drop bars, wind resistance

General cycling advice ( NOT technical ! )
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squeaker
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Re: drop bars, wind resistance

Post by squeaker »

Have a play here ;)
HTH
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NATURAL ANKLING
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Re: drop bars, wind resistance

Post by NATURAL ANKLING »

Hi,
Interesting, my BMI is 23.8 :? ...........more work :(
NA Thinks Just End 2 End Return + Bivvy - Some day Soon I hope
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niggle
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Re: drop bars, wind resistance

Post by niggle »

Found this chart earlier:

Image

A gradient of 3% apparently slows you more than air resistance :? I am unconvinced as they don't mention speed, and a strong headwind does slow a cyclist significantly even downhill IME.
BigG
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Re: drop bars, wind resistance

Post by BigG »

The 300W power input used in the chart is quite high for most of us except in short bursts. A lower figure would have the effect of moving all of the columns in the cart one or more places to the left.
karlt
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Re: drop bars, wind resistance

Post by karlt »

Bloody hell! 300Watts for a rider weighing about 65Kg after the weight of the bike's taken off?

Can we have another chart at say 150Watts for a rider+bike combination of around 100Kg, like in the real world ;)
MikeF
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Re: drop bars, wind resistance

Post by MikeF »

I always try to remember that when the going seems to better than usual there'll be a headwind on the way back :roll:
"It takes a genius to spot the obvious" - my old physics master.
I don't peddle bikes.
Ayesha
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Re: drop bars, wind resistance

Post by Ayesha »

karlt wrote:Bloody hell! 300Watts for a rider weighing about 65Kg after the weight of the bike's taken off?

Can we have another chart at say 150Watts for a rider+bike combination of around 100Kg, like in the real world ;)


Note the logo in the top RH corner of the page. Does it say "Sport"?

What it don't say is,,,

The 300 Watts was deduced by the rider's O2/CO2 gas exchange. If it is, 300 W represents the TOTAL calorific ( or Joules ) expenditure, which includes thermal expulsion, windchill and a correction for solar gain.

It could be only 60 Watts getting to the tarmac.

It was probably gained by using a PowerTap hub, so its 300 W at the tarmac, and 900 - 1000 going out as heat.
niggle
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Re: drop bars, wind resistance

Post by niggle »

Thinking about it the chart probably does take account of the expected speed, as affected by the gradient.

However it still does not take into account head winds, and does not cover descending either.
Ayesha
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Re: drop bars, wind resistance

Post by Ayesha »

I’ve entered the details on the chart into PowerCalc.xls which was the calculator on the CTC website.
For the details, 300 W on level ground comes to 39 kmh.
300 W up a 3% is 27.5 kmh.
Up a 7%, its 17 kmh.

The details, 0.3 CdA ( 0.3 m^2 area and 1.00 Cd.) and 0.005 Crr are representative of a slender race boy on 22 mm HPs riding ‘On the hoods’.
My results here are Elite race speeds.
IMHO. This chart is ‘Theoretical’ and not constructed from test data.


“First, formulate a theory. Then explain it with the math. Then prove it with experiments. If the experimental results differ from the math, the theory is wrong.”
R Feynman.

The giveaway on the chart is the figure for drivetrain losses. 97.5% at 300 Watts transmission ????
The Mechanic
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Location: Scotland

Re: drop bars, wind resistance

Post by The Mechanic »

Ayesha wrote:I’ve entered the details on the chart into PowerCalc.xls which was the calculator on the CTC website.
For the details, 300 W on level ground comes to 39 kmh.
300 W up a 3% is 27.5 kmh.
Up a 7%, its 17 kmh.

The details, 0.3 CdA ( 0.3 m^2 area and 1.00 Cd.) and 0.005 Crr are representative of a slender race boy on 22 mm HPs riding ‘On the hoods’.
My results here are Elite race speeds.
IMHO. This chart is ‘Theoretical’ and not constructed from test data.


“First, formulate a theory. Then explain it with the math. Then prove it with experiments. If the experimental results differ from the math, the theory is wrong.”
R Feynman.

The giveaway on the chart is the figure for drivetrain losses. 97.5% at 300 Watts transmission ????


I don't think that is drive train losses. It clearly says Drive Train efficiency 97.5% That is only 2.5% loss but I agree that does seem low.
Cancer changes your outlook on life. Change yours before it changes you.
Brucey
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Re: drop bars, wind resistance

Post by Brucey »

the drivetrain and bearing losses are a little optimistic but this matters little in the grand scheme of things. For a touring bike/rider the aero losses will be a smaller portion and the rolling resistance losses likely greater. However the rate at which gradient alters the relative contributions may be similar, because the all up weight is greater.

My 'top takeaway' from this is that even on a very slight gradient, if you can put out more power by sitting up slightly, you will probably go faster. If you are going more slowly and/or pushing out less power to start with, this counts double, I'd say.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Ayesha
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Re: drop bars, wind resistance

Post by Ayesha »

Brucey wrote:the drivetrain and bearing losses are a little optimistic but this matters little in the grand scheme of things. For a touring bike/rider the aero losses will be a smaller portion and the rolling resistance losses likely greater. However the rate at which gradient alters the relative contributions may be similar, because the all up weight is greater.

My 'top takeaway' from this is that even on a very slight gradient, if you can put out more power by sitting up slightly, you will probably go faster. If you are going more slowly and/or pushing out less power to start with, this counts double, I'd say.

cheers


:wink:
My 'top takeaway' forty years ago was "go out and ride for miles, and find out what works."
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