I think Zipp says their bars are worth about 6 watts and there is a bar width windtunnel comparison out there somewhere on the web that tested differences in bar width. The drag reductions for narrower bars was pretty surprising. I don't remember the details, but let's say it was 3-5 watts for a width reduction of 2 cm..

I would first suggest just calculating the difference on frontal area of the two bars, which is just height and length of the airfoil vs round tube. Your CdA reduction should be at least that much. Then figure the Cd for the airfoil is about 10% of the Cd for a cylinder. If you aren't seeing something around this large a reduction in your field testing, the it is time to figure out if the bars are changing your position.

http://www.aeroweenie.com/...a/tour-road-bars.png



2 things:
1. When you say drag differences of .05, do you mean in m^2? If so...that's kind of large...
2. IME, road positions for field testing are tough to stay as consistent in as TT/Tri positions. If you really want to test out the road setups, I would suggest attaching some shorty clip-ons to help keep your body in a more consistent position.

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http://bikeblather.blogspot.com/

Tom,

What's your opinion of the likely validity of the data presented in the graph you linked to?
The wrinkled jacket and gloves always struck me as being unnecessary confounding variables (different creases and folds on different runs etc).

Plus, the magnitude of difference between a round and aero bar of the same width seems *very* high to me. I feel that if these types of gains were legitimate then the likes of Zipp and Enve would be shouting them from the rooftops. Instead, they all seem to quote the same ~5w figures.

I recall doing a "sanity check" calculation using the differences in surface area for a cylinder parallel to the flow, and finding the Tour data better matched the theory than the Zipp/Enve claims...but, don't quote me on that. I'll either have to find that previous estimate, or redo the calcs...

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http://bikeblather.blogspot.com/

So what's the narrowest aero profile drop bar that accepts clip on aero bars?

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Want: 58cm Cervelo Soloist. PM me if you have one to sell

Vintage Cervelo: A Resource

Probably 3T Aeronova or Aerotundo...

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http://bikeblather.blogspot.com/

I meant 0.005 m^2...!

I 'm pretty confident I hold the position tested well( hoods,straight elbows),and can quite good repeatability.

It's a question with no real easy answer.The real difference between frames might be anywhere between NO difference to +/- 0.015m^2

Thanks, just bought a Zefiro off eBay...

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Want: 58cm Cervelo Soloist. PM me if you have one to sell

Vintage Cervelo: A Resource

A 40cm width aero road bar probably has somewhere between 25 and 30 cm of aerofoil - the rest being the round stem area or the ends at the brake levers. Let's call it 28 cm. The diameter of a round bar is what, 28 mm? So that's 28 cm x 2.8 cm = 78 cm2. Cd of a cylinder (though I actually think a lot of bars are aerodynamically a little better than completely round) is somewhat above 1, and using the ROT we then get ~8-10W at ~45 kph.

To get whatever an aero road bar saves you have to subtract the drag the aerofoil makes (probably 1-2W) and whatever drafting effect you have - both from rider to bar and vice versa. I think the manufacturers' claims of ~5W seem pretty legit. I can't see Tour's testing showing 15-20W can be legit.

As a side note, I believe it was also Tour that didn't find any material difference in aero road bar vs. non-aero road bare when testing aero road frames a couple of years ago. I believe this was with the pedalling lower-body mannequin.