The chassis - Leading the pack

Mar 15, 2004
  • Newly developed front axle and steering ensure dynamic handling
  • Sporty set-up for multi-link independent rear suspension
  • ESP® available as an option with automatic tyre pressure monitoring
  • 17-inch light-alloy wheels standard for SLK 350
Vibrant dynamism, light-footed motoring pleasure, maximum safety - three hallmark characteristics of the SLK-Class which are moulded to a great degree by the Roadster's chassis. The axles, steering and brakes have all been developed anew or redeveloped by the Mercedes engineers in an effort to surpass even the high standards set by the model it replaces. The advances that have been achieved make their presence felt within the first few miles and help create the inimitable motoring experience – above all thanks to the sporty handling, high-precision steering, excellent ride comfort, sure handling right up to the car's limits and exemplary braking stability.
The previous double-wishbone front suspension with recirculating-ball steering has now been superseded by a three-link axle featuring McPherson spring struts and a rack-and-pinion steering system. This new axle technology revolves around two individual link elements which serve as torque and cross struts. Apart from more precise wheel location, the prime benefit offered by these two links is the ability to compensate for vibrations caused by tyre imbalances or brake force fluctuations more effectively than rigid wishbone designs. Added to this is the fact that, in the event of a frontal collision, the crumple zones in the vicinity of the bottom link level are larger, allowing the front end of the vehicle to absorb more of the impact energy. The torque struts of the SLK's front axle are made from aluminium, whilst the cross struts are manufactured from forged steel.
The third front axle link is the track rod which connects the laterally positioned steering gear to the wheels. The spring struts also fulfil more than just one function, as, apart from being responsible for axle suspension and damping, they also have an active role to play in wheel location.
The spring struts consist of coil springs, twin-tube, gas-filled shock absorbers and compact head bearings. The standard-fit anti-roll bar is linked to the spring struts by means of a torsion-bar linkage, with rebound buffer springs being used to boost the effect of the anti-roll bar when the vehicle is cornering at speed.
The lower components of the front axle, plus the steering gear and the engine bearings, are connected to an assembly carrier, which is in turn bolted directly to the vehicle body. Following on from its successful implementation in other model series, Mercedes-Benz is now transferring this technology to the SLK-Class for the first time, as it offers straightforward assembly coupled with significant safety benefits: in the event of a front-end collision, the assembly carrier will crumple to absorb a portion of the impact energy.
Steering: new technology for sporty handling
There were a number of good reasons for switching to the new steering system. The most pressing argument was the more direct response offered by rack-and-pinion steering which helps underline the dynamic, sporty credentials of the new SLK-Class. Furthermore, positioning the steering gear in front of the wheel centre produces a tendency to understeer, enhancing handling safety when cornering. Other aspects in favour of the new technology are its contribution to occupant protection and its lightweight design principle: whereas the gear of a recirculating-ball steering system forms a rigid block which is incapable of absorbing energy in a frontal collision, the rack-and-pinion steering can be mounted in a crossways configuration on the axle carrier, meaning that it does not interfere with energy absorption in any way. And as the system does without additional components, such as a pitman arm, drag link, steering idler arm and strengthening plate, it weighs far less than the recirculating-ball steering featured on the predecessor model.
The steering continues to be power-assisted to reduce the effort required to turn the wheel. Making its debut in the SLK-Class, however, is the speed-sensitive steering which is available as an option, and which is even smoother and more closely geared towards the driver's needs. It is designed to reduce steering torque in relation to the current road speed by up to 50 percent.
Drivers of the new SLK-Class have a number of options for setting the steering wheel to the ideal position: by merely pulling out the handle below the steering column, the steering wheel can be smoothly adjusted for height (by +/- 25 millimetres) and for reach (by +/-30 millimetres). The electrical steering column adjustment, which is available as an option in conjunction with the memory package for the seats and exterior mirrors, offers drivers even greater ease of use.
Rear axle: multi-link independent design with improved vibration characteristics
The multi-link independent rear suspension which has already proved so successful in the past will continue to be fitted on the new SLK-Class where it combines with the newly developed front axle, the extended wheelbase and the standard-specification ESP® Electronic Stability Program to deliver a high degree of handling safety, dynamism and passenger comfort. Modifications made to the kinematics and elasto-kinematics, stemming primarily from the use of optimised bearings, both improve the vibration characteristics yet further, as well as reinforcing the two-seater's tendency to understeer, which is in itself a guarantee of excellent handling safety. The multi-link independent suspension has also been adapted to the sports car's increased track width, while the anti-roll bar fitted as standard on all models is attached directly to the body.
Suspension and damping of the rear wheels is the task of coil springs working together with single-tube, gas-filled shock absorbers.
Drivers with a passion for sporty motoring can opt for the SLK-Class chassis to be given firmer suspension and damping settings. With the sports chassis fitted, the body is lowered by ten millimetres at the front and the rear. In this sportier set-up, total spring travel at both axles is shortened by ten millimetres compared to the standard chassis, while the spring rates increase by as much as ten percent.
Brakes: state-of-the-art technology for maximising safety
Mercedes engineers have once again made tremendous progress in the field of braking technology too, particularly when it comes to braking performance and smoothness. Each of the different models in the range comes off the assembly line complete with internally ventilated disc brakes measuring between 288 and 340 millimetres in diameter, depending on the model in question.
The SLK 350 is equipped with a state-of-the-art, lightweight braking system including perforated front brake discs. The perforations are an efficient means of dispelling dirt and water, meaning that the brakes continue to deliver excellent stopping power in inclement weather conditions. The cover plates underwent development in the wind tunnel: they have been styled in such a way that the airstream flows from the inside outwards to keep the brake discs free of spray water. At the same time, cooling of the brake discs and the wheel bearings has also been enhanced. Reliable deceleration at the rear of the new SLK-Class comes in the form of solid disc brakes. The fixed-calliper brakes used here by Mercedes-Benz feature twin-piston technology.
Brake data for the new SLK-Class
Front wheels Single-piston, floating callipers, internally ventilated brake discs
288 x 25 mm
4-piston, fixed callipers, internally ventilated brake discs, perforated 330 x 28 mm 6-piston, fixed callipers, internally ventilated and perforated composite brake discs 340 x 32mm
Rear wheels 2-piston fixed callipers, solid brake discs
278 x 9 mm
2-piston, fixed callipers, solid brake discs
290 x 10 mm
4-piston, fixed callipers internally ventilated and perforated brake discs 330 x 26 mm
Mercedes-Benz has used an electronically controlled solenoid valve for the brake force booster which allows brake pressure to be metered with particularly high precision. This also helps to improve the dynamics of the brake pulses emitted by the ESP® Electronic Stability Program and by Brake Assist.
Control systems: ESP® with warning function to indicate low tyre pressure (optional)
The new SLK-Class, like all Mercedes-Benz passenger cars, is equipped as standard with the most advanced and most efficient driving safety systems in the world. They reduce the risk of skidding when cornering, keep the sports Roadster safely on course when braking, make pulling away on a slippery surface easier and shorten the braking distance in emergency situations. Such sophisticated technology is an important component of the safety concept applied at Mercedes-Benz and helps to prevent road traffic accidents.
ESP®, the Electronic Stability Program, is at the heart of all dynamic handling control systems. It reduces the risk of skidding and keeps the SLK safely on track. Sensors monitor driving style and the vehicle's handling characteristics, and relay their data to a powerful micro-computer which has been programmed with a mathematical model. This allows it to compare the vehicle's actual operating status with an appropriate target status for the current driving situation. Where there is a serious discrepancy, the system intervenes by applying a specially developed logic, triggering precisely metered brake pulses at the front and rear wheels, as well as carefully throttling the engine torque. This allows the ESP® system to stabilise the vehicle, even when it is skidding as a result of either extreme driving manoeuvres or of adverse road surface conditions, such as those caused by ice, rain or loose chippings.
In the new version of the Mercedes-Benz Roadster, ESP® is also able to offer a further function as an option which warns drivers of a loss of pressure in the tyres. ESP® constantly monitors the rotation speed of the wheels, which depends mainly on road speed, the vehicle load and the air pressure in the tyres. Because the ESP® Stability Program permanently records the wheel rotation speeds and compares the values with one another, it is able to detect any significant deviations in the readings. The control module also automatically checks other handling dynamics variables, such as lateral acceleration, yaw rate and wheel torque, in order to reliably diagnose a loss of air pressure in any one tyre. The system does not, however, measure the actual tyre air pressure. If the system detects that pressure is being lost in any of the tyres, a red warning appears in the cockpit's central display which reads "Tyre pressure, check tyres."
Wheels and tyres: extensive factory-fitted range to choose from
The SLK 200 KOMPRESSOR is shod as standard with 205/55 R 16 wide-base tyres and 16-inch light-alloy wheels sporting an attractive seven-spoke design. The six-cylinder SLK 350 model comes with 17-inch wheels featuring an even sportier five-spoke design, and is fitted with wider tyres at the rear (245/40 R 17) than at the front (225/45 R 17).
Further wheel designs are also available to order as an option; the range includes six different styles in all. The SLK 55 AMG emphasises its high-performance character with tyres measuring 225/40 R 18 at the front and 245/35 R 18 at the rear, which sit on specially styled, silver-painted AMG light-alloy wheels.
So that Mercedes customers can keep on the move, even if they suffer a puncture, the Stuttgart-based car manufacturer is also offering run-flat tyres as an option for the new SLK-Class in conjunction with the ESP® program's tyre pressure loss warning system. These tyres use self-supporting side walls which maintain the tyre's structure following a loss of pressure so that the vehicle can continue to be driven for a short time. The vehicle's range under these conditions is around 50 kilometres if it is partially laden and around 30 kilometres when the boot is fully loaded, whilst top speed is restricted to 80 km/h in both cases. The TIREFIT tyre repair kit that is included with the car as standard can also be used by motorists to repair minor damage to the tyre and increase this range significantly. However, in this case too the vehicle still may not be driven any faster than 80 km/h.
The wheels and tyres fitted on the new SLK-Class*
Front Tyres 205/55 R 16 Wheels 7 J x 16 ET 34 Tyres 225/45 R 17 Wheels 7.5 J x 17 ET 36 Tyres 225/40 R 18
Wheels 7.5 J x 18 ET 37
Rear Tyres 205/55 R 16 Wheels 7 J x 16 ET 34 Tyres 245/40 R 17
Wheels 8.5 J x 17 ET 30
Tyres 245/35 R 18
Wheels 8.5 J x 18 ET 30
*Standard specification