A few of us motorcycle nerds recently wrote an SAE paper discussing tire and roadway evidence generated during aggressive braking maneuvers with ABS-equipped bikes. Spoiler alert: very few of the tests generated roadway evidence, but they all generated tire evidence.

Evidence worth looking for

During a braking maneuver, and more so during an aggressive braking maneuver, tires are rotating at a speed below their translational speed. In other words, they're slipping (I'm not talking about a locked tire here). As the slipping tire encounters road debris such as dirt, rocks, and leaves, the debris is streaked along the tire, ultimately generating a speckled circumferential pattern as shown below (ensure "display images" is selected). The full-size image can be downloaded here.

This evidence helps us determine what brakes were being utilized, and therefore helps establish the initial speed of the motorcycle. However, the evidence is volatile and likely to vanish within 10-20 rotations of the tire (maybe fewer depending on the nature of the traversed surface). As such, if possible, investigators should examine and document motorcycle tires prior to transportation from the collision scene. It makes a big difference down the line!

Thanks for reading, I hope you have a lovely weekend!

Lou Peck
​Lightpoint | Axiom​

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