Well, all I can say is that the single bolt design on my Madone 5.9 never gave me an issue after I figured it out. Many years and thousands of miles on rough roads with no slipping at all. Even during the times I weighed north of 200 lbs. So that's straight truth from an owner, not Internet rumor or someone's opinion of the design. That said, the single bolt design enve seat post on my Lynskey was slipping pretty much on ever other ride on the same roads my Trek never gave me issues on. Go figure...