Motorcyclists sometimes run wide when negotiating a turn, even in the absence of mechanical limitations, like scraping hard parts or losing traction. Instead, these riders are limited by their willingness to assume a deeper lean angle.

In The Upper Half of the Motorcycle, Bernt Spiegel argues - through the lens of evolutionary psychology - that humans will not exceed a 20° lean angle without a long period of continuous practice.

“As soon as a person has more or less learned to ride a two-wheeler, he will immediately make use of the “naturally” available 20 degrees of lean angle, but he will not go beyond those 20 degrees.”
— Bernt Spiegel

I dove down the rabbit hole this week to explore the related empirical data, and this is what I’ve found. If you're aware of anything I didn’t mention, please let me know. This one will likely become a full article or paper.

​1973 – Watanabe and Yoshida​
​Riders of varying skill piloted a motorcycle at various speeds and swerved around a one-meter obstacle. Limited lean angle data were reported, but we know a highly skilled rider topped out at 37.8° and a low-skilled rider (harsh!) at 16.3°.

​2011 – Bartlett, Baxter, and Wright​
​93 riders were videoed traversing an offramp and basic photogrammetry was used to establish lean angle. The average was 17.9°, with only three riders exceeding 28°. The authors also analyzed the Watanabe and Yoshida data to determine the experienced riders demonstrated lean angles between 34 and 40° while novices only hit 15 to 25°. A twofer.

​2013 – Hadrich and Hugemann​
​29 riders were instructed to ride normally along a twisty route and their speed and position were documented via GPS. With knowledge of the riders’ speed and roadway geometry, the authors calculated the theoretical lean angle. The average for smaller radii turns was 33° and 21° for larger radii turns.

​2016 – Bauer, Peldschus, and Schick​
​Reconstructing 22 fatal motorcycle crashes in Germany, the authors determined “none of the riders exceeded a stable lean angle of 20° during the entire accident sequence.” Their calculations indicate all crashes could have been avoided if the riders were willing to hit 35°. Track days are invaluable!

​2018 – Winkelbauer, Krack, and Lamp​
​Imagery was captured of 213 riders navigating mountainous roads in Austria and basic photogrammetry was performed to estimate their lean angles. Most riders chose lean angles between 24 and 30°. Full paper.

​2020 – Pleß, Will, and Neukum​
​38 riders were split into two groups and asked to ride normally on different routes. 73% of one group and 65% of the other didn’t exceed 20°.

Wrap-up
​There’s a lot to this topic, and I’m summarizing lengthy papers in a couple lines here. As such, I recommend reading each paper.

If applying these findings to a reconstruction, it’s important to consider the type of motorcycle involved, its condition, the rider’s experience/training, roadway conditions, etc. Also, after years of trying to accurately measure motorcycle lean angle, I’m a bit skeptical about some methods used in the papers above. I believe there’s still work to be done.

In next week’s installment, I’ll show you the system I use to measure lean angle, and what my personal, public-road lean angle tolerance is.

Until then, keep exploring!

Lou Peck
​Lightpoint | Axiom

P.S. I’m excited to announce my next motorcycle recon course, running this December! All prior courses have sold out and I’ll be announcing the course to the gen pop (recons who don’t get To the Point) in a week. As such, if you know you’d like to attend, please sign up soon!