Team Sky and the mystery of the exploding wheels at Tirreno-Adriatico

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Team Sky’s hopes of a high finish in the team time trial at this year’s Tirreno-Adriatico were shattered — quite literally, in fact — when not one, but three riders suffered dramatically catastrophic front wheel failures on the 22.7km-long route around Lido di Camaiore.

While the team managed to finish, it placed deep in the rankings at 18th, 1:42 down on stage winner BMC, and raised plenty of questions in the process about the structural integrity of its PRO three-spoke aero wheels.

Team leader Geraint Thomas said in a post-race interview that all three riders had hit potholes shortly before the wheel failures. Even with the greater loads time trial bikes place on the front wheel, though, such common impacts shouldn’t have produced that result.

Moreover, the three-spoke PRO carbon fiber wheels used by Sky have been available since 2014 with no well-known major incidents, suggesting that the Sky riders either hit something much harder than is typical or received a batch of flawed wheels.

Notably, the BMC team also rode the same make and model of front wheel that day with no issues.

As expected, PRO has released only cursory statements on the subject, saying that it would reserve final judgment until more information is available.

“PRO is continuing its investigation into the issue we saw with Team Sky at the team time trial of Tirreno-Adriatico. We are continuing to look closely into all factors that could cause the incident. During production, the three-spoke wheel passed PRO’s extremely high internal quality control and ISO/UCI standards. PRO’s three-spoke wheel was introduced in 2014 and has a flawless record, achieving countless time trial victories since, including BMC’s team time trial win in the same stage.”

Either way, such total disintegration does call into doubt some of the testing requirements put in place by the sport’s governing body.

In order to gain UCI approval, wheels must survive a 40-joule (30 ft-lb) impact without showing any visible signs of cracking or delamination, and with no change in true or roundness greater than 1mm.

It’s a visually dramatic test to observe in person, and seemingly quite robust. However, the UCI protocol dictates a flat steel anvil surface, which is also covered with a 20mm-thick rubber pad (presumably to predictably simulate the cushioning effect of a tire).

Such a test wouldn’t have accurately replicated the more square-edged impact that a nasty pothole might dole out, and given that manufacturers often tailor their products specifically to meet established test requirements, it’s unclear whether PRO — or any other wheel companies, in fairness — engineered their wheels to survive such abuse.

Even so, the UCI’s technical guidelines only mandate that front wheels for mass start events be tested; specialty wheels such as the ones commonly used in time trials are wholly exempt, as are all rear wheels in general.

The UCI’s wheel test protocol is visually dramatic, but may or may not accurately reflect loads experienced in the real world. Photo: UCI.

“The current safety based test replaced our rupture test on 1 January 2016,” said UCI technical director Mark Barfield via the organization’s press officer, Louis Chenaille. “Our safety-based test replaced this to improve rider’s safety. The incident yesterday, which we are investigating along with the team and manufacturer, is very rare and as such something we will take note of for future consideration.”

The UCI’s efforts to use empirical safety-based criteria for equipment testing is admirable, and should be applauded. Clearly, though, even aero wheels aren’t immune to impact damage. Perhaps it’s time for the UCI to revamp its guidelines yet again.

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