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Anatomy of a Crash

Last updated on October 26, 2020


Today’s weather was cold — right about freezing — but sunny and with very low wind, which is just about perfect for getting in a mid-afternoon ride on hard, snowless trails. Riding this time of year is almost like riding on concrete trails and generally quite fast, save for the occasional spots where a thin top layer has thawed in the sun. These spots end up acting like grease sitting on pavement and require a bit of caution and attentiveness. Riding today… one got me.

I was following the 6/12 Hour Route that I so love, and just after the Grassy Knoll heading towards Woohoo Hill there is a long, sweeping turn section that’s fairly flat and pretty basic. It can usually be ridden quite quickly, but today 50′ or so had a thin greasy layer and I ended up crashing on it, sliding along for a ways on my hip.

The photo above shows where my bike ended up (click here to embiggen), and what I find most fascinating about it is the forensic evidence it contains:

  • Lower left corner of the image is where the normal tread (45NRTH Hüsker Dü) in the mud layer ends. I would have been leaning the bike slightly at this point.
  • The long bar-like tread marks are where the tire began to slide, and the wide side knobs left grooves in the direction of the bike sliding to the outside of the turn as the tire rotated forward. This indicates the bike was leaning quite far by this point.
  • Rear tire track is on the left, evidenced by it being on top of the track on the right.
  • The tires then hit a small root, which being on an unsuspended bike impart a bit of bounce. This is why there is a gap in tire marks after the root.
  • Rear wheel was moving in a wider radius than the front, which is not what normally happens. The bike was thus no longer pointed in the direction of travel.
  • Wobbles and gaps in the tire marks indicate that the bike was pretty much sideways and out of control at this point.
  • The flattened-smooth part of the tire marks is where my hip/right leg first made contact with the ground and I began sliding.
  • The S curve and straight grooves in the dirt (directly below the top of the rear tire in the image) are from the brake lever and end of the handle bar. The brake lever made the S mark as it compressed and while pushing into the ground.
  • Light mud is visible on only the right half of each tire. This shows that I was already leaning the bike when I hit the greasy mud.

So, what’s the takeaway? It’s a pretty simple message: don’t lean the bike when encountering greasy mud, and if there’s a need to two-wheel side through an area like that, try to avoid bumps that’ll contribute to a loss of traction. Normally I’m good about both of these, but today… I wasn’t. And I have the bruised hip and scraped knee to show it.

On the next pass through this section I was much, much more careful… This isn’t something that I needed a photo to know, but I do think it’s pretty nifty to see post facto.



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