Ryka seems to be the only athletic shoe that I found that actually runs true to size. I usually wear an 8M but always order 8.5M in athletic shoes because with socks and room for movement, that seems to be what every other brand requires. But Ryka shoes really are meant for women's feet and the sizing is true! These were too large for me at 8.5M and also slip in the heel. Maybe because they were just too large overall but I also tried a smaller size and found out that the Ryka Influence shoe was a more comfortable fit and better support for my feet. I purchased them for Zumba, RIPPED and other high-aerobic classes and the soles seem perfect.