Originally Posted by
FBinNY
lt's clear up the first misconception. Friction isn't dependent on surface area, it's related to the clamping force. There is a benefit in terms of slippage by increasing the torque at the slipping surface, but not enough to justify the effort.
If we go back in history, the real reason for a bulged center becomes obvious. It's so the bar can be slipped through the stem freely and only be a close fit at the center. In this way, the bulge on bars is like the raised crown sear on fork steerers..
The current nearly universal removable face plate stem design has made the need for slipping a convoluted bar through the stem clamp a non-issue and these stems are about all that's made for the 31.8 center bulge bars.
I will also note that the two and four bolt removable face plates have made bar slippage nearly a thing of the past. I recall going through all sorts of trials to keep the bars from slipping in the older circular clamp stems including using rubber cement, sandpaper and Loctite and torquing the bolt until I was sure it would snap. Nothing worked for long. The removable faceplate stem was the salvation and didn't need to be gorilla tight either.