It goes without saying that if you are going to design with composite materials you are going to have to use some form of computer modeling. We use finite element analysis (FEA) for our computer modeling. Composite materials are anisotropic (mechanical properties vary with orientation). Typically a frame is made up of 8 to 20 plies of carbon fiber. Each one of these plies can have a different orientation and this greatly effects the stiffness and strength of the frame. Add to that the option of 180 degrees of orientation for each ply over the entire sculptured shape of the frame and it gets real complicated. You need a computer to keep tack of resultant material properties.
Further, you have to determine how these ply orientations will react to the loading conditions of the bicyclist. FEA is the only way to optimize a composite design.
The ZXT FEA model at the left is just an example of where some of the “hot” spots on the frame would be under one set of loading conditions. It takes many FEA iterations to get the design in the ballpark.
The same is true for the ZR frame shown on the right.
We look at stress plots and deflection plots to determine what is the best composite design we can offer. We use this information to design an efficient frame, which is light and stiff.
The FEA models below compare the ZR to an aluminum frame with the same geometry & loads. The tube set is an Easton Elite 7005. You can clearly see the excessive head tube twisting on the Al. frame as opposed to the very stable head tube on the ZR. The 7005 frame twists far more than the ZR. Excessive twisting basically sucks the energy out of your legs. Your energy is used to twist the frame rather than going forward.