Quote:
Originally Posted by Grant-53
The air hitting the chest is the main source of drag. The aero bars help in two ways. First the shoulders are lower for less frontal area. Second if the hands are closer together the air flows around the arms and away from the chest.
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I would consider most drag being on back's side as in aerodynamics it is more important how object leaves air rather than how it enters.
One can experiment this with triangular long rod, having taper towards direction of motion is nearly same resistance when swinging it than I shaped plank of same size, but have taper behind (enough low angle of course) there is clearly less resistance when swinging thing in air.
Front has of course a role in it too, but not so great as often is thought.
With bicycle one creates kind of parachute in upright position, arms closer reduces this effect and lower position reduces further rear area that causes lot of drag, of course also frontal area is smaller that is big contributor too, but if rear would be perfect shape frontal area's effect can be minimized.
CwA is Cw multiplied by frontal area, thus reducing either one is reducing effect of other one, leaned over with triathlon bars area becomes 2/3-1/2 of original I guess, Cw is probably also less and even Cw would not be greatly less as area is it is reducing a lot of drag, same could be applied by upright position with fairings that reduce Cw by relatively similar amount.
That is why added Kammbacks in cars also work so well, they reduce Cw, not area, by reducing rear area and making air leave more cleanly rear of vehicle, it is helping great deal.
So I believe that thinking of chest being big part is perhaps bit misleading, I would consider back being more important in upright position, what do you think?
Yesterday it was 22km/h headwind with over 30km/h in gusts, I did ride 25km/h against that in relatively small effort, so in gusts airspeed was more than 55km/h that is bit over 34Mph, now one must think that it is equal to ride 34Mph at calm weather.
That makes quite a difference to importance of aero compared to if you would forget wind aspect.
Very windy day it can be 36km/h headwind with gusts of 60km/h, that would mean easily 50Mph airspeeds in gusts and it starts to get frustrating to ride in such weather, but such happen every now and then. 30km/h gusts and 22km/h headwind is quite common, but then again it can be week or two with only 12km/h wind.