I bought the medium in yellow colour and it fit fairly large in the hips (I'm normally a medium in other pants styles). So I bought the small in black. Fits perfectly. I use the medium with my full (ACL) knee brace when mtbing as it offers more room than the small. And, I use the smalls for gravel/road rides where I don't need my ACL brace.
The pants are flexible and hold my knee pads (and brace) in place, Great pockets (depth and location) and fit. Lightweight yet warm enough for cool autumn riding. I really like the yellow (more mustard) colour!