In 2010, the infamous Jabulani balls for the World Cup in South Africa transitioned from turbulent to laminar flow between 50 and 45 miles per hour, right at the speed for corner and free kicks. The transition between these different types of flow causes even more drag on the ball, which caused the Jabulani to wobble in the air and drop in ways that players weren’t expecting.
Using a wind tunnel, Goff has researched the flight properties of the Telstar 18, drawing its drag curve to discover where the ball might dip and swerve in the air, similar to the knuckleball free kicks favored by Cristiano Ronaldo “Even if aerodynamically the Telstar 18 isn’t that different from the Brazuca, it’s still going to wobble a little bit differently because the panel shapes are different,” Goff says.
Despite the similarities with the Brazuca, the few differences between this ball and what players have gotten used to over the last four years will have an impact on play, says Firoz Alam, an aerodynamics engineer at the Royal Melbourne Institute of Technology in Australia, who has also performed wind tunnel tests on the Telstar 18. “When the player is making a short pass, they have to push a little harder, because at less then 60 kilometers per hour [or 37 miles per hour]it has more flight resistance than the Brazuca,” says Alam. The mid-range passes and corner kicks that gave the Jabulani so much trouble have been resolved. Compared to the Brazuca, the Telstar 18 is also more aerodynamically efficient in the 40-50 mile an hour range, so Alam says players will actually have to kick a little softer or they’re likely to overshoot. Over 55 miles an hour the two balls will feel very similar.
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With the increased seam length, Goff says there was actually a risk that this ball would be too rough. “Very little changes in those textures can have noticeable aerodynamic effects,” he says. The fact that the Telstar 18 has almost the same drag curve as the Brazuca, with aerodynamic properties changing at about the same speeds, is impressive. “It has to be an engineering and technical challenge,” he says.
Although the length of kick may end up being a little shorter, the changes make the Telstar 18 more balanced, says Alam. On other balls, Alam and his team have found that there is a difference in how the ball flies based on where it’s kicked in relation to the seams. His tests have found that the Telstar 18 ball doesn’t have as much variation. The total length of seam of the Telstar 18 is 14.1 feet, 3.28 feet more than on the Brazuca. With the longer seam, and more symmetric panels, no matter how the ball is turned there is the same amount of seam exposed. “The other two balls were not like that, they were significantly different,” he says.
On the other hand, replicas (sometimes called training balls or gliders) are designed to be just like the official match balls but are much cheaper. Their panels are often stitched rather than thermally-bonded and are made of a different material. However, they’re not necessarily less durable than official match balls. So, they’re the recommended option for most players. https://www.youtube.com/watch?v=j2Xn84L3Kcs