A brief diversion...
One of my co-workers crashed on the MS150 ride this weekend when his front wheel dropped into an expansion joint on the road. His helmet shattered and he broke two ribs. An ambulance arrived to transport him to the local hospital, and while they loaded him aboard, another cyclist crashed in the same spot.
This type of fall, where the front wheel gets trapped or suddenly thrown to one side, is commonly called a diversion fall. Anything that causes the front tire to lose adhesion can bring about an unexpected, very sudden crash. The contact patch under the tire is roughly the size of a thumb print. It does about 2/3 of the braking and provides all directional control.
Besides the obvious hazards of wheel-trapping drain grates, we have to be wary of railroad tracks, streetcar tracks, pavement cracks or expansion joints parallel to our direction of travel, patches of oil or diesel fuel, sand, gravel, leaves, and manhole covers. Rain increases the hazard because it reduces traction.
I wish I could tell you there's a technique to recover from an incipient diversion fall, but the best recommendation is to be attentive and avoid getting your wheel trapped in the first place. Yeah, that sounds good. It's not a universal solution, and even for those of us commuting on the same roads day after day, it doesn't always work. And when we're riding a new, strange road, paying attention is even more critical.
It's certainly true we can be too complacent. I'm thinking about a near-tumble a few months ago. In the pre-dawn darkness, I was maneuvering left across two lanes of traffic onto a dedicated left turn lane. I'd done this hundreds of times, but that morning as I went from the left-most travel lane into the dedicated turn lane, my front tire dropped into a deep expansion joint. It stuck for only an instant, but in that instant my heart rate went way, way up! I was very fortunate not to crash as there was motor vehicle traffic to my right. I stopped under a street light to inspect the sidewalls for damage because a crevice or expansion joint can cut the side of the tire.
But as I said, I'd been through there hundreds of times without any problems. I assumed that the road surface was the same every day and that I rode on the same space every day. Big mistake.
Likewise, when I turn south onto Mingo Road from 76th Street, I've learned to expect something unusual. There's a streetlight on the north side of 76th, but it doesn't illuminate the downhill turn onto Mingo very well. Sometimes there's debris strewn across the lane and I can't see it. I hear it crunching under my wheels. The best way to avoid a fall there is to be sure I'm not turning when I hit a patch of sand or gravel. Turn, straighten up across the sand, then turn again.
So let's be careful out there. Pay attention to the road surface in front of you, especially if you're riding somewhere new and different, and don't fall into the trap of complacency on the routes you know like your own living room.