its not that there isnt enough lock, which there is, you have to have it set up properly, its just that the frame will mostly likely give before anything, and as for everyone saying, Go Maggie! :) i do not trust them, ive ridden about 10+ bikes with them, and they all didnt compare to my V brakes, i would love to go rear disc if there was a frame that suits me, but there isnt, so rear V is the way to be! (Y) :-" (Y) ;)