From R231 to R232 seems to be a small change, but it actually represents a step change in many ways. First of all, the SL-class is now an AMG-exclusive model line, so the familiar label SL500 finally rests into history. In recent years, the once popular luxury roadster faces dropping sales in a market trend that shifts from coupes and roadsters to SUVs and crossovers. Not even a brand as strong as Mercedes could resist the trend. On the one hand, it puts the S-class Coupe and Cabriolet into retirement. On the other hand, it hands over the SL-class to its AMG division so that the latter can build it on the platform of the next generation AMG GT to save money. This means, the R232 will have a narrower but more upmarket range, consisting of SL55, SL63 and, later on, SL63 E Performance plug-in hybrid.

The second and third changes are reverting to soft top and 2+2 layout, both last seen on R129. Why? I guess the intent is to broaden its customer appeal. The AMG GT is already a 2-seater, so there is no reason to build another. By adding a pair of rear seats - even though they are suitable to only small children or most likely to be used as extra luggage space - the SL may steal sales from Porsche 911 Cabriolet. This would not have been possible with a bulky retractable metal roof. Modern soft top is not only lighter and more space-saving but also provides similar level of heat and noise insulation. That's why no one builds retractable metal roof anymore.



As it needs to accommodate rear seats, the new SL has its wheelbase stretched by 115 mm to 2700 mm. Even though the overhangs have been shortened, its 4705 mm length still exceeds the old car's by 74mm. It is also wider by 38 mm at 1915 mm and taller by 44 mm at 1359 mm. In short, this is the largest SL ever. This reflects on scale as well. The SL55 has a DIN kerb weight of 1875 kg, 155 kg more than its predecessor SL500. The SL63 weighs 1895 kg, 125 kg heftier than the old car.

On the plus side, torsional rigidity of the chassis is lifted by 18 percent, while transverse and longitudinal rigidity are up by 50 and 40 percent, respectively. As before, the chasiss is primarily an aluminum spaceframe structure, but now some parts are made of hot-formed high-strength steel (e.g. windscreen frames and pop-up roll over bars), magnesium (dashboard support) and a mixture of glass-fiber and carbon-fiber composites (transmission tunnel). Needless to say, all suspensions use forged aluminum links.

The exterior styling is a mixed bag in my opinion. Compared with its predecessor, it is rounder and more refined in detailed design. Panamericana front grille gives it a more distinctive AMG look. On the downside, the waistline has been raised considerably and the tail slopes like 911 - it does look like a 911 from behind. It loses the low-slung, light and airy feel of traditional SL. AMG said it just returns to the roots of the original 1954 300SL, but hey, that one was a race car, even with gullwing doors.



If you think the rounder body returns better aerodynamics, you will be disappointed. The R232 has a drag coefficient of 0.31 (when was the last time you hear a figure starting with point-3 ?), while its angular-looking predecessor managed 0.27. Sure, the fabric roof has some influence in it, but the fact that BMW 8-Series Cabriolet achieves 0.29 should give Mercedes some thought. Mercedes is right at the top of aerodynamics game, so we should expect better results.

A sloping back should generate a lot of aerodynamic lift, so the car needs some active aerodynamic aids to counter. A retractable rear wing pops up from 50 mph and adjusts its angle according to speed. This is balanced by an active aero foil located at the underbody of front overhang, which extends downward by 40mm at speed.

Both SL55 and SL63 are powered by the familar 4.0-liter twin-turbo V8. Their chief differences are turbos and intake system. The SL55 produces 476 hp and 516 lbft, good for 183 mph and 0-60 in 3.8 seconds. The SL63 lifts those figures to 585 hp, 590 lbft, 196 mph and 3.5 seconds. They are so quick in standing start because they employ 4matic+ system and 9-speed MCT gearbox as standard. Yes, this is the first all-wheel-drive SL.

It is also the first 4-wheel-steer SL. To counter the longer wheelbase and extra weight, AMG equips all SL models with active rear-wheel steering as standard. The rear wheels steer in opposite direction at speeds up to 62 mph (100 km/h), sharpening turn-in and shortening turning radius.



Apart from more power, the SL63 gains active engine mounts, electronic-controlled LSD, larger wheels and 10mm wider tires, although it shares the same brakes with SL55. These brakes consist of 390mm discs and 6-piston calipers up front, 360mm discs and single-pot calipers at the rear. Ceramic brakes are optional.

To me, the most interesting part is suspension. The rear axle remains a multi-link setup as before, but the front suspension has been changed from 4-link to 5-link, which is housed entirely within the wheel rim. Being an exclusive AMG model, the SL employs conventional steel springs instead of the air suspension preferred by Mercedes' production cars. The SL55 is served with adaptive dampers, while SL63 introduces a new kind of suspension technology called "Active Ride Control". What is it? It sounds very similar in principle to the Tenneco Kinetic suspension used by McLaren. At each axle, the compression chamber of the right wheel damper is linked hydraulically to the expansion chamber of the left wheel damper. Vice versa, the expansion chamber of the right wheel damper is linked hydraulically to the compression chamber of the left wheel damper. There is a fluid accumulator in each hydraulic circuit, whose pressure can be changed by a pump. Meanwhile, flow rate at each chamber can be altered by control valves. By increasing or decreasing the fluid pressure in each accumulator, fliud can be pushed to the compressed wheel to resist body roll. By adjusting the flow rate via control valves, damping rate can be changed. In short, ARC is a hydraulic suspension that achieves the function of both adaptive damping and active anti-roll. As the car can skip a conventional anti-roll bar, ride comfort in straight is improved. Judging from the superb ride comfort and control displayed by McLaren, ARC is very promising. It is fitted to SL63 as standard but also available to SL55 as option.



Inside, the cabin seems more like a cocoon as it is now surrounded by a higher cowl and wider shoulders. The prominent transmission tunnel takes some space. It is certainly more spacious than an AMG GT, but unlikely to match the old SL. The interior design theme is far sportier than before, thanks in part to turbine-style air vents and a flat-bottom steering wheel. Instrumentation is implemented by a 12.3-in TFT screen housed in a small instrument pod. The 11.9-inch portrait touchscreen on transmission tunnel can be adjusted for an incline angle between 12 and 32 degree.

The fabric soft top can be opened or closed in 15 seconds and at speeds up to 37 mph (60 km/h). As before, a pair of protection bars pop up from the rear bulkhead during roll over. The soft top saves 21kg compared with retractable metal roof, thus helps lowering center of gravity.

Unexpectedly, boot volume has taken a setback, and considerably. While the old car swallowed 345-485 liters depending on the position of metal roof, the new car leaves only 213-240 liters at the boot, even though Mercedes insists it is sufficient to place a pair of golf bags.

Switching to mid-engined architecture, C8 is the most radical Corvette in history. However, it keeps using a small-block push-rod V8, which might keep the car affordable and please traditionalists, but it could feel incredibly strange for a mid-engined junior supercar, especially whenever you hit its 6500 rpm rev limiter. Now that link with the past is finally cut in the new Z06, which switches to an all-new quad-cam V8.

Codenamed LT6, the DOHC 32-valve V8 keeps the same 112mm bore spacing of the existing small-block V8 for ease of installation, but it is a completely new design. Like Ferrari's V8, it employs flat-plane crankshaft to cut inertia and enhance rev, which redlines at 8600 rpm. Displacemment drops from 6.2 to 5.5 liters (5463 c.c.) in the process of chasing rev, as bore is enlarged to 104.25mm while stroke is shortened massively to 80.0mm. The shorter stroke, in combination with using forged titanium connecting rods, help reducing the second-order vibration known to flat-crank V8s. Vibration damper, stiffer engine mounts and a stronger transmission casing take care of the remaining vibration.



The combustion chambers run at 12.5:1 compression ratio. The CNC-machined cylinder heads house carbon-coated finger followers, titanium intake valves and sodium-filled stainless steel exhaust valves. Like Ferrari's V8 on 458 Italia, a car its engineers bought for studying and benchmarking, the LT6 employs 2 intake plenums (though made of thermoplastic here) which are interconnected through 3 valves to form a resonance-type variable intake system. This improves torque delivery across the entire rev range. The 4-2-1 stainless steel exhausts connect to a quad-tailpipe, which has been relocated from the sides to the center of the tail.

The LT6 produces 670 horsepower (SAE, equivalent to 679 hp DIN) at 8400 rpm, 175 hp more than the standard Corvette. Its specific output of 124 hp per liter exceeds that of Ferrari 800 Superfast (123 hp/liter), if not the old 458 Speciale (135 hp/liter) or the Cosworth V12 on Gordon Murray T.50 (166 hp/liter). That makes it the most powerful production atmospheric V8 in history, beating out the 631 hp (DIN) Mercedes-AMG SLS Black series. Admittedly, aside from Detroit makers, no one still builds NA V8 anymore.



However, with reduced displacement, it is not surprising to see its maximum torque drops from the standard car's 470 lbft to 460 lbft, and this is not available until hitting 6300 rpm. To compensate, the Z06 employs a shorter final drive ratio. The Tremec 8-speed dual-clutch transmission has strengthened clutch pack and the aforementioned stronger casing. Electronic LSD is standard. GM has yet to reveal full performance data, but claims 0-60 mph in an astonishing 2.6 seconds.

More power needs fatter rubbers and larger brakes. The Z06 employs forged aluminum wheels that are an inch larger in diameter. The Michelin Pilot Sport 4S tires are 275/30ZR20 up front (vs 245/35ZR19), 345/25ZR21 at the rear (vs 305/30ZR20). The Brembo brakes get 6-piston calipers and 370mm discs up front, 380mm and 4-pot calipers at the back. These larger footwears take wider fenders which make the car 94mm wider overall than the standard C8. The suspension is stiffened by 35 percent compared with the standard C8 fitted with Z51 handling package, thanks to stiffer springs and retuned magnetic dampers. Helper springs are employed.



And then there is an optional performance package confusingly named Z07. It stiffens the suspension by a further 8 percent, turns to Michelin Cup 2 R track tires, Brembo CCM ceramic brakes and added carbon-fiber aero kits like a large rear wing, larger front splitter, front dive planes and underbody strakes. Chevy said it produces 333 kg of downforce at 186 mph. Besides, you may pay extra for a set of carbon-fiber wheels, which cuts 18.5 kg of unsprung mass.

With Z07 package and carbon wheels, the car weighs 1557kg dry, so it is slightly heavier than the standard Corvette, but at least 200kg more than the latest Porsche 911 GT3. However, starting at an estimated $90,000 and topping at just over $100,000 with Z07 package, the new Z06 is a lot cheaper than any European exotics offering similar level of performance.