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on 27
Oct
2011 |
All rights reserved.
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When Mercedes-Benz
launched the innovative sandwich platform with A-class in 1997, we
thought it could change the automotive world forever. Yes, in terms of
space efficiency the sandwich platform was a step ahead of modern FF
layout pioneered by Alexander Issigonis' Mini. Its advantage was
especially obvious in the presence of stricter crash protection
regulations. During collision, the powertrain slid underneath the
floorpan rather than towards the passenger cell. This mean it did not
need bulky crumple zone to pass crash test. As a result, it was capable
of allocating more of its length to wheelbase, hence more cabin space
can be extracted from a small package.
Unfortunately, the sandwich platform was too costly to build.
Its uniqueness means most critical components – suspensions, engines,
gearbox and
steering – were dedicated to the platform and could not be used by
other (rear-drive) Mercedes, let alone share with other car makers like
the case of BMW Prince engine. The low production volume resulted in
unusually high unit costs. In the second generation sandwich platform,
Mercedes tried to increase volume with the addition of B-class, but
even so the combined volume was just 222,400 units last year. This
compare unfavourably with the industrial norm which talks about 2
million cars a year on a single platform!
Eventually, Stuttgart has to give up the sandwich platform. The next
generation A and B-class are to be based on a conventional FF platform
dubbed MFA (Modular Front Architecture). It is not as space efficient
as the old one, but it is more flexible, allowing not only A and
B-class but also the next generation CLC-class (which will switch to
front-wheel drive) and a small SUV called GLC to be derived from it. If
the combined production volume is not high enough, you can also count
on some Nissan and Infiniti models coming in the future. This is
because the MFA is part of the joint-venture agreement between Daimler
and Renault-Nissan signed in early 2010. Although its engineering was
done purely by Stuttgart, Mercedes is willing to let Nissan take a free
ride in order to get the economy of scale it needs.
The first product derived from the new MFA platform is the second
generation B-class, codenamed W246. Looking from outside, you can
already tell the switch to conventional platform. It gets a longer nose
to accommodate the engine and crumple zone. The result is a profile
more 2-box than monospace. The car measures 4359 mm in length, some 89
mm longer than the old car. Its width gets a slight increase of 9 mm,
but the most change is height, which is reduced by as much as 47 mm to
1557 mm.
Despite of the added length, the wheelbase shrank by 80 mm as more
space is spent to the overhangs. However, at 2700 mm the wheelbase is
by no means short for a 5-seat MPV.
Inside, the change is equally obvious. The gone of sandwich structure
means a much lower cabin floor. The driver seat is now mounted 86 mm
lower, too, so it offers a more natural and comfortable driving
position.
The new front seats are also far more supportive than before. The new
dashboard is definitely more stylish, with SLS-style circular air
vents. Its
sporty look is certainly a sharp contrast to the bland exterior design.
The dashboard is also made of much higher quality materials. It finally
looks and smells like a premium product.
With four passengers on board, the new B-class should feel roomy.
Thanks to the lower hip point in relation to the roof, it affords
excellent headroom. Knee room is also good, thanks to a rear bench that
can slide back and forth for a range of 140 mm. At its rearmost
position, the rear seat offers more legroom than an S-class. At the
foremost position, luggage capacity is a remarkable 666 liters. You
cannot have both, but it is up to you to decide the priority. If rear
seat is not in use, you can fold it to expand luggage space
further to 1545 liters. Nevertheless, it still fails to match the old
car's
1995 liters. Also, the expanded load bay is not completely flat, unlike
before.
Unfortunately, the B-class does not accommodate the fifth passenger
very well, blame to a prominent tunnel running through the center of
the cabin. This is also the key disadvantage of the MFA compared with
sandwich platform, which had a flat floor. Theoretically, the
front-drive platform does not need a transmission tunnel, so the
prominent tunnel is probably introduced to boost chassis strength, or
reserve space for a possible 4matic option.
Anyway, we found no such thing on most other MPVs. It would be a big
minus point when compare with rivals.
Another disadvantage is the lack of long-wheelbase 7-seat version,
unlike Ford C-Max, Citroen C4 Picasso or Renault Scenic etc. This could
put off many family buyers.
With a conventional architecture, the mechanical package is easily
predictable. It rides on suspensions consisting of MacPherson struts up
front and a new multi-link setup at the rear – the latter contrasts to
the old car's torsion-beam. Steering is now assisted
electromechanically rather than hydraulically to save fuel. Engine can
be either a 1.6-liter turbo petrol or 1.8-liter turbo diesel, both have
been downsized. The petrol engine is finally up to date, with twin-cam
16 valves, variable valve timing and direct injection to insult the old
8-valver, although we would have liked the addition of twin-scroll
turbo like its BMW rivals. It produces either 156 hp / 184 lbft or 122
hp / 147 lbft, depending on state of tune. The common-rail diesel
offers 136 hp / 221 lbft or 109 hp / 189 lbft. Both engines are
equipped with fuel-saving automatic stop-start facility and brake
energy regeneration alternator – a must these days. Transmissions have
been upgraded as well, with the choice of 6-speed manual or 7-speed
twin-clutch gearbox. Finally, the new B-class has a class-leading drag
coefficient of 0.26, benefiting fuel economy.
On the road, the new B-class is definitely better to drive than the old
car. Its chassis controls body movement better and resists understeer
stronger, thanks to the more sophisticated suspensions and a center of
gravity 20 mm lower than before. The electromechanical steering is also
satisfying, with consistent, natural weighting and good response.
Unless you opt for sport suspensions, 18-inch wheels and low profile
tires, the ride quality is much more compliant than the old car.
However, the Mercedes chassis is not as well engineered as Ford C-Max.
It never feels as light and agile as the latter around tighter bends.
The powertrain also gives a mixed impression. The 1.6 turbo petrol
works smoothly but it needs rev to keep its turbo spinning, even though
the spec. shows peak torque arrives at just 1250 rpm. The diesel engine
is better, offering stronger low-end punch and demanding less effort
from the driver. The paddle-shift gearbox responds well to manual
shift, but in auto mode it does not work as smoothly as it should.
Overall, the dynamic aspect of the car is satisfying rather than
outstanding.
Unquestionably, the new B-class is less compromising than the old car,
mainly owing to its abandonment of sandwich platform. However, compare
with many mainstream compact MPVs, especially the class-leading Ford
C-Max, it is not good enough to justify its premium prices. Poor
accommodation for the 5th passenger is its biggest flaw. Some other
areas like interior flexibility, cargo space and an average petrol
motor are also slightly underwhelming. For a car wearing a
three-pointed star badge, we have to admit a slight disappointment.
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Verdict:  |
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