Titanium vs. Aluminum, ad infinitum
- By Laurie Watanabe
- Apr 30, 2014
When you hear the word "titanium," what comes to mind?
Lightweight. Strong. Space age. Lustrous, silvery, beautiful. Exclusive!
How about the word "aluminum"?
Soft but strong. Lightweight. Silvery. Versatile. Rust-proof. Everywhere!
People who aren't familiar with the mobility world might think of titanium in relation to aerospace engineering, jewelry, and equipment for sports in which light weight is an advantage (think: tennis rackets, golf clubs).
And they might think of aluminum in relation to, well, just about everything, from soda cans to baseball bats, frames for windows and doors, and the cases for consumer electronics such as cameras and laptop computers.
Of course, you also know titanium and aluminum from another critical application: the creation of ultralightweight manual wheelchairs, built for active consumers who demand the highest performance capabilities from the products they use.
Is It (Still) All About Weight?
Back when consumers struggled to push themselves in steel-framed wheelchairs, the need for a lighter chair that could be propelled all day was obvious and self explanatory. And when manufacturers first moved from steel to other materials - aluminum, titanium, carbon fiber - they saw dramatic weight savings.
But today when manufacturers introduce a new ultralightweight chair that weighs less, they're typically talking about having shaved ounces from the previous generation rather than pounds.
So given the typical frame weights of today's ultralight chairs, should weight be a wheelchair's top selling point?
"No," says Josh Anderson, VP of product & brand management, TiLite. "It is not my number-one priority, and I'm a quad who transports his chair in and out of a car. I don't think it is the number-one concern for other chair riders or clinicians, either. Weight is just one of several concerns. It should not be treated as a be-all-end-all."
Wheelchair user Alan Ludovici, design project engineer for Ki Mobility, concurs: "Many consumers and clinicians still consider weight to be the primary requirement of a wheelchair. Today there are so many chair options in the market around 16 lbs. that we need to start looking beyond just weight. With weight already addressed, we now have the opportunity to pay more attention to these essential factors."
Mark Greig, VP of research & development for Sunrise Medical, also points out that there's a practical limit to how lightweight a wheelchair frame can be.
"The weight of the frame is just a portion of the overall weight of the chair," he notes. "By the time you put a cushion and a backrest on it and all that, the frame constitutes 15 to 20 percent of the weight of the overall chair. So shaving a little bit of weight off the frame doesn't get you that much."
Greig estimates that manufacturers could probably reduce current frame weights a little more in the future, but cautions, "At some point, you start compromising the durability of the product."
Thomas Whelan, VP of product development at Ki Mobility, adds that the frame isn't the only part of the chair that needs examining.
"The frame is only a small portion of the weight of a wheelchair," he explains. "Most of the weight of an ultralight wheelchair is in the 'other' components. If we want to make lighter chairs, we need to look for design improvements in these components."
The New Gold Standards
So if weight should not be the number-one factor in choosing the right chair, what should the top priority be?
Jeff Adams, president/CEO of Icon Wheelchairs and a wheelchair user himself, says, "The weight of the chair can be very important, but we strongly believe that it should be prioritized behind fit and configuration/geometry. The only time a pound or two makes a difference is in transport weight - when the chair is being lifted/loaded."
Ludovici listed several factors that should be examined: "Propulsion efficiency: How much effort will it take to push the chair around for 12 hours? Ride quality: Are the shock and vibration from riding the chair going to cause discomfort and fatigue? Ease of use: Do the armrests and wheel locks work for the user? Can they get close to things? Can they transfer from the chair? How easily can they get it in and out of their car?"
"To me the most important aspect is fit," Anderson says. "A person's wheelchair must be fitted correctly, like a wheeled prosthetic. Proper wheelchair selection and fitting must be focused on the individual and his or her specific characteristics. This should include the person's clinical needs, lifestyle requirements and physical capabilities. So weight becomes a single aspect that should be considered among other important aspects leading to a well-selected wheelchair. Other important aspects are frame type (rigid/folding), frame style (mono-tube/dual tube), level of adjustability, frame material, and wheelchair options that optimize the wheelchair experience."
Brent Hatch, director of product management, Sunrise Medical, says overall performance in multiple environments has been a key goal.
"We talked about weight being important, and it certainly is to someone who propels 2,000 to 4,000 times a day," he says. "We're also looking at how the chair and the seating system interact, how the user interacts with propulsion, the efficiency of the whole motion and how the chair rolls and performs in turning and in close environments - not just over a long haul of a thousand meters, but how does it work inside an office or a home? Performance goes to speed and light weight, but you also start to think of how people use the chair, and the most highly used function within a small environment. The stroke distance is often short: 10, 15, 20 feet. So how is the usability of the chair moving in and out of different areas?"
The Titanium-vs.-Aluminum Question
While the "titanium vs. aluminum" concept may be outdated thanks to evolving engineering practices, many wheelchair users still believe the performance of the chair hinges on its materials.
"Yes, titanium has been synonymous with 'ultra-light weight' because of the high-strength characteristics - so you can use less material," says Anderson, who works for a manufacturer with extensive lines of both aluminum and titanium high-performance wheelchairs. "But again, it is not just about weight. Titanium is also vibration dampening and is a material that lends itself to design innovation. Yes, there are other factors that affect weight. Weight is affected by the overall design of the chair, how any material is incorporated, what frame style is used (mono-tube or dual-tube), well-designed clamps used instead of bolts that weaken a chair, etc. Weight is also affected in both directions by additional options that are selected to enhance the entire chair experience, such as seat backs, cushions, wheels, tires, handrims, wheel locks and more."
"Titanium has been trumpeted as some kind of miracle material in the wheelchair industry for close to 20 years now, but there are more appropriate materials that can achieve the same weight benchmarks, and better," Adams says. "An examination of the bicycle industry is telling: Titanium had a brief moment in the sun for a few years in the mid '90s, but really isn't used much at all anymore.
"Something that could help achieve lower weights without compromising durability is sophisticated design paired with pure engineering, meaning that once the design phase is done, the design then goes through a formal engineering process, using Computer Assisted Drawing (CAD), Finite Element Analysis (FEA), and real-world testing (RESNA standards and other). This will allow the manufacturer to fine-tune what materials are used, and when and where material can be taken away from the various parts of the wheelchair without compromising strength or durability."
Then why are so many ultralightweight wheelchair users - maybe you know some of them - completely convinced that a certain type of metal is the most important aspect of a wheelchair?
Hatch says, "I think there is a group of consumers who automatically [prefers titanium] maybe because of the price point. They make assumptions around that. But when you start asking questions - like what are you really after, is it the lightest weight? - and if you take that next step or two and look out there and educate yourself on how they're being used or the design techniques, you can achieve a lot more than maybe 10 or 15 years ago just with the materials processes."
Greig suggests that consumers' gravitation to titanium might be caused by something else: "They want to distill it down into one fact. They want to simplify the choices and say, 'Titanium is better than aluminum. It's more expensive and that's what I want.' Or 'I want the lightest-weight chair.' They try to distill it down to one thing that they can compare against and make their decision on, when in fact wheelchairs are much more than the materials they're made out of. It's how it performs, how it allows them to transfer in and out, how it functions for that person. Those things are hard to quantify, but probably more important than the materials or the weight of the chair."
Focusing on the Critical Factors
So if you and your clinical team take frame weight and frame material out of the equation - assuming that the chairs you're considering are of similar weights - what criteria should you be using to make your decision?
In addition to factors mentioned earlier, Anderson says, "The lifestyle part of selecting a chair is truly important. Chair selection starts with the person. Where do they live? What is the weather like - and I don't mean making the chair 2" wider to accommodate a winter coat! Do they commute to work or work from home? Do they have a car or a van? Are they active users that travel quite a bit, or are they more homebodies? The bottom line is how you select, sit and fit in the chair is the greatest predictor of performance, comfort and independence over the long term, and these processes must be centered around the needs of the person and his or her lifestyle, and then matching those needs with the chair selection process."
"We believe other elements like adjustability and suspension are game changers," Adams says. "Incorporating adjustable suspension in a way that doesn't compromise efficiency, performance or weight makes the experience of using a wheelchair entirely different and takes 'vibration management' to the next level. It's not about dropping into skate parks or going off foot-high curbs; it's about cracks in the sidewalk and crossing over thresholds from one room to another.
"In average use, wheelchairs don't achieve speeds high enough to create 'vibration' - that effect usually only happens in bicycles at speeds well in excess of any that could be safely achieved in an everyday wheelchair. Wheelchairs typically see one-time concussive forces - sometimes in rapid succession, but still not 'vibration' - which we believe are better managed with suspension rather than a frame material that amplifies vibrations less than others."
Whelan points out that ongoing research on ultralights and the propulsion process will ultimately enable engineers to continue to fine-tune and improve their creations.
"Weights will continue to drop, though not at the same rate," he says. "A wheelchair is a mechanical system, and its performance reflects the sum of the design, not just the choice of frame material. More research, new test methods, new manufacturing techniques and new materials will allow us to improve a wheelchair's propulsion efficiency, ride quality and ease of use."
Greig says that ultralight conversations at Sunrise Medical have been focused on "How do we ensure that someone using our products can continue to use our products for as long as possible? It's a function of the chair, but it's also a function of the seating system and how the seating system interacts with the chair."
Creating Chairs that Empower
And as you're paying attention to how well a chair fits into your life - that means fitting you well in both form and function - then what should wheelchair manufacturers pay attention to? Besides focusing on design and performance, two of our experts, both full-time wheelchair consumers themselves, said manufacturers should also pay attention to social factors.
"Color is very important to the pediatric consumers and the clinicians who provide care to them," Adams says. "We haven't offered color options to date because of the difficulty it presents in the manufacturing process, but we've recently reached an agreement with a custom powder-coating shop that will paint our chassis and front end in up to 16 colors, with more that can be added. We'll officially launch our custom paint program in the late spring."
"It's not often mentioned," Anderson says, "but I feel another very important lifestyle factor is self-image, and the chair you use can impact your self-image. If you look in the mirror and you look active and mobile, then you will feel active and mobile. No one is defined by their chair, but the chair - just like clothing - can influence the way you feel about yourself.
"Without us fully realizing it, our chairs can sometimes put up barriers. I believe that if you are using an older-style ultralightweight chair that closely resembles a hospital chair, then you will naturally feel more disabled. But if you're using a chair that more closely resembles a bike or modern sculpture, then you will feel more empowered."