All Audi vehicles offer luxury, but the brand has a three-tiered approach when it comes to performance.

Base Audis, especially sedans and coupes, are fairly sporty, but the uplevel S models definitely amp up the sporty feel. There is a third level, though, the RS models, that push the envelope further and these are the cars with the performance bona fides.

Motor Authority spoke to Stephan Reil, head of Audi Sport product development, who defined the differences between the three levels.

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"We have a clear separation in the Audi car lineup. We have the base model, which is the A model--A4, A5, so on. And then we have the S models, which are characterized by more performance, slight changes in the exterior, more sporty," Reil said. "And then we have on top of that the RS model, which stands for the maximum that is possible in this segment in terms of longitudinal performance, corning abilities, driving dynamics. The changes are far more than going from an A to an S model."

The RS models get high-performance engines and suspensions, lightweight materials (though they may weigh more than their A and S counterparts due to their addition performance parts), as well as carbon fiber trim, and wider bodies.

Like all Audis, RS models are subject to durability tests, such as testing in the heat, in Scandanavia on snow and ice, and in extensive stop-and-go city traffic.

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But Reil says the RS cars have to cover a much wider spectrum of use cases than the other cars. "That means that when we do our final durability tests, we have the standard durability test program...But, as we have another use-case that means some of our cars will be used on the track, there we have an 8,000-kilometer durability test on the Nürburgring Nordschliefe with our professional drivers in the car, sometimes race drivers."

That's why Reil can say: "Our claim is born on a track, built for the road."

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This testing can take two to three weeks and Audi has parameters that the tires, brakes, and other components must meet during the testing, though Audi isn't sharing what those parameters are.

We also spoke to Anthony Garbis, product manager for the A4/A5/Q5/R8, who said that while part of the development of the A and S models is done on the Nürburgring, those models are not subject to the same final testing as the RS models. Reil confirmed that the A and S models don't take part in the final Nürburgring testing.

Our read? If you are looking for an Audi track car, go for an RS. Yes, the S models have some performance bits, but Audi confirms that the RS models can handle the rigors of what is widely considered the toughest track in the world...for almost 5,000 miles no less.