Since then I found a credible case of people riding their bicycles up a paved road about 35-40 vertical meters at steepness around 31% grade, namely Fargo St (just east of the Glendale freeway in Los Angeles, California).
31% grade. What struck me was that in the photos it didn't like the riders were any sort of pros. Seemed like local athletic riders who had gotten good at "tacking" up a steep hill -- riding a zig-zag path with big curves -- and the street looked decently wide and decently smoothly paved.
- I've ridden about that much vertical at 20% grade going straight up the hill, so I guess I could ride up 31% if I practiced "tacking"(?)
How steep are some of the trails people ride up on mountain bikes?
What are some of the steepest sections of trail on some cross-country ski courses?
I think it's pretty well established that there's no asphalt road in the world at least a block long that's as steep as 40% grade.