Oh what’s in a frame? Comparing aluminium, titanium, carbon fibre and magnesium

Manual wheelchair frame

In this post we’re going to look at manual wheelchair frame materials, the most common being aluminium, titanium, carbon fibre and magnesium, and why wheelchairs are made from these materials. But before we delve into that, let’s address the first thing most people think about when they consider wheelchair frame material: weight.

One of the aspects of wheelchair frame materials that people like to compare is weight. We’re often asked how light a wheelchair is, and it is often automatically assumed that the lighter frame option must be better. Although weight is important, it is not the actual weight of the wheelchair that is the only factor when considering ease of propulsion and reducing the physical impact on the upper limbs. Wheelchair ‘A’ could be 8.5kg with wheels and seating fitted, and wheelchair ‘B’ could be 9.5kg with the same wheels and seating. You would assume that wheelchair ‘A’ is going to be easier to propel and feel more comfortable, but that is not necessarily the case. The set-up and configuration of the wheelchair is as much, if not more important, than the weight. We can take an ultralight 6kg wheelchair and set it up so that it feels like you’re pushing through mud, or take a 12kg wheelchair and make it feel like it takes no effort to push. You’ll still feel a difference when physically lifting the wheelchair, but not necessarily when propelling. The rear wheel position, castor position, wheel and castor choice and all those measurements and angles that make up a custom manual wheelchair prescription are so important when making a wheelchair feel light to push. When thinking about trying to get the lightest wheelchair to push, remember that weight itself is only one piece of the puzzle.

Now that we’ve somewhat addressed the ‘weight’ issue, let’s go back to discussing the frame materials. Most wheelchair frame material development comes from the sporting equipment world, particularly bicycle frames. Wheelchairs are often made with a mix of materials, with a frame being one material and accessories made of another. It is common to have an aluminium or titanium framed wheelchair with carbon fibre accessories, such as side guards. As carbon fibre is a lighter material, this can help reduce the overall weight of the wheelchair (and some people enjoy the aesthetic appeal of carbon fibre accessories).

Aluminium is a lightweight material that is easy to bend and weld into the desired frame shape. Wheelchair frames are typically made with an aluminium alloy, which allows the performance of the base aluminium to be improved by adding trace amounts of other metallic ‘alloying’ elements to it. This gives the various aluminium alloys varying characteristics, and these aluminium alloys are categorised into different series. Most wheelchairs are constructed of Series 6000 (aluminium with alloying elements of magnesium and silicon) or Series 7000 (aluminium with alloying element of zinc) aluminium alloys. Because Series 6000 and 7000 use different alloying elements, they have different strengths and weaknesses, and wheelchair manufacturers usually choose an aluminium series based on how they choose to use the aluminium.

Aluminium is the most common wheelchair frame material. It is strong, resistant to corrosion, is very successful when used for wheelchairs, and is cost effective. For many people an aluminium wheelchair is perfect for their needs.

Titanium has the highest tensile strength to density ratio of any metal. Titanium is extremely resistant to corrosion, can be easily machined into shape for a wheelchair frame, and does not transmit as many vibrations through the frame. For some users that feel every jolt or experience back pain when hitting bumps and lips, titanium might be a great option for them. Users also report that one of their favoured characteristics of titanium is that the wheelchair frame does not have to be powder coated, which means it does not develop scratches or have chipped paint. Although titanium has many benefits, it is a more expensive metal, and therefore the base price for a titanium frame will be more than an aluminium frame.

Carbon fibres are tiny filaments mainly consisting of carbon atoms which are combined and used on their own or woven into a fabric. The carbon fibre fabric can be mixed a plastic resin to create a strong and light composite material, and this material is what is commonly referred to as carbon fibre. Carbon fibre has a very strong strength to weight ratio, superior fatigue resistance compared to metals and is extremely resistant to corrosion. It is a lighter material than both aluminium and titanium.

Carbon fibre technology has significantly improved over the last decade, and some of the previous concerns regarding carbon fibre have been allayed. One of the main prior concerns regarding carbon fibre was that if it failed, it would fail catastrophically. For a wheelchair user, an aluminium frame that slowly developed a stress fracture that could be seen before it broke completely was much preferred over a material that would break completely with no warning. However advances in the way carbon fibre is aligned has meant that the material is now strong but flexible. Carbon fibre is a more expensive material than aluminium or titanium so wheelchairs made from carbon fibre do cost more.

Magnesium is the newest wheelchair frame material on the block, although there have been bike frames available in magnesium for a couple of decades. As it is a newer material for wheelchairs, there are very few magnesium wheelchairs available. Magnesium is said to have the same strength as titanium, while being lighter than aluminium, titanium and carbon fibre. Magnesium frame development is slow, as the manufacturing process is energy intensive and as magnesium can be prone to corrosion it is vital to mix it with an alloy material to make it suitable for use. As wheelchair frame development continues, we may start seeing magnesium used for wheelchair frames more frequently.

As you can see, each wheelchair frame material has its pros and cons. The secret to scripting the best wheelchair is matching the frame material to the user, while ensuring the configuration of the wheelchair is optimally set up for the individual.

Our GTK Consultants are always available to provide advice on wheelchair frames and configuration. Contact us today to see how we can help.