The sell line for the oversized (31.8mm) handlebars is that they flex less. I made the switch from standard to oversized and there really is a noticable decrease in handlebar flex. I think the handlebar/stem combo that I got rid of was somewhat flexier than others to begin with though. And I also went from 46 to 44 on my handlebar width. So it's hard to say just how much of the increased stiffness is on account of the larger diameter. I kind of like the stiffer set-up though.