2010 Audi S5 Cabriolet - Click above for high-res image gallery

Taking a great looking performance car and chopping off its roof is risky business – compromises are inevitable. That's especially true in this modern age of unibody structures. Removing a big chunk of a vehicle's architecture without adequately reinforcing what's left can yield a chassis incapable of managing the position of the wheels, let alone result in a vehicle that loses its level of driver engagement and enthusiasm. On the other hand, reinforcements add mass – often lots of it. It's a treacherous path, as both flaccid body control and weight are the mortal enemy of performance.

You can understand our trepidation, then, upon learning that Audi was planning on introducing its S5 Cabriolet at the 2009 Geneva Motor Show. By our reckoning, the German debutante's rollout was cause for both consternation and celebration. When the A5 and S5 coupes arrived in 2007, they were hailed as being among the best looking cars ever to wear the brand's Four Rings. The new Cabriolet models would bring with them the euphoria of open-air motoring, but we had to wonder – would Audi's rakish new hardtop be turned into a floppy flier just by giving it a roofectomy? Equally as important, would the model's newly downsized engine drop the performance? There was only one thing to do: Put the range-topping S5 Cabriolet through a week-long test.

Photos by Sam Abuelsamid / Max Abuelsamid / Copyright ©2010 Weblogs, Inc.

The first decision that Audi's engineers faced in designing their new A5/S5 cabrio was deciding what kind of roof to specify. The trend over the last decade has been toward complex folding hardtop mechanisms, as they tend to provide the same sort of quiet interior as a regular coupe, along with a bit more security. Unfortunately, these hardtops simply don't like to fold up as compactly as fabric lids. As a result, cars equipped with folding tin tops tend to have excessively long rear decks and greatly compromised trunk space – particularly when the top is down.

Thus, the al fresco driving fans among us were thrilled to see that Audi instead opted to specify a more traditional fabric top for its A5 and S5. This pays huge dividends for both the utility and aesthetics of these models. When Audi developed the B8 platform that underpins the A5/S5 and A4, it stretched the wheelbase, in the process moving the front axle forward about six inches compared to the (somewhat frumpy looking) outgoing A4 Cabriolet. As a result, the new coupe had a much more balanced and cab rearward profile than its predecessor. Going with a softtop has helped Audi largely maintain the coupe's winning profile while avoiding the big-butt appearance of cars like the Lexus SC 430 and IS 350 convertible.

The other half of the hard/soft top debate is utility. Even with an extended rear deck, a folding hardtop usually consumes much of the available trunk space. For example, cargo space in the Lexus IS C contracts from 10.8 cubic feet with the top up to less than 2.4 cubic feet top down. The S5 retains the same 10.2 cubic feet regardless of its roof's orientation. Of course, rear seat volume always shrinks regardless of the top mechanism, and while the S5's rear headroom goes down by less than an inch, available leg and shoulder room each drop by about six inches. As a result, the second row of S5 Cabrio is best reserved for short jaunts, or for consenting adults under about five-feet, four-inches.

Aside from the abbreviated rear seat capacity, the interior of the S5 Cabrio is essentially carried over from the coupe and ought to be instantly familiar to anyone who has spent time in an Audi over the last half-dozen years. While the interior appearance doesn't offer any breakthroughs, we really couldn't find much of anything to complain about aside from our usual gripes with the brand's fiddly all-in-one MMI infotainment interface. The materials used are typically first-rate, with excellent fit and finish. To the left of the cupholders are two additional switches that look like oversized versions of the usual power window buttons. The forward switch allows the top to be raised or lowered, and the transformation can occur even while in motion at speeds up to about 15 mph – useful when crawling along in a traffic jam or while at a stop light when the rain sets in. The second switch allows all four windows to be lifted or dropped with a single touch.

The Audi S5 Cabrio also has the same, more aggressive sport seats found in the coupe, with fixed headrests and adjustable thigh bolsters for those with longer legs. On our test car, the seats were finished in an attractive mix of black and Tuscan brown leather. Like several other premium German convertibles and coupes that lack a conventional B-pillar, Audi compensates for the loss of a seatbelt mounting point with mechanized arms that automatically present the belts to front seat occupants upon entry. If you do happen to convince one or more of your friends to squeeze into the back, they will find a switch on the back of the front chairs that enables them to power those seats forward on their own, an inclusion that helps with ease of exit, particularly when the top is up. Even still, ingress and egress to the second row is hardly a graceful process, but it isn't demonstrably worse than it is in the coupe.

While the S5 coupe retains Audi's marvelous high-revving 4.2-liter naturally aspirated V8, the Cabrio is instead propelled by the automaker's newer 3.0-liter TFSI V6 that debuted in the S4 sedan. Despite what the "T" in the name implies, the direct injected V6 isn't turbocharged – it's boosted by a mechanically driven supercharger that provides instant response to throttle commands. The V6 offers the same 325 pound-feet of torque as the larger engine, and while the V8 peaks at 3,500 rpm, the V6 produces maximum torque from 2,900 rpm all the way to 5,300 rpm. That said, the V8 has a 21-horsepower advantage, producing a maximum output of 354 horses to the V6's 333.

One other big difference between the two: The V8 in the coupe is available with either manual or Tiptronic automatic six-speed transmissions, but the only gearbox available with the V6 in the S5 Cabrio is Audi's new seven-speed S-Tronic dual clutch unit. All S5s pack the brand's signature Quattro all-wheel-drive system, and like all models built on the B8 platform, it's the company's more performance-oriented rear-biased variant. Under nominal driving conditions, the torque is split 40 percent front and 60 percent rear, a strategy that helps alleviate some of the persistent understeer that has plagued most Quattros for three decades. After spending time with the S-Tronic S5, we can only say that Audi desperately needs to adapt this gearbox to its R8 supercar and ditch that model's awful automated R-Tronic unit.

Our test car was also fitted with the optional Prestige package, a grouping that includes Audi Drive Select, a system that lets the driver choose from comfort, automatic, dynamic or individual modes. The first three settings are self explanatory, but the latter lets the driver set the damping, throttle response, steering and shift calibrations independently. We mainly just selected the dynamic mode that sets everything to the highest performance-oriented settings, although comfort mode came in handy on some of the more abusive sections of pavement around Ann Arbor, MI.

By not offering a traditional three-pedal setup, it might seem that Audi sees the S5 Cabrio as more of a cruiser than an all-out performance car. This may be true to some extent, but frankly, this 'box is so quick and competent that we can't fully agree with that assessment. The S5 Cabrio is definitely not as aggressive as the coupe – carrying nearly 500 pounds of avoirdupois everywhere it goes is never a good thing for performance. At a curb weight of 4,310 pounds, this droptop is actually downright porky. However, driving those aforementioned Michigan roads clearly demonstrates what some of that extra poundage has been used for. The last Audi convertible this writer drove was an RS4 nearly two years ago, and it was not exactly a paragon of structural integrity. To be honest, the cowl shake in that rare bird was actually distressing considering the amount of power lurking underhood. The S5 Cabrio, while still not quite bank vault solid is far better than the RS4, and one of the stiffest convertibles we've tried recently – especially for a four-seater.

One of the claimed advantages of a hardtop is a quieter, more refined interior with the lid on. Yet at any legal highway speeds, we found the fully lined top of the S5 to offer a driving environment very nearly as serene as its coupe brethren, with very little wind noise and no noticeable fluttering of the fabric. Having said that, we firmly believe that any car with a retractable top should be driven with the roof down whenever possible. Thus, in spite of early morning temps in the low-30s while we had the car, we dropped the fully automatic lid before pulling out the driveway. And we never bothered to pull the fold-out wind-blocker out of the trunk, because with the windows up, buffeting is well controlled.

"Refinement" is the operative word all around for the S5 Cabrio, a revelation that actually left us a bit disappointed in at least one respect. The coupe's 4.2-liter V8 has a wonderfully sonorous engine note and exhaust tone that constantly urges you to feed the beast more high-test gasoline. The blown V6, on the other hand, is pleasant enough, but a bit on the muted side – even at wide-open throttle.

Audi officially lists a 0-60 mph time of 5.2 seconds for the Cabrio compared to a 5.1 seconds for the automatic coupe and 4.9 for the manual. Our own informal runs actually got us to 60 in just under the five second mark. As those figures attest, speed builds rapidly and the dual-clutch transmission adds to the seamless nature of the S5. The S-Tronic gearbox offers lightning quick ratio changes with no throttle lift and almost no perceptible cessation in acceleration. The blend of the S5's seamless acceleration and its relative lack of noise means that the Cabrio actually doesn't feel as quick or involving as it actually is. It's more like being teleported from one speed to another with little of the commotion or the aural excitement that performance-minded drivers tend to favor. The combination of the V6 engine's vibration-free revving all the way to its 7,000 rpm redline and its somewhat anodyne soundtrack may point to its efficiency and good manners, but part of the reason we like convertibles is because going topless is a great way to hear a car's mechanicals working. In this regard, the S5's blown V6 is just too quiet for its own good, particularly compared to the coupe.

With that in mind, in order to maximize driver engagement, you'll want to tap the shift lever over into its manual gate, which allows you to pretend you are Tom Kristensen. The paddles on the back side of the leather-wrapped three-spoke wheel provide instant control over the gearbox. The engine revs are auto-magically synced and the simultaneous clutch-declutch virtually eliminates that flat spot you typically find in the acceleration curve. Many vehicles with either CVTs or torque converter automatics register your paddle inputs, yet only swap their cogs when they are good and ready – the S5's gearbox, by contrast, is all but instantaneous.

Bend the S5 into a curve and the electrically assisted steering provides surprisingly clear communication about what is going on at the front corners. All that extra mass and the snow tires that were still fitted to our test Cabrio when we got it means that it didn't feel quite as precise or nimble as the coupe, but that observation could be attributable to the winter rubber as much as anything else.

Aside from elevating the Audi's ride quality over bad roads like most driver selectable control systems, the behavioral differences between comfort and dynamic on Audi's Drive Select were not particularly dramatic in street driving – these sorts of things often really only come into play when the car is pushed toward its limits, as they might be on a track or a particularly sinewy stretch of tarmac. The 40:60 split quattro system means that the car's overall balance is better than the RS4 Cabrio was, and the car's much improved structure makes it feel more confident.

Of course, the S5 Cabrio is not inexpensive, carrying an opening MSRP of $59,550 delivered. Our navigation and Drive Select-equipped version tacked over ten grand onto the base price, for a bottom line of $69,625. Is the S5 Cabrio worth 70 grand? Only you can decide, but given our automotive proclivities, we'll probably hold out in the hope of an RS5 Cabrio with that marvelous V8 and the S-Tronic, all while hoping for a nice inheritance check to appear from somewhere. In the meantime, those looking for a more aggressive drive will probably want to get the lighter manual transmission coupe with its more exuberant V8 engine – or wait for the RS5 to (possibly-maybe) arrive. If what you want is a quick, luxurious convertible that offers seating for four, gorgeous styling with the top up or down, a usable trunk and confident, all-weather capability, the S5 Cabriolet may well be the car for you. Audi has done an admirable job of keeping this convertible's compromises to a minimum, and it shows.

Photos by Sam Abuelsamid / Max Abuelsamid / Copyright ©2010 Weblogs, Inc.

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