Lean times for Audi TT

Sports cars don't seem like a natural fit for plug-in hybrid fuel efficiency, but Audi's new third-generation TT may be the car to change that paradigm.

Built on the same MQB platform as the Volkswagen Golf and Audi A3, the TT could be a candidate for the e-tron treatment already brought to market in Audi's A3 range.

Until such time as Audi gets around to building a 1.8-litre entry-level TT, the most efficient model in the sports car range is the 2.0-litre TFSI front-wheel drive variant with six-speed manual transmission. According to official fuel consumption testing, this particular variant is rated at 5.9L/100km – a good start, but leaving plenty of room for further efficiency gains.

Unfortunately, any such gains are unlikely to come from conventional design practices like aerodynamic styling, for instance. Audi's Technical Project Manager for the TT, Markus Siewert intimated to motoring.com.au that most of the aerodynamic tricks from the basket of low-hanging fruit have been exhausted for the new car.

The TT's drag coefficient – 0.29Cd – is described by Audi as "class leading," but it falls a long way short of the Toyota Prius or the Mercedes E-Class.

Why?

Aerodynamics in a short sports car with iconic styling cannot hope to match or better the wind-cheating qualities of cars not subject to the same design restrictions. It's the same for the TT's competitors as well, notes Siewert.

"Porsche's is as good, but [the TT's drag coefficient is] better than the others," Siewert told motoring.com.au during the TT's launch.

"When you look at that segment, you are limited because of the type of the cars and the design."

Nonetheless, there has been some major work done for the TT to glide easily through the air – it's just that the work done is mostly underneath the car.

"What we did is we put everything on the ground floor: the cooling system, where the air goes in and out – the underfloor – we put a lot of work [into] the spoiler, and so on..." Siewert explained.

"We figured out a lot of little things that benefited us, so we are able to have this figure [0.29Cd] – but a figure... [like 0.24Cd] for a sedan or bigger car or whatever... we won't see in the segment. I can't imagine how [such a car would] look."

For a two-seat or 2+2 sports car the footprint is everything – and that's established by the car's wheelbase, which will always have some impact on aerodynamics. However, having a wheel in each corner is of greater importance to TT owners than having the frugal drag coefficient of a Toyota Prius.

That brings Siewert to another aerodynamic issue that will always be uppermost in mind for TT stylists and designers, after the first-generation TT was roundly criticised for its high-speed stability.

"You also have to look at the downforces... it's really much more important than the drag coefficient for such a car... that's always number one," Siewert remarked.

As a consequence, aerodynamic design looks to offer limited scope at best, as a means to achieving significantly improved fuel efficiency for the TT. Audi has other tricks up its sleeve, however; drivetrain efficiency for one and weight reduction for another.

"A really big step was [taken] by the engine guys. There's more power, more torque, but less consumption," Siewert noted. The Audi exec also mentioned the 50kg weight saving in the migration from the second-generation TT to the new model, built on the MQB modular platform.

Seats, the electrical system and body construction have all contributed to the new TT's lower weight. Making the change from copper wiring to aluminium has helped, Siewert explained, since the cabling from the rear-mounted battery to the front of the car is long and heavy.

"It was worth it," Siewert continued, "because we saved nearly 2.7kg – and I'm sure we'll see [aluminium wiring] in other cars as well.

The Audi exec didn't say whether the aluminium wiring lends itself to Audi's new 48-volt electrical system. Siewert hinted that such technology will be cheaper to incorporate into a larger – and more expensive car first.

"From a technical point of view it's great – the 48-volt system – but you have to adapt everything... every single electrical part... whatever. I think you will see it first in bigger cars – A8, A6, Q7..."

Asked when such a technological advance might trickle down to the A1 – the smallest car in Audi's range – Siewert said that he could "imagine that", but couldn't "see a timeline" for such an event.

For smaller cars to benefit from a whole-of-car 48-volt system, the technology would have to be developed across models on shared platforms to deliver maximum bang for the buck. In other words, TT will have to wait for Golf, A3 and perhaps Skoda Octavia to be revamped first for the higher voltage system.

"It would be nonsense to do it alone – with TT."

But the adoption of the MQB platform expands the economies of scale available to Audi's engineers working on the TT. In light of Siewert's remarks concerning the need for TT to piggy-back off technological developments for the Golf and A3 that share the same platform, what's stopping Audi developing an e-tron version of the TT in time for a mid-life refresh?

After all, unlike the 48-volt system, the electric turbocharger or the Wankel rotary range extender, the e-tron technology has already been developed for both Golf GTE and the A3 e-tron.

And if not the TT coupe, perhaps e-tron technology will find its way into either of the rumoured SUV and sedan projects that will expand the TT family.