Dropping the bars can increase aerodynamic drag
Wind tunnel testing or using an on-road aero drag testing protocol with a power meter can be very effective for precisely figuring out where a ri der’s ideal aerobar height lies. Below are actual coefficient of drag (CdA, the number defining a body’s aerodynamic characteristics) numbers gained using University of Utah professor Jim Martin, Ph.D.’s field testing protocol that demonstrate where the “aerodynamic line” for aerobar height was for an accomplished athlete.
17cm drop: CdA = 0.286 — 234 watts
19cm drop: CdA = 0.289 — 237 watts
21cm drop: CdA = 0.295 — 242 watts
Riding at 40km/h, this athlete would have to produce 234 watts, 237 watts and 242 watts to overcome aerodynamic drag in those three cases. This athlete is tall and capable of riding a fair amount lower than average comfortably, but the data shows that anything below 17cm of drop actually started increasing drag and costing him time. Not taken into account in the raw CdA numbers was the power differential between positions, which further benefited the 17cm drop over the 19cm.