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A shattering experience – A post-recall, R-Sys wheel failure

  • By Steve Frothingham
  • Published Jun. 9, 2009
  • Updated Jun. 10, 2009 at 7:02 AM EDT

By Ben Delaney

The new Mavic R-Sys front wheel fell apart about 30 feet after a corner.

Photo: Brad Kaminski

Editor’s Note: VeloNews is not a safety agency. On occasion, bicycle products being tested by VeloNews editors suffer structural failure — saddles break, spokes snap and even crank arms crack. We often do not report such issues as they can be caused by rider error or a manufacturing anomaly, or because the failure happens in a safe way, such as a broken spoke simply causing a wheel to go out of true. Ben Delaney’s experience doesn’t fall into that latter category and he thought it important to let his fellow cyclists know about it.

Coming around a corner, I felt a shimmy through the front of my bike. I straightened up out of the turn to bring the bike under control. A second or two later I catapulted over the handlebars. The rim of my front wheel had completely detached from the hub. I had not hit anything — not another rider, a curb or even a rock. I landed on my head and broke my shoulder.

The front wheel was Mavic’s second generation, post-recall carbon-spoke R-Sys wheel.

I entered the corner second in a line of four, with a clear line of sight.

Photo: Deirdre Moynihan

The original R-Sys wheels were recalled in January after several riders experienced problems with multiple and concurrent spoke failures.

Mavic has earned its reputation as a dependable manufacturer of quality products. I have ridden and raced Mavic wheels for years, and will continue to do so. My confidence in the company was demonstrated by the fact I chose to ride a post-recall wheel. If Mavic said it was fixed, I reasoned, then that’s good enough for me. I do not have a problem with Mavic — but I do have a problem with this particular wheel.

Wheel structure

The unique features of the R-Sys wheel are its spokes, and the manner in which they are used to support the wheel.

Made from tubular carbon fiber, the R-Sys spokes are used in tension and compression. Most wheels primarily use only tension — the spokes pull the rim and hub together. The R-Sys design relies on the pushing force of compression, too, as a wagon wheel does with wooden spokes. This design is structurally sound so long as the piece being pushed on maintains its integrity. Think of an empty aluminum can — you can stand on it and the tubular aluminum in compression will hold your weight, until someone flicks the can from the side and it crumples.

The three bands shown here indicate a post-recall, second-generation spoke.

Photo: Brad Kaminski

In a steel-spoke wheel, at least four or five spokes must break before the wheel will crumple or taco. With the original R-Sys, it appeared that only one spoke needed to fail before the whole system came undone. Mavic contends that this problem was solved in the second-generation wheel.

Mavic’s response

In the days and weeks following my accident, I had numerous phone and email conversations with Mavic staff. Five Mavic representatives traveled to Boulder to investigate further. After close inspection of the scene, the wheel, the bike frame (the carbon top tube cracked), the tire and the tube (the top of the Presta valve stem was sheared off), Mavic was stumped.

According to Mavic, this is the first such incident involving this second-generation R-Sys.

Mavic uses a battery of standard and proprietary tests for product safety. Wheels are tested with simulated rider loads while rolling on a drum, and also tested laterally by applying sideways force to the hub and the rim. For the R-Sys, each and every spoke is tested in tension before they are built into a wheel. They are not tested individually for compression, however.

Every single spoke broke. The wheel was new, and had not been trued or otherwise tampered with.

Photo: Brad Kaminski

I weigh 190 pounds, but the R-Sys wheels do not come with a weight limit.

Although Mavic representatives were careful not to draw conclusions — none of them saw the accident — it was suggested that perhaps rider error could have caused the wheel to fail through a loss of control.

Eyewitness accounts

Although I was certain of what I experienced, I spent more than two weeks tracking down people who had seen the crash and asking them what they saw. Scores of people saw me flip over the handlebars — one of the race announcers described it as “the Bin Laden of Endos” — without me or my bike hitting anything or anyone. But I continued making phone calls, sending emails and knocking on doors along the racecourse until I connected with people who saw the incident up close.

First, here is my description of what happened. I was the second of four riders through the corner. I entered the left-hand turn for the umpteenth time that day with a clear line of sight. According to my PowerTap data, I was going between 23 and 25mph — average for that corner when riding in single file. There is a slight dip in the road in the corner, which at speed adds a bit of torsional force when leaning into the turn. After the apex of the turn, I suddenly felt something was not right with the wheel. I straightened up, and knew things were not OK. I was no longer thinking about racing. I unclipped one foot and started slowing down, riding in a straight line, now about 30 feet from the corner. I heard a frictional sound, which surprised me as my shoe had not yet touched the ground. A split-second later the front end dove and I catapulted over onto my head and shoulder.

Tire skid marks on the inside of the fork.

Photo: Brad Kaminski

The crotch of the fork shows rubber skid marks in line with the direction of the rotating wheel. The rim, which has no deep scratches on it, is ovalized. It appears that when the spokes all broke, the fork dropped down onto the wheel, stopping it abruptly and throwing me over.

The second rider behind me in the corner saw me enter the corner normally, then quickly jerk the bike upright as I exited. He said he did not think my wheel washed out, reasoning that if it had, I would have crashed, with my trajectory taking me straight into the curb on the right. Instead, I turned further left before straightening out, and he came around me to the right. Once my bike was upright and heading straight, he saw me pull my foot out “and the front just buckled and threw you over like a trout.”

A woman, who was course marshalling that corner, saw the crash from behind. She saw the front of my bike dip down and then saw me go over the bars. A man who was sitting on the outside of the corner said it appeared I “did a little drift to the right in the corner” before straightening out and then “lurched over the bars as the wheel came apart. It was all rather sudden, but it seemed that the wheel failure caused the crash, rather than a crash causing the wheel to break.”

I spoke with two veteran bicycle mechanics, both of whom were standing in the yard — 30 or 40 feet down from the corner — in front of which I crashed.

Scott Holm, a mechanic at Freewheel Bike in Minneapolis, was standing at the edge of a friend’s front yard from where he saw me come out of the corner to his left, ride straight down the street, and crash immediately in front of him. He said the wheel “looked like it just self-destructed.”

Holm said he saw our group come around the corner and straighten out. “It looked like you were upright and going straight again,” he told me. “There was no contact with anyone. It looked like the front wheel just gave up. I saw your front end completely drop. I saw the wheel collapse.”

A view of the corner in reverse, showing the cement dip down between the two asphalt roads.

Photo: Zack Vestal

Wheel history

The recalled front wheels used hollow spokes made with unidirectional carbon fiber. The second-generation spokes have five layers of unidirectional fibers wrapped with two angled layers.

The new spokes also feature Kevlar fibers running inside the carbon. Those were added to comply with UCI rules that require that the components of a wheel stay within the volume of that wheel after the wheel is destroyed in a crash. The new spokes are marked with three silver bands around their circumference to differentiate from the pre-recall spokes.

The first-generation wheels were recalled, Mavic says, to improve spoke strength against penetration by outside objects, such as a pedal or derailleur. A colleague experienced such a situation in a cyclocross race, where another competitor stepped on his wheel and shattered a handful of spokes.

Crash pictures circulating on the Internet show first-generation wheels with numerous shattered spokes, but Mavic contends these wheels were all subjected to forces that would cause any wheel to fail.

Conclusion

I certainly can’t say all R-Sys front wheels will fail. Obviously there are many R-Sys wheels out there that have not. What I can say is what happened to me: I turned a corner under normal racing conditions. The rim separated from the hub. I crashed.

There are two types of failure: safe, and unacceptable. For a wheel, safe failure is when a spoke breaks or a rim cracks, but the wheel remains generally intact until you can come to a stop and address the problem. Unsafe failure is when, for example, the steering wheel comes clean off of the steering column of your car. I put this particular R-Sys front wheel failure in that second category.

Once my shoulder heals, I will continue to ride Mavic wheels with confidence — but only those with metal spokes.

Mavic is continuing to investigate this incident, as is the Consumer Product Safety Commission.

If you have experienced anything similar with an R-Sys wheel, please contact me at velonewsben@competitorgroup.com

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