I'm running a cdD521 on the rear and it's brilliant!! Even with me being a light person, but heavy riding as I'm not that smooth yet. My next front rim'll be a mavic x517 as my front D521's wearing away at the brake surface. I'm gettin an X517 as they're light and cheap...ish. It'll be built by a really good builder and I'll be running a front disk by then so it should be alright.... if not sweet!!