Originally Posted by
cplager
Almost, yes, if he's going slowly enough. But not at 10 mph is where the difference will become less as the aerodynamic drag becomes important.
No, you're wrong now. The guy specified a steep hill where the cyclist could only make 10mph and at this speed aero is NOT important. Power needed for work against gravity and RR is LINEAR with speed, but aero is SQUARED. Which means that aero dominates at speed but drops away to be trivial at lower speeds.
You shouldn't take the particular values in that graph as gospel - just that AR is a curve and that RR and gravity are linear.
It's important to understand this, because when you do then you understand that what is optimal for TDF racing speed is not necessarily relevant to Audax or commute speed. A TDF team uses narrower tyres with higher RR for their low aero drag, but at the speed of an Audax or commute then a wider tyre with higher AR but lower RR will be faster.