roca rule wrote:well i do not know how, or why road bikes have remained almost unchanged for the past century. one of the reasons might be because the two triangle shape is mandatory for most professional racing
Paragraph breaks would have made that easier to read.
Anyway, the "two triangle" shape is in part dictated by UCI/Racing regulations, but even more so it is a factor of weight and performance.
The "two triangles" you are referring to are ultimately truss systems, which are among the strongest design methods in the world. Reduce the depth of the truss and you will decrease stiffness and strength, however this can be compensated by increasing the properties of the material being used.
Four cases in point (although the concepts of designing a frame and taking it to market, in various sizes, is far more complex) :
-A road bike typically uses the best achievable depth of truss to achieve maximum stiffness from the minimal amount of material necessary, thereby reducing weight.
-A mountain bike is a bit less concerned about weight, more concerned about durability. Depth of truss can be reduced or modified to a certain extent. Still, the best XC race frames out there still use a shape that draws closer to a truss pattern whereas a DH frame is built with increased weight a benefit, the truss can be reduced to increase suspension properties, material can be oversized and robust.
-A bmx bike (or a trials bike) has an extremely reduced truss. This is intentional as the bike frame itself will be spun and manipulated while in motion moreso than any other frame. Materials are exceedingly robust for the amount of abuse it takes. Ever wonder why a small BMX frame can weight three or four times the weight of a much larger road frame?
-A folding bike (with the exception of Ritchey breakway or SS-Coupler modified frames) is intended for minimal volume while in folded position, therefore the truss must be reduced or altogether eliminated, stiffness of frame is instead relied upon a stout beam design approach. Again, reducing the truss depth to basically zero the designer must now utilize material properties to increase stiffness... and the weight of the frame (even the carbon folding frames) is increased dramatically.
Although we have seen designs such as Trek's Y-Foil and the Softride style, and we do have some riders reminiscing about the past as if it were truly amazing (which it wasn't), those frame weights wouldn't sell in today's market. Back then people ignored frame weights.
