wind resistance

[Trev The Rev]

I ain't no professor neither.

I reckon that 15mph is about the speed when wind resistance actually makes a difference. WR is squared when speed is doubled I believe, and WR is there at any speed above zero of course. However, at the power outputs of a cyclist, it takes it to about 15mph before he notices it much.

This is is still air of course, as if it's windy, it's always against you!

15 mph would be 50 to 90 watts to overcome wind resistance, 25 mph might be around 200 to 250 watts depending on CdA.
trevtherev@ymail.com

[freeflow]

Interesting reading

http://users.frii.com/katana/biketext.html

[Ayesha]

Pf = ( Crr x (lb/375) x V ) + ( CdA x (V^2/391) * (V/375) )

Where Pf is Power ( ferkystarks )
Crr is coeff of rolling resistance
lb is Imperial pounds
V is Velocity in mph
CdA is Coefficient of drag x Cross section area in sqft.


Cd x A = ( (Pf-Prr) x 391 x 375 ) / V^3

Where

Prr = Crr x (lb/375) x V


For an 'Equilibrium Velocity' test

Power Pf = Slope x weight x (Velocity / 375)

Where slope is %, weight is Imperial pounds and Velocity is mph.


You don't need to measure your Cross section area. You need weight in lbs, the slope in % and a freewheeling maximum attained speed.

[SilverBadge]

I reckon that 15mph is about the speed when wind resistance actually makes a difference. WR is squared when speed is doubled I believe, and WR is there at any speed above zero of course. However, at the power outputs of a cyclist, it takes it to about 15mph before he notices it much.

Putting reasonable numbers for a racing cyclist into the equations of motion, I reckon 80% aero losses at 40kph, 50% at 20kph, 20% at 10kph. Touring cyclists generate greater aero and rolling resistance - the proportions won't be wildly different for them.

[Ontherivet77]

Here's a couple of web based calculators for wind resistance. I'm not sure they match up though?

http://www.analyticcycling.com/ForcesPower_Page.html

http://www.exploratorium.edu/cycling/aerodynamics1.html