The Penalty for 50,000 Feet of Freedom? About 200 Pounds
Jared Gall at Car and Driver has compiled a fantastic list of coupe vs. convertible weights and found that, on average, roughly 200 pounds is needed to give God a direct look into your car. But there’s hardly any consensus among different automakers.
Porsche, for example, has no difference in weight between its Cayman and Boxster, whereas BMW’s 4-series carries a 500-pound penalty for plein-air cruising. Many bespoke two-seaters carried small penalties for drop-top enthusiasts: Jaguar’s F-Type, Alfa Romeo’s 4C and Chevrolet Corvette convertibles were all only 1 to 2 percent heavier.
The story notes that the BMW 4-Series is the only four-seater with a folding hardtop left — and not for long.
The story also measures the sound difference between coupe and soft-top versions with the roof up, which was virtually imperceptible for all cars. The Corvette and Bentley Continental GT V-8 S had the largest measurable noise differences, a whopping 3 decibels above the coupe versions at 70 mph.
Basically, to get a car full of hot air you either need 200 pounds of retractable roof or a coupe with a TTAC editor riding shotgun.
* rimshot*
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In the era of modern CAD-generated super-rigid unibody frames, cars originally designed to accommodate a convertible version should not see a significant weight difference between hardtop and convertible. Any significant weight would come from a retractable hardtop assembly. Tub-centric cars like the Alfa 4C may not even have traditional roof rails as the body does not rely on the roof for its rigidity. Roll protection is provided by front (windshield) and rear roll bars. In this case, the 4C Spider's targa top is of no structural consequence and therefore also of very little weight penalty. My favourite structural rigidity story is the Ferrari 348. Early pre-production 348TS (the targa version) were literally tested to destruction. After a hard drive, the doors would no longer open and close properly. One car's targa top would no longer fit because the roof opening had collapsed by 2 inches after track testing. Early customer cars had already left the factory and had to be recalled for additional structural reinforcement.
My Corvair is actually quieter with the top down. The top when down fills in the section behind the back seat and cuts down on engine noise of the rear engine. The not very aerodynamic top catches the wind and causes wind noise. It's not the greatest fit.
That's because two-seaters like the 4C, Corvette and Boxster/Cayman tend to be engineered as roadsters from the start, so that the top carries little to no structural duty. The vehicle doesn't require any extra bracing when an integrated top is taken out of the equation, and that the small weight gain on the cabriolet version comes solely from the mechanisms that fold and store the roof. Meanwhile, a cabriolet as large as the 4-Series is going to need a lot of help staying rigid without the top, and so is noticeably heavier...not to mention the added weight of the folding hardtop ballet.
I think one issue we have is that of expectations. We have seen the best out there and thats a fully electric folding metal top... and we want to do it while the car is in motion (up to a reasonable speed). So in anything less, we ask why? Dont get me wrong, I like the Corvette style pop out top which is minimal impact. But if you ask me to pay $50k for a car that has a fabric manual top then I have to question why I'm doing this?