Now and again it’s important to know the coast-down deceleration of a motorcycle…how much speed is lost while the motorcycle is in gear, upright, and with no rider input. While there aren't a lot of pertinent data available, there is some, and I got a bit more this week.

Good article to have in the library

Motorcycle extraordinaire Steve Anderson (check out that resume!) published a little-known article in Cycle World (August 2003) that does an excellent job describing what contributes to coast-down deceleration, and relays very useful data from six motorcycles. It’s worth reading the whole article, which can be found here, but ultimately the deceleration is a result of aerodynamic drag, engine friction, and engine pumping loss. A graphic summarizing the results from the article is below:

Adding to the mix, I recently threw my beloved ScenePro on my beloved 2016 Yamaha XSR900 and measured deceleration in 3rd (N=4), 4th (N=5), and 5th (N=4) gears, coasting down from 50 mph to 20 mph. Interestingly, gear position made little difference with averages being -0.11, -0.10, and -0.08 g’s, respectively. The tests were conducted on level asphalt with tire pressure set as recommended (42/36 psi), and I was in a normal upright riding position. If you’d like the raw data, please shoot me an email. Gratuitous motorcycle/ScenePro photo below:

Thanks for reading along! I hope the data helps with an analysis down the line.

Lou Peck
​Lightpoint | Axiom