Technical FAQ: Miguel Ángel López’s and Chloé Dygert’s time trial crashes

VeloNews tech expert Lennard Zinn examines possible causes of recent crashes in time trial events.

Photo: Stuart Franklin/Getty Images

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Have a question for Lennard? Please email him at to be included in Technical FAQ.

Dear Lennard,
Will we also be having a forensic crash reconstruction of Miguel Ángel López’s recent Giro TT crash in the next Tech FAQ as we had of Chloé Dygert’s crash in the worlds time trial?
— Matthew

Dear Matthew,
Sure, I’ll give you my take on López’s crash. Unlike Dygert, he was not going for the win, and that may have had as much to do with it as anything. He was probably just trying to cruise the TT and save his matches for stage wins later and/or helping Fuglsang in the mountains.

It was windy, and the road was bumpy. Rather than focusing on getting as much speed as possible and aggressively pulling on the bars while pedaling hard, which would have concentrated his weight on the elbow pads and the saddle, he instead seemed more focused on safely making it to the line. He appeared to fairly passively lift his elbows off of the elbow pads and his butt off of the saddle at the same time, unweighting both wheels while coasting, standing on his right foot.

He moved his right hand to the base bar and had lifted his left arm off and was in the process of moving it to the base bar as well when he lifted his butt off the saddle (presumably because he saw the bumps he was about to hit). With his left hand off of the bar without either elbow (or his butt) firmly planted, hitting the pair of bumps caused him to fall down onto the front of the bike. His left elbow fell down onto the base bar, causing the bike to swerve to the right as his chest fell to the bar. It all went sideways (literally) due to off-center weight out on the tip of the left aero bar and left elbow on the left side of the base bar putting a net torque on the steering while both wheels were free to flail back and forth due to not having weight on the saddle or balanced weight on the bar.
― Lennard

Dear Lennard,
Here is a scenario that happened to me years ago that may give some insight into Dygert’s TT crash.

I was descending a series of turns on a road called Palos Verdes Drive East on the Palos Verdes Peninsula. While in the drops at the exit of a turn, I lost traction of both wheels simultaneously. Instead of sliding out, I was able to save it until both wheels hooked up, which then caused me to “high side”. In a fraction of a second, I was looking at the road coming up at me.

I have ridden MTBs along with motorcycles during a stint as a test rider for Honda research — I know tank slappers.

My crash was caused by either diesel fuel or transmission fluid. I have ridden across black ice on a mountain bike. That was an 11 on the “pucker factor” scale. The scariest crashes were crossing patches of green filamentous algae. Once was a road crossing a shallow culvert across a seasonal stream crossing and other a sidewalk that had “greened” from a broken sprinkler head.

Being that this was in Italy, my bet is diesel fuel.
— Randy

Dear Lennard,
Great review of Chloé Dygert’s tank slapper crash.

In Grand Prix motorcycle road racing, we see this with inexperienced riders. The most immediate way to correct a tank slapper on a motorcycle is more throttle, which is counter-intuitive. It’s difficult to condition your brain to grab for more power, when slowing down seems to be the better idea. But as you stated in your article, forward transfer of weight is a part of the problem.

The other cause/contributing factor to tank slappers, is a slower rotating front wheel. As she traveled over the mid-road ripples (you could see them on the video), it may have offset the rotating speed as the front brake was applied. If she held the front brake on, this just compounds the problem.

Chloe Dygert at the 2019 UCI Road World Championships
Photo: Casey B. Gibson

As you know, modern TT bikes have steep steering tube angles and short rake. She’s a big girl and a lot of weight transferred. Unlike motorcycles, it is very difficult for a bike rider to generate enough new torque on the crank in such a tucked position so that the weight transfers to the rear tire.
— Tom

Dear Lennard,
Thanks for the thoughtful analysis of Chloé Dygert’s crash. Here’s an idea that might be complementary to your analysis and also with the experiences of the riders who have wobbled while cornering on the extensions: A crucial factor in the sequence that causes wobble to become uncontrollable might involve the length (“moment”) and mass of a human forearm. If a tire wobbles even once, the forearms swing a bit to one side. The rider will try to control the wobble via the forearms, but these efforts will depend on reaction time in applying force to counter both the forearm swing and the wobble. The forearm swing might, in some cases, synchronize disadvantageously with the wobble of the wheel, the human body is full of flex and geometry just like a bike.
— Roger

Dear Lennard,
This email is just to add a figure to the ones in your article. Looking at the video frame by frame (25fps), you can see that the oscillation frequency is between 5 and 6 Hz, i.e., it is in the range of typical wobble frequencies, and beyond the human being bandwidth.

If you are interested, here you can find a careful analysis of on-road shimmy.
— Gianantonio

Dear Lennard,
Thanks for picking up this topic — I was really surprised that there hadn’t been any other big press on the cause.

I have a theory that she broke a spoke.

To add a conspiracy theory twist, I suspect her equipment manufacturer does not want word of this to get out, which is why we haven’t seen any photos of the bike/wheel and there hasn’t been any announcement from the team/rider as to what happened.

A broken spoke would lead to the once per revolution wobble that you saw, right? Seems to me to fit the symptoms.

Is there anything you saw that would make you think it was not a broken spoke?
— Jeff

Dear Lennard,
Has anyone considered the possibility of a broken spoke as the cause of the TT crash involving Chloé Dygert? It appears to me, a spoke on the front wheel failed and caused the wheel to instantly change shape, and consequently made the bike impossible to control in the turn. I would be interested in your thoughts regarding my theory.

Dear Mark and Jeff,
Yes, a broken spoke could have initiated the loss of front tire traction that started the tank-slapper. And no, I didn’t see after photos of her wheels, so I have no evidence one way or the other about the integrity of the spokes.
― Lennard

Dear Lennard,
Thanks very much for your column about Chloé Dygert’s crash in the individual time trial at the 2020 world championships, recently. Just throwing in a bit of supporting info: there’s a moment just as the rear wheel of her bike passes the end of the padding where the bike (at max oversteer), the roadway, and the padding are more or less parallel and one can try to compare them. At that moment it looks to me like the padding sections are about 2 bicycle-wheelbases long, or perhaps a bit more. That seems to support the high-speed wobble conclusion you came to.

I really hated to see her wreck so badly, and while riding so well to boot! It would have been wonderful to see her repeat the title. I’m certainly glad her injuries may not be as severe as it looked initially.
— Greg

Dear Lennard,
I enjoyed reading your analysis. One data point that I can add is the guardrail spacing. From what I can tell from researching Italian standards, the length of the metal panel is 4 meters (splice center to center). The standard I saw indicated posts at the overlap of the panels and also at the midpoint for a 2-meter spacing (US spacing is 12’6″ for the rail splice to rail splice and 6’3″ for post spacing).

My video is not that clear but there may be an intermediate (2m spacing) post at the approach nose of the rail on her left. Where the car stops it seems to be at the 4m spacing. This may be useful for determining the corner entry speed if the railing joints/posts are visible enough.
— Tim

Dear Lennard,
My $0.02 on Chloe’s worlds TT crash from which I hope she has a fast and complete recovery.

A factor deserving additional discussion is the motion of Chloé’s saddle beneath her during the wobble. When I first saw the video, I thought she was actually standing up on the pedals, but after watching it a few times, I believe she got bumped up off of the saddle, such as by a bump in the road or by a momentary loss (or gain) of traction in the corner.

Why is that important? Let’s go back to the days of relatively flexible frames. As an aspiring junior racer, I was taught to prevent or counteract a speed wobble on a fast descent by clamping my knees on the top tube. I hypothesize what this does is to stiffen the rider-bike system about the steerer axis, thereby increasing the resonant frequency well above the input frequencies, getting the system away from resonance, and stopping the wobble.

Chloé was flying, she was committed to the corner, and she was committed to staying in the aero bars. In that scenario, once she got bumped up off the saddle, she lost one of her main contact points with the bike, and being in the aero bars reduced her ability to apply torque to the handlebars. The bike’s resonant frequency about the steerer axis decreased, and she got walloped by a nasty wobble at a very bad time.

Chloé lost her chance at rainbow stripes this time around, but she showed us all what it means to really go for it in pursuit of them. Chapeau to her.
— Garrick

Dear Lennard,
I read your recent article about Chloé Dygert’s front wheel wobble on her time trial bike, as I have always been fascinated with TT bikes. I’ve never ridden one, so I have no idea how they handle, and my question is probably ill-informed. Why are the front ends so short and steep on these bikes? Would a longer, slacker bike not be more efficient for a TT if the rider could stay in the more aerodynamic position for longer?

Image: courtesy Trek bicycles

I copied some side-view images of Trek’s SpeedConcept time trial bike and Madone road bike, and you can see how the rider’s hands are always in front of the front tire’s contact patch. This is in contrast to a typical road bike, which only has the rider’s hands in front of the contact patch when way up on the hoods (a position I have always found to be sketchy on descents). Of course, a mountain bike places the rider’s hands way behind the tire’s contact patch.

Maybe I’m focusing on the wrong detail, I’m just trying to figure out why these bikes are designed the way they are when it looks like they’re about to send the rider over the handlebars at any moment.
— John-Paul

Dear John-Paul,
Yes, a longer front end could add more stability to the bike, and the aero bar and forward saddle move more weight to the bars. On taller bikes (not probably playing a role with Dygert’s bike), one limitation to front end length is the UCI maximum front-center dimension of 65cm (see diagram). When combined with a steep seat angle pulling the bottom bracket back and a long top tube, the front end must be reeled in quite a bit to meet this standard.
― Lennard

Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder ( and purveyor of non-custom huge bikes (, a former U.S. national team rider, co-author of “The Haywire Heart,” and author of many bicycle books including “Zinn and the Art of Road Bike Maintenance,” “DVD, as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.” He holds a bachelor’s in physics from Colorado College.

Follow @lennardzinn on Twitter.

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