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If you have been to Sanya in recent years, you should pay attention to the rental convertibles running around the streets. From the Lambord Ferrari to the MINI Beetle, the abundance is made up of people; from the open-top Aurora four-seat SUV, to the TT and Z4 two-person worlds, the world is at your disposal.
I don't know whether the tourism rental business is too prosperous, or the pockets of the people are indeed rich. Although the niche car market is getting worse and worse every year, the open-top dream of independent brands "since ancient times" has rekindled.
Picture: @Weidian New Energy Automobile Community
In the past year alone, bydir Han EV convertible version and Geely Binrui convertible version have emerged one after another, although it is produced by a private modification factory (only electric & craftsman school), it has done a good job. Personally off the scene is Wuling, Hongguang MINIEV officially announced the existence of the mass production convertible version. On the other hand, Chery Ant and Euler also launched an open-top concept car. It is like a momentum of independent large factories coming together.
MiniEV's mass production declaration chart
In the early years, people's impression of convertibles was equivalent to "sports cars" and "luxury cars", and after the baptism of the presence of batches of medium-priced convertibles over the years, most consumers should have walked out of this misunderstanding. Today's convertibles are no longer associated with local tycoons and rich people, but more represent a way of life.
There is an unwritten little advice about what kind of car is suitable for the convertible: either give up on yourself and choose those people-friendly cars just to enjoy the sky, or head to the end and go straight to the top supercars "I want it all". This stems from the seemingly simple change of the open top, behind which there are some imperceptible costs.
Sexier, but also more "fat"
If you pay attention to the quality of the overhaul of models that have both convertible and non-convertible versions, it's easy to see that the convertible version is generally much heavier than the regular version.
The F32 BMW 4 Series Coupe weighs about 1550kg, and the same power 4 Series Convertible weighs more than 1725kg; the Audi TT Coupe weighs about 1295kg, while the TT Roadster weighs 1385kg; the Wuling Hongguang MINIEV weighs 660-700kg in the ordinary version, while the open-top version declares a curb weight of 925kg.
Contrary to people's preconceived instincts, it is common to change from a coupe to a convertible, and the quality of the whole is 10-20% more. The reason is that to cover the same roof area, the moving parts will always weigh more than the fixed parts - especially today's convertibles are mostly electric roofs, plus the weight of the folding operating system.
But before it was over, the weight increase brought by the convertible was not only due to the fact that the roof was fixed to active. Like those soft-top convertibles, the cloth soft top is obviously lighter than the steel roof of the hard-top model, and even if the electric folding structure is added, it will not be more essential than the latter, but the whole vehicle is still generally heavier than the non-open-top version.
The soft-topped convertible is lighter, but pays off
The aforementioned Audi TT belongs to the soft-top convertible, and the weight increase of the convertible version is significantly less than that of the 4 Series F32/F33. BMW changed the original hard top to a soft top on the G22 Generation 4 Series, so the weight difference between the new generation of 4 Series convertibles and the hardtop Coupe was reduced to less than 150kg.
The problems caused by weight gain are familiar to everyone: increased fuel consumption, decreased performance, reduced battery life of electric vehicles...
More chic, but also more "soft"
The remaining weight, which cannot be compensated even with a soft roof, comes from the body reinforcement necessary after the roof is cut off.
In the eyes of people who do not know much about the body of the car, all parts of the car are steel and iron bones, and there is no difference. But Ben Hu in "Why Do I Have to Make You Care About the "Car Shell"? It has been explained that the doors, front and rear bumpers, and some fenders are all body coverings and do not participate in the normal body force and stiffness construction.
For us humans, the door is almost integrated with the whole car when the door is closed. But the door is a moving part, it actually only has a few "points" of hinges and locks connected to the body, and these connection points are very fragile relative to the body body. For the body-in-white body force, the door not only does not help in any way, but in turn requires the body to have enough stiffness to ensure that there will be no abnormal noise or even abnormal opening and closing caused by deformation near the door.
This is true of the doors, and of course the roof. The soft top does not have any reinforcing effect on the body, which is easy for everyone to understand, and the folding hard top that looks stronger is not much stronger than the soft top. The hard roof, which is divided into two and three folds, is more precise, has a smaller fault tolerance rate, and requires a high stiffness of the body-in-white body to avoid deformation and abnormal noise. Regardless of whether it is soft or hard, the roof structure of the convertible has zero reinforcement effect on the body.
The mid-body-in-white section of the convertible is almost two-dimensional
The body-in-white body is also difficult on its own. For non-convertible models, the body floor, side to the roof is a complete three-dimensional cage structure; for the convertible car, the roof and doors that are almost useless to the body load are removed, and the middle of the body in white is essentially only a base plate left - which is a disaster for the important indicator of stiffness.
The central tunnel height of the AMG SL improves the torsional resistance of the baseplate
The central tunnel of the bottom plate of the fuel vehicle body and the base plate beam can help to some extent, but the effect is limited compared to the complete frame of the hard-top model. One is a box express box that has been sealed, and the other is that the two sides of the open carton are still missing mouths, which is more resistant to twisting, which is more resistant to manufacturing is obvious.
The bad news continues. The roof of most convertibles needs to be folded into the trunk (or a special position between the seat back and the trunk). In order to allow the folded roof to enter and exit smoothly, it is required that the trunk/roof storage space can not be hindered in any way, and such a cavity structure is an unfavorable factor for improving the stiffness.
A 10-20% weight gain is nothing compared to a "huge" stiffness loss:
Porsche 911 Turbo (996), hardtop and convertible versions have a torsional stiffness of 27,000 Nm/deg and 11,600 Nm/deg, respectively; BMW Z4 (E87/E86), 32,000 Nm/deg and 14,500 Nm/deg, respectively; Ford Mustang (previous generation Mustang), hardtop version of 21,000 Nm/deg, and the convertible version has only a pitiful 9,500 Nm/deg.
The above models are somewhat ancient, but what is important is not the specific value but the relative order of magnitude: hard top to open top, body stiffness is almost directly cut in half. Among the major body type categories (sedan/SUV/travel, etc.), the convertible is one of the lowest body stiffness. Even if it is a million-level convertible luxury car, the body stiffness is probably the same level as the mainstream family car of the same era.
And this performance is still obtained in the case that car companies generally increase body reinforcements (another main reason for weight gain).
Typical convertible bottom body reinforcements
What stiffness means, Ben Hu has talked about many times in past articles, including the previous link. The simple summary here is that it is the cornerstone of the vehicle's driving quality, which is both the foundation of comfort and NVH, and the upper limit of handling performance. Whether you are the safe guy who picks up and drops off his mother-in-law, or the ghost fire teenager who drifts to brush the circle, it is inseparable from the contribution of the rigidity of the body.
For the convertible, because of the complexity and fragility of the folding roof (especially the hard-top convertible), the stiffness affects the reliability and durability of the convertible mechanism in the process of long-term use, and even affects the second-hand salvage rate of the whole vehicle - who will trust a convertible with a roof creaking?
Want it all? You get the answer
Freedom always comes at a price. Reason and "Why do hatchback sedans always go into the flow?" Whether it is the convenience of the hatchback tailgate, the large space of the SUV and the station wagon, or the dashing handsomeness of the convertible, there is always a price behind it, and there is no free lunch in this world.
However, at some point when there is enough room for the technical ceiling, it is indeed possible to spend a lot of money on "I want it all" to a large extent – of course, the cost itself is also a price. Derived from F1, the carbon fiber monocoque is a magic item that makes the convertible easily comparable to the hard-top model.
Please note that not all "(so-called) carbon fibre bodies" are equivalent to "carbon fibre monocoque bodies", of which there are many abusers. The monocoque means that the body is almost entirely carbon-fibre monolithic, rather than using carbon fibre only on partial overlays or reinforcements. The latter is becoming more common today, and monocoques are almost exclusively used in (multi-million yuan) supercars.
918 Spyder monocoque body (aluminum for front and rear stringers)
As the pyramid tip of the current body material, the density of carbon fiber is only about 1/4 of that of steel, and a variety of fiber weaving methods can adapt to the force in different directions, and carbon fiber composite materials can shape various shapes. These innate advantages allow the all-carbon fiber monocoque body to have a much higher body stiffness than the traditional steel and aluminum car under the premise of lighter weight.
Although I am reluctant to use such a simple and rude network cool word, the four words of "dimensionality reduction strike" are not exaggerated here.
So you can also understand why there is a saying that the convertible either abandons the treatment or steps to the top. The choice of affordable convertible is because since the driving quality is destined to be pulled down by the half, it is better to simply open for the purpose, other needs can be put into another car; choose the top supercar, because there is a bathtub-style carbon fiber monocoque shell body, to ensure that the performance is not inferior to the hardtop version, which is the money smashed out of the effect.