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Eliud Kipchoge has a claim to being the best male marathoner of all time. His race record speaks for itself: he has run seven marathons and won six of them. In the one race Kipchoge didn't take top spot, he came second. He's also the fastest man ever to run 26.2 miles. Yet there is one thing that has eluded him – the world record.
How can this be? As Kipchoge crossed the line of Nike's staged attempt to run a marathon in under two hours in May 2017, the clock read: 2:00:25. However, despite missing the two-hour barrier by roughly one second per mile, an unsanctioned course, including pacers, stopped his valiant effort from being an official world record. Thus the male marathon record still stands at 2:02:57.
When Kipchoge tried to best the time in September's 2017 Berlin marathon, rain and wind scuppered the attempt. Kipchoge said the fabric of his trainers became too wet, adding extra weight.
Now, Nike has turned to 3D printing to reduce the weight of Kipchoge's running shoes, which it originally designed for the sub two-hour attempt. At this weekend's 2018 London Marathon, Kipchoge's trainers will have a 3D-printed upper. Almost everything above the foam on the trainers has been printed, while the bottom half has not been changed.
"We've been using 3D printing for a variety of things at Nike for around a decade, but most heavily in prototyping," explains Bret Schoolmeester, Nike's senior director for global running footwear. "This is the first upper and the first one that will be more mass applicable."
The top section of the trainers are made from individually printed 3D threads – Nike is calling the technology 'Flyprint' and says it is 3D-printed fabric. Each thread runs along the entire length of the trainer and is created through the printing technique of solid deposit modelling. They're less than a millimetre thick and printed almost next to each other.
The 3D-printing process sees a thermoplastic polyurethane filament be unwound from a coil, melted and layered. Roger Cheng, a 3D-printing expert at the sports company, says the shoes can be printed in 30 minutes, and crucially the firm has precise control over how the threads are positioned. "We can get down into the specific thread level and control everything: length, curvature, diameter," Cheng says. The company used its own printer for the technique.
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Each of the pairs of trainers Nike has developed for elite long-distance runners have been created differently. They are more personalised than previous performance trainers and six per cent (roughly 11 grams) lighter than the Breaking2 trainers. The individual threads on Kipchoge's trainers cross each other diagonally. As the threads extend down the length of the shoe, they turn into wavy lines.
After working with Kipchoge, Nike's designers added the waves to allow for more movement around his feet. Each side of Kipchoge's trainers have different thread curves to fit his foot. When redesigning new trainers for Kipchoge, Nike's designers were able to recreate, print, build and ship the trainers from the US to Kenya in nine days.
Nike made the diagonal crosses at the front of his shoes tighter after he asked for more support. Fellow Kenyan Geoffrey Kamworor won the world half-marathon champion on March 24 wearing his own version of the trainers, and US athlete Galen Rupp ran yesterday's Boston Marathon in a pair designed for him.
"I can go in and manipulate every single thread and how it is going through the entire upper, but the data will ensure I am not going to do something that will hurt performance," Cheng says. He adds that Nike used Kipchoge's foot scans, pressure data, and 3D scans of his foot while moving to design the shoes. "The level of the precision that a designer has now is amazing," Cheng says.
Nike isn't the first sports brand to use 3D printing in the production of its running trainers. Rival adidas has committed to mass producing 3D-printed shoes this year and Brooks has allow runners to have their feet scanned and custom shoes made. Elsewhere, Under Armour and New Balance has also dabbled with 3D-printed shoes. However, in these cases the printed parts of the shoes were the midsole, rather than the upper fabric part.
Although this is Nike's biggest push into 3D printing shoes to date, only a limited amount of the Flyprint trainers are being made available for the public to buy. They're being priced at £499, and will be on sale before this weekend's London Marathon.
Schoolmeester says the company is looking to work on 3D-printed trainers for everyday runners. "The reason we're here is because our teams are shifting focus back to a training shoe application," he says. "The rate of iteration and improvement, you know where that sort of thing is going to get in a pretty short amount of time."
During the race through the capital, Kipchoge will be wearing the trainers. Nike also says Mo Farah, one of the Kenyan's biggest rivals for the 26.2 miles, may be wearing the Flyprint trainers. As for the 2:02:57 world record attempt, it may be out of Kipchoge's hands: temperatures are uncharacteristically being forecast up to 25C.
This article was originally published by WIRED UK
