A bicycle handlebar assembly that includes a number of grip sites, forearm supports, and a number of structures that have airfoil shaped cross-sections and that provide a highly adjustable handlebar assembly with improved aerodynamic performance across the range of adjustment of the handlebar assembly. The handlebar assembly includes a pair of shim stacks that each includes a number of shims that are selectively mountable to the handlebar assembly to adjust a relative vertical height of left hand and right hand aerobars and arm pads. The aerobars and arm pads are secured to the handlebar by way of corresponding clamping assemblies such that the aerobars and arm pads are movably secured to the handlebar assembly to provide the highly adjustable aero handlebar assembly.