Ever since I saw the Cinelli Ram handle-stem, I have been fascinated with why we haven't moved to integrating in BMX. In this posting, I aim to to address the issues that come up in the upper steering system. Note: a discussion on BikeGuide has pointed out two things: 1) I jump to the conclusion that forward/backward loads will not bend your bars without evidence; 2) The major challenge with 1-piece systems are their lack of adjustability both in reach (stem length) and bar angle (if, for some reason you don't want it in line...)
Vertical loads defined by loading both ends of the bar equally. In this case, the bends are stressed, and once the load exceeds the yield strength of the material, it will deform plastically (i.e. bend). During vertical loads, the stem is stressed vertically. Although longer stems will act as longer levers, when was the last time you bent a stem down?
Torsional Loads are typically qualified by loading of one side of the handlebar. These loads exhibit the traditional stress to the bends, but create a torsional load on the stem. A quick side note: torsional stiffness is proportional to stem body diameter, material choice, and thickness
Forward Loads are those times when you land a bit flat-bottom and find yourself shoving the handlebars forward. These loads are not characterized by large forces, but often end in the bars slipping in the stem. Promptly followed by a trip to the tool bag. Now some people claim that it is better the bar slips in this situation (or the opposite load where the front of the bars are loaded backward). The probability that either of these situations would end in plastic deformation is very small. Seeing as forward/backward loads are the only loads that can make the stem slip, and there is little chance of damaging the bars, I see little reason to not fix the bars to the stem.
So what do I propose? I would like to see more integrated bar-stems in the BMX market. As we get more market saturation, integrated bar-stems will be available in all the different geometries stems and handlebars come in. And let's face it, there are so few innovations in handlebars, the sector could use a bit more spice. We'll have to change our perspective on how these are clamped on the steerer tube, but that will spur innovation, and reduce overall weight.
Some examples...
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