i have a pair of AC wheels built with velocity 'escape' (tubular) rims and the rear is showing a couple of cracks around some nipple holes. does anyone have any experience with or can compare these to the sun M19II rim. both are slightly aero and around the same weight. i was surprised to see the velocity's crack & am not really inclined to use them again-although i could have gotten a bad one or hit a pothole/tracks a litle harder than i thought. thanks.