Published
on 19
Nov 2022
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All rights reserved.
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SL
turns 2+2 in attempt to steal sales from Porsche 911.
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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 is now responsible by the AMG division, 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 has a narrower but more upmarket range,
consisting of SL43, 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 and taller by 44 mm. In short, this is the
largest SL ever. This reflects on scale as well, even though it doesn’t
look that way in photos. 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. Part of the cause is getting 4-wheel drive.
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4-wheel
drive and 4-wheel steering are standard on V8 models.
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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 chassis 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 far rounder and more refined in detailed design,
while “Panamericana” 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
originally 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 0.325 for the base
model, 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, requiring
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.
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Poor
packaging means a smaller boot and nearly useless rear seats.
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Both SL55 and SL63 are powered by the familiar 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 mass, 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, sharpening turn-in and shortening turning radius.
Apart from more power, the SL63 gains active engine mounts,
electronic-controlled LSD, larger wheels and 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, fluid 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.
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Prominent
transmission tunnel eats into passenger space. V8 is still a highlight.
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Inside, the cabin gets more like a cocoon as you are now surrounded by
a higher cowl and wider shoulders. The sense of airiness downgrades,
although you are also less likely to be exposed to buffeting. In terms
of packaging, it is a nightmare. The prominent transmission tunnel
takes a lot of passenger space. The rear seat is nearly useless, but
because of its existence, very tall drivers will complain for lack of
legroom up front.
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 degrees to avoid reflection, something useful on an open car. Build
quality looks classy, but some materials feel flimsy in touch.
The seats are supportive yet comfortable, and completed with “Airscarf”
neck warmer. Mercedes’ MBUX system is both powerful and fancy, though
conventional physical switches would have been easier to use.
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 21 kg
compared with retractable metal roof, thus helps lowering center of
gravity. Unfortunately, boot volume has taken a setback, and
considerably. Theoretically, a soft top should save luggage space, but
perhaps due to that 911 tail or the rear seats, the boot suffers. 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. The new
SL is a packaging disaster.
Another disappointment is the wind blocker behind the seats, as you
need to fit it manually in place. For a car costing so much money –
£148K for SL55 and £172K for SL63, about 10 percent more
than comparable 911 Cabriolet models – it sounds too cheap.
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Even
in Comfort mode, the suspension feels firm, more sports car than grand
tourer.
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On the Road
It is hard to define the new SL in a few words. It is a very
sophisticated car, equipped with 4WD, 4WS, a complicated hydraulic
suspension and 5 driving modes (Slippery, Comfort, Sport, Sport+ and
Race), plus an Individual mode to let you customize everything. The
stability control alone has 4 modes. Immersed in the snug cockpit,
surrounded by flashy screen graphics and data and looking forward
through a shallow windscreen over the long bonnet, the driving
environment feels definitely more serious, or even stressful, than in
any old SLs bar the first generation race machine.
First thing to notice is the impressive rigidity of the chassis, but as
soon as you ride over bumps, you also notice a stiffness not seen in
any of its predecessors. Now you realize this is a thoroughbred AMG
rather than a Mercedes SL badged AMG. On smooth highway, the SL feels
composed and highly stable. On poorer surfaces, however, it borderlines
on the acceptability of most drivers. Even in Comfort mode, the
suspension feels firm, more sports car than grand tourer. Road roar
from the fat rubbers also hurts its cruising refinement.
On the flipside, the handling is much improved, particularly SL63. It
grips hard, resists roll remarkably and turns in responsively. The
steering is very direct at only 1.75 turns lock to lock, if not totally
transparent. The car is also well balanced, although the front axle
takes 54 percent of all weight. However, it is also less talkative and
less interactive with the driver than a 911, Ferrari Roma, Portofino or
Aston Martin DB11 Volante.
Despite the tremendous power offered by the twin-turbo V8, there is so
much grip to overcome. It is harder to oversteer and flow in the
twisty. The only undisputable strength is the V8 engine, but you can
get a more powerful version with less money in the form of E63 S.
The new SL is neither a true sports car nor a competent GT. It tries to
deliver the best of both worlds, but ends up satisfying neither sides.
It seems to me that Mercedes has lost its own vision in an attempt to
replicate the success of Porsche 911. The SL used to be a
luxury-oriented, laid-back roadster. There is no point to try to be a
Mercedes 911
or a 2+2 version of AMG GT. If Mercedes wants to broaden its appeal, it
should shift towards the GT side, taking inspiration from Maserati
GranCabrio or Bentley Continental GTC, especially as the S-class Coupe
has retired.
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Verdict:  |
Published on 19
Nov 2022
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All rights reserved.
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SL43
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Some
might accept a 4-cylinder SL, but at £108,000, it is another
matter.
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Ridiculously, Formula One
is ditching the complex MGU-H electric turbo from the next generation
power units coming out in 2026, but Mercedes-AMG is introducing the
same thing to its road cars. The new SL43 is the first road car to
employ electrified exhaust gas turbocharger, and Mercedes is probably
the only manufacturer to do so before the ultimate demise of internal
combustion engines.
The said engine is based on the existing M139 2.0-liter four-cylinder
that powers A45. In that application, it employs a large turbo to
produce up to 421 hp and 369 lbft of torque. On the SL43, however, the
focus is not on big power but refinement and drivability. By replacing
the conventional turbo with a smaller but electrified turbo, it can be
spooled up immediately on throttle, eliminating turbo lag. The result
is 381hp at 6750 rpm and 354 lbft of torque from 3250 to 5000 rpm. The
latter compares fabourably with A45 S, whose full torque does not
arrive until 5000 rpm.
Electric compressor is not new, of course. Mercedes, Audi, Land Rover
and Hyundai have such devices on their road-going engines. However,
these are actually electric superchargers instead of electric
turbochargers, because they don't have anything to do with exhaust gas.
Exhaust gas turbo is still the most efficient way to recapture the
energy that would be otherwise wasted in exhaust. The only downside is
turbo lag.
In Formula One engines, the MGU-H (Motor Generator Unit - Heat) is
actually a turbocharger added with a thin electric motor between the
compressor wheel and exhaust turbine. At lower revs when the exhaust
gas is not sufficient to drive the turbine, the electric motor takes
the responsibility to spool up the turbine and produce boost. When the
engine revs up and produces more exhaust gas than the turbocharger
needs, the MGU-H acts as a generator, recapturing the heat energy from
exhaust stream that would be otherwise released from the wastegate. It
sounds easy, but the most difficult is to minimize the size of this
electric motor to fit into the limited space of turbocharger while is
also heat-resisting enough to sustain the high temperatures found in a
turbocharger.
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SL43
is the first production car to get F1-style electrified turbo. Probably
the last one as well.
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After succeeding in F1 racing for so many years, Mercedes-AMG finally
transfers its know-how to production engines, even though that could be
short-lived. Its electric exhaust gas turbo is developed in partnership
with Garrett and produced by the latter. Its chief function is to cut
turbo lag and maintain a linear power delivery. However, it is not
known whether it includes the energy recovery function of MGU-H, as the
press release did not mention. Its power comes from a 48V electrical
system, which can be supplied by the belt-driven starter motor
generator of mild-hybrid system.
On the SL43, the M139 is mounted longitudinally and drives the rear
wheels only, unlike the V8-powered SL55 and SL63 which have standard
4WD. It takes 4.7 seconds to go from 0-60 mph, and top speed is 171
mph. No match for the V8 siblings, of course, but pretty good for an
entry-level SL model.
However, downsizing from 8 to 4 cylinders is a step too far, and I
suppose not many buyers will be pleased, especially as this one costs
£108,000. A 911 Carrera Cabriolet undercuts it by nearly
£10K yet offers 6-cylinder boxer power and higher performance. No
matter how technologically advanced it is, a four-cylinder is still a
four-cylinder. Its smoothness and sound are no match for a proper
6-cylinder engine, such as Mercedes’ own 3.0-liter straight-six with
turbo and electric supercharger. That one produces more power and
torque as well – 435 hp and 383 lbft. It would be a nice fit under the
long bonnet of the SL. Could have revived the legendary 300SL badge,
too. Yes, the SL43 is not the first four-cylinder SL, but the last time
Mercedes built such an SL was almost 60 years ago, and the tiny 190SL
was never regarded as a true SL. The new one will be the same.
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