I think Irulan is on to something - my Shimano clipless sandals (look like sport sandals) used to make my toes numb all the time. Now, I have a pair of regular road shoes - Sidi - and I never have that problem. I always thought with the sandals it was because my toes were curved upward, and they should be with the Sidi's, too, but I just don't have the issue anymore. My vote is due to the stiffness of the sole...

~Angie