I have been wearing my very comfortable but almost treadless Trailfly Ultra G 300 Max's a lot recently, as it has been so dry and grip has not been a particular issue, with a few exceptions. They do not like gravel, even at a trivial gradient, nor do they like steep (dry, green) grass. I have found a new surface that I need to be careful on - short dry brown grass - like gravel, even with a trivial gradient, they can slip.