At times, I am curious when a "grade" becomes impossible to climb. Of course with Mountain Bikes, you've got some steep grades mushing around the trails.
There is one hill here with a bike path and someone said it is a 30% grade. I don't know but I know there are instruments to measure a grade. It's a bear. If that is what it is, I don't think I could ever do any more than that. That little bit on a hill will set your wheels to spinning and maybe sliding as many know that sentiment. I've almost come to the conclusion that maybe I should not be testing some bikes on some grades like that hill because, maybe it challenges a bike too much. I'm going to get a 3rd chainring, that should solve it.