Comparison: BMW Z4 sDrive35is vs. Mercedes-Benz SLK350
Toe-to-toe at last
We've been waiting a long time for this meeting. The predecessors to the two cars you see here debuted back in the booming late 1990s, but were as different as Newt Gingrich and Bill Clinton, or Friends and Seinfeld. The bulldog-faced Z3 oozed machismo, performance, and back-to-basics simplicity. James Bond drove one. The SLK, in contrast, had a steel folding hard top, came in colors like copper and electric green, and had recirculating-ball steering. Your wife wanted one.
It's a lot more complicated these days. Everyone knows Newt's a philanderer, too, and no one knows what's on NBC Thursday nights. More to the point, with the two-seat convertible segment shriveling to a size that can no longer support multiple niches, BMW and Mercedes have moved away from their extremes and have, in the process, created very similar roadsters. In the Z3's transformation to the Z4 and now the second-generation Z4, it aped the SLK's luxurious appointments and its folding hardtop. Mercedes, meanwhile, has quietly injected testosterone into its "chick car" such that the new SLK350, which went on sale earlier this month, puts down 302 hp and carves corners like an honest-to-goodness sports car. Call it evolution; call it regression to the mean; call it business. We'd call it the makings of a great showdown.
Uniqueness counts. Or does it?
A comparison of lesser hardtop convertibles would no doubt spend much time talking about which did a better job disguising the frumpy rear quarters. This, however, is the master class, and there's no trace of awkwardness in either our diamond white metallic SLK350 or Melbourne red metallic Z4 sDrive35is. Instead, we can consider the SLK and Z4 on the merits of their overall design.
Much like buying the cheapest house in a ritzy neighborhood, the SLK clearly benefits aesthetically from having very expensive older siblings. The roofline whispers "SL550" and the upright front end barks "SLS AMG." And yet unlike the last model's drooping SLR McLaren nose, the cues on the new SLK don't seem tacked on in a vain effort to convince dates that you're a movie star rather than an orthodontist. It's convincing, mature, and masculine without being butch.
The Z4, in contrast, will never be mistaken for anything other than a Z4. Even though BMW designers toned down Chris Bangle's controversial (but influential) flame surfacing for the current generation, the Z4's styling remains polarizing. Some, including design editor Robert Cumberford, think it's exceptional. Others, including this humble writer, still find it a bit overwrought. That impression is enhanced by our model's M aerodynamics package, which adds aggressive rocker and fascia extensions.
Both cars maintain a high level of style in their cabins. The SLK's interior here again borrows successfully from the SLS to great effect. Though we actually find the switchgear and details a bit pedestrian in the $183,000 Gullwing, it's more than enough to impress on a $66,805 SLK. In fact, the materials quality edges out that of the Z4, which as equipped is $64,225, although we still fancy the BMW's unique layout and circular secondary controls.
When it comes to more functional aspects of design, neither car avoids hardtop compromises completely. To lower the top - a process that takes about twenty seconds in either car - you need to first slide in place a trunk divider that slashes cargo room from 10.9 to 6.4 cubic feet in the Z4 and from a slightly better 11.8 to 7.9-cubic feet in the SLK. With the top up, however, the Mercedes scores a clear victory thanks to its general quietness - the Z4 rattles some over bumps - and a new parlor trick called Magic Sky Control. Introduced last year on the outgoing SLK, the optional panoramic sunroof automatically adjusts its tint level to let in just the right amount of sun. We won't go so far as to say we'd part with $2500 of our own money for the option, but on this test car it certainly relieved the cramped, dank atmosphere common to convertibles when the top is up.
Sweet six-cylinder sound, sour SLK seven-speed shifting
The engine downsizing zeitgeist will soon catch up with these roadsters - Mercedes and BMW will each introduce 2.0-liter four-cylinder variants within the next twelve months. For this fleeting moment though, power still rules and both these test cars produce lots of it. The "350" nomenclature for the SLK refers to a heartier version of the new, direct-injected 3.5-liter V-6 in the C-class, good for 302 hp and 273 lb-ft of torque. The sDrive35is muster even more. BMW's familiar 3.0-liter turbocharged inline-six here is tuned to deliver the same 335 hp and 369 lb-ft of torque as the 1-series M.
Tops lowered to worship the summer sun, we stomp on gas pedals and shoot down the rural roads outside of Ann Arbor. The SLK and Z4, despite weighing some 3400- and 3500-pounds respectively, reward our indulgence with effortless acceleration and exhaust notes raspy enough to dispel any remaining notions that these are mere poseurs. We're impressed by the smoothness and flexibility of the SLK's big V-6, which responds enthusiastically regardless of the tachometer needle's position. That said, this is still BMW's dominion. Its inline-six reacts instantly to commands of the throttle and at full howl drowns out the Mercedes.
Both cars might be described as having seven-speed automatics, but the BMW unit has the key modifier, "dual-clutch." As a result, the SLK simply can't match the ferociousness of the Z4's upshifts nor the immediacy of its downshifts, especially when we apply multiple taps to the steering-wheel-mounted paddle. We suspect this quick shifting, as much as the 33-hp advantage, explains why the Z4 is about a half second faster to 60 mph, according to factory estimates. Still, we're more annoyed with the Mercedes' software than the hardware. Regardless of whether it's in economy or sport mode, the gearbox proves too eager to upshift and isn't nearly proactive enough in downshifting under hard braking. There is a manual mode, but even that won't keep it from upshifting if you happen to hit the rev limiter - not what we want during cornering.
The Z4's gearbox does not entirely escape criticism. We still think BMW's insistence that each paddle should be able to call up either upshifts or downshifts (tap forward for upshift, pull back for upshift) is confusing. And for all its sporting credentials, the Z4, like the SLK, often refuses to hold a gear at redline, even with the transmission in manual mode and all the adjustable electronic settings dialed up to eleven.
Heavy steering is not always good steering
The SLK and Z4 are both fantastic handlers in the modern idiom, which is to say they rely on high levels of grip, excellent body control, and some high-tech wizardry. The sDrive35is has adaptive dampers with the usual sport and comfort settings (the SLK350 can be equipped similarly, but only as a special order option that was not on our test vehicle). In the real world, at least, it's tough to discern a substantial difference in body control, especially since the Z4 is so stiffly sprung to begin with.
The Mercedes, for its part, boasts variable ratio steering that quickens during aggressive driving. We feared this would feel unnatural, as many such setups are, but Mercedes has executed it nearly to perfection. The variable effect is transparent, and the steering itself is light, precise, and extremely communicative. We wish we could say the same of the Z4's steering. It's a variable effort setup that seems to have two settings: "heavy" and "heavier." We'd happily live with this extra forearm exercise if the reward was excellent feel and feedback but, sadly, it is not.
The BMW Z4 sDrive35is proves once and for all that a hardtop convertible can be aggressive, macho, and sporty. And yet, the Mercedes-Benz SLK350 is also aggressive, macho, and sporty without needing to prove it constantly. It looks muscular without a million creases in its sheetmetal; it handles well without the pretense of heavy steering or adaptive dampers. If you want a the most performance and attitude you can get for your dollar, then by all means, go for the Z4 and its iron-fist-in-a-velvet-glove powertrain. Just make sure you don't actually want a Porsche Boxster, first. Most hardtop convertible buyers, however, would do better to choose the SLK350, which provides as much real world driving pleasure but never hides or apologizes for being what it is: a very comfortable, stylish hardtop convertible.