Cycling is a competitive sport such that there is a significant amount of rivalry between cyclists to have any slight advantage. This has created competition between manufacturers to develop the lightest, stiffest and most aerodynamic bicycles on the market. However the Union Cycliste Internationale (UCI), the governing body of competitive cycling has placed weight restrictions on competition bicycles to 6.8 kilograms (UCI Article 1.3.019, 2010). This has resulted in cyclists having to attach weight to the bicycle as companies are now manufacturing bicycles less than 6.8kgs. The stiffness of the frame is important since the stiffer the frame, the greater transfer of power from the pedals to the wheels. This thesis topic will focus on increasing the stiffness of bicycle frames using internal bracing in the tubing.
A theoretical analysis has been conducted calculating the stiffness of an internally braced tube and a standard tube to find the improvement in stiffness. A representation of the stiffness was calculated for both a standard tube and an internally supported tube. The internally braced tube had a greater stiffness. The theoretical analysis included a finite element model that was used to find the bending directions and locations of maximum deflection.
Following the theoretical analysis an experimental analysis was conducted. This first included a test to validate that stiffness was proportional to the second moment of area for composites. This was validated by a load test comparing two tubes without internal stiffening. A standard tube with two layers of carbon fibre was compared to an identical tube manufactured under vacuum pressure, having a lower thickness. The deflection under load of the vacuum tube was greater than that of the standard tube, validating that the stiffness is proportional to the second moment of area.
A deflection test was then done comparing the standard tube to the internally braced tube. The standard tube had 63.79% greater deflection than the internally braced tube, making the internally braced tube significantly stiffer experimentally, and confirmed that the stiffness would be increased substantially with the addition of internal bracing as ovalization is reduced.
A bicycle frame was constructed using tubing with internal bracing. The frame was designed with the same dimensions as that of the Specialized Tarmac. A deflection test was done on the frame and compared to that of the Specialized Tarmac which has standard tubes. The stiffness of the internally braced frame was 4.41 times more than the Specialized Tarmac.