Originally Posted by
Drew Eckhardt
I replaced the stock metric 10.9 bolts with 12.9 having 20% higher yield strength.
It took 1693 miles to break the front bolt again, although my weight decreased over that period from 154 to 140 pounds.
I gave up at that point.
How much torque are you putting on the bolts? Unlike a single-bolt post, you don't need a huge amount of torque to hold the saddle in place. In fact, too much torque increases the static load on the bolts, making it more likely that a dynamic load (i.e. pothole) will increase the load beyond the point the bolt can handle.
N.B. I haven't used Velo-Orange's post, just two-bolt posts from Campagnolo, Zeus, and Sakae Ringyo.