drops vs aero bars?

mogse

i was riding today on my road bike which has aero bars and i was weighing up the
aerodynamics of tri bars vs drops.
is the any scientific evidence that one is faster than the other?
the wind can travel threw your arms with drops and i feel i can generate more power event tucked in nice and low down.
with aero bars you are causing a triangle with elbows close to the chest stopping wind passing threw but you are generating a spear head shape in effect to punch threw the wind.

just wondering what your thoughts are on this?

dsschanze

Well...I don't know if there is much aero advantage to aerobars vs. drops, but aerobars do have other advantages. These include support for you elbows and shoulders (where as drops you have to completely support them) and since aerobars are not typically in such an aggressive position, they allow one to breathe easier than on drops. Not to mention, they are also easier on your back.

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alienator

Well, you can look at the rider positions coming out of windtunnels for TT's for the answer. Whether or not the aero advantages are big enough to matter for you, well, that's something only you can decide.

sogood

As I understand it, a narrower profile is more aero than a lower but wide profile. At the same time, it'll depend on your specific posture. A bad aerobar position may be worse than a perfect dropbar position, and vice versa.

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daveryanwyoming

Yes, there is a substantial amount of scientific evidence in the form of wind tunnel and field CdA testing that demonstrates that well fitted aero bars are far more aerodynamic than riding in the drops of your road bike. That doesn't mean that aero bars can't be fitted high or in a way that doesn't do much for lowering your CdA. plenty of folks ride centuries and other tours with "comfort bars" that allow you to rest on your elbows but don't get you very low but a well fitted set of areo bars on a TT or triathlon bike can cut your frontal area down substantially and that reduces drag.

As Alienator points out you can also look at the top riders in any time trial or triathlon, many of whom arrived at their best fit by spending a lot of time and money on wind tunnel testing. Not too many recent podium finishes by folks riding drop bars instead of aero bars.


-Dave

531Aussie

here are a couple of areo tests written in German. If you can be bothered, you can find the html versions on Google, then put through the Google translator, but it's not a perfect result; and for some reason I couldn't save the Google translated versions in my favourites. Anyway, the German pdf versions have cool pictures.

http://www.dk-content.de/tour/pdf-a...terial_0107.pdf
http://www.cervelo.com/reviews/aerotest.pdf

To answer your question, the guy cuts 37 Watts of drag in the first test by going from the drops to aero bars. I haven't looked at the other test for a while, so I dunno what's in it.

This is my poor translation of the reults in the first article I did ages ages ago:



Output required to sustain 45kph.

Stevens San Remo 'normal' road bike with hands on hoods: 465 Watts
Same bike, hands down on the drops: 406 watts
Same bike, Easton Aeroforce aero bars: 369 Watts
Same bike Triathlon position (5.5 cm lower bar, saddle forwards): 360 Watts
Same as above, with 2 tri-spoke wheels: 345 Watts
Cervelo tri bike + Tri spoke wheels: 328 Watts
Cervelo tri bike + Tri spoke front + disk rear wheel : 320 Watts
Same as above with Giro aero helmet: 317 Watts
Same as above with speed suit: 307 Watts

Peter@vecchios

First, if you can easily reach the ends of aero bars, then some compromise has been reached that means your fit onto the drop bars isn't ideal..on true, longish aero bars where the hand position is much longer than the distance to the hoods. If you are using the aerobars for an elbow rest, and need this to rest your back, etc, then I suggest your fit is improper. On a well fitting bike there is little relative weight on your hands, arms and back and there is no need to 'rest' on your elbows. Aerobars are not a comfort item and if used for that, the fit to the drop bars and bicycle isn't ideal, IMO.

Generally when many people install aerobars either the fit to the drop bars suffers or the fit to the aerobars. On most, when riding aerobars, they feel comfy riding upright with their hands on the pads and seem extended when trying to reach the aerobars. On these setups there is little aero advantage from being in the drops to reaching for the end of the aerobars. If your fit on a road bike is good and you just slap aertobars onto the bike, the fit to these will be poor.

Camilo

I don't believe a narrower profile is inherantly more aero than a lower/wider profile. It's the total area of the profile: height X width (roughly). You can indeed compensate somewhat for the inability to get really low by making yourself as narrow as possible. But the person who can do that (get as narrow as possible) and also get lower will still have the advantage. At least that's how I understand it.

I'm one of those who tries to follow your advice - I really concentrate on tucking everything as narrow as I can because I'm not flexible and fit enough to really get low for any meaningful length of time.

TheDarkLord

It is the overall geometry that counts, not area of the profile. You can take a certain area, shape it as a sphere, and as an ellipsoid with a pointed tip. The second figure will be more aero. That said, I agree with what you have mentioned above - the most aero position will be where your head is as low as possible in addition to having a narrow profile. If the head is at a position where it doesn't cause an obstruction to the streamline, it would be ideal, but that is not possible in practice.

sogood

On the width issue, it's not that hard to understand it conceptually. A square frontal area would be more difficult for the airflow to stay streamlined than one that is narrow and long.

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alienator

Unfortunately wind tunnel tests are resulting in rider's with wider arm position. Drag on a human isn't just a matter of frontal area. It's a lot more complex than that. A narrow position on the wrong body just might push the pressure distribution the wrong way. The reverse, with a wide position is equally true.

There is no way to make a general statement about whether a narrow or wide position is more aero.

threaded

On my regular commuter I have these bullhorn bar ends, and can get into this 'Chris Boardman'esque position which I find is really quite aerodynamic, if a little uncomfortable. Is good for catching up with a sprinter on a fancy bike and then drafting them until they run out of puff or turn off.

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PeterF

They do make you a little faster, but when you show up for a club ride, leave them in the car. Or at least don't take your pulls in them.

jD_Empath

There is also the phenomenon known as "closing the cup".

If you examine a rider in the drops from the front, his body is shaped like a *scoop* (arms forming the sides of the scoop or cup). This is analogous to riding with an air-brake like they use on jet aircraft to slow down on the runway.

When using the aerobars, especially with elbow pads that are close together, this scoop no longer exists. The upper body is shaped more like a missile, with the fists forming the pointy end and breaking the high-pressure zone first. This is likely the main reason why the superman position was so fast.