[This is Steve Crandall. Colleen is letting me write a few guest posts on her blog.]
Thinking about trading that fifteen mpg SUV for something that gets better mileage?
Hmmm ... many mid sized cars get about twenty mpg in town, a few subcompacts get about thirty, and hybrids can do a bit better. Of course all of this depends on how you drive.
As a driver you aren't moving just yourself, but several thousand pounds of steel, rubber, glass, plastic, and gasoline. Wouldn't it be sweet if there was a thirty pound vehicle to move your one hundred and seventy pounds rather than the thirty five hundred pound gas burner?
It turns out there is...
Colleen can get nearly one thousand miles per gallon. Her trick is to use a bike. Someone her size, riding on a normal bike at 13 miles per hour, burns about 400 calories an hour above and beyond what it takes to keep her alive. That works out to about 31 calories per mile (since we are using approximate figures, we'll round off).
So how do we find what this is in miles per gallon?
We humans get our energy from food rather than gasoline. It turns out a gallon of vegetable oil, peanut oil for example, has about 31,500 calories. This turns out to be very similar to the number of calories in a gallon of gasoline - so close that we can consider them approximately equal. It turns out a diesel engine can burn vegetable oil and gets about the same mileage as it does on diesel.
Calories are just a unit of energy. We'll get into that later, but for now all you need to know that a calorie from a bit of gasoline has the same amount of energy as a calorie from fruit or from uranium. The trick is you need the right machine to use the energy.
We now have all the information we need. 31,500 calories per gallon divided by Colleen's 31 calories per mile gives a bit over 1000 miles per gallon! Los Angeles to New York on about three gallons. The mind wobbles.
Your own mileage may vary. Colleen is a serious athlete, but is too tall to be an extremely efficient bike rider. Heavy and out of shape riders will do worse. Smaller athletic riders better. If you are a kid, there is a lot less of you to haul around, so you will probably get even better mileage. Some bikes are more efficient than others using tricks like light weight and lower rolling resistance. But the important thing is a person on a bike is an amazingly efficient way of moving a person around.
Just like cars or planes there is a speed range where you and your bike will be most efficient. When you ride you can "feel" it when you are in this range. Colleen is very competitive and if you are riding next to her she might take off and lose you in her dust. She'll be burning more energy - her mileage will drop - but we aren't talking about dangerous levels of carbon dioxide production or refuelings that will break the bank What she is getting is a better workout which means better health and getting into even better physical shape.
But you protest that vegetable oil isn't the most exciting food.
The label on a container of Ben and Jerry's Brownie Batter ice cream tells us there are 1240 calories per pint. At 31 calories per mile, Colleen can get 1240/31 or 40 miles on a pint of that heaven from Vermont. And according to the New York Times, a slice of pizza from Ray's in Greenwich Village is a bit over 600 calories. Colleen can get almost 80 miles on four slices of the gooey goodness. Or she can burn food that won't lead to heart trouble or a stroke. She'll eat a bit more, but the efficiency is still amazing.
So what kind of mileage can you expect? If you are a heavy or out of shape person, probably a bit worse because your body is struggling. But if you keep at it, you will get in better shape and your mileage will improve. If you are light you can expect better mileage. But at a moderate speed it will probably be close to a thousand miles per gallon give or take a few hundred.
Tell that to your friends.