The Death Wobble

Mark and I went out for another ride yesterday:  a 25-miler to Sandy and back.  According to Mark's Garmin, we each burned about 2400 calories.  I was amazed; that's quite a cardio workout.  I mean, I knew it was hard in places (like those hills where I wondered if I was going to hyper-ventilate); but I really didn't realize that cycling burned so many calories.  I'm all for that.

Last Friday, I wrote about the phenomenon I experienced while riding downhill on Wasatch Boulevard that scared the hell out of me.  I had experienced something similar on our very first ride coming down 3900 South, but the episode last Friday was far worse.  Frankly, it was terrifying.  Once I had a chance to recover, it occurred to me that the problem very well may have been caused by my position on the bike, i.e., being too far forward, shifting weight to the front wheel, causing it to wobble like hell.

I didn't have another episode that day, but Mark, after discussing it with a work colleague who will also be going on our Corsica trip, decided to have the bike checked to make sure there wasn't a crack in the frame. We got the all clear yesterday afternoon, so we picked it up today and went for the ride.  Fortunately, no wobbling, but I made sure to keep my derriere well back on the seat as we went downhill.

Then, yesterday evening, I consulted the Oracle (Google) and found a very interesting article on the website of an Australian bike shop.  I'd like to quote parts of it:

How many times have you pedalled like stink down a steep and straight sealed road, tucked into an aero position and watched the speed ramp up? It’s fun isn’t it? What is your best ever speed? 

Let me now spoil these idyllic thoughts – there is a dark, dark side to this practice, the rare but dreaded death wobble. 

Under certain conditions (over which you have little control) the front wheel and handlebars can start to shimmy or wobble. This very quickly develops into an uncontrollable shaking, which becomes so violent that you could be catapulted off the bike when the front wheel wobbles too far. To make matters worse, this tends to happen when you are going at your fastest speed ever (picture yourself hitting gravel at 84 kph) …

Your immediate instincts are to suspect something wrong with the bike (loose head set, loose or broken skewer, loose wheel bearings/cones, cracked frame etc).  

Have you experienced it? If you have not, be warned, it is seriously frightening … 

It is a well recognised problem with bicycles at high speed. There is nothing wrong with the bikes – any bike can do it given the right circumstances. It has to do with the dynamics of forward motion and the gyroscopic forces of wheels ...  The smoother everything is, the more likely it will happen. It is said that the shivering of a cold road rider can set it off because human shivering is very close to the natural resonance of a bike frame!

That last line caused me to smile, because I had commented to Mark last Friday that perhaps what had started the bike wobbling in the first place was my nervousness, which of course became much greater as the wobbling started, i.e., when my nervousness transmuted to all-out fright.

The author of the article, after doing extensive research on the phenomenon, offered two recommendations for dealing with it.  First, unweigh the seat, i.e., stand up on the pedals for a moment or two.  “The tremor from the front,” he wrote, “ultimately causes the frame to increasingly oscillate (wobble). The rider’s weight on the seat acts to maintain these wobbles as an anchor point for them. If you take your weight off the seat, the wobbles dissipate.”

The other suggestion was to squeeze one’s knees/legs tightly onto the top tube.  The author didn’t put much credence in this suggestion, however, and I would tend – from the depths of my ignorance concerning cycling – to agree.  I mean, the last thing I would be inclined to do, gripped by the terror of a wobbling bike going downhill at 50 mph would be to effectively embrace the frigging thing.  Just saying.