Go to the Globe and Mail homepage

Jump to main navigationJump to main content

The wind blasts you from all directions in the 1967 Pontiac GTO. (Peter Cheney/The Globe and Mail)
The wind blasts you from all directions in the 1967 Pontiac GTO. (Peter Cheney/The Globe and Mail)

Road Rush

Why convertibles are a bad idea, and why I love them anyway Add to ...

Like the Double Down sandwich and the breast implant, convertible cars aren’t the best idea. But we want them anyway. I thought of this when my friend Yvonne asked me when Porsche was bringing out a convertible version of the Panamera.

In case you don’t already know, the Panamera is a four-seater that looks like a supercharged athletic shoe – Porsche snobs don’t like it, but it sells really well.

More Related to this Story

The Panamera is a triumph of consumer demand over the forces of design logic and automotive purity: the people wanted a big, luxury-laden barge of a Porsche, and they got it. And now my friend wants a convertible version. The writing was on the wall – a convertible Panamera might be an engineering nightmare, but the elves are probably working on it as we speak, because people like my friend Yvonne desire it.

The spray tan is already with us, as is the Big Gulp soft drink and the expandable waistband. And now the Panamera cabriolet may be on the horizon – Western civilization, it seems, has a little further to fall.

I went home and contemplated the structural, mechanical and aerodynamic problems that would be involved in turning the Panamera into a cabriolet. How many reinforcing members would it take to stiffen that plus-sized body? How many motors, micro-switches and labyrinthine mechanisms would it take to construct an origami-style folding metal top – or, God forbid, a fabric one? I was suddenly glad that I was not a Porsche designer.

The convertible conundrum had reared its ugly head yet again.

Cutting the top off a car is never a good idea. (If the engineers had their way, there would be no topless vehicles.) But the convertible car is not a product based on best engineering practice. Instead, it is the bastard child of overweening vanity and irrational desire – we want the sun on our face, the wind in our hair, and all eyes upon us. (I admit that I have a weak spot for convertibles.)

Even though I enjoy driving them, convertible cars are an engineering travesty – by removing a car’s top, you compromise its structure, and reduce its strength in virtually every plane. (Removing one side of a box is not a wise plan.) Compared to a car with a roof, a convertible is a wet noodle, with vastly reduced torsional stiffness.

To the average driver, “torsional stiffness” is an abstract term. To understand its true meaning, try driving a convertible over railroad tracks at speed, and feel the car moving beneath you like a horse. In some convertibles, you get the sense that the steering wheel and dashboard are moving in a different direction than yourself (unfortunately, they are.) Known as “cowl shake” or “scuttle twist,” the flexible body phenomenon has plagued convertibles since the time of Henry Ford.

Although many modern convertibles have minimized cowl shake with high-strength materials and computer-assisted design, no convertible can equal its hardtop counterpart for strength (except by adding massive reinforcement that increases weight to unacceptable levels.)

I’ve driven some exceptional convertibles (the new Porsche Boxster comes to mind) that reduce cowl shake so effectively that the car feels completely solid. But not even the best designers can overcome the laws of physics – the Boxster’s hardtop brother, the Cayman, is stiffer, lighter and safer (if you go upside down, a roof is always better than a roll bar.)

To really experience cowl shake (and understand what a bad idea going topless can be) you need to try a convertible along the lines of a mid-1980s Chrysler LeBaron (a K-car with its top hacked off and a few stiffeners welded into the sills) or an English classic like a 1950s Morgan, MG TC or early Triumph.

Back in the early 1970s, I got the opportunity to drive a Triumph TR3, a roadster with cut-down doors and a Battle of Britain-style dash lined with crackle-finish Smiths gauges and steel toggle switches. I loved the idea of the TR. The reality was something else again.

As I passed over bumps, the TR writhed and contorted beneath me as if half of its bolts had been removed. The car was alive, and not in a good way – I believed that I could actually feel the steering geometry altering as the car twisted and heaved, shifting the relationship of the suspension arms and steering rack as if they were made of taffy. This was cowl shake at its worst – the angle of the TR’s hood altered before my very eyes, snapping and bending back and forth like the deck of a tramp steamer caught in a storm.

Every time I drive a convertible, I am struck by the Faustian bargain involved in its essential design – taking the top off a car heightens the sensation of driving, but it makes the car perform worse. Over the years, I realized that the convertible top is a bad deal in virtually every sense – it is less weatherproof than a hardtop, it steals trunk space when it’s folded away, and it offers all the security of a pup tent (a thief can slice through it with a pen knife and make off with your prized possessions.)

These deficiencies never stopped me from loving convertibles. And when I get my hands on one, I make the most of it – the top stays down almost all the time. (Some of you may recall my top-down winter drive from Ontario to Georgia with my wife in a Porsche Boxster – and yes, we are still married.)

The modern convertible represents an improbable triumph over the forces arrayed against it. As I piloted the Boxster southward, I was amazed not only at its structural stiffness, but at the way Porsche’s designers had managed to control the airflow over the car – my wife and I rode in a bubble of still air, with only a light breeze wafting over our heads and shoulders.

A couple of days later, we found ourselves in an old-school convertible – my friend Matt’s 1967 GTO, a black, fat-tired throwback to the days of Jimi Hendrix and seven-litre V-8s. The GTO was a classic, but compared to the Boxster, it was like riding on the wing of an airplane – the wind blasted us from all directions (including behind.)

The GTO was built in an era when designers worked with drafting boards and slide rules, and the limitations of its structure were apparent – I could feel the big V-8 and massive tires twisting the GTO’s body as we hammered through the curves.

It was still a great ride. My friend Matt and I were driving a car we had dreamed of ever since we were boys. The sun was shining, and the women we loved were with us, their hair blowing in the wind. We were in a convertible. Logic had gone out the window – or maybe it had blown out the top. Either way, it was a good time.

For more from Peter Cheney, go to facebook.com/cheneydrive (No login required!)

Twitter: Peter Cheney@cheneydrive

E-mail: pcheney@globeandmail.com

Globe and Mail Road Rush archive: http://www.theglobeandmail.com/globe-drive/car-life/cheney/

In the know

Most popular video »

Highlights

More from The Globe and Mail

Most Popular Stories