Wind Speed and Resistance

Greg T

So then - I often say that Resistance increases exponentially with Speed.

Every time you increase your speed by an extra 1mph is takes more energy and effort than it did to get you to your current speed. It gets much harder the faster you go. Above 20 and you are really working yourself into a corner.

I know this is "kinda" true but how true is it?

Where are the Fizzy-cysts when you need them.

amnezia

UndercoverElephant

Crickey Greg, I thought that if there was one expert on drag round here, it would be you.

The power required to overcome the aerodynamic drag is given by:



Note that the power needed to push an object through a fluid increases as the cube of the velocity. A car cruising on a highway at 50 mph (80 km/h) may require only 10 horsepower (7.5 kW) to overcome air drag, but that same car at 100 mph (160 km/h) requires 80 hp (60 kW). With a doubling of speed the drag (force) quadruples per the formula. Exerting four times the force over a fixed distance produces four times as much work. At twice the speed the work (resulting in displacement over a fixed distance) is done twice as fast. Since power is the rate of doing work, four times the work done in half the time requires eight times the power.

il_principe

It's all about aero these days eh!

Deep rims please...

Sleeptech

Some Fizzy-cyst type marlarkey on here: http://en.wikipedia.org/wiki/Bicycle_pe ... s_vs_power

* 175W for a 90 kg bike + rider to go 9m/s (20 mph or 32 km/h) on the flats (76% of effort to overcome aerodynamic drag), or 2.6m/s (5.8 mph or 9.4 km/h) on a 7% grade (21% of effort to overcome aerodynamic drag).

* 300W for a 90 kg bike + rider at 11m/s (25 mph or 40 km/h) on the flats (83% of effort to overcome aerodynamic drag) or 4.3m/s (9.5 mph or 15 km/h) on a 7% grade (42% of effort to overcome aerodynamic drag).

* 165W for a 65 kg bike + rider to go 9m/s (20 mph or 32 km/h) on the flats (82% of effort to overcome aerodynamic drag), or 3.3m/s (7.4 mph or 12 km/h) on a 7% grade (37% of effort to overcome aerodynamic drag).

* 285W for a 65 kg bike + rider at 11m/s (25 mph or 40 km/h) on the flats (87% of effort to overcome aerodynamic drag) or 5.3m/s (12 mph or 19 km/h) on a 7% grade (61% of effort to overcome aerodynamic drag).

Greg T

amnezia wrote:

Ah!

Loving it.

Also

if there was one expert on drag round here, it would be you.

Arf Arf Arf