If you were watching Stage 12 of the 2011 Tour, you saw Team Sky racer Geraint Thomas go down while descending on a wet, oily mountain road in the Pyrenees. But he crashed about as smoothly and softly as was possible in that case, winding up rolling in the grass instead of post-holing the pavement. Here's a breakdown of what he did, and what you can learn from it.
1. Assume the Right Position
Thomas had his elbows bent and head up, looking through the corner. The inside knee was pointed into the turn and he pressed down on the inside of the handlebar and put his weight on the outside pedal, which he kept down. The bike leaned underneath him, but his body remained straight. It's a common misconception that you lean with the bike, but in fact it's important to keep your weight over the tires, so that if they start to slide, they're still underneath you--the bike doesn't skip away and leave you cantilevered over nothing.
2. Correct a Slide
Under braking, the rear tire slipped on the slick road. Because of his body position, Thomas had some time to react because the bike was still underneath him as it slid. There are two side forces on the tire: the actual force of the turn, and the force of braking, which makes the bike want to push to the outside and also will, as soon as braking force exceeds grip, stop the wheel from turning and make it slide. So as soon as the wheel started sliding, Thomas removed one of those forces by letting off the brakes. The sliding wheel could then resume turning and regain grip, which brought the bike underneath him again. He also countersteered, pointing the front wheel to the outside of the turn. That helped the bike straighten out and right itself faster.
3. Find the Exit
Riding in a straight line helped him stay upright because it limits all the forces on the bike. You can brake harder in a straight line than on a turn. But because of that line, even with his quick reaction, Thomas could no longer make the switchback. The easiest thing to do was make a controlled exit from the road. As the bike stood up underneath him, Thomas pointed it straight and aimed at a gap between cars and onto the grassy surface along the side of the road.
4. Pick a Soft Landing
At this point, he had scrubbed a lot of speed. But he didn't have the benefit of a long runout; the hillside dropped away dramatically after he shot the gap between two cars. So the safest thing to do was to dump the bike in as controlled a fashion as possible.
5. Drop and Roll
He had already clipped out on the right pedal, so he put his leg out and his arms. (You might put only your arms out.) As he landed, his arms bent at the elbows to absorb the first part of the impact, and then he immediately rolled to his left shoulder and hip.