Carbon fibre running shoes have taken the running world by storm over the last few years; they have been used in the world’s fasted marathon attempt, which came in under two hours. The world record has been broken twice by Eliud Kipchoge while wearing shoes that use it in the sole.
Why is carbon fibre used in running shoes?
Fundamentally, running shoes that use carbon fibre in their soles do so to improve the performance of the runners that wear them. The extent to which this is the case is debated, but the figure that is regularly touted is 4%, meaning that runners should be able to run 4% faster at an equivalent level of exertion on an equivalent track. Studies have shown that this improvement generally exists somewhere between 1.6% and 6.3%.
Carbon-fibre plated running shoes improve runner performance through two important ways. One way, is by essentially providing a larger lever below the foot, meaning that the ankle does not have to flex as far in order to run at the desired speed, which reduces leg fatigue for the runner.
The other and perhaps more significant way that a carbon plate improves a runner’s performance is by enabling the use of more advanced foams. Running shoes that incorporate it often use foams that are far springier than those in non-carbon composite shoes, meaning that the shoe returns more energy with every step. However, these foams tend to be less stable under foot, which is mitigated by the inclusion of the composite plate.
How is carbon fibre used in running shoes?
The most common way that carbon fibre is used in running shoes is in a plate sandwiched into the foam sole of the shoe, extending throughout the length of the sole. These plates can have a variety of shapes, the most common being a gentle S curve, or a less common V-shape. The less common V-shape is used when extra stability is required, like in trail running shoes. In some cases, the plate does not extend the length of the shoe, such as with the Asics Magic Speed running shoe.
Adidas, however, do something different. Instead of a long plate, they place five carbon composite rods that run down the length of the shoe, which broadly mimic the metatarsals in the foot. To reinforce the heel, they still use a small carbon composite plate that improves performance when striking with the heel.
Are there any drawbacks to using carbon fibre in running shoes?
As with any new technology, there are some drawbacks. While the plates enable the use of softer foams that are more reactive, the they do not stabilise the shoe in every axis. Practically speaking, this means that most carbon fibre running shoes are best suited to even terrain where the foot will land flat on the ground. Specialised trail running shoes are available with carbon fibre, but they are less common than those designed for even terrain.
Also, as is often the case with carbon fibre, there is a price premium in exchange for the extra performance. For this reason, and at least for now, running shoes that use it are unlikely to be found on the budget end of the spectrum. Carbon plates are generally only available in the premium offerings from most brands. However, the technology does seem to be trickling down to more affordable running shoes with time, as seen with Decathlon’s Kiprun KD900X.
Have other composite materials been used in running shoes?
While it may seem that this is a very new technology, there have been attempts in the past to use carbon composite plates in running shoes. These projects date back to Reebok’s Graphite Road, which was followed by Adidas’ Equipment Gazelle Pro Plate. They were not large commercial successes and did not last long on the market.
The new focus on carbon plates in shoes has inspired Mizuno to produce a shoe that uses a more cost-effective fibreglass plate in the sole of their Wave Rebellion shoe.