Convertible (car)

Convertible

[kuhn-vur-tuh-buhl]
A convertible is a type of automobile in which the vehicle's roof can retract and fold away, converting it from an enclosed to an open-air vehicle. Many different automobile body styles are manufactured and marketed in convertible form.

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 of the vehicle. The roof may be designed to operate either by hand or automatically using hydraulic or electrical actuators.

Roofs can be made out of a wide variety of materials, and are usually divided in two types: soft-tops and hard-tops. Soft-tops are made of vinyl, canvas or other textile material, while hard-tops are usually made of the same material as the car's body (usually steel or aluminium).

Convertibles are known by different terms, mainly due to convergence of various body styles and also different marketing terms used. A soft-top convertible may also be referred to as a cabriolet, although two-seater soft tops retain the name roadster, referring to their body style. Hard-tops are marketed under the terms coupé cabriolet, coupé convertible or simply retractable hardtop.

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 (e.g.,Volkswagen Beetle) or interior cosmetic headliner (to hide the frame) (e.g.,Chrysler LeBaron) — 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 (e.g.,Alfa Romeo Spider), semi-manual latches, or fully automatic latches (e.g.,Volvo C70). The folded convertible top is called the stack.

Pros and 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 cars's roof. For example, a 2007 article in the New York Times, referring to the Volkswagen Eos, reported:

''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 floor pan’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"

  • specifically poor structural rigidity, such as pronounced skuttle 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.

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 MKI (first generation) MGB (1964) roadster featured a manually-assembled convertible frame which required the driver to install the separate vinyl or cloth convertible top — from outside the car. Likewise, a similar detachable frame installed to support a foldable vinyl tonneau cover with a series of twenty press fit snaps.
  • Convertibles such as the Chrysler LeBaron (c.1988) used sleeve and groove systems to anchor 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.

See also: Chevrolet Corvette (C6, c.2005) with integral rigid tonneau and manual cloth top, in action

  • Convertibles such as first Porsche Boxster, Toyota MR2 and third generation Mazda MX5 (NC) featured Z-fold (aka zig-zag fold) 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 lbs.

Convertible windows

Convertible side windows have evolved from non-existent in the earliest models, to detachable side screens and manually or power operated glass side windows. 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, also known as wind screens or wind deflectors, minimize noise and rushing air from 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 currently offers a feature that routes a heating duct to the neck area of the seat on SLK and SL models, marketed as the "Air Scarf".

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

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-pillers, 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. 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.

As an example of current convertible safety, the Citroën C3 Pluriel received the following European New Car Assessment Program (Euro NCAP) ratings:

  • Adult Occupant: , score 31
  • Pedestrian: , score 13

View: Citroën C3 Pluriel Encap crash testing

Variations

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

Roadster: Originally the term roadster suggested a minimal convertible, possibly with a frame that required actual assembly (i.e., not retracting) and separately installable soft "window" panels — offering little protection from inclement weather and requiring a time-consuming, complicated installation. A contemporary roadster is a two-seater convertible.

Landau & Rigid Door: Citroën's early Citroën 2CV featured a roof that rolled back on itself leaving rigidly framed side doors in place — 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:

  • a hatchback with a multi-layer insulated top.
  • 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.
  • a semi-convertible, with the roof open to the back window, the roof assembly folds into a well in the trunk floor.
  • a full convertible, whereby roof side rails are unlatched and removed.
  • a roadster pick-up, where the back seats fold to a pickup-like bed with a drop-down tailgate.

View: Citroën C3 Pluriel diagram

The Four Door: A four door converitble is referred to as a phaeton, while a two-door is referred to as a cabriolet. Modern 4-door models, e.g., the Lincoln Continental, c.1960.

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

View: Peugeot 407 Macarena, in action.

All-Wheel drive: AMC offered a four-wheel drive Eagle with a steel targa bar and removable fiberglass roof section. The Jeep Wrangler has four-wheel drive and a manually folded top. Audi offers the all-wheel drive A4 Cabriolet.

Drophead Coupe, Cabriolet or Cabrio: A type of convertible with only two doors and thereby recalling the cabriolet carriage. With its Mazda RX7 convertible, Mazda introduced a two-seater convertible with a removeable rigid section over the passengers, removable independently of power operated textile section behind with heatable glass rear window. During the 80's, 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.

History in the United States

Until the 1910 introduction by Cadillac of the 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 alternatives.

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 hardtops

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 retractable hardtop solves some issues with the 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, 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."

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.
  • The Cadillac XLR features a retractable hardtop of aluminum (i.e.,lightweight) requiring 6'-10½" of vertical clearance during retraction, and manufactured by a supplier joint venture between Mercedes-Benz and Porsche.
  • The Mercedes SL hardtop features a glass section that rotates during retraction to provide a more compact "stack."
  • The Mazda MX-5 retractable hardtop is manufactured by the German firm Webasto and is marketed alongside a largely identical folding-textile convertible, with an increase of and no reduction in cargo capacity — the hardtop is constructed of polycarbonate.
  • Daihatsu marketed the Copen in the ultra-compact Japanese Kei class.
  • The Chrysler Sebring's retractable hardtop is marketed also alongside a softop. According to development engineer Dave Lauzun, during construction, the Karmann-made tops are dropped into a body that is largely identical: both softop and retractable feature the same automatic tonneau cover, luggage divider and luggage space. The retractable does feature an underbody cross-brace not included in the softop.
  • The Volvo C70, it's retractable hardtop manufactured by Webasto includes a global window switch that allows simultanious 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.

View: Photo of Cadillac XLR roof during retraction

Pros and cons

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

Pro: The retractable hardtop 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.
  • the need to protect the vulnerable underside of a folded textile top from UV fading.
  • 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 1988.

Con: In addition to higher initial cost, diminished trunk space, and increased mechanical complexity — and thereby potentially higher repair cost:

  • The retractable hardtop may lift the articulating sections of the roof during retraction, requiring increased vertical clearance. For example, the Volvo C70 requires of clearance during operation. 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. The Cadillac XLR owners manual contains seven pages of detailed instructions on how to manually raise the top.
  • With numerous articulated sections, each joint or seal is an opportunity for water leakage.

History

1922 An American named 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 — but never saw production.

1935 Peugeot introduced the first production, power-operated retractable hardtop in 1935, the 402 Éclipse Décapotable, designed and patented by Georges Paulin, a Parisian, Jewish dentist and part-time car designer who later died in the Holocaust. The French coachbuilder, Marcel Pourtout, custom-built other examples of Paulins designs on a larger Peugeot chassis as well. The first Eclipse 402s offered a power-retractable top, but in 1936, that was replaced by a manually operated version on a stretched chassis, built in limited numbers until World War II.

1941 Chrysler presents the retractable hardtop concept, the Thunderbolt "dream car."

1953 Ford Motor Company next spent an estimated $2 million to engineer a Continental Mark II with a servo-operated retractable roof — the project having been headed in 1953 by a 30-year-old draftsman named Ben Smith. Though successful, the concept was rejected for marketing reasons.

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

1957 Shortly thereafter, Ford marketed the Skyliner in the United States beginning in 1957. Noted for its complexity and only intermitant reliability, 48,394 were built from 1957 to 1959. In the pre-transistor era, its mechanism with 10 power relays, 10 limit switches, four lock motors, three drive motors, eight circuit breakers and of electrical wire could raise the or lower the top in about 40 seconds — when functioning. The Skyliner was a halo vehicle with little luggage space (i.e., practicality), costing twice that of a baseline Ford sedan — to be withdrawn from the market after three years.

1995 The era of the modern retractable hardtop began with the 1995 Mitsubishi 3000GT Spyder, sold in Japan and the US — and further popularized by such cars as the 1998 Mercedes-Benz SLK and 2001 Peugeot 206 CC.

Notably, Peugeot presented the a concept four-door retractable hardtop convertible, the Peugeot 407 Macarena in 2006. Produced by French coachbuilding specialist Heuliez, the Macarena's top can be folded in about 30 seconds, and to incorporated a steel reinforcing beam behind the front seats, incorporates LCD screens for the rear passengers into the crossmember.

View: 1957 TV ad for the Ford Skyliner featuring [[Lucille Ball] and Desi Arnaz.]
View: Peugeot 407 Macarena, with top retracting.
View: Photographs of a 1938 Peugeot 402 Éclipse Décapotable
View: time lapse photograph of Mercedes SLK, with top retracting
View: Sales brochure of the 1995 Mitsubishi Spyder

List of retractable hardtop models

Early Models

Later Models

Convertible Gallery

Retractable Hardtop Gallery

See also

References

External links

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