Convertible

For the currency reference, see convertibility. For the stock trading reference, see convertible security. For the carriage, see Cabriolet (carriage)

A convertible is a type of automobile in which the roof can retract and fold away having windows which wind-down inside the doors, converting it from an enclosed to an open-air vehicle. Many different automobile body styles are manufactured and marketed in convertible form.

Open cars may have a folding roof but only detachable sidescreens which snap-on, they do not convert into a fully enclosed car with proper weather-protection. The wind-up windows make the distinction between an open car and an all-weather car now known as a convertible.

Convertibles are a luxury because they are more expensive to build than closed cars, the matching sedans or saloons. Open cars were significantly cheaper to build and very much lighter than sedans, saloons or convertibles and usually very flexible.

Open cars often have or had four doors but with the later emphasis on rigidity of construction four-door convertibles became extremely rare.

Flexible or rigid roofs

Roof designs vary widely, but a few characteristics are common to all convertibles. Roofs are affixed to the body of the vehicle and are usually not detachable. Instead the roof is hinged and folds away, either into a recess behind the rear seats or into the boot or trunk of the vehicle. The roof may operate either manually or automatically via hydraulic or electrical actuators; the roof itself may be constructed of soft or rigid material. Soft-tops are made of vinyl, canvas or other textile material; hard-top convertibles have roofs made from steel, aluminium, carbon fibre or plastic materials.

Descriptions

Contemporary convertibles are known and marketed under several different terms due to the convergence of body styles over the years. A convertible may be described as a drop-head coupé, a cabriolet or cabrio, an open 2-seater without wind-up windows as a spyder, or spider or roadster. Retractable rigid roof (or hard-top) cars are marketed as simply retractable hardtop and French versions as coupé cabriolet or coupé convertible.

Folding textile roof

The collapsible textile roof section (of cloth or vinyl) over an articulated folding frame may include linings such as a sound-deadening layer or interior cosmetic headliner (to hide the frame)  – or both – and may have electrical or electro-hydraulic mechanisms for raising the roof. The erected top secures to the windshield frame header with manual latches, semi-manual latches, or fully automatic latches. The folded convertible top is called the stack.

Cons

Convertibles offer the flexibility of an open top in trade for:

• potentially reduced safety
• poor break-in protection
• deterioration and shrinkage of the sun-exposed textile fabric over time
• diminished rear visibility, from a large roof structure, small rear window, or obstructed rear window – or all of these: e.g., Mini convertible.
• generally poor structural rigidity. Contemporary engineering goes to great length to counteract the effects of removal of a car's roof. For example, a 2007 article in the New York Times, referring to the Volkswagen Eos, reported:^[1]

To neutralize the loss of torsional rigidity inherent in any convertible, VW engineers cleverly took the basket-handle roll bar of the VW Cabrio, inverted it and placed it under the rear seat pedestal. A beefed-up windshield frame of hot-stamped ultra-high-strength steel is connected directly to the floorpan’s reinforced frame rails. Steel tubing provides more stiffness behind the doors for an extra layer of safety. Partly as a consequence, rear seat passengers have about 10 inches less shoulder room than in the smaller Rabbit.

— Jerry Garrett ,  New York Times

• specifically poor structural rigidity, such as pronounced scuttle shake, a characteristic whereby the structural design of the bulkhead between engine and passenger compartment of a convertible suffers sufficiently poor rigidity to negatively impact ride or handling – or allow noticeable vibration, shudder or chassis-flexing into the passenger compartment.
• lesser handling qualities in sports models due to lower torsional stiffness – and therefore requiring harder suspensions to achieve the equivalent roadholding, but at the expense of worse ride quality.
• higher curb weight due to mass of the automatic raising mechanism, as well as the extra structural reinforcement to compensate for lesser rigidity. This invariably means weaker performance than an equivalent coupe.
• In most cases, less cargo space,^[2] with some models the "trunk space is ridiculously skimpy"^[3] or almost none such as in the Volvo C70 when the hard roof is stowed.

Tonneau covers

Folding textile convertible tops often do not hide completely the mechanism of the folded top or can expose the vulnerable underside of the folded top to sun exposure and fading – in which case tonneau covers of various designs snap or secure into place to protect the folded roof and hide the mechanicals. Detachable foldable, rigid or semi-rigid covers require space-consuming storage inside the vehicle – and sometimes complicated installation from outside the stationary vehicle. Foldable vinyl and cloth covers can be prone to shrinkage, further complicating installation.

Evolution of the tonneau cover

• The tonneau of a car is the rear part of an open car, usually passenger seats, other times just a luggage well. A tonneau cover protects that area when its not in use. The tonneau cover may also extend over the folded roof and an unused front passenger seat and further extend over the entire passenger compartment particularly for an open car without side-weather-protection (windows sliding down into the doors). It then provides complete weather protection for the entire passenger compartment and some sense of security to the owner.

• The MKI (first generation) MGB (1963) roadster could be supplied with a foldable vinyl tonneau cover, often supported by a light detachable tube installed to span behind the seats, the cover being attached to the car with a series of twenty press fit snaps. The standard cover was a permanent vinyl or cloth roof or convertible top – fixed to a relatively complex manually erected convertible frame. Weather-proof erection required the use of those same snaps from outside the car if a tonneau cover had just been removed.

• Convertibles such as the Chrysler LeBaron (c. 1988) used sleeve and groove systems to anchor a foldable vinyl tonneau cover, again installed manually from outside the car. Later textile convertibles used semi-rigid plastic tonneau covers, e.g., the first generation Audi TT and Cadillac Allanté.

• Convertibles such as the fifth generation of the Cadillac Eldorado featured a detachable two-part, fully rigid, manually installed tonneau sufficiently strong to support a seated person – also known as a parade boot.

• Convertibles such as the second generation Mercedes SL popularized the integral manually operated self-storing rigid tonneau cover – in its case accompanied by a separate removable hardtop. In either case, the design required manual operation from outside the stationary vehicle.

• Convertibles such as first Porsche Boxster,^[4] Toyota MR2 and third generation Mazda MX5 (NC) featured Z-fold (aka zig-zag fold^[4]) tops, whereby the exterior of the neatly retracted fabric roof also protected the remaining roof from sun exposure – eliminating the aesthetic or protective need for a tonneau cover.

• Convertibles such as the second generation Ford Thunderbird (1958) convertible and the fourth generation Mercedes SL popularized the complex electro-hydraulic roof mechanism that automatically secured the folded top under a rigid tonneau – button activated by a seated driver – and later more routinely available on convertibles such as the Volvo C70, Chrysler Sebring and Mitsubishi Eclipse Spyder.

• The contemporary retractable hardtop convertible such as the Chevrolet SSR include tonneau covers that "self-store" the roof assembly.

Detachable hardtops

Convertibles such as both the first and eleventh generation of the Ford Thunderbird and the second and third generations of the Mercedes SL featured as standard or optional equipment fully rigid, manually installable hardtops – later examples including heatable rear windows. These hardtops provided acoustic insulation but also required space-consuming off-season storage – and a cumbersome two-person installation. The optional aluminum (i.e., lightweight) detachable hardtop for a Porsche Boxster weighed 51 lb (23 kg).^[4] Two current-day examples of vehicles with a detachable hardtop available are the Jeep Wrangler, and the Mazda MX-5.

Convertible windows

Side windows non-existent in open cars which may have detachable side screens, are manually or power operated glass side windows as in a saloon or sedan. Rear-windows have evolved similarly, with plastic rear-windows appearing as late as the first generation Porsche Boxster. Contemporary convertibles and retractable hardtops feature heatable glass rear windows to maximize visibility – though rear windows often can compromise visibility by their size, as with the case of the very small rear window and restricted visibility of the Mitsubishi Eclipse Spider. Plastic windows can degrade, fade, yellow and crack over time, diminishing visibility.

Windblockers

Windblockers or wind deflectors minimize noise and rushing air reaching the occupants – specifically cold air (and the noise that comes with it) rushing from behind the passengers having been forced over the windshield then returning to the natural lower-pressure zone where the passengers sit.

Mazda pioneered the windblocker with its Mazda RX7 convertible featuring an integral rigid opaque panel that folded up from behind the two seats. Current convertibles feature windblockers of various designs including detachable fold-up designs (e.g.,Toyota Solara), vertically retractable glass (e.g.,Audi TT), carefully designed minimal flaps (e.g.,Mazda Miata) – or other integrated wind controlling systems.

Mercedes and Audi currently offer a feature that routes a heating duct to the neck area of the seat on SLK, SL and A5/S5 models, marketed as the "Air Scarf".

According to the chief engineer for the 2008 Chrysler Sebring, Jim Issner, the windblocker for the Sebring reduces "wind noise by approximately 11 to 12 decibels".^[5]

Safety

Contemporary convertible design may include such features as electrically heated glass rear window (for improved visibility), seat belt pre-tensioners, boron steel reinforced A-pillars, front and side airbags, safety cage construction – a horseshoe like structure around the passenger compartment – and roll over protection structures or (ROPS) with pyrotechnically charged roll hoops hidden behind the rear seats that deploy under roll-over conditions whether the roof is retracted or not.

Notably, the Volvo C70 retractable hardtop includes a door-mounted side impact protection inflatable curtain which inflates upward from the interior belt-line – vs. downward like the typical curtain airbag.^[6] The curtain has an extra stiff construction with double rows of slats that are slightly offset from each other. This allows them to remain upright and offer effective head protection even an open window. The curtain also deflates slowly to provide protection should the car roll over.

Variations

Convertibles have offered numerous iterations that fall between the first mechanically simple but attention-demanding fabric tops to highly complex modern retractable hardtops:

Roadster: A roadster was an open two-seater possibly with a frame that required actual assembly (i.e., not retracting) and separately installable soft side "window" panels – offering little protection from inclement weather and often requiring time-consuming apparently complicated installation. Examples range from the very first cars to the vintage Porsche Speedster introduced in 1955, and the classic Jaguar XK120 Roadster unveiled in 1948 right up to the most recent Porsche Spyders. For most in the U.S. a contemporary roadster is now just a two-seater convertible like the Audi TT, the modern classic BMW Z8, and Pontiac Solstice.

Landau & Rigid Door: Citroën's 1948 Citroën 2CV featured a sunroof that rolled back on itself, and extended to the rear bumper in place of a separate boot/trunk lid. This was for loading versatility that pre-dated hatchbacks. Later models had a boot/trunk lid or an optional hatchback, and an internally opening sunroof, with a secured 'half-open' position. It had rigid body sides framing two doors on each side – followed in concept by such cars as the 1950 Nash Rambler Convertible Coupe.

Citroën currently markets the C3 Pluriel (Pluriel is a cognate with the English plural), which can be configured into five iterations, hence the name:^[7]

• a hatchback with a multi-layer insulated top.^[8]
• a full-length "landau" sedan, operable partially or to the back window or any stage in between, with a buffet-minimizing wind deflector over the windshield.^[8]
• a semi-convertible, with the roof open to the back window, the roof assembly folds into a well in the trunk floor.^[8]
• a full convertible, whereby roof side rails are unlatched and removed.^[8]
• a roadster pick-up, where the back seats fold to a pickup-like bed with a drop-down tailgate.^[8]

The Four Door: A four door convertible is a phaeton in the U.S., elsewhere any convertible may be a cabriolet. The Lincoln Continental was available as a 4-door convertible in model years 1961 to 1967.^[9] A current example of a 4-door convertible is the Jeep Wrangler Unlimited.

Peugeot presented the a concept four-door retractable hardtop convertible, the Peugeot 407 Macarena in 2006.^[10] Produced by French coachbuilding specialist Heuliez, the Macarena's top can be folded in 60 seconds,^[10] with a steel reinforcing beam behind the front seats incorporating LCD screens for the rear passengers into the crossmember.^[10]

Drophead Coupe, Coupé Cabriolet or Coupé Cabrio: A type of convertible with only two doors,^[11] and thereby recalling the cabriolet carriage. With its Mazda RX7 convertible, Mazda introduced a two-seater convertible with a removable rigid section over the passengers, removable independently of power operated textile section behind with heatable glass rear window. During the 1980s, Jaguar produced an XJ-SC with two removable panels over the front seats and a partial fold-down convertible section in the back. It retained the rear side windows of the coupe and had fixed cant rails above these and the door glass. This allowed an almost full convertible with roll-over safety. Going back in Jaguar history, during the 1950s the XK 120 Drophead Coupe (DHC) and later variants, provided open-air motoring with quite civilized fully lined insulated tops with the weather-protection of the hardtop models.

History in the United States

Until the 1910 introduction by Cadillac of the United States' first closed-body car, the convertible was the primary body style. US automakers manufactured a broad range of models during the 1950s and 1960s – from economical compact-sized models such as the Rambler American and the Studebaker Lark to the more expensive models such as the Packard Caribbean, Oldsmobile 98, and Imperial by Chrysler.

Threatened rollover safety regulations in the mid-1970s led to diminished popularity by the 1970s. In 1976 Cadillac marketed the Eldorado as "The last convertible in America". During this period of very low convertible production, T-tops became a popular alternative.

Elsewhere globally, convertible production continued throughout this era with models such as the Mercedes SL, the VW Beetle Cabriolet, the VW Golf Cabriolet, and the Jaguar E-type.

In the 1980s convertibles such as the Chrysler LeBaron and Saab 900 revived the body style in the United States – followed by models such as the Mazda Miata, Porsche Boxster, Audi TT and later retractable hardtop models.

Retractable hardtop roof

A retractable hardtop, also known as coupé convertible or coupé cabriolet, is a type of convertible that forgoes a folding textile roof in favor of an automatically operated, multi-part, self-storing hardtop where the rigid roof sections are opaque, translucent or independently operable.

The first retractable hardtop was from France when in 1934 Peugeot introduced the 601 Éclipse, designed by Georges Paulin.^[12][13]

The retractable hardtop solves some issues with the soft-top convertible, but has its own compromises, namely mechanical complexity, expense and more often than not, reduced luggage capacity.

A 2006 New York Times article suggested the retractable hardtop may herald the demise of the textile-roofed convertible,^[14] and a 2007 Wall Street Journal article suggested "more and more convertibles are eschewing soft cloth tops in favor of sophisticated folding metal roofs, making them practical in all climates, year-round."^[15]

Construction

Retractable hardtops can vary in material (steel, plastic or aluminum), can vary from two to five in the number of rigid sections and often rely on complex dual-hinged trunk (British: boot) lids that enable the trunk lid to both receive the retracting top from the front and also receive parcels or luggage from the rear – along with complex trunk divider mechanisms to prevent loading of luggage that would conflict with the operation of the hardtop.

Construction variations

• The Volkswagen Eos features a five-segment retractable roof where one section is itself an independently sliding transparent sunroof.^[15]
• The Cadillac XLR features a retractable aluminum hardtop requiring 6'-10½" of vertical clearance during retraction, and manufactured by a supplier joint venture between Mercedes-Benz and Porsche.^[16]
• The Mercedes SL hardtop features a glass section that rotates during retraction to provide a more compact "stack."
• The Mazda MX-5 has been available since the 2006 model year with an optional power retractable hardtop, in lieu of the standard folding-textile soft-top. The cost of the retractable hardtop is actually less than the price premium charged to a separate hardtop. Compared to the regular soft-top, the hardtop weighs 77 lb (35 kg) more yet has no reduction in cargo capacity.^[17] The MX-5 is one of the few cars offering both hardtop and soft-top convertible choices, so it is possible to make a direct performance comparison; the hardtop has slower acceleration but a higher top speed. The hardtop roof is constructed of polycarbonate and manufactured by the German firm Webasto.^[18]
• Daihatsu marketed the Copen in the ultra-compact Japanese Kei class.
• The Chrysler Sebring's (and its successor the Chrysler 200's) retractable hardtop also is marketed alongside a soft-top. According to development engineer Dave Lauzun, during construction, the Karmann-made tops are dropped into a body that is largely identical: both soft-top and retractable feature the same automatic tonneau cover, luggage divider and luggage space.^[19] The retractable does feature an underbody cross-brace not included in the softtop.
• The Volvo C70, its retractable hardtop manufactured by Webasto^[18] includes a global window switch that allows simultaneous raising or lowering of all windows,^[20] and a button to power-activate the raising of the folded top stack within the trunk to access cargo below.^[20]
• The Vauxhaul/Opel Astra TwinTop, its three-piece retractable hardtop manufactured by Webasto^[18] includes a global window switch that allows simultaneous raising or lowering of all windows and a button to power-activate the raising of the folded top stack within the trunk to access cargo below.^[20]

Pros and cons

The retractable hardtop convertible trades higher initial cost, mechanical complexity and, with rare exception, diminished trunk space – for increased acoustic insulation, durability and break-in protection similar to that of a fixed roof coupe.

Pro: The retractable hardtop's advantages are:

• more practical in all climates year-round, compared to soft-tops which are more prone to leakage in heavy rain or winter. In addition, hardtops minimize wind noise and are more secure (the cloth of certain soft-tops can be slashed by a knife).^[21][15]
• increased structural rigidity over a soft-top.
• eliminates the need for a storage-consuming, manually-from-outside-the-vehicle-installable, separate or integral, rigid or foldable, tonneau cover to conceal the mechanicals of a folded textile top.
• eliminates the need to protect the vulnerable underside of a folded textile top from UV fading.
• eliminates the need for a separate rigid hardtop requiring space-consuming off-season storage and a cumbersome twice-yearly, two-person manual installation and removal – a system popularized, for example, by the Mercedes-Benz SL-Class of 1963 to 1989.
• may enable consolidation/simplification of a manufacturer's car lineup; for instance the current BMW Z4 (E89) is offering only as a coupé-convertible (hardtop), compared to the preceding E85 generation that had separate coupé and cabriolet (soft-top) variants.
• part of a popular trend that automakers have been following in the late 2000s. Hardtops are nicknamed "metal origami" and top-up they are considered more attractive than soft-tops.^[22] A 2006 New York Times article suggested the retractable hardtop may herald the demise of the textile-roofed convertible,^[14] and a 2007 Wall Street Journal article suggested "more and more convertibles are eschewing soft cloth tops in favor of sophisticated folding metal roofs".^[15]
• Soft-top convertibles are often considered by the automotive press to not be in the "same league" as more complex hardtops.^[23]

Con: In addition to higher initial cost, increased mechanical complexity – and thereby potentially higher repair cost, hardtops have the general disadvatages of:

• Diminished passenger and trunk space compared to a soft-top convertible. Indeed some hardtops have a nearly unusable trunk once the roof is down.^[24][25][26] Even some soft-top models use the trunk for storage of top.
• Hardtops typically have a higher weight and center of gravity which reduces handling dynamics, so the Audi R8 Spyder, Porsche Boxster and 911 Cabriolet have retained soft-tops. Audi has yet to produce a hardtop convertible as of 2011, since they include quattro as standard equipment in their convertibles (after the discontinuation of the 2007 Audi A4 2.0T cabriolet) which already adds extra weight.^{[24][25][26][27]}
• decreased structural rigidity compared to a fixed-roof coupe. The 2010 Infiniti G37 Convertible tries to solve this problem with a folding steel roof, however this adds considerable mass to the vehicle.^[28]
• The retractable hardtop may lift the articulating sections of the roof during retraction, requiring increased vertical clearance. For example, the Volvo C70 requires 6.5 feet (2.0 m) of clearance during operation.^[29] The Cadillac XLR requires 6'-10½" of vertical clearance.
• The retractable hardtop may, such as in the case of the Mercedes SLK, require additional rear clearance behind the car during operation of the top, the trunklid extending rearward while retracting or raising the top.
• The retractable hardtop relies on battery power, and in the event of battery failure, can leave a retracted roof vulnerable to a downpour. Volvo includes an emergency roof cover with each Volvo C70.^[29] The Cadillac XLR owners manual contains seven pages of detailed instructions on how to manually raise the top. This problem is not unique to retractable hardtops since some soft-tops rely on battery power as well.
• With numerous articulated sections, each joint or seal is an opportunity for water leakage.
• Failure of hydraulics or electrical systems may result in substantial repair bills, though some models of ragtops have similar setbacks when they employ a powered top-down sequence.

History

1922 Ben P. Ellerbeck conceived the first practical retractable hardtop system in 1922 – a manually operated system on a Hudson coupe that allowed unimpeded use of the rumble seat even with the top down^[30] – but never saw production.^[31]

1935 Peugeot introduced the first production, power-operated retractable hardtop in 1935, the 402 Éclipse Décapotable,^[14] designed and patented by Georges Paulin.^[14] The French coachbuilder, Marcel Pourtout, custom-built other examples of Paulins designs on a larger Peugeot chassis as well.^[14] The first Eclipse 402s offered a power-retractable top, but in 1936 was replaced by a manually operated version on a stretched chassis, built in limited numbers until World War II.^[30]

1941 Chrysler presents the retractable hardtop concept car, the Chrysler Thunderbolt.^[30]

1953 Ford Motor Company spent an estimated US$2 million (US$16,424,469 in 2012 dollars^[32]) to engineer a Continental Mark II with a servo-operated retractable roof. The project was headed by Ben Smith, a 30-year-old draftsman.^[33] The concept was rejected for cost and marketing reasons.^[30]

1955 Brothers Ed and Jim Gaylord showed their first prototype at the 1955 Paris motor show,^[34] but the car failed to reach production.

1957 Ford introduced the Skyliner in the United States. A total of 48,394 were built from 1957 to 1959.^[30] The retractable top was noted for its complexity and usually decent reliability^[35][36] in the pre-transistor era. Its mechanism contained 10 power relays, 10 limit switches, four lock motors, three drive motors, eight circuit breakers, as well as 610 feet (190 m) of electrical wire,^[30] and could raise the or lower the top in about 40 seconds. The Skyliner was a halo car with little luggage space (i.e., practicality), and cost twice that of a baseline Ford sedan.

1989 Toyota introduced a modern retractable hardtop, the MZ20 Soarer Aerocabin. The car featured an electric folding hardtop and was a marketed as a 2-seater with a cargo area behind the front seats. Production was 500 units.

1995 The Mitsubishi 3000GT Spyder convertible by ASC was marketed in the U.S.^[31] The design was further popularized by such cars as the 1996 Mercedes-Benz SLK.^[14] and 2001 Peugeot 206 CC.

2006 Peugeot presented the a concept four-door retractable hardtop convertible, the Peugeot 407 Macarena.^[10] Produced by French coachbuilding specialist Heuliez, the Macarena's top can be folded in about 30 seconds.^[10] It has a reinforcing beam behind the front seats which incorporates LCD screens into the crossmember for the rear passengers.^[10]

List of retractable hardtop models

Early models

• Peugeot 402 Éclipse Décapotable (1935)
• Chrysler Thunderbolt concept car 1941
• Continental Mark II concept car c.1953
• Ford Skyliner (1957–1959)
• Gaylord (1956)^[37]

Later models

Open car and roadster gallery

Convertible gallery

Retractable hardtop gallery

See also

• Cabrio coach
• Car body style
• Carson top
• Roadster
• T-top
• Targa top
• NASCAR Convertible Division

References

Notes

Bibliography

• Georgano, Nick (2001). Beaulieu Encyclopedia of the Automobile. Routledge. ISBN 9781579583675. 
• Beattie, Ian (1987). Automobile Body Design. Haynes Manuals. ISBN 9780854292172. 

External links

• Convertible Car Magazine