MG TD with Tonneau cover over passenger seat and luggage well
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, 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.