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Old 06-23-13, 06:34 PM   #1
sreten
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Speed into wind and with the wind

Hi,

Not sure this is the best forum but it is the most technical.

Anyway today I rode on the flat into a 20mph+ headwind doing about 10mph.
So aero drag is equivalent to doing 30mph and should totally dominate.

Fact is I can't remotely do 30mph on the flat no wind, around 20mph, so how can
I do 10mph into a 20mph wind ? Coming back the other way with the wind I think
I hit 25mph maximum on the flat, how does that work with a 20mph tailwind ?

Before you say the wind simply wasn't that strong I can assure you it was.

rgds, sreten.

Last edited by sreten; 06-23-13 at 06:37 PM.
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Old 06-23-13, 06:51 PM   #2
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Hi,

Why on earth has this been moved to folding bikes ?
Its related to my road bike not my folder.
Move it to to Road Cycling.

rgds, sreten.

Last edited by sreten; 06-23-13 at 06:54 PM.
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Old 06-23-13, 06:53 PM   #3
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Quote:
Originally Posted by sreten View Post
Hi,

Why on earth has this been moved to folding bikes.
Its related to my road bike not my folder.

rgds, sreten.
Your Bike List: Say 20" Folder road bike. Duh
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Old 06-23-13, 07:22 PM   #4
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Quote:
Originally Posted by sreten View Post
Anyway today I rode on the flat into a 20mph+ headwind doing about 10mph.
So aero drag is equivalent to doing 30mph and should totally dominate.

Fact is I can't remotely do 30mph on the flat no wind, around 20mph, so how can
I do 10mph into a 20mph wind ?
Aero drag goes as the square of wind velocity and power is proportional to the drag times the ground velocity. So in a 20 mph headwind the required power is proportional to 30^2 x 10 or 9000. That's the same as if you were riding 20.8 mph with no wind at all (20.8^3 = 9000). Of course that's assuming that aero drag was the only force working against you (no rolling resistance, gradient, mech. inefficiency) so in practice your equivalent speed without wind would be a little less - maybe 19 mph or so.

If you can't go close to 20 mph using the same level of effort then I do question whether the wind was really that strong. Keep in mind that the wind speed down near the ground is usually significantly reduced. So your wheels, legs, and lower part of the bike may have been seeing a wind speed of less than 20 mph.

Note to 10 Wheels: The topic of this question would seem to relate equally to all types of bicycles and is certainly not specific to folders. Just because someone lists a folder under his list of bikes shouldn't prohibit him from posing reasonable questions to other subforums where they apply. Furthermore, sreten lists 'Folder, Road Bike' under his list of bicycles - I read that as indicating both a folder and a regular road bike (but again, the relevant question should be about the topic of the thread, not the bicycle owned by the poster).

Last edited by prathmann; 06-24-13 at 03:28 PM.
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Old 06-23-13, 08:56 PM   #5
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Originally Posted by 10 Wheels View Post
Your Bike List: Say 20" Folder road bike. Duh

Hi, it says [20" Folder, Road Bike], rgds, sreten.
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Old 06-24-13, 04:44 AM   #6
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Your Bike List: Say 20" Folder road bike. Duh
20" Folder , Road bike... FWIW a lot of us didn't notice that our bikes were being listed under our names...

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Old 06-24-13, 07:12 AM   #7
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prathmann +1
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Old 06-24-13, 03:21 PM   #8
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A question, are you including the apparent wind?
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Old 06-25-13, 04:14 AM   #9
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Good answer techinal answer earlier.
More simply. I will try!
There is a relationship between effort and wind but it is not a simple portional one, there is a square law involved. ( Or something simular)
Because of this greater effort is required to increase speed into wind restence or air resistance as the speed increases.
Ie if you double the power of a truck it might only go +10 mph top speed or say 15%. However if you doulbed the power of a truck that could only max 10 mph the increase would be more like 80%
Another factor is the fact that bikes present differently at each end. Ie thay are not javerlins!
At slow speeds you may get proportinal more benifiet from a tailwind if you sit up and act as a sail even though this increases drag. At higher speeds in the same wind this would slow you down as the effect of air resistance is higher than the benefit of the sail effect.
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