new, securely taped shut – both top and bottom.

Strong, isn’t it? Nice and rigid, resisting forces applied to it with stern resilience.

Now slice the top off and see what it becomes: a feeble, floppy mess, twisting this way and that at the slightest pressure. Removing the extra support provided by the top dramatically reduces the strength of the box as a whole.

The same, on a larger scale, is true of cars. A strong coupé or saloon body shell can be rendered a bendy embarrassment by cutting the roof off in a bid to manufacture wind-in-the-hair glee.

Car makers are usually faced with a choice between accepting the sloppy handling a weakened chop-top chassis inevitably creates or adding strengthening girders to the remaining bottom portion of the car to stiffen things up, resulting in extra weight.

The new open-topped Spider edition of McLaren’s 570S sports car, however, is neither heavy nor floppy. The convertible is every bit as stiff and agile as its fixed-roof siblings, while squashing the scales with about the same heft.

The source of this have-your-cake-and-eat-it miracle is a solid chunk of racing car technology at the heart of all modern McLaren models – a carbon fibre ‘tub’. Most cars derive their strength from a continuous metal body shell, with forces spread across the floor and roof. By contrast, McLaren’s carbon fibre tub – so called because it’s shaped like a broad bathtub – holds strong with or without a roof.

The benefits of this carbon fibre backbone are numerous. Increased stiffness makes for more predictable and consistent handling, with the suspension geometry undisturbed by chassis flex. Reduced weight makes the car more agile, allowing for quicker acceleration and improved braking around corners.

The tub also acts as a survival cell, armouring occupants against crash damage. But perhaps the biggest boon is the feeling of shared experience with professional racers that a 570S Spider owner derives from knowing that this car is based on Formula 1 technology.

That sense of kinship with those who wear scorch-proof onesies and spray champagne for a living is further underlined by the Spider’s driving experience. It’s amazingly fast.

From a standing start, the 494kw 3.8-litre twin-turbo V8 will hurl the McLaren’s 1,498kg to 100kph in just 3.2 seconds. Given enough road and enough bravery, a top speed of 328kph is possible.

These abstract numbers do little to communicate the startlingly rapid way that the world rushes to meet the driver.

After the mental shock comes the physical. Accelerating hard isn’t so bad; simply lean back and let the headrest take the strain. Braking is a different matter. Squeezing on the optional carbon ceramic brakes is like crash landing in water. Neck muscles strain to keep one’s focal point ahead rather than straight down.

The brakes are one of the few flat notes in the Spider’s symphony of speed. While they respond well –  translating foot pressure into deceleration promptly and predictably – there’s little feel through the pedal, making the job of judging grip levels more difficult.

As a high-speed attack weapon, the Spider is an impressive performer, but it’s capable of more than one trick. With the roof fixed in place and a gentle touch on the controls, it’s also a civilised and comfortable everyday car.

Offering good all-round visibility and taking up a sensible portion of road space, it’s easy to drive through crowded city streets and manoeuvre into cramped parking spots. Although stiffer than an SUV, the suspension will soak up lumps, bumps and potholes well enough to prevent discomfort.

It’s also a competent long-distance weekend cruiser. With the roof in place there’s little clue that the Spider is in fact a convertible. The wind roar at high speeds is minimal and the road noise is acceptable, albeit more than one might expect from a typical luxury saloon or coupé.

Overall, the Spider does everything a fixed-head 570S does, with the added element of open-top driving pleasure. The only question is whether those advantages justify the HK$205,000 price increase over the Coupé. A quick top-down, full-throttle blast through a tunnel should be answer enough for anyone.

Text: James O’Donnell
Photos: McLaren

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