Team Sky experienced a dramatic mechanical failure at Tirreno-Adriatico earlier this spring. Three riders broke front wheels during the team time trial, according to Geraint Thomas. The most dramatic failure happened midway through the opening stage’s 22-kilometer TTT course. Gianni Moscon’s Pro 3-Spoke tubular wheel splintered into pieces after hitting what appeared to be a manhole cover. Moscon crashed, suffering bruises and road rash, but escaped without more serious injuries.

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Following the incident, Pro conducted an investigation to replicate the circumstances of the crash and found that Sky’s narrow tire choice was to blame. “The incident occurred because the rider hit a pothole at high speed on a tire that did not meet the minimum tire width specification as advised by Pro,” the company said in a statement to VeloNews.

Pro is a component manufacturer that is part of the Shimano corporation.

According to Pro’s technical manual, the 3-Spoke tubular wheel (PRWH0038) has a minimum tire width specification of 25mm. Known for pushing the limits with aerodynamics and gear choices, it’s easy to imagine Sky opting for a narrower front tire. Most pro riders and mechanics choose 23mm or narrower with time trial bikes for a sleeker aerodynamic profile.

Team Sky was riding Continental tires at Tirreno-Adriatico during the TTT meltdown. Continental only offers its tubular competition tires in sizes 25mm, 22mm, and 19mm. So, we can assume that Moscon and his teammates were either riding 22mm- or 19mm-wide tires. These narrow tires paired with Pro’s wide 24mm rims (external rim width) proved to be incompatible over damaged roads.

In light of these findings, Pro says that its 3-spoke wheel is safe to continue riding. However, riders must continue follow the company’s specifications. The company also advises riders to inspect the wheel for damage following impact and to stop riding in the event of a puncture.