Originally Posted by
DannoXYZ
Those aren't as good as a design as one that has one side fully touching and tightened down. What happens when a bolt is exposed is that all the loads goes through the bolt. The actual amount of preload is very low due to the maximum clamping force you can apply to the bar. When this amount of preload is exceeded, the joint will loosen and the bars will slip.
However, if you have one side of the plate in contact (similar to fork-end clamps on motorcycles that hold the front-axle), that side can have the bolts tightened much higher, like 20-30lb*ft. This joint can actually take tensile-forces much, much higher than the bolt-preload itself. Here's some info on bolted joints:
http://www.boltscience.com
The usual removable face plate handle bar clamp design may not be optimum but that's the way the manufacturers recommend they be assembled. I've always done it their way and never had the bars loosen or slip. I always put a dot of red nail polish on the exposed part of the bars inside the gap as a witness mark to see if the bars have rotated. None ever have.
That certainly wasn't the case with the old "full wrap", single bolt stems that were the norm before the removable face plates were introduced. Even with gorilla torque on the clamp bolt, the bars would either creak or slip or both.