Mercedes-Benz SL550 vs.BMW 650i Convertible

Even though money can't buy happiness, it sure gives a shot of its flavor. The SL550 and the 650i Convertible are in their element when they waft past Beverly Hills' premium shops, or cruise along Pacific Coast Highway, even when challenged up and down the rocky canyon roads above Malibu.
The BMW 6 Series has received several body retouches (mainly in the controversial rear end), improvements on the dashboard and some hocus-pocus in the powerplant, with the stated aim to give it better performance and lower consumption. The SL has been through a similar process, although the aesthetic changes are definitely easier to identify at the front end, but we also find new cooling vents and engine upgrades. The SL offers the 550, the 600, plus the two AMGs (SL 63 and SL65), against the 650i and the M6 from BMW.

 
So we have a roadster and a two-plus-two convertible. The former carrying the weight of history on its shoulders (the original SL roadster dates back to 1957), the latter improved from a 2004 original, even though BMW has a history of more than four decades of sporty convertibles. The SL advantage in this respect seems to be undisputed if we keep in mind that it really offers two bodies in one vehicle (a coupe and a cabriolet), whereas the 6 Series presents the buyer with a one or the other's conundrum.

It soon becomes obvious that the BMW is larger than its rival. Over seven inches in length, mainly because it has to allow some room for rear passengers (either short adults or kids), which is also why the wheelbase is greater. The 6 Series is wider and lower into the bargain, which brings a sense of proportion to the external dimensions and the accommodations therein.

This might be treading on thin ice, but it seems that, for such an elitist segment, it makes more sense to assume exclusiveness and go for a two-seater configuration instead of attempting to please everyone by offering cursory rear seats (which Mercedes has anyway in the form of the admittedly less upscale CLK cabrio). By doing this, the Benz also gains some points in handling.

The new SL sports redesigned front headlamps (both cars now have adaptive bi-xenon headlamps), separated by the new single-bar chrome grille (with obvious visual links to the SL from the 60s and 70s), new wheels, dark highlighted fog lamps and side vents. The BMW has bulkier front and rear bumpers and the aforementioned retouches out back.

Once inside, it's harder to spot the differences, although there are new materials and color trims, tweaks in the instrument panel and equipment upgrades on either side). More meaningful improvements lie beneath the body shell.

If there is one segment where looks count, this is it. There is no more emotional decision than to buy a luxury open-top. The slimmer overall design (mainly the profile and rear) of the Mercedes once again catches the eye, even though this is all a matter of taste. Clearly more objective is the SL's advantage as far as the roof is concerned (which now takes 16 seconds to retract, four seconds faster than before, thanks to new hydraulic pistons and software). Because it's a hard top, there are benefits both in terms of acoustic and thermal isolation. And, at the same time, it improves the torsion and bending stiffness of this car with the chameleon personality.

BMW's engineers took a different route and extracted a convertible from a coupe base, but its (excellent) canvas top sets higher challenges to the vehicle's structure, mainly under transversal acceleration. On the other hand, the cloth top is faster and can operate with the car in motion (up to 18 mph), but it may make the owner feel uncomfortable each time the car is parked in a public area.
 

 
It's impossible to ignore the feeling of luxury when accessing the interiors. The most relevant new introduction in the SL is the sporty three-spoke sporty steering wheel featuring shift paddles on the back (as in the BMW). In both cases, the leather seats have integrated seatbelts to provide better body retention and display a remarkable ability to wrap around the driver and front passenger. The front seats also include heating and cooling functions while the SL even includes an `Airscarf' feature to warm the driver's neck when driving topless on cold days.

Both cars feature centrally mounted joysticks to control the audio system, cell phone, navigation and on-board computer info. After constant criticism of BMW's first generation of its iDrive system (allegedly because mastering it would be too complicated for drivers who haven't spent their childhood engrossed in video game consoles and the internet), it has now been simplified and is clearly more intuitive. It eventually proves to be the right solution for controlling such a vast number of functions without transforming the dash into something like an airplane control panel.

For those who appreciate and get some benefit from the rear seats, the BMW has some added value (as long as those passengers are not taller than five foot six and don't mind traveling with their backs in an exceptionally upright position). The luggage capacity is, however, just marginally bigger than that offered by the SL: 12.4 to 12 cubic feet, with the top up.

One of the main improvements the new SL has is in the engine, which now has a 5.5-liter displacement and generates 382 hp, and 391 lb-ft of torque available from 2800 rpm. Despite the 26-percent power increase, fuel consumption has decreased very slightly. But there is still a more progressive and prompt response than with the previous SL550. The new seven-speed transmission (with a Sport program which makes shifting 30 percent faster) allows greater exploitation of the car's performance while lowering carbon dioxide emissions (which nevertheless are higher than the BMW's).

An obvious element to the Benz's improvement in handling is its new direct steering. A variable system (simpler and cheaper than the active steering arrangement from BMW) performs in an equally satisfactory way. Even through the most compelling curves, there's never that odd `more hands than wheel' sensation. Even in the situations where the front wheels must turn through 90 degrees. The combined effect of the steering feel, body control system (both cars have their own versions) and the refined chassis tuning makes this is the sportiest SL ever. It gives nothing away to the BMW in this respect (which was not the case with the previous model).

A playful driving style may even be adopted in total safety by disconnecting the stability control and teasing it through sharper turns, where it responds by displaying a tail-happy character. If up to now the 6 Series Convertible was the sole bearer of the Most Efficient Luxury Convertible crown, it now has to split it with its Stuttgart arch-rival.

Under braking, no fading problems were felt on either car, although BMW's brake pedal provides a better response. On the other hand, the SL has a slight advantage, again thanks to the seven-speed transmission (which is also easier to handle since upshifts are executed with the right pad and downshifts with the left. In the BMW, you shift up by pushing and down by pulling either pad). Anyhow, when provoked to their maximum, both all-aluminum V8 engines move their masses with a truly impressive celerity. The automatic gearboxes glue occupants to the backs of their seats when the kickdown comes into play.

Both chassis make use of independent suspensions, benefit from a healthy weight distribution, rear-wheel drive and sophisticated stability control systems with ABS, traction control and corner stability functions. The availability of sport programs in both gearbox and throttle is truly welcomed when in the mood for more enthusiastic driving.

Last but not least, the SL must be praised for its superior nimbleness, which derives from its smaller dimensions. It's also more suitable for urban driving (especially when having to park or perform 180-degree turns in the minimum possible space).

2009 Mercedes-Benz SL550
Layout
Longitudinal front-engine, rear-wheel drive
Engine
5.5-liter V8, dohc, 32-valve
Transmission
Seven-speed automatic
Performance
Peak Power: 382 hp @ 6000 rpm
Peak Torque: 391 lb-ft @ 2800 rpm
0-60 mph: 5.3 sec. (est.)
Top Speed: 155 mph (electronically limited)
Dimensions
Length/Width/Height (in.): 179.6/71.6/51.1
Wheelbase 100.8 in.
Curb Weight 4,202 lb
Price $95,300 (est.)
2008 BMW 650i Convertible
Layout
Longitudinal front-engine, rear-wheel drive
Engine
4.8-liter V8, dohc, 32-valve
Transmission
Six-speed automatic
Performance
Peak Power: 360 hp @ 6300 rpm
Peak Torque: 360 lb-ft @ 3400
0-60 mph: 5.6 seconds (est.)
Top Speed: 155 mph (electronically limited)
Dimensions
Length/Width/Height (in.): 190.2/73.0/54.1
Wheelbase : 109.4 in.
Curb Weight: 4,277 lb
Price: $82,700