Ingenious engineering meets timeless design: A look into the ALPINA wheel development

Twenty sleek spokes evenly arranged in a starburst pattern – an iconic wheel design that has played a decisive role in shaping the brand identity of BMW ALPINA automobiles since as early as the 1970s. Timeless, without ever aging, the ALPINA wheel continues to develop with each new model generation both visually and technically – always true to the ALPINA credo “form follows function”.

Daan Klabbers, the development engineer responsible at ALPINA for wheels since 2016, provides insights into ALPINA wheel development process and explains the technical refinements and philosophy behind the iconic design.

The wheel as part of the identity

Commonly underestimated as an elegant design detail, the wheel is attributed a great deal of importance at ALPINA: “We consider the wheel to be part of the vehicle’s DNA, part of the bigger picture.” says Klabbers. “Especially when you think about how the transfer of power works in a vehicle, it becomes clear, why we place such importance on wheel development. Because ultimately, it is the wheel and the tyre that are responsible for transferring all power from the drivetrain on to the road. The entire power of the engine is transmitted through twenty delicate spokes, which in addition also carry the entire weight of the vehicle. The importance of the wheel should not be underestimated. No matter how powerful and brilliant the engine may be, if the wheel is not able to cope, for example because the spokes allow too much deformation during dynamic cornering or because the tyre can contort on the wheel, then you have gained nothing.”

Furthermore, the wheel/tyre combination also directly influences ride comfort. “A harmonious chassis won’t work if the wheel and tyre do not match the vehicle concept, and vice versa. The wheel has a substantial influence on handling, suspension comfort, steering feel, roll dynamics and many other parameters. This is why wheel development is always closely coordinated with all other ALPINA development departments, including the departments responsible for Tyre Development, Drivetrain Development and Chassis Development.” continues Klabbers. The declared goal of each wheel development: harmonisation of performance and comfort!

Precision down to the last millimetre

To achieve this development goal, a new wheel generation is designed for each new BMW ALPINA model. The fundamental design question must be resolved first: Which design is best suited for the model in question, the 5x4 spoke arrangement of the ALPINA DYNAMIC design or the iconic twenty spokes of the ALPINA CLASSIC design?

Once the design has been decided, the first stage of development is a CAD kinematics model. The construction data of the vehicle is digitally analysed in order to ascertain how much space there is available for the planned wheel/tyre combination and if the desired camber and caster can be achieved. Precision in this area is critical so that the wheel can best deal with the demands placed upon it by the high performance drivetrain. “We always strive to increase the wheel’s contact area with the road as much as possible so that the full power of the engine can be transferred on to the road. So with a new wheel, literally every millimetre counts. This alone makes it worthwhile to construct a new wheel from the ground-up for every new model generation – if the geometry of the axle or the wheel housing changes only minimally, we need to take an entirely different approach when designing the wheel. For example mounting an existing wheel using wheels spacers or similar simply does not satisfy our standards and quality criteria that we have as an automobile manufacturer. This would for example result in vibrations and a host of other even more serious problems, especially considering our automobiles can achieve speeds well in excess of 250 km/h, sometimes even 300 km/h.” continues Klabbers.

Once the initial wheel design and construction has been completed the so-called “body-to-tyre” clearance of the tyre is validated directly on a test track: Will the dimensions calculated in the kinematics model also work in real live test operations? Once this is confirmed, the wheel design moves into a more subtle direction: different material thicknesses are tested, corresponding bending loads during cornering are simulated and further design details are defined. Wheel simulations illustrate why the ALPINA multi-spoke design has stood the test of time for decades: “Our twenty spokes are not only a visual highlight, the arrangement of the spokes also distributes the drive forces evenly onto the rim well. Yet another advantage of the delicate design is that the weight of the wheels, the so called unsprung mass, has a direct effect on ride comfort and handling.” says the wheel expert.

Forging or casting?

The chosen production method also has a significant influence on the weight of the wheel. ALPINA utilises both casting and forging production processes. “In the case of an casted alloy wheel, we put a lot of development effort into the mould. The material is not compressed during casting, which is why the material behaves differently than for example when it is forged, this requires adjustments to be made to the material thickness. The production of a forged wheel, on the other hand, is very complex, but has the advantage that the material is significantly stronger and more homogeneous, thus allowing a much more delicate design. This allows us to save even more weight. In the forging process, all 20 spokes are milled one by one out of a compressed aluminium block. The turning and milling of our design takes about 6 to 7 hours – per wheel, that is.” explains Klabbers.

Tradition, innovation, perfection

Daan Klabbers summarises in three succinct words exactly what ultimately distinguishes the ALPINA wheel: “Tradition, innovation, perfection. Tradition is the most important aspect in this. The ALPINA wheel undergoes a continual evolution from one generation to the next but without compromising its iconic, instantly recognisable design. The innovation is in the detail. And the outcome in the end is an engineering masterpiece.”