Body structure reinforcements give the TT Roadster a torsional rigidity of 10,000 N•m/°.
The more powerful engine for the Audi TT Roadster delivers 165 kW (225 hp).
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When Audi revealed its highly individualistic TT Coupe and Roadster concept cars in 1995, there were those who thought the likelihood of one reaching production to be questionable, and both as next to impossible. But Audi confounded the skeptics by producing the Coupe last year, with the Roadster slated to follow soon after. In fact, the introduction of the Roadster has been delayed by several months because of manufacturing pressure on the Coupe lines (assembly in Germany; powertrain from Audi's factory at Gyor, Hungary), such has been the car's popularity, but now the Roadster is also in production. Like the Coupe, it is little different from the original concept.
Great attention has been paid to making the Roadster's structure torsionally rigid. Audi quotes 10,000 N•m/°, which is excellent for an open-top car. Natural body frequency is 22 Hz. Compared to the Coupe, mass is up, but at 40 kg (88 lb), not by as much as might have been expected. Audi says the Roadster has a "massive portal frame structure" behind the seats, which constitutes a link between floor assembly and side panels of "extreme torsional stiffness." There is also a rectangular aluminum crossmember, which makes a flexurally stiff mounting for the car's twin rollover bars. The rollover bars can impart loads of up to 3.2 t (3.5 ton) to the structure without any noticeable deformation, according to Audi. Rollover protection also comes from interlocking, high-strength, steel tubular reinforcements in the A-pillars anchored in a high-strength node at the door sill, plus connecting points in the front-end structure. Compared to the Coupe, the Roadster's instrument-panel module support has been further developed as an effective body-stiffening member and is integrated into the structure via a number of robust screw connections. The front-end structure is stiffened by a rigidly mounted subframe with diagonal support against the side member and door sill structure; additional spring-strut mounting by means of a dome cross-brace; and tubular reinforcements already used on the Coupe at the front of the side members. Large-profile door sills have been carried over from the Coupe but reinforced via thicker material and the use of gusset plates at the connection points.
The company estimates that, in theory, a mass increase of around 100 kg (220 lb) might have been expected for its roadster stiffening program. But it states that by using targeted optimization measures, together with experience in aluminum technology for production applications (the A8 sedan in particular), Audi engineers were able to undercut the theoretical figure by 60%. Body stiffness is a contributor to primary and secondary safety. Other safety aspects of the Roadster include seatbelt tensioners with belt-force limiters and four airbags. The side airbags are integrated into the seat backs.
The folding roof of the TT is available with manual or powered operation. In powered form, a single handle needs to be turned manually to release the roof from the windshield header rail before it is lowered. Closing the roof calls for a final sharp pull and twist movement to secure it. Great attention has been paid to the shape of the folding roof to ensure that it contributes to the car's overall Cd (0.36) and helps keep noise levels down. A quarter-scale model of the TT Roadster was subjected to water tank tests, and a prototype was tested in Audi's new wind tunnel, resulting in design work that helped reduce turbulence around the car's wheels. A rear spoiler is fitted to the underbody. A toughened-glass, powered windbreak can be raised between the roll bars to give effective protection from buffeting at speed. The roof folds into a recess and can be hidden by a hard cover made of composite material. This fits neatly into the trunk when not in use and in theory is a clever design element. However, it must be unclipped and removed before the hood can be raised, which in the event of a sudden rainstorm is likely to dampen more than the occupants' spirits. Also, the contents of the trunk must be removed to stow the cover, which is hardly ideal. This AEI editor suspects that most owners will not use the cover if there is any question about weather stability. Questioned as to why a hinged cover forming part of the bodywork could not have been used, Audi designers explained that this would have necessitated a shut line imposing on the rear fender, which was regarded as aesthetically unacceptable.
The TT Roadster is available with a choice of power units, both turbocharged and of 1.8-L capacity, producing 132 kW (180 hp) or 165 kW (225 hp), the more powerful having two intercoolers. The lower-powered car is available with front-wheel drive or quattro all-wheel drive, whereas the higher powered car is available only as a quattro. It also has a six-speed gearbox instead of five for the 132-kW version. Performance figures for the 165-kW car include a 0-100 km (0-62 mph) time of 6.7 s, with a top speed of 237 km/h (147 mph). Unladen weight without driver is 1475 kg (3245 lb). Suspension differs between two and all-wheel-drive TT. At the front, both versions use MacPherson struts, but at the rear, the quattro has a trailing arm and two wishbones at each side, with separate spring and shock-absorber mountings; the front-wheel-drive car uses a torsion-crank system.
Trim options include leather-upholstered seats with contrasting color. The effect is distinctive. Audi decided to use the space between the soft-top storage compartment and the car's floor to accommodate various components, including hydraulic units for the roof system, central locking control unit, telephone interface, navigation unit, CD changer, and first-aid kit. The space also provides three storage compartments, two of which lock automatically with operation of the car's central locking system.
Stuart Birch
