BMW to offer carbon fiber wheels in a year or two

Sun, 23 Feb 2014

The Citroën SM sat on the first set of production glass fiber and resin wheels in 1972 when parent company Michelin developed the exotic hoops in order to take the SM rallying. It wasn't until 2008 that we got the first all-carbon-fiber wheel for passenger cars in the form of a prototype model from Weds Sports in Japan that remained a prototype. Australian company Carbon Revolution followed that a year later with its CR-9 all-CF wheel, first introduced on the Shelby Ultimate Aero and now available for independent purchase for about $15,000 per set. BMW could be the first OEM to offer entire wheels in carbon fiber reinforced plastic in two years.

The wheels - either all-CFRP or using a CFRP rim and alloy spokes - were shown off during BMW's Innovation Days in Munich and are products of the development work done on its i-branded cars. The full-CFRP wheel is 35-percent lighter than a forged alloy wheel, the hybrid alloy and CFRP wheel is 25-percent lighter, making for a decent drop in unsprung rotating weight. As demonstrators during a tech day the wheels aren't yet in the pipeline for production and EU approval, but an article in Auto Express claims that they could be on the market as soon as two years from now.

Other possible parts include a full carbon fiber steering wheel and propeller shaft, the latter of which is coming as a single-piece component on the new M3 and M4. BMW is also talking up its use of secondary carbon fiber - waste material from i3 and i8 production - that can be used for items like IP support structures, seat frames and spare wheels in place of traditional metals like aluminum and magnesium. There's an excerpt of the Innovation Day press release below with more details.

International Media Event
Innovation Days 2014: Efficient Dynamics.

Intelligent lightweight design and finely honed aerodynamics:
Winning solutions in the quest for efficiency and sporty performance.

All new systems developed by the BMW Group are designed with an eye to optimal overall vehicle efficiency. Hallmarks of an efficient vehicle concept include intelligent lightweight design and optimal active and passive aerodynamics, geared to reducing driving resistances.

Intelligent lightweight design.
Lightweight design is an important component in the Efficient Dynamics strategy and has always been part of the BMW Group's basic design philosophy. Vehicles of the BMW Group achieve an optimal balance between the requirements of the individual product and lowest possible specific weight.

Sporty vehicles should have a low centre of gravity and a balanced 50:50 axle load distribution, while their masses should be concentrated as far as possible at the centre of the vehicle and they should have a low weight for their specific market segment.

Intelligent lightweight design is important for ensuring the ideal balance between product requirements and lowest possible specific weight. At the end of the day, optimal overall efficiency can only be achieved on the basis of low-weight design, appropriate use of innovative materials and systematic use of material mixes that offer high standards of functional performance.

Intelligent lightweight design is implemented in every area of vehicle development at BMW, and in all assemblies and components. The vehicle body is a particular focus, since it continues to account for the largest fraction of total vehicle weight. That said, in addition to weight, advanced body design must also take into account functional aspects and dimensions. Through continuous evolutionary advances, the BMW Group engineers have repeatedly reduced the contribution of bodyshell weight to total vehicle kerb weight, despite simultaneous functional improvements in the area of safety and comfort. Greater body stiffness also has benefits in terms of reduced vibration and improved steering precision, while the simultaneous reductions in weight also make an important contribution to the efficiency and agility of the vehicle, and therefore also to driving dynamics. Increased use of aluminium and magnesium in the engine and chassis has been a further contributor to lightweight design. As a result, although many new BMW Group models may be larger than their predecessors, they are no heavier, and in many cases are actually considerably lighter. The third-generation BMW X5 models, for example, are up to 90 kilograms lighter than the comparable predecessor models – with important benefits for driving dynamics and fuel consumption.

Innovative use of materials in the BMW i3 and BMW i8.
Systematic lightweight design is particularly important on electrically powered vehicles, given that vehicle weight is one of two main constraints on vehicle range, along with battery capacity. For EVs, too, reduced weight means reduced energy consumption and improved driving dynamics. In order to offset the weight penalty of the electric components, the BMW Group came up with a rigorous lightweight design strategy for the BMW i brand in the form of the LifeDrive concept, an innovative vehicle architecture which for the first time combines an aluminium chassis and a CFRP passenger cell.

CFRP: high-tech material of the future.
Carbon-fibre-reinforced plastic (CFRP) boasts a particularly favourable strength-to-weight ratio and is therefore an ideal material for use in the vehicle body. For the same functionality, CFRP is around 30 per cent lighter than aluminium and 50 per cent lighter than steel. Used in the right places, this material therefore reduces weight, optimises the vehicle's centre of gravity and improves body strength. This material is currently being used not only in the new BMW i3 and BMW i8 models: the sporty BMW M3/M4 and BMW M6 models have likewise been utilising the benefits of this high-tech material for some time. Components such as their roof and bumper supports are made of CFRP. The BMW Group is currently working on further potential applications, including the use of this material in rotating-mass components. Examples include hybrid aluminium/CFRP wheel rims, while CFRP's high rigidity and low weight allow the CFRP propeller shaft on the BMW M3/M4 to be produced as a single-piece component, without a centre bearing. This results in 40 per cent weight savings over the previous model and reduced rotating masses, leading to further improved response.

In future, other BMW and MINI models will also benefit from this lightweight material in various ways. For example, production offcuts can be reprocessed into "secondary" (recycled-content) CFRP, which can be used to reduce the weight of components such as seat frames, instrument panel frames and spare wheels by up to 30 per cent, with simultaneous improvements in terms of cost-efficient, environmentally friendly manufacturing.

Technology leader in mass production of CFRP components.
After more than ten years of intensive research, resulting in improvements to processes, materials, production machinery and tools, the BMW Group has today become the first and only car manufacturer in the world with the necessary know-how to use CFRP in mass production. The processing technology used is unique and cycle times for even the more complex CFRP components are unusually short. The same is true of the specially developed bonding process used in the fully automated assembly of body parts.

As well as setting standards in the production of CFRP finished components, the BMW Group also attaches utmost importance to the use of environmentally friendly, resource-efficient and largely CO2-free processes in the manufacture and processing of the raw materials themselves. From fibre production right through to recycling of fibres and composites, the company is involved in all the various process steps in a state-of-the-art CFRP production chain that begins in Moses Lake in the USA and moves through Wackersdorf and Landshut to final assembly in Leipzig.

By Jonathon Ramsey