Steering in right direction

Sensors are a key feature of Mercedes-Benz' latest electronic steering system, writes motoring editor ALASTAIR SLOANE.

The electronic "steer-by-wire" system in the Mercedes-Benz F400 Carving concept car does away with the traditional steering column. Instead, sensors pick up what the driver is doing with the steering wheel, relay it to two microcomputers which, in turn, tell the electric steering gear where to point the car's front wheels.

This is where things get interesting. The outside wheels on the F400 lean into corners, using what Mercedes-Benz calls "active camber control."

This system tilts the angle on the outside wheels inwards by up to 20 degrees and, combined with specially designed tyres, boosts the car's cornering power by nearly 30 per cent, or a force of up to 1.28g.

That's where the name Carving comes in. It is a skiing term for sharp turns. A road-going sports car on high-performance tyres develops cornering forces of 1g on the limit.

The asymmetrical-tread tyres on the F400 Carving are equally as important as the lean-in system itself. The inner tread of the tyres has a specific and slightly rounded-off tread pattern to aid cornering, because cornering forces in this case are concentrated on the inner area of the outside tyre.

But in a straight line or under normal braking, the flat face of the tyre - which has a regular tread pattern and design - is in contact with the road. Under emergency braking, all four wheels can be tilted almost immediately to increase stability and reduce stopping distance at 100 km/h by five metres. The car's Electronic Stability Programme has a role to play here.

The use of wing fenders instead of typical mudguards gives the wheels room to do their thing when the active camber control is at work.

The F400 Carving also uses an active hydro-pneumatic suspension that reacts to changing road conditions. Its lighting system is new, too. Space-saving fibre-optic cables transmit light to the main headlamps from xenon lamps beneath the main bonnet.

The F400 was unveiled at the Tokyo motor show this week. Mercedes-Benz says the two-seater body "emphasises the youthful and highly adventurous nature" of the concept.

It calls the car its "mobile research laboratory" and says it will use it to explore the "undoubted further potential of this new chassis technology."

The company has almost certainly earmarked some of the car's technology for a future model.

The F400 Carving is a development of the three-wheeled F 300 Life-jet concept, unveiled at the Frankfurt motor show in 1997.

It uses technology first hinted at in the concept SLR supercar, which is expected to go into production in 2003.

The results of Stuttgart's continuing research is obvious in three new Mercedes-Benz models - the specialist AMG Kompressor C 32 and Kompressor SLK 32, and the updated ML 500 four-wheel-drive.

The four-door C 32 costs $155,000 and the two-door, tin-top convertible SLK 32 $149,000. Both cars are powered by a supercharged 3.2-litre V6 engine producing a class-leading 260kW (349 bhp) at 6100 rpm and a whopping 450Nm of torque at 4400 rpm. Most of the torque is available from 2300 rpm. Take it as read that both cars come with every comfort and safety device imaginable.

The ML 500, the top-line model in the revised off-road range, costs $136,000 and replaces the ML 430. The new 5-litre V8 produces 215kW (292 bhp) at 5600 rpm and 440Nm of torque (13 per cent more than the 4.3-litre V8) between 2700 and 4250 rpm. The new-look ML 320 V6 and ML 270 turbo-diesel will arrive in New Zealand soon. Again, these models have everything that opens and shuts.

If there is one thing cars such as the two AMG models need in New Zealand it is a suitable private road or track to let them warm to the task. A ready-made circuit like Germany's Nurburgring would do nicely.

The rear-drive cars can iron out corners at ridiculous speeds, so advanced are the chassis dynamics and so secure the roadholding, although the SLK 32 lacks the supple flexibility of the C 32 chassis. The SLK 32 is 140kg lighter than the C 32 but they both sprint from zero to 100 km/h in about 5s.

Mid-corner adjustments are a doddle, too, but again the SLK 32 isn't as composed nor the recirculating-ball steering quite as accurate in such situations as the rack and pinion setup in the storming C 32 sedan.

One of the strengths of the SLK 32 is the lack of scuttle shake - body squeaks and movements, an inherent weakness in convertibles - thanks largely to Mercedes-Benz beefing up the bodyshell.

The company says front, side and rear aerodynamic aids also help to stabilise the car, improving downforce on the rear wheels by up to 50 per cent.

Straight-line speed has always been a standout feature of AMG cars. One of the highlights of the C 32 and SLK 32 is the explosive - and noisy - response of the supercharger. Especially in the two seconds or so it takes to get from 80 km/h to 120 km/h. This is barnstorming acceleration. David Tua couldn't hit any harder.

The C 32 sedan is much better all round than the C 43 and C 55 models it replaces. Its low-speed ride around town is the best in the high-performance business. Its five-speed automatic/manual Speedshift transmission is pretty slick, too, automatically shifting down a cog under brakes. The SLK 32 uses the same transmission but it is better suited to the better dynamics of the sedan.

Mercedes-Benz says it has made more than 1100 improvements to the facelifted ML range. One of the best is to the steering. It is more accurate and self-centres better at low speeds, especially when parking.

The new-look includes colour-coordinated front and rear bumpers, different wheels, tail-lights, fog lamps and range of colours.

Inside, the centre console has been improved. So has the front and rear air-conditioning system, stowage facilities and the choice of wood trim. There is also a 12-volt power socket for rear passengers.

Mercedes-Benz has sold nearly 500 four-wheel-drive ML models since the range appeared here in August 1998. The next-generation short and long-wheelbase vehicles are expected in 2004-2005. Meantime, the updated ML range is easy to live with.