Goethe, the great German poet, was an avid lover of fast driving and was friends with coachmen. If he had lived to this day, he would surely have been amazed that just a few letters in the name — S, AMG, or M — can convey the spirit of speed and freedom. We are not surprised by this, but it is still interesting to test in practice what these additional letters in the name of a roadster provide.
Representing BMW in this comparison is the fresh roadster Z4 M. Under its hood is the familiar inline six-cylinder engine from the M3 model, with a displacement of 3.2 liters and developing 343 horsepower. It is joined by the Mercedes-Benz SLK in the tuned AMG version with a 5.5-liter V8 producing 360 hp. And Porsche, of course, brings the Boxster S to the fight, with a mid-mounted engine and an output of 280 hp. Let's set aside the formal power figures: any of this trio is capable of shaking you up so much after a drive with the top down that you'll need to pull yourself together.
However, today's roadsters are no longer the Spartans their ancestors were. All three cars delight with quality trim and solid build. In this regard, the Porsche is especially good, although visibility from its cockpit is not the best. But the SLK AMG looks the most convenient for the driver in terms of visibility and comfort.
Potential owners of these cars should remember: their trunks are designed only for a short trip. The BMW has from 220 liters, the Mercedes-Benz up to 300. True, with the roof folded, the SLK's useful volume shrinks to 208 liters — the rest is eaten up by the top mechanism. In the Porsche, due to the mid-engine layout, there are trunks both front and rear, but the rear one is of an inconvenient flat shape.
The roofs of all three cars are well fitted: no squeaks or knocks even on broken roads. If the car is needed year-round, the SLK will be the most practical — its top is steel. All have electric folding drives, and only the Porsche has a manual backup system for opening and locking with a lever on the windshield frame.
The chassis of all three roadsters is good, and they offer a reasonable balance between ride smoothness and handling. The Porsche is noticeably nervous on uneven surfaces, while the SLK takes them much more calmly. The Mercedes' stability at high speed brings it extra points for comfort. The BMW, however, squats slightly at the rear, and on broken roads the rear shock absorbers sometimes bottom out.
Acoustic comfort plays a significant role in comfort. And here again the SLK is ahead: it is the quietest, and the engine sound is very pleasant. In the BMW and Porsche, the sound insulation copes with road noise worse.
The climate system is also better in the Mercedes-Benz — which once again emphasizes its comfortable character. The cabin warms up quickly and efficiently, and the Airscarf option (supplying warm air to the neck area, costing 458 euros) is an extremely useful thing for a roadster. On the test day it was only +3° outside, so the benefits of neck heating were easy to appreciate. Plus, the Mercedes also has the most comfortable seats — another plus in its favor.
Unsurprisingly, the most powerful V8 in the SLK most actively supplies traction to the rear wheels and provides excellent dynamics. The picture is complemented by the high culture of engine operation — it is equally good at idle and at high revs. But the gearbox lets it down a bit: the seven-speed automatic jerks when downshifting when cold, and in manual mode it responds with a noticeable delay.
The BMW engine responds more lively to the throttle, pulls great at the top end, and simply provokes more frequent gear changes. The six-speed manual with well-chosen ratios only contributes to this — the process is a pleasure. True, at high revs the engine starts to ring, which may not appeal to everyone, although there are almost no vibrations.
The Porsche flat-six is similar in character but sounds softer and works more refined. For an extra 557 euros, you can get a short-throw gearbox, but the standard manual works flawlessly.
In fuel consumption measurements, the Mercedes-Benz showed 13.5 liters per hundred. The most economical was the BMW — 12.4 liters. The Porsche came in at 12.6 liters. Electronics limit the top speed of the BMW and Mercedes to 250 km/h, while the Boxster can reach 268 km/h.
Thanks to ceramic brakes (an option for 7830 euros) and 19-inch wheels (1839 euros), the Porsche demonstrates phenomenal results: braking distance from 100 km/h — 35.6 meters on cold mechanisms and 33.8 meters on warm ones. On the slalom and handling track, the Boxster, despite less power, thanks to better handling showed the best time. In extreme modes, the Porsche stays neutral, and you can only provoke it into a drift artificially by turning off the stability system.
The BMW with a self-locking differential behaves similarly, but at the limit of tire grip requires more active steering work. On the slalom, the BMW's steering sometimes lacks feedback, but on the handling track it works as well as the Porsche's.
But in braking, the Mercedes and BMW unconditionally yield to the Porsche. On high-speed sections, the SLK's brakes fade. The large turning circle is also not pleasing, and the heavy V8 (the car weighs 846 kilograms) loads the front axle almost 200 kg more than the Porsche. This explains the sluggish response to the steering wheel and the SLK's pronounced tendency to oversteer.
Technical specifications BMW Z4 M Roadster // MB SLK 55 AMG // Porsche Boxster S
Body – roadster
Curb weight, kg – 1410 // 1465 // 1345
Gross weight, kg – 1705 // 1850 // 1630
Dimensions, mm:
- length – 4113 // 4082 // 4329
- width – 1781 // 1777 // 1801
- height – 1302 // 1278 // 1285
Wheelbase, mm – 2497 // 2430 // 2415
Trunk volume, l – 240–260 // 208–300 // 340
Maximum speed, km/h – 250 (limited) // 268
Acceleration time to 100 km/h, s – 5.00 // 4.90 // 5.50
Braking distance from 100 km/h, m – 36.9 // 36.7 // 35.6
Control fuel consumption (combined cycle), l/100km – 12.10 // 12.00 // 10.40
Engine:
- type – inline, 6-cyl., 24-valve // V8, 24-valve // flat-6
- displacement, cm3 – 3246 // 5439 // 3179
- power, hp at rpm – 343/7900 // 360/5750 // 280/6200
- torque, Nm at rpm – 365/4900 // 510/4000 // 320/4700–6000
Transmission – 6MT // 7AT // 6MT
Drive – rear
Brakes (front/rear) – disc, ventilated
Price, euros – 78 500 // 83 400 // 67 800
Advantages and disadvantages
Porsche Boxster S
+ Handling, brakes, quality, layout.
– Insufficient comfort.
MB SLK AMG
+ Comfort, power.
– Handling, brakes.
BMW Z4 M Roadster
+ Handling, gearbox.
– Visibility, comfort.