By the time Roger Federer steps onto a tennis court, it's already been a long day for Ron Yu. For the last 15 years, in nondescript hotel rooms around the world, Yu has personally strung Federer's rackets — nine fresh ones per match.
"The 4:30 wakeup to start stringing tennis rackets is not the most pleasurable thing in the world," Yu said.
The rackets Yu strings will be used in about six or seven hours, when the strings start to lose tension.
"The same swing could correlate to a few inches," Yu said. "So that's an in and out call."
Most pros just use local stringers provided by the tournament. That was good enough for the players who made this year's U.S. Open finals, but for a hefty fee, some elite players hire one stringer to follow them around the world.
Yu said his pitch to those players is "consistency."
"I mean, there are very good stringers out there who are on-site stringers," he said. "But everyone might string slightly different."
That fixation on consistency is what created the personal stringing business. Ivan Lendl — a star of the 1980s — obsessed over perfectly strung rackets. Other top players soon noticed.
"It's comfort," said Mats Wilander, who was ranked number one in the world in the late '80s. "You wanna be 100% sure that your rackets are exactly the same, exactly how you want them. For a normal player, I'm telling you that you're not gonna feel that difference. But for these guys, yes, of course they feel it."
Before strings even go on a frame, someone like Roman Prokes has studied the player's swing to decide exactly how to build their racket. In 2017, he suggested changes for Novak Djokvic. "It became somewhat predictable on the court, where he can go with certain shots, because the racket wouldn't allow him to use the whole court from certain shots," Prokes said.
To fix the problem, Prokes took away some of his strings. "We actually took away a little bit of [the] strings, so he can generate more spin, you know, we made the racket lighter. We made the weight distribution on the racket different," he said. "After two minutes of hitting, Novak basically said 'Throw all my rackets away. This is my new racket.'"
But this level of customization presents another challenge: each one has to be handmade. That includes adding weighted tape, and a custom-fit and hand-poured handle. Each racket takes about three hours to make.
"When you watch a guy smash it on the court, what do you feel?" asked CBS News' Brook Silva-Braga.
"Cha-ching," Prokes responded with a laugh. "More money. They have plenty more rackets in the bag, and I can always make more."
A fully customized racket costs about $500. Prokes will make them for amateur players, too — but the custom racket Federer uses is not available for sale, due to concerns that people would fraudulently sell them as match-used rackets. Most of the real rackets are auctioned off for charity.