The Gel DS Racer 10 initially fit a tad snug, but when I hit the road for a 7 miler they felt great. The shoe fit guide advised to order a half a size larger, but for a light weight trainer and racer I prefer snug to sloppy. My 5k times are 20 minutes and my half marathon times are 1:30. I chose this shoe because it provides some support while being light in weight - the alternative was to purchase a true racing flat.