Road impressions: Mercedes SL

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A new benchmark

We reported in some detail on the technical aspects of the new Mercedes sports-car in the April issue, before we had had the chance to drive it. However, we have now had the pleasure of trying all the SLs on the recent international launch.

As a base reference, we started with the 300, the plain 190 bhp 3-litre twin-cam fitted with the optional four-speed automatic box. This box, also fitted to SL-24 and 500 models, offers a sport/economy choice, but seemed a poor match for the smallest engine. Even in “sport” it was slow to change down on demand, and would stay in the lower gear only momentarily, making it hard to escape from the steady trickle of buses and old lorries winding along the convoluted roads around the Estoril circuit in Portugal.

This disappointment did not however mask the basic qualities of the SL. Mercedes’ aim of exceptionally high body rigidity is amply vindicated; frame distortion is no higher than the company’s saloons, and it shows on the road. The lack of body grumbles is almost uncanny to one used to normal convertibles, even through the worst holes, and mechanical noise suppression is superb. With the top down, even the swish of the big tyres (225/55 ZR16) is lost to the skies, and after the hood mechanism has flexed its hydraulic muscles and closed in the occupants the noises increase only to a restrained rumble of rubber on tarmac. Below about 80 mph wind noise is virtually absent, but above that point there is a mild degree of it as the roof seals lose some of their grip.

Refinement with both the six-cylinder engines is superb: smooth from the peak of their power curves down to a silky idle, only the extra pull of 231 bhp instead of 190 betraying the 24-valve unit with its variable cam timing. By playing with the throttle it is possible to feel the cam advance come in, but in ordinary use it is unnoticeable; the unit simply feels like a 31/2-litre engine.

In the top model, the 500SL (at least until the 600SL V12 arrives), the 5-litre V8 also has the variable timing system on its two inlet camshafts, churning out a hearty 326 bhp. It comes only with the auto-box, but although this is the same unit as fitted to the lesser cars, it responds much better to the massive 321 lb ft of torque. Kickdown is brisk in “sport”, and the unit responds to varying throttle pressures so that the driver can choose 3 or 2 with a stretch of the ankle. The “economy” option gives very quiet gentle changes.

Compared to the sixes, the V8 is less composed, a mild shudder passing through the engine compartment under hard acceleration and the typical growl spilling out of the bonnet. But the overriding sensation is of the strength of the forces pushing you back in the seat as the car accelerates. It really is brilliantly quick, not just in standing starts (0-60 mph takes 6.2 seconds), but on the road. Overtaking is effortless, and the instant response, so rare in an auto, makes the 500 a pleasure to guide over sinuous back-roads.

Suspension follows the current middle-range saloons in using a vertical shock-absorber strut at the front, with a separate coil spring, while the five-link rear axle is broadly unchanged. Mercedes compares its effectiveness with passive rear-wheel steering; certainly it offers handling which in viceless and forgiving.

Theoretically there is no chassis difference between the two-valve six and the heavier V8, but in fact some minor geometry and spring rate variations give the 500 stodgier steering than the pleasantly weighted 300; something of the precision of the lighter car is lost in transmission.

A chance to drive a 500 on the Estoril race-track showed that it was not flustered by extremes of punishment, either. Admittedly the track cars were not quite standard — they boasted stiffer springing which will be offered as a performance package later on, plus harder brake pads. Yet instead of ploughing on as a big automatic might be expected to, the SL retained a steady and reassuringly small amount of understeer while subjecting the crew to truly impressive cornering forces. But the copious electronics allow no bravery: ASR, or acceleration skid control, is standard on all 500s, and this actually feathers the throttle if the rear wheels begin to slide. Thus it is impossible to attain opposite lock without actually spinning the car.

This is certainly a sophisticated system, but it cannot be switched off, and more than one journalist at the launch felt that this in itself would prevent him choosing this car as his own transport, not because a responsible driver seriously wishes to drive sideways on public roads, but because there are occasional moments when it is comforting to have that option in answer to a crisis. ASR is an option on the six-cylinder cars; all models come with ASD, the electronic locking differential, which triggers an orange dashboard light when it operates.

To round off the initials, the new feature is ADS — adaptive damping. This is an option on all cars and takes existing systems another step on, with four levels of damping which depend on a series of inputs including vertical acceleration of wheels and of body, steering wheel angle and load, and road speed. It is a complex but successful way of reconciling a gentle ride with a sporting chassis, though for the SL the base condition is nothing like as soft as the big saloon.

In action the device is not apparent at all, except inasmuch as body movements hardly vary in amplitude whether parking or sprinting along a hill-road. At all times the chassis seems taut, but the ride is never hard. This is the first time I have been impressed by such a system. However, the ride quality of the non-ADS cars was in any case first-rate by conventional standards, not as liquid as an XJ-S, but happier in successive tight bends.

After 500 and 300 autos, we drove a manual 300SL-24, equipped in this case with the optional sports box. Its dog-leg first pattern is a benefit for fast driving, and even reverse is synchronised, but the change itself could be more positive. Still, a fast passage from Estoril south to the Algarve along smooth roads through some dramatic valleys crystallised the picture of the SL; very relaxing at speed, extremely refined, with complete choice as to driving style. Leave it in fifth and rely on the torque even from 1000 rpm, or keep the gear lever moving and the tach needle between five and seven. It will successfully fulfil its role as a cruiser for the States, and still satisfy European drivers.

In amongst all the electronics, the simplest new feature is the draught-stop. This net panel flips up behind the seats and cuts out most of the buffeting which is otherwise apparent at speeds over 60 mph, but also decreases the rear visibility. Thick pillars to the immensely strong screen surround can also restrict the view a little on tight bends. Interior fittings are simple and clear, following other Mercedes models with unfussy styling and good large controls set in pleasant wood veneer. The only flaw I found was that selecting “park” or first invariably started up the cassette.

Five motors are built into the new seats, whose cast magnesium alloy frames strengthen the floorpan and protect their occupants. An optional position memory also ties in mirrors, including the interior, and the steering column. Belts are integral with the seat, and are adjusted for height along with the head-rest. I found these very hard in the German style, and was glad to emerge and stretch after an hour or so.

A single switch triggers the roof, which folds away in about 25 seconds under its metal cover, and needs no manual unclipping. When up it is nicely taut, tensioned against billowing up by steel cables, though the mechanism is exposed, surprising in this day of lined hoods.

To wrap up my introduction to this impressive newcomer, I took out a plain 300SL with manual gearbox, which transformed my previous view of the auto. In a couple of hours tackling little hill-roads and then plunging through steep valleys on narrow main routes, the car thrived on hard use. Though not a small machine, its precision is memorable, its balance a delight, and its comfort is likely to become a benchmark. GC