I can safely say I have never bottomed out, and my brackets have both cracked, my top brackets have also started to bend slightly.(I do weigh 16 stone though).What I have noticed though is the foot bolt has a smaller diameter than the internal of the tube, which means if the bolt is slightly loose the bracket will actually hit the ally foot,what it needs is a tube with a smaller internal diameter. I have made a temp fix by covering the bent/cracked brackets with a piece of 1/8 plate, I am waiting for my mate to come back off hols, then we will be making some stronger brackets,also sorting out the small bolt problem.