Doing the math on mountain trail impact |

Doing the math on mountain trail impact

Of the letters recently published regarding the hiker/biker trail-impact issue, one was particularly marvelous – citing studies from the University of Guelph and Oakland together concluding “with average amounts of activity, cycling and hiking have similar effects on terrain.”

Bear with me while I run these numbers: Say I weigh 160, carry a 20-pound pack, and my average stride is 28 inches. Each hiking boot spreads my 180-pound load over about 30 square inches as it contacts the trail. The surface pressure on the trail is about 6 pounds for each square inch of boot sole. This is my hiker’s impact for each 28 lineal inches of trail.

If I’m a mountain biker with a 25-pound bike and the same pack, my load on the trail is 205 pounds. Instead of setting down my boot every 28 inches, now my two tires contact the trail surface CONTINUOUSLY. Say I have a 2-inch tire tread width and 1 inch of each tire’s outer circumference contacts the trail surface at any one time. Then, for that 1 lineal inch, I’m loading the trail with my 205 pounds at a surface pressure of about 50 pounds/square inch for each tire. But when I travel the next lineal inch along the trail, I’m loading it again with the same amount; and so on for the entire 28 inches. This is my biker’s impact for each 28 lineal inches of trail.

The purist can find flaws in this comparison because it is oversimplified. Things like dynamic force vectors and tread details are omitted. But then, you can run your own numbers if you don’t like mine.

The point is it doesn’t take a rocket scientist to understand that relative trail impacts between hiker and biker are dramatically different. Anyhow, I’ll bet that any candid mountain biker will tell you that these assumptions have been kind because if the tires aren’t skidding a lot of the time, it’s not as much fun.

George Morin

Nevada City

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