By on October 26, 2015

2014 BMW 4 Series Convertible 01

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.


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28 Comments on “The Penalty for 50,000 Feet of Freedom? About 200 Pounds...”

  • avatar

    Who at BMW really thought that hood cutline was acceptable?

  • avatar

    A 3dB difference between the soft and hard top is not “whopping”. While on a raw power basis, it represents a doubling of power, the whole reason we measure sound in decibels is because the ears perceive sound on a logarithmic scale; a human will only perceive it as approx. 20% louder.

    Perceptible (3dB is around the minimum where you’ll say: “Hey this car is louder than the other”), but hardly “whopping”… (As in, not a Lexus Sedan (silent) vs. Wrangler (wear earplugs on the interstate) difference.)

    • 0 avatar

      I believe that 2dB is the minimum difference that’s audible for most people, depending on the frequency of the audio.

      I was working with some electric guitar pickups, trying to get a handle on the relationship between the distance of the pickup from the vibrating element and the output of the pickup. I first did some tests using my ears, figuring out the smallest distance that yielded an audible difference out of the amp and speaker. I followed up with tests with a sound pressure level meter and the minimal audible difference to my ears worked out to ~2dB on the meter.

    • 0 avatar

      3 dB makes quite the difference over a day’s worth of exposure. Early tractor cabs were uninsulated–just metal boxes. They were never tested for sound at Nebraska, but came in anywhere between 90 and 100 dB–enough to cause serious hearing damage. My great-grandfather bought a John Deere 4020 with a cab brand-new in 1970, and was all but deaf in 5 years.

      When John Deere introduced the Sound-Gard cab in 1973, which was not only insulated but also isolated, sound tests came in at 78 dB, which pretty much got rid of the deafness issue. The tractors we use with the newer ComfortGard cab are down to about 73 dB (or maybe a little higher because some of the rubber strips are coming off the windows), which is noticeably less headache-inducing over the entire day.

  • avatar

    I test drove an ND Miata 2 weeks ago. While I loved the light weight and the great handling, the noise with the top up would be an absolute deal breaker. It was fantastic with the top down. I’d need to live somewhere that I could keep the top down 80% of the time to even consider it.

    • 0 avatar

      If you stay above 50 mph, the rain flies right over your head.

      As for cold vs. hot, I find it easier to drive my NB with the top down when it’s near freezing (as cold as it gets here) vs. 95 degrees. The heater’s great; the A/C isn’t.

    • 0 avatar

      Older cars with problematic power-folding tops should just be kept with the top always down, and only taken out in good weather.

      I know someone with an F355 Spider who isn’t sure whether his top even works anymore. It’s notoriously tricky to keep working properly, and some owners have even converted it to manual operation to remove the headache and wallet-bleed.

      • 0 avatar

        I had a SN95 Mustang Cobra Hardtop Convertible for about ten years. I would habitually leave off the hardtop assembly as it was bulky and simply leave the soft top in stowage with the tonneau covering it. However, even kept sweetly in the garage, I would have to clean the leather and interior at least once a month from the Kansas dust (and occasional cat!) that would coat the inside. Not a good idea in the long run.

  • avatar

    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.

    • 0 avatar

      Agree with what you say about body design. The M3/4 seems to be an exception where a particularly clever design has limited weight to about 3600 lbs for the normal roof versions.

      I posit the absence of the roof negates the cleverness and requires extensive reinforcement for the convertible. Since it is a niche version of a niche model, it probably wasn’t worth strengthening the sedan/coupe and bloating weight on the far more popular body style. Let the sun-worshippers pay for their affliction instead, sort of thing.

      Just a guess.

  • avatar

    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.

  • avatar
    Kyree S. Williams

    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.

    • 0 avatar

      That may be true, but the roof can still make a difference. If I jam my finger in the gap between the door panel and the dash while driving my C7 convertible on badly broken pavement I can feel differential movement between the two. The coupe I drove did not exhibit that trait. Still, much much more rigid than my friend’s 2012 Camaro convertible.

  • avatar

    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?

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