Tapering vs. External Butting

As noted earlier in Ovalizing and Tapering, tapering is a convention inherited from traditional frame design, where it was used to provide a softer, more flexible ride over the rough roads common at the turn of the century. It is of limited value in a modern titanium frame.

Titanium tubing can be tapered by diameter sinking; the tubing is forced through a die (swaged) until the final dimensions are reached. Tapered tubing can also be created by rolling titanium sheet into a tapered tube form and welding the seam.

Both processes have drawbacks. The molecular structure of the metal is severely affected during the tapering process, altering the CSR and thus the fatigue endurance and the ductility of the tubing. Diameter sinking reduces CSR, and decreases fatigue strength. In fact, the negative effects of diameter sinking on fatigue endurance are quite dramatic.

Tapered tubing can be of some use where severe clearance restrictions exist due to component design or geometry constraints. However, every effort should be made to employ untapered tubing instead, with the need for tapering to be carefully weighed against the shorter service life of a tapered tube.