Bar position and efficiency

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Bar position and efficiency

Postby population100 » Mon Apr 30, 2012 9:18 am

Hi all,

I was hoping to get a bit of an idea of increased efficiency whist riding on drops compared to the hoods. I'm sure I can't give you all the metrics to provide a completely accurate answer, but some rough approximations would be very helpful.

Lets say I'm riding at 30kph in still air. How much is my efficiency improved if I go from the hoods to the bottom of the drops?

Some (potentially helpful) info. I'm 176cm and approx 'normal' body proportions. Saddle to bar drop is 117mm, and drop and reach on the bars is 128/83mm.

If I maintain the same power output (don't have a power meter etc), are you able to be me a rough approximation of a change in kph? Also, am I right in assuming the efficiency change would not be linear with kph?

Thanks for any help.
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by BNA » Mon Apr 30, 2012 9:41 am

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Re: Bar position and efficiency

Postby gururug » Mon Apr 30, 2012 9:41 am

Must be some formula with surface area vs speed or something......

Hate complex maths so I'll make a rough guess at 6%.

No it would not be linear. In addition to surface area, streamlining and respiratory constriction will also have an effect amongst other things.
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Re: Bar position and efficiency

Postby population100 » Mon Apr 30, 2012 1:45 pm

gururug wrote:Must be some formula with surface area vs speed or something......


Yeah I was unsure how much of a reduction in surface area one would have by going to the drops. Also, how much 'chest area' is of total drag. I guess a good old fashioned googling session may yield some results.
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Re: Bar position and efficiency

Postby philip » Mon Apr 30, 2012 2:13 pm

I know Alex has written about this in the past but my search-foo is failing me. I remember his findings confirmed that on the hoods in an aero position (i.e. forearms horizontal) was faster than in the drops too.
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Re: Bar position and efficiency

Postby Alex Simmons/RST » Mon Apr 30, 2012 5:59 pm

population100 wrote:Hi all,

I was hoping to get a bit of an idea of increased efficiency whist riding on drops compared to the hoods. I'm sure I can't give you all the metrics to provide a completely accurate answer, but some rough approximations would be very helpful.

Lets say I'm riding at 30kph in still air. How much is my efficiency improved if I go from the hoods to the bottom of the drops?

Some (potentially helpful) info. I'm 176cm and approx 'normal' body proportions. Saddle to bar drop is 117mm, and drop and reach on the bars is 128/83mm.

If I maintain the same power output (don't have a power meter etc), are you able to be me a rough approximation of a change in kph? Also, am I right in assuming the efficiency change would not be linear with kph?

Thanks for any help.

There's not likely to be much, if any, impact on efficiency (as that's a measure of energy delivered to cranks as a proportion of energy metabolised), but if you mean the relationship between speed and power output depending upon your position on the bike, well the question is impossible to answer as it depends on your individual aerodynamics in each position. It's is entirely possible that one or the other may be more aerodynamic, or the same.
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Re: Bar position and efficiency

Postby toolonglegs » Mon Apr 30, 2012 7:03 pm

Isn't it about getting your head out of the way?. ie: in line with your body instead of sticking up. I did some front on photos on the trainer to compare TT bike to Road... in the drops on the roadie I look like a rugby forward!...which I suppose I was for half my life :mrgreen: .
In my race yesterday I didn't leave the drops for 70kms... when I finally sat up with my hands on the hoods my bike felt foreign to me, like I was on a tourist bicycle or something :lol: . Then I thought maybe I need a downward sloping stem (already slammed) ... but then I thought leave it as is and always ride in the drops when needing speed or with forearms on the tops (which feels more aero to me but less control in a bunch).
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Re: Bar position and efficiency

Postby population100 » Wed May 02, 2012 8:38 am

Thanks for the replies.

Alex Simmons/RST wrote:if you mean the relationship between speed and power output depending upon your position on the bike


Yes I guess that's what I mean. It certainly feels more 'efficient' on the drops. The scientist in me wants to quantify this, but I'm guessing I need a power meter for that?
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Re: Bar position and efficiency

Postby gururug » Wed May 02, 2012 10:45 am

population100 wrote:The scientist in me wants to quantify this, but I'm guessing I need a power meter for that?


Find a few chain smokers and borrow your missus' hairdryer...
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Re: Bar position and efficiency

Postby population100 » Wed May 02, 2012 1:23 pm

gururug wrote:Find a few chain smokers and borrow your missus' hairdryer...


hmm??
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Re: Bar position and efficiency

Postby Mulger bill » Wed May 02, 2012 10:46 pm

population100 wrote:
gururug wrote:Find a few chain smokers and borrow your missus' hairdryer...


hmm??


Ghetto wind tunnel? :?
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