It’s time to say goodbye to normal street shoes and start wearing trendy sneakers again – footwear fashion for spring has a chic and sporty air to it. And the same is true of cars when the time comes to switch back to summer tyres: attractive light-alloy wheels from Mercedes-Benz Accessories enhance the appearance of any vehicle while lending an added touch of sportiness and elegance. The trend for the summer 2015: big wheels with fine details.

From fleeting fashion to lasting trend: even compact-class models such as the Mercedes-Benz A-Class are now riding on 18-inch wheels, while the range of sizes extends to as large as 21 inches on SUV vehicles like the new Mercedes GLE.

Big wheels are in, according to the Mercedes-Benz designers, but they are shown off to particularly striking effect by fine details such as rim flanges painted in a different colour. Two-tone finishes continue to be popular, as do high-sheen light-alloy wheels, whose special appeal stems from the contrast between the seemingly bare metal and the painted surfaces.

A selection of new Mercedes-Benz light-alloy wheels

A-Class (also suitable for CLA and B-Class)

• 5-twin-spoke wheel, 45.7 cm (18-inch)
• Surface: black, rim flange: red
• Wheel size: 7.5 J x 18 ET 52
• Article number A24640106009Y23

CLA Shooting Brake (also suitable for A- and B-Class and CLA Coupé)

• 5-twin-spoke wheel, 45.7 cm (18-inch)
• Surface: black, rim flange: high-sheen
• Wheel size: 7.5 J x 18 ET 52
• Article number A24640106007X72

GLA

• 5-spoke wheel, 48.3 cm (19-inch)
• Surface: matt black, rim flange: red
• Wheel size: 8 J x 19 ET 43.5
• Article number A15640104009Y22

C-Class

• 5-spoke wheel, 45.7 cm (18-inch)
• Surface: matt black
• Wheel size: 7.5 J x 18 ET 44
• Article number A20540106007X35

C-Class

• 10-spoke wheel, 48.3 cm (19-inch)
• Surface: black, rim flange: high-sheen
• Wheel size: 7.5 J x 19 ET 44
• Article number A20540129007X72

E-Class

• 5-twin-spoke wheel, 48.3 cm (19-inch)
• Surface: matt black, high-sheen finish
• Wheel size: 8.5 J x 19 ET 48
• Article number A21240148027X36

GLE (also suitable for M-Class)

• 10-spoke wheel, 50.8 cm (20-inch)
• Surface: matt black, high-sheen finish
• Wheel size: 9 J x 20 ET 57
• Article number A16640116007X36

GLE (also suitable for M-Class)

• 10-spoke wheel, 53.3 cm (21-inch)
• Surface: black, high-sheen finish
• Wheel size: 9 J x 21 ET 53
• Article number A16640117007X23

S-Class

• 10-spoke wheel, 50.8 cm (20-inch)
• Surface: palladium silver
• Wheel size: 9.5 J x 20 ET 43.5
• Article number A22240128027X19

SL-Class

• Multi-spoke wheel, 48.3 cm (19-inch)
• Surface: palladium silver, high-sheen finish
• Wheel size: 8.5 J x 19 ET 35.5
• Article number A23140127027X19

V-Class

• 10-twin-spoke wheel, 45.7 cm (18-inch)
• Surface: black, high-sheen finish
• Wheel size: 7.5 J x 18 ET 52
• Article number A44740137007X23

With the help of the accessories configurator on the www.mercedes-benz.de website, suitable wheels and the correct tyre size can be found for practically any Mercedes-Benz. In addition to this, when configuring the vehicle, the appropriate complete summer or winter wheels can also be ordered and then requested from any authorised Mercedes-Benz dealer in Germany when the seasons change.

High-sheen bichromatic wheels and large wheels up to size 53.34 cm (21-inch) continue to enjoy great popularity. Accordingly, Mercedes-Benz Accessories GmbH is expanding its range of these light-alloy wheels. Just in time for the changeover from winter to summer tires, the new models are available for numerous model series. In all, the diverse product range from Mercedes-Benz Accessories currently comprises around 170 different wheel designs, including two models for the new Mercedes-Benz SL, that is available at Mercedes-Benz dealerships as of March 31.

High-sheen bichromatic light-alloy wheels derive their additional appeal from the interesting contrast between the apparently bare metal surface and the painted areas. They lend the vehicle a yet more exclusive appearance and are considered by the designers at Mercedes-Benz to be more than just a passing fad. Accordingly, Mercedes-Benz Accessories GmbH is now extending its range of bichromatic wheels. The popular wheels in single-tone painted finish also remain available.

The trend towards larger wheels fitted flush with the outer body contours is also continuing in all categories of vehicle. This design style signals power, dynamism and driving stability. Mercedes-Benz Accessories GmbH also has new products to offer in this area – such as the 5-twin-spoke wheel in bichromatic design in size 53.34 cm (21-inch) for the M-Class.

For spring 2012, Mercedes-Benz Accessories is offering new light-alloy wheels for numerous vehicles including the following model series (situation as per March 2012):

SL-Class

• incenio 5-spoke wheel, 45.7 cm (18-inch)
• Surface finish: matt satin silver / high-sheen
• Wheel size: 8.5J x 18 ET 35.5 (A231 401 2902 7×34)
• Wheel size: 9.5J x 18 ET 47.5 (A231 401 3002 7×34)

• incenio multi-spoke wheel, 48.3 cm (19-inch)
• Surface finish: palladium silver / high-sheen
• Wheel size: 8.5J x 19 ET 35.5 (A231 401 2702 7×19)
• Wheel size: 9.5J x 19 ET 47.5 (A231 401 2802 7×19)

M-Class

• incenio 5-twin-spoke wheel, 53.34 cm (21-inch)
• Surface finish: Himalayas grey / high-sheen
• Wheel size: 9J x 21 ET 53 (A166 401 2707 7×21)

GLK-Class

• incenio 5-spoke wheel, 48.3 cm (19-inch)
• Surface finish: tremolite metallic
• Wheel size: 7.5J x 19 ET 47 (A204 401 8902 7×28)
• Wheel size: 8.5J x 19 ET 52 (A204 401 9302 7×28)

C-Class

• incenio 5-twin-spoke wheel, 45.7 cm (18-inch)
• Surface finish: Himalayas grey
• Wheel size: 7.5 J x 18 ET 47 (A204 401 9102 7756)
• Wheel size: 8.5 J x 18 ET 54 (A204 4019 202 7756)

E-Class (Saloon and Estate)

• incenio 5-twin-spoke wheel, 48.3 cm (19-inch)
• Surface finish: Himalayas grey / high-sheen
• Wheel size: 8.5J x 19 ET 48 (A212 401 4802 7×21)
• Wheel size: 9.5J x 19 ET 48 (A212 401 4902 7×21)

E-Class (Coupé and Cabrio)

• incenio 5-twin-spoke wheel, 48.3 cm (19-inch)
• Surface finish: Himalayas grey / high-sheen
• Wheel size: 8J x 19 8 ET 44 (A207 401 1902 7×21)
• Wheel size: 8.5J x 19 ET 48 (A212 401 4802 7×21)

Highest quality standards

The same high safety standards apply to all the light-alloy wheels on offer – there are no differences in quality between the models belonging to the standard and optional equipment and the versions available from Mercedes-Benz Accessories. All wheels are required to meet the same high standards. Neither certification nor registration with the TÜV technical inspection authority are required when fitting the light-alloy wheels from Mercedes-Benz Accessories, as they all form part of the vehicle homologation. The customer always receives a product which is tailored perfectly to Mercedes-Benz vehicles: it supports their exemplary ride comfort and high driving dynamics and fulfils the high requirements of the design idiom, additionally combining high performance with an outstanding service life.

These merits result on the one hand from close collaboration between the vehicle development staff and the wheel development specialists. In order to win their Mercedes stars, wheels additionally have to pass a comprehensive test programme which goes well beyond the statutory licensing requirements for use in road traffic. This includes effective testing procedures geared towards the toughest service conditions encountered in real driving conditions, even extending to tests in cutting-edge x-ray systems and computer tomographs.

Care and handling tips

Even the best development programme, the most innovative production technology and a perfectly coordinated test programme are unable to influence how customers treat their vehicles, including the valuable light-alloy wheels. The manner in which wheels are handled continues to have a major influence on their value retention and the safety of the vehicle. Useful tips:

• Clean the winter/summer wheels thoroughly after changing in the spring/autumn, regardless of whether steel or light-alloy wheels are fitted
• Do not use aggressive cleaners. Products recommended by Mercedes-Benz are gentle agents which will clean the wheels effectively
• Do not clean with sharp or rough sponges
• Observe the specified wheel tightening torques. Wheel bolts which are too tight or too loose will damage the wheel in the long term
• Do not oil or grease wheel bolts, as at the specified tightening torque this will result in excessive pre-stressing, which may cause damage to both wheels and bolts
• Use only genuine Mercedes-Benz wheel bolts
• Check the wheels after they have taken heavy knocks, e.g. when driving through deep potholes. If deformation is visible, be sure to have the damage checked at a dealership
• Fit only the size of tyre approved for the wheel
• When carrying high payloads and/or towing a trailer, adjust the tyre pressure accordingly and be sure to observe the permissible wheel loads

Information on changing wheels or tyres as well as storing wheels is available at every Mercedes-Benz partner.

Obviously without wheels a vehicle is going nowhere – this simple observation not only describes the basic technical requirement for a properly functioning motor car, but also highlights the importance of the wheel as part of a powerful vehicle design. At Mercedes-Benz, high-quality wheels which match the bodywork and form a logical continuation of the design therefore play a significant role in the high design standards of the overall vehicle. At the Mercedes-Benz design centre, light-alloy wheels available either as standard or as optional extras are designed by specialists in the area which is also responsible for creating the entire exterior form of the vehicle.

The heritage behind Mercedes-Benz wheel design

Basically all Mercedes-Benz wheels follow a specific design guideline which nevertheless gives sufficient scope for a wide variety of styles, such that individualisation options in this area are not limited. The characteristics of wheels bearing the Mercedes star primarily adhere to the principle of highlighting the vehicle design in the respective model families. To this end, the designers make particular use of sculptured, modelled areas with powerfully flowing lines, while pure, basic geometry is usually always avoided. This can also lead to completely different design approaches being adopted within a model series. Take the S-Class as an example: most customers want elegant wheels, which can result in a delicate, multi-spoke design on the one hand, or a generously sized and less structured design on the other. Once on the vehicle, however, both solutions achieve the desired elegance. In contrast, SUV models and off-road vehicles always require striking, powerful, almost muscular wheels. For Roadsters and Coupés, the focus is squarely on sportiness. Among other things, the wheels look as big as possible thanks to maximum “connection with the outside”: for the most part the wheel spokes blend smoothly and seamlessly into the wheel rim flange. As a result, these models have a road stance which is powerful, almost crouching, ready for the off.

The development engineers define the design space which is available for the designers to work in. This leads to the creation of wheels which, thanks to their exceptional performance, support the high level of driving dynamics, excellent comfort and pioneering safety which are typical of Mercedes-Benz vehicles. By the same token, the designers can also work freely within the available space to come up with impressive wheel models which feature the customary high level of design quality.

A glimpse of the wheels of the future

Just like vehicle designers, wheel designers must also be able to look into the future, since due to the complex development process it can take some time before their designs actually appear on the market. But of course they are not able to use a crystal ball to help with their predictions. Research into the future and the recognition of trends is supported by Mercedes-Benz Advanced Design Studios located throughout the world, intensive customer surveys, contact with dealerships, market research and specialist agencies. These investigations have resulted in the following specific basic principles:

• The trend towards larger wheels, mounted so that they are flush with the outer edge of the vehicle body, continues to apply in all vehicle classes. This style reflects power, dynamism and driving stability.

• In the future, Mercedes-Benz customers want even higher value wheels with elaborately processed surfaces and more sophisticated colour designs.

• Mercedes-Benz and Mercedes-Benz Accessories will further expand the diversity of their product ranges from the current 130 wheel models in order to provide customers with even more individualisation options.

It all starts with product development: Complex programme for the best quality

Mercedes-Benz guarantees the quality of its new wheel models with a comprehensive development programme. As part of this, the tests and inspections which are carried out go far beyond the statutory requirements. Even when it comes to wheel development, one basic principle is applied: in the development and testing phases, Mercedes-Benz bases its work on the actual load profile of light-alloy wheels under real operating conditions and coordinates its programme accordingly. As a result, light-alloy wheels bearing the Mercedes star are among the safest, best performing and most durable products on the entire automotive market. At the same time, it is irrelevant whether we are talking about a wheel from the standard or optional ranges, or one from the wide range of accessories available from Mercedes-Benz Accessories – the process is always based on the same high standards.

Development dominated by the digital worlds

Early in the development phase of a new light-alloy wheel, engineers first specify the rough framework conditions within which to work: new wheel types for car models are determined in close cooperation with those responsible for the vehicle model series. At the same time, wheel specialists examine wheel market trends. These parameters then define the necessary wheel dimensions. The following basic principle is applied: data such as the gross axle weight, the size of the wheel well or any necessary brake clearance provide the installation space within which the designers have free space for their designs – all of course in accordance with exacting Mercedes-Benz design requirements. After a technical feasibility study, the final wheel design is determined.

A three-dimensional volume model is then produced using modern 3D computer programs. For visualisation and discussion purposes with the development team, developers can use this model to create three-dimensional drawings, or to specify component properties such as weight, machining options in the subsequent

production process, material distribution or even natural resonances and inertia moments. On the basis of these data records, the wheel is optimised with virtual test data using finite element analysis (FE analysis for short). In the digital world, it is possible to simulate demanding mechanical or thermal operating conditions: for example, cornering at maximum wheel load, or driving over a pothole or the kerb, or the brake heat load generated on a long downhill stretch. As such, conclusions can also be drawn about the subsequent production process and how it can be improved: if the intended wheel model is gravity die-cast and the material solidifies as required, will it be possible to remove the cast wheel blank from the mould without any problems? After preparing the light-alloy wheel in this virtual world, a digital mock-up is created – a computer-aided wheel model – which serves as the basis for all subsequent steps.

Based on the mock-up, the wheel manufacturer responsible for production sets up the necessary moulds, production tools and processes, after which the first sample wheels are produced. In this “prototype phase”, the wheel manufacturer conducts detailed examinations in cooperation with Mercedes-Benz to assess the resulting wheels and the entire production process. The objective: to optimise production at a high quality level. If this objective is reached, a true ordeal awaits the new wheels, which will be taken from the finely-tuned large-scale production test run.

In cooperation with the vehicle development divisions, aerodynamic aspects can also be incorporated into the design process. Flow simulations have shown that aerodynamically optimised light-alloy wheels and tyres can improve the overall aerodynamics of the vehicle, which in real driving conditions helps to reduce fuel consumption and can lead to a reduction in CO2 of one gram per kilometre.

“ZWARP” replaces six weeks of test driving at the Hockenheimring

One of the most effective test methods for assessing a new light-alloy wheel is “ZWARP”, from the German “ZWei-Axiale Räder-Prüfstand” (biaxial wheel test bench). Unlike a conventional rolling test in which the wheels run straight on an external roller with a specific ground contact force, the ZWARP uses an oversized roller to subject the wheels to both ground contact and lateral forces generated as a result of additional transverse movement of the test system in two directions. This is why it is called ZWARP (biaxial).

First of all the wheels are fitted with the corresponding tyre size, and to make the test conditions tougher they are initially damaged on the inner wheel rim flange by simulating driving over a kerb at 2.5 times the normal wheel load. At the same time this initial damage is also used as an individual “inner rim flange impact” test, in which deformation is not to exceed a few millimetres. Once this starting requirement is met, the actual test run takes place, divided into 22 load blocks. The load blocks are based on the subsequent application profile of the vehicle – so according to whether the wheel is intended for a saloon, a roadster, an off-road vehicle or a people carrier. The test conditions are extreme: as part of the test run the wheels are subjected to a ground contact force of up to 35 kN over several thousand kilometres, which in real operating terms equates to the distance travelled over the entire service life of the vehicle. By applying steering movements, the wheel is also pressed against the side lip of the rotating drum with a lateral force of up to 25 kN, thus simulating the wheel loads generated during sharp cornering. The requirement imposed by Mercedes-Benz for this marathon is that despite initial mechanical damage, the test wheel should not show signs of any cracks over the test distance. If a wheel passes the ZWARP test, based on experience it will usually last the life of the vehicle several times over under normal operating conditions.

Looking back, we can now appreciate the significance of the ZWARP: previously these loads were applied to the vehicle in test drives on the race track in Hockenheim and took around six to eight weeks. At that time, together with the other tests, only around 10 light-alloy wheels could therefore be tested and finally approved in a year. The ZWARP, on the other hand, is significantly more consistent over just a few days since, unlike the practical test drives in Hockenheim which were influenced by changing weather conditions, it always runs under the same, defined conditions. Today it takes around four weeks for complete approval. In one year, therefore, the engineers and technicians can issue approvals for around 150 new light-alloy wheels. Currently, however, the test programme does not run completely without any practical tests: prototypes of new vehicle models are for the most part fitted with new wheel types for their trials and test drives. These test results are also incorporated into the assessment and approval of new types. And there is an interesting point to note here: you may not be aware but for the most part photos of prototypes therefore not only depict new vehicles, but also new wheels.

From bending to breaking: the rotary bending fatigue test

Another stress test is the rotary bending fatigue test. For this, employees clamp wheels with the inner rim side locked positively in a jig, and fix the wheel disc to a hub using the normal holes for the wheel bolts, as when fitting a wheel to a vehicle normally. This stresses the wheel structure with load cycles through oscillating movements, simulating maximum cornering in which bending moments of between 1900 and 11,000 Nm are applied. This test is conducted in parallel on several wheels and under different load conditions:

• 4 wheels successfully complete 200,000 load cycles with a 100% bending moment
• 4 wheels successfully complete 800,000 load cycles with a 75% bending moment – this is four times the statutory requirement

All wheels have to survive under these conditions without any cracks forming. However, the test is continued until such time as initial cracks start to appear. This has shown that light-alloy wheels from Mercedes-Benz are able to withstand up to several million load cycles without suffering any damage – which means they are able to last for quite a few vehicle lifetimes under normal operating conditions.

Convincing proof of stability

In addition to the inner wheel rim flange impact test forming part of the ZWARP test, light-alloy wheels aspiring to bear the Mercedes star must also withstand two further attacks. This is where, figuratively speaking, the tests turn medieval, since the wheels are placed under a type of guillotine. In the so-called impact test, which simulates driving over an obstacle such as a kerb at an angle, the wheel is fixed horizontally at a slight tilting angle under a blunt guillotine. The guillotine blade is then dropped at a weight which is calculated according to the permissible wheel load (0.6 times the wheel load plus 180 in kilograms), and from a specified height, onto the outer wheel rim flange. This not only results in an ear-deafening impact, but also in deformation of the impacted area of the wheel rim. This deformation should not exceed a specified level, and there should also be no chips or leaks. The tyre which is fitted must retain its pressure after the impact, in order to enable the vehicle to continue to be driven if this were to happen in reality.

The second guillotine process is similar, only this time the wheel is stood up vertically and the tyre tread is struck by the guillotine blade with greater force so that it goes through to the wheel rim flanges. Here too the damage must not lead to the complete failure of the wheel/tyre system.

Often underestimated: the wheel bolt connection

The importance of secure wheel bolt connection requires no further explanation. Achieving a secure connection, however, is not as simple as is generally assumed. The bolt connection system – comprising the wheel bolts, the new light-alloy wheel and the vehicle wheel hub – is therefore checked and if necessary optimised using a special test facility. Of key importance for correct wheel bolt connection is the specified torque for tightening the wheel bolts. There is a defined prestress for this, which is responsible for connecting the wheel to the vehicle. The engineers at the Mercedes Technology Centre (MTC) carry out extensive fine-tuning in this area in order to ensure that the bolt connection guarantees the highest possible level of safety. This is because prestress is influenced by a number of factors: the frictional force of the bolt thread in the wheel hub thread, the frictional force of the bolt head in the wheel crown, and the contact areas between wheel, brake disc and wheel hub.

If the frictional force of the bolt connection is too low, the wheel nut could overstretch at the specified tightening torque due to the prestress being too high. Although it sounds ironic, these circumstances could lead to the bolt connection becoming loose. The wheel bolts should also therefore not be greased when being fitted as this could reduce the frictional force. If, in the opposite case, the frictional force is too high, the bolt connection would not have the necessary prestress at the specified tightening torque, and the wheel could also work loose. It is therefore absolutely vital that only original Mercedes-Benz wheel bolts are used, since they provide the optimum frictional force and therefore guarantee a secure bolt connection. Mercedes-Benz relies on the safest type of bolt connection by using wheel bolts which have a spherical crown behind the bolt head so that they fit precisely into the bolt holes of the wheel, which are also spherical. The correct prestress also supports the slightly concave contact area with which the wheel fits against the vehicle wheel hub.

Final OK after 3D measuring machine and visual inspection

The approval process for new light-alloy wheels also includes checking the geometric data with a 3D measuring machine using a fully automatic process. After the test wheel has been clamped in, the highly-precise system checks 20 main dimensions at 150 different points down to micro-level accuracy, and compares them against stored CAD data. Only when several wheels have also successfully passed this test within the very narrow tolerances, like all the other tests, is the Mercedes-Benz wheel development team able to carry out a final test for granting the final approval. Despite all of the technical options, these “human factor” assessments are also important. In particular, the team assesses:

Paint quality: in addition to the tests conducted in the corrosion test centre, the paint finish is examined for its colour scheme, layer thickness, inclusions or pores. In addition, contact areas and wheel holes must be free of any paint.

• Quality of the casting: no porosity or surface cavities.
• Machining: clean deburring.
• Specified weight check.
• Correct designation.
• Trouble-free fitting of the valve and tyre pressure monitoring system sensor.
• Valve for the tyre pressure monitoring system is accessible using air refill systems normally available at filling stations.
• Hub cover fits correctly.
• Runout check.

Whatever model of Mercedes you may drive, Mercedes-Benz and its subsidiary Mercedes-Benz Accessories GmbH have just the right light-alloy wheel to suit every taste. When ordering a vehicle, customers can currently choose their perfect wheel from a selection of around 20 different design variations per model series, which are available either as standard or as optional extras. In addition, almost as many wheel models are also available from Mercedes-Benz Accessories for the current model range.

All of the light-alloy wheels on offer have to meet the same high safety standards – there is no difference whatsoever in term of quality between the models available as standard or as optional extras, or even the versions available from Mercedes-Benz Accessories. The customer always receives a product which has been optimally tuned for Mercedes-Benz vehicles: it will provide exemplary ride comfort and high driving dynamics, meet demanding design standards, and will also be characterised by high performance combined with an excellent service life. These benefits are not only the result of close collaboration between vehicle development and specialists from wheel development. Wheels which are to bear the Mercedes star must also pass a comprehensive test programme which goes far beyond the statutory requirements laid down by the German road traffic type approval law. This includes actual test procedures which are based on the harshest of operating conditions in real driving situations, as well as inspections carried out using the latest x-ray systems and computed tomography scanners.

Mercedes-Benz Accessories: high-sheen two-tone wheels top the popularity charts in spring 2010

Topping the popularity charts this spring are Mercedes-Benz wheels featuring a two-tone finish. According to the Mercedes-Benz designers, however, they are more than just a passing fad and are set to enjoy increasing popularity in the future. These high-quality wheels enjoy additional appeal thanks to the interesting contrast created between the bare-look metal surface and the dark painted areas, thus giving the vehicle an even more exclusive appearance. Mercedes-Benz Accessories is currently offering the following wheels in a high-sheen two-tone finish (as at April 2010):

40.6 cm (16 inches):
A/B-Class:	10-spoke wheel in two-tone palladium silver
43.2 cm (17 inches):
B-Class:	5-twin-spoke wheel in two-tone palladium silver
C-Class:	7-spoke Redali wheel in two-tone palladium silver
C-Class, CLC, CLK and SLK:	7-twin-spoke wheel in two-tone palladium silver
45.7 cm (18 inches):
E-Class Saloon:	5-spoke Xentres wheel in two-tone black
E-Class Coupé:	5-twin-spoke wheel in two-tone black
48.3 cm (19 inches):
SL-Class:	6-spoke Himalayas wheel in two-tone grey
GL-Class:	10-spoke wheel in two-tone black
50.8 cm (20 inches):
S and CL-Class:	5-Y-spoke Behes wheel in two-tone black
GLK:	5-twin-spoke Bigawa wheel in two-tone black
M and GL-Class:	10-spoke Tomeko wheel in two-tone black
	5-twin-spoke Himalayas wheel in two-tone grey

The fitting of wheels does not require any reports or Technical Inspection Association registrations to be carried out, since all wheels form an integral part of vehicle type approval.

Wheel design: bringing everything together

Obviously without wheels a vehicle is going nowhere – this simple observation not only describes the basic technical requirement for a properly functioning motor car, but also highlights the importance of the wheel as part of a powerful vehicle design. At Mercedes-Benz, high-quality wheels which match the bodywork and form a logical continuation of the design therefore play a significant role in the high design standards of the overall vehicle. At the Mercedes-Benz design centre, light-alloy wheels available either as standard or as optional extras are designed by specialists in the area which is also responsible for creating the entire exterior form of the vehicle.

Complex test programme forms part of product development

Mercedes-Benz guarantees the quality of its new wheel models with a comprehensive development programme. As part of this, the tests and inspections which are carried out go far beyond the statutory requirements. Even when it comes to wheel development, one basic principle is applied: in the development and testing phases, Mercedes-Benz bases its work on the actual load profile of light-alloy wheels under real operating conditions and coordinates its programme accordingly. As a result, light-alloy wheels bearing the Mercedes star are among the safest, best performing and most durable products on the entire automotive market.

One of the most effective test methods for assessing a new light-alloy wheel is “ZWARP”, from the German “ZWei-Axiale Räder-Prüfstand” (biaxial wheel test bench). Unlike a conventional rolling test in which the wheels run straight on an external roller with a specific ground contact force, the ZWARP uses an oversized roller to subject the wheels to both ground contact and lateral forces generated as a result of additional transverse movement of the test system. This is why it is called ZWARP (biaxial).

The test conditions are extreme: as part of the test run the wheels are subjected to a ground contact force of up to 35 kN over several thousand kilometres, which in real operating terms equates to the distance travelled over the entire service life of the vehicle. By applying steering movements, the wheel is also pressed against the side lip of the rotating drum with a lateral force of up to 25 kN, thus simulating the wheel loads generated during sharp cornering. The requirement imposed by Mercedes-Benz for this marathon is that despite initial mechanical damage, the test wheel should not show signs of any cracks over the test distance. If a wheel passes the ZWARP test, based on experience it will usually last the life of the vehicle several times over under normal operating conditions.

Another stress test is the rotary bending fatigue test, which subjects the wheel structure to load cycles through oscillating movements, simulating maximum cornering in which bending moments of between 1900 and 11,000 Nm are applied. This test is conducted in parallel on several wheels and under different load conditions:

• 4 wheels successfully complete 200,000 load cycles with a 100% bending moment

• 4 wheels successfully complete 800,000 load cycles with a 75% bending
  moment – this is four times the statutory requirement

All wheels have to survive under these conditions without any cracks forming. However, the test is continued until such time as initial cracks start to appear. This has shown that light-alloy wheels from Mercedes-Benz are able to withstand several million load cycles without suffering any damage – which means they are able to last for quite a few vehicle lifetimes under normal operating conditions.

Leading role in industrial computed tomography

An important part of the development process for new light-alloy wheels are examinations which look at the internal microstructure of the wheel, right down to atom level. While the examinations conducted on the various test systems and facilities give an indication of whether the performance of a new wheel is able to meet the high standards required by Mercedes-Benz, supplementary examinations using reflected-light or scanning electron microscopes, and both x-ray and computed tomography systems, provide an insight into why some wheel prototypes are more resilient than others.

While it is always necessary to destroy the test wheel in order to produce samples for examination under reflected-light or scanning electron microscopes, non-destructive testing on the other hand is also used to supplement the development phase and makes an important contribution to checking subsequent series production at suppliers. The wheels are inspected at the acceptance stage using x-ray systems and examined for cavities (air pockets) and imperfections larger than 0.3 of a millimetre. If even more detailed examinations are necessary then computed tomography (CT) is used. This is a process used in the medical field and was introduced by Daimler AG for industrial use – the first automotive company to do so – as early as 1995. The company now plays a leading role in this field. The Stuttgart-Untertürkheim plant currently has the most modern CT system for industrial use in the world.

Unlike x-ray examination, CT produces three-dimensional images. As a result, the position and size of the slightest weak spots caused during the casting process, such as cavities or gas pockets, can be accurately determined. Used in conjunction with the tests conducted on the test benches, these CT assessments provide evidence of where the smallest imperfections might have a big impact on performance. These component areas can then be enhanced during the technical casting and production processes. In addition, the knowledge gained can be carried over into future wheel development.

Special corrosion tests for high-sheen wheels

High-sheen light-alloy wheels require a very special paint structure which provides reliable protection against corrosion for the bare-look metal surfaces.  In developing new anti-corrosion paints for high-sheen wheels, Mercedes-Benz introduced the toughest of test methods – a series of ultimate tests for wheel coatings.

To begin with, staff at the corrosion test centre prepare individual wheel segments by scribing deep marks on high-sheen areas which penetrate down to the bare light alloy. These prepared wheel segments then undergo the so-called CASS test for 24 hours. In this chamber-like system, the paint finishes are permanently subjected to different, highly-corrosive salt sprays. The next stage for the test samples is the filiform chamber. Here the test samples – now partly coated in a crust of salt from the CASS test – must withstand a 28-day variable climate programme. As part of the final evaluation, the employees assess the filiform corrosion around the scribed marks. Approval is only granted for those anti-corrosion paints which reduce undercutting corrosion to a minimum and at the same time do not negatively impact on other properties.

Around 250 wheels per year undergo this test marathon. But it is not only new wheel models which are approved on the test bench. The specialists also carry out the comprehensive test programme when a wheel supplier wants to introduce new materials, such as a base coats, clear coats, functional coatings such as anti-corrosion paints, and also primers or pre-treatments. The changes only receive a “basic material approval” once all tests have been passed without any issues. At the same time, wheels from current production are also tested to ensure that they meet strict Mercedes-Benz quality criteria. The severity of the test series conducted in the climate chamber is demonstrated by the enormous amount of salt which is consumed at the corrosion test centre: the plant requires around 5 tons of salt each year. Used salt is recycled in the basement of the test facilities.

High quality from the best and most prestigious suppliers

When it comes to producing light-alloy wheels, Mercedes-Benz only trusts the world’s best and most prestigious suppliers. These companies have a high level of know-how and produce wheels in accordance with strict Mercedes specifications. Numerous test procedures, both on current production as well as in the laboratory, help to guarantee a high standard of quality. These procedures include monitoring the raw materials at the time of delivery and during subsequent processing, 100-percent x-ray examination, leakage tests, continual monitoring of strict geometric data and concentricity during machining, as well as monitoring the painting process.

The production of two-tone wheels involves a considerable amount of additional effort since special coatings are applied to provide reliable protection against corrosion. After the first coating the system removes these wheels from the production process and transports them to special turning machines fitted with diamond cutting tools which remove the coating layers in specifically defined areas of the wheel – mostly on the spokes or the outer wheel rim base. This so-called “high-sheen polishing” process creates metallic high-gloss areas which contrast against the remaining coating. Of course these areas must be resealed as part of a new coating process. This has a three-layer structure: after being pretreated once more, the wheel then receives a transparent anti-corrosion coating, specially developed for Mercedes-Benz wheels, followed by various clear coatings to build up the final glossy finish.

A smooth process – flowforming

In conjunction with cast, one-piece aluminium wheels, “flowforming” is a relatively recent machining method. Basically wheels which have been machined using the flowforming method offer the best of both worlds. Not only does the designer retain the high degree of freedom over the design which a cast wheel provides, but a flowformed wheel also enjoys the advantages afforded by forged wheels, which are expensive and complex to produce: high strength combined with optimised component weight.

As with the wheel production process described above, first of all a blank is cast which has a very narrow wheel rim base but with significantly greater wall thickness. After being heated up to around 350 degrees, this blank is then stretched on a cylinder which tapers slightly towards a cone at the top. The blank and cylinder are rotated while three rolling heads, which are also rotating, are pressed against the blank from the outside in a downward motion and at high pressure – around 120 tons. This forces the metal into the desired shape over the cylinder, hence “flowforming”, and at the same time compresses it. A wheel rim base created in this way has a similar structure to a forged wheel, offering the highest degree of stability with the lowest possible weight. Subsequent heat treatment of the flowformed wheel then gives it its final strength.

Care tips and methods

There is one thing which the best development programme, the most innovative production technology or a perfectly tuned test programme cannot affect, however: how customers treat their vehicles, and as a result their valuable light-alloy wheels. As always, how the wheels are treated has a significant influence on their value retention and also the safety of the vehicle. Here are some useful tips:

• Do not use abrasive cleaning agents. The products recommended by Mercedes-Benz will clean the wheels gently and effectively.

• Do not use rough or abrasive sponges for cleaning wheels.

• Observe the specified wheel tightening torques. Tightening the wheel bolts too much, or not enough, can damage the wheel over time.

• Do not oil or grease the wheel bolts, since the initial stress will be higher than the specified tightening torques and could damage both the wheel and the bolts.

• Use original Mercedes-Benz wheel bolts only.

• If the wheels are subjected to a heavy blow, e.g. after driving over deep potholes, check the wheels. If there is visible deformation you must have the damage checked by a dealer.

• Mechanical or thermal wheel repairs, such as welding, bending or grinding can reduce the stability of the wheel due to changing the microstructure of the metal and are therefore not permitted. Any wheels which are damaged should be exchanged!

• Only recoat scratched wheels with cold varnishes. Bake-on coatings can also change the microstructure of the metal and therefore reduce the strength of the wheel.

• Only fit tyres of the size permitted for the wheel.

• When driving with a heavy load and/or a trailer, adjust tyre pressure accordingly and observe the permitted wheel loads.

Legendary light-alloy wheels from Mercedes-Benz

Mercedes-Benz introduced the use of light-alloy wheels on volume produced vehicles at the start of the 1970’s, with forged aluminium wheels from well-known producer Fuchs. The “premiere wheel” was the first to be made available as an optional extra for the 280 S to 300 SEL 6.3 W 108 series Saloons, and was later christened the “baroque wheel” on account of its ornate design. After this initial foray into the world of light-alloy wheels the range continued to be expanded. For the 190 compact model series and models from the 200 to 300 E mid-size model series, a 20-spoke light-alloy wheel first appeared in the accessory catalogue from the mid-1980’s, which thanks to its characteristic wheel disc shape soon earned the nickname the “police star wheel”. The final triumphant move came in the same decade in the form of the legendary “manhole cover wheel” which – as its charming name already suggests – resembled a manhole cover.

Today, with a few exceptions, almost all of the series production vehicles from Mercedes-Benz run on light-alloy wheels. How successful they have been is reflected in the following comparison: around 4600 examples of the “baroque” model were sold each year. In 2009, the majority of new Mercedes-Benz vehicles were on “alloys”. Together with the sales figures from Mercedes-Benz Accessories, the number of alloy wheels brought into circulation has increased to around 4 million per year.

BRABUS is launching a new lineup of Monoblock light-alloy wheels for Mercedes-Benz and Maybach and Maybach models, and what better way to usher in the new rims than by posting a corresponding press release and photo gallery highlighting each of them? We couldn’t agree more, so that’s exactly what we have for you this April morning.

In total, there’s three new wheel families: the BRABUS Monoblock F, the BRABUS Monoblock G and the BRABUS Monoblock Q. On the Monoblock F wheels, highlights include a 21-inch diameter size along with a cross-spoke design, making them ideal for Mercedes CL-, GL-, GLK-, M-, R- and S-Class models.

The BRABUS Monoblock G’s, on the other hand, feature a five-spoke design in titanium-look anthracite-colored paint, while their size of 10Jx22 is approved for all Mercedes SUVs, the CL-, S- and R-Class as well as the Maybach models.

And last but not least, the BRABUS Monoblock Q wheels come in a variety of sizes ranging from 18 to 22 inches and feature a five double-spoke design, with the wheel family fitting all Mercedes models from the C-Class and higher.