Someone had the bright idea to hang a motor on one of these frames and motor-cycles were born. The materials and the joining methods evolved to include forgings and welding, but the basic method stayed the same. Join together a bunch of pieces of metal to make the chassis. 50+ years later, the pinnacle of technology was the legendary hotness of the Norton Featherbed (humina-humina-humina. Credit for this brazed example to Norley Cafe Racers):
It is breathtaking, but it is still made by forming a bunch of tubes and plates and joining them all together. This produces a very light, very strong frame that will make old British men swoon on their peglegs, but it requires a lot of very skilled hands to create. Not only is the welding (brazing shown above, but usually welding) itself a challenge, but the heat from the welds weakens the material and warps the whole frame, necessitating re-alignment (i.e. bending the $^&# out of it) after the welding.
Eventually, motorcycle manufacturers started experimenting with aluminum, which is has a much higher strength for the weight than steel, but is even harder to weld and even weaker afterward. Now we have to heat-treat AND re-align frames after assembly. The results look like this:
There is a huge amount of technology built into this Honda motocross frame. It is extraordinarily lightweight, strong, and compact. But it is still built the way frames have always been built, by welding a bunch of pieces together.
If the motorcycle were invented today, in a world that includes aerospace metals, computer-numerically-controlled (CNC) machinery, and machine automation… if we didn’t already have a factory with an assembly line of skilled welders, would we still build frames this way? Now Jeff can lay down some of the prettiest welds you’ve even seen this side of a Seven Axiom, but just because you can doesn’t mean you should (unless the “can” involves a rope-swing, a ski-doo, firearms, and an old couch)
BRD’s chassis (conceived and created by Jeff, Derek, and Dave) doesn’t have a weld on it. We cast it as two monocoque units, and then machine all of the interface surfaces on each casting with a single fixturing (that is, we put it in the machine once, and take it out when its complete).
Casting is often thought of as lower strength than other forming methods (like extrusion and forging) which is true of the base material, but doesn’t take into account the whole system. Our method means we have no heat-affected-zone (HAZ) or contaminants from welding which weaken the frame; we have no warping or re-alignment. It means all of our bearing surfaces are perfectly referenced to each other. We can use high-strength materials that you couldn’t weld even if you wanted to. We can integrate the complexity and weight of our mounting tabs, component features, even the outer casing of the motor, into the frame. We can make our bikes in San Francisco, to the highest standards, with our small team. It also means our frame looks like nothing else on two-wheels, but that appearance is a result of the technology, not the reason for it.
This innovation resulted specifically from BRD being small and constrained, rather than big and powerful. To wax self-important: innovation like this could bring manufacturing back to California. It could change the way every motorcycle is built, gas or electric. It is innovation like this is going to bring our dream not just to reality (as it has), but to production.