Monday, December 6, 2021

Air Speed Versus Ground Speed on a Bicycle

 

Riding around the airstrip at Camp Adder, Iraq

One afternoon in Iraq in 2009, I decided to ride to supper from the motor pool on a day with a howling wind out of the west. I rode two miles in a crosswind then had to make a left and ride a half mile straight into that 30-mph wind.  Ten feet after the intersection I stopped.  I could not make my single-speed bike move another foot.  

A couple of Special Forces soldiers in an SUV saw me. They gave me and the bike a ride to the mess hall.  I assured them the ride back would be a "breeze."  I thanked them and went to dinner.  That sandstorm was the only time the wind completely stopped my ride.  

In the last week I was paying attention to air speed versus ground speed on my bike.  The group that I ride with has not gotten together because of rain and detours on the route.  I did my usual 25-mile solo ride that is 12.5 miles south ending in a 3-mile uphill, followed by 12.5 miles north beginning with a series of downhills covering three miles.  

The second of the four hills is the steepest.  Last Saturday Strava my top speed (ground speed) was 49mph.  Sunday it was 52mph. Today it was 48mph. As I was riding home today, I was thinking about my air speed.  

On Saturday, the wind was out of the northwest at 10 mph.  The north component of the wind was 7mph so my air speed was 56mph.  On Sunday the air was calm.  Ground and air speed equal.  Today the wind was 5mph out of the north northeast. That put the headwind a 4mph and my air speed at 52mph.  So Saturday was clearly the fastest ride down the 12 percent grade on Route 272 North.  

 Air is always apparent on a bike.

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