Bike versus Biodiesel
I played yesterday with the equivalence of crude oil and food oils through some fuzzy math. I’m going to continue today with the idea that they are equal. We eat food oils while we feed crude oil to our machines. At the outset I’m going to assume that we have the edge in efficiency, that billions of years of evolution have given our bodies the most efficient oil-to-motion conversion possible. Machines, with only a few centuries of innovation must be further behind. We might be able to test this assumption later, with some more fuzzy math.
The idea of equivalence is certainly supported by the biodiesel enthusiasts. Some of them run Straight Vegetable Oil (SVO) through their cars and report “Power and mpg numbers don’t change significantly on vegetable oil.”
OK! So biodiesel is something we can eat for energy or feed our cars. This gives us the opportunity for a little more calculation.
Bikemetro (a great site looking to serve more cities!) includes a calorie calculator. If I accept their defaults and plug in 1.0 miles, I get 41 calories burned. That assumes a flat ride though, which is probably not typical. Looking the value bikemetro calculated for Friday’s semi-hilly ride (1169 calories over 26 miles), that yields 45 calories per mile. That’s not much difference, but I’ll go with 45.
A gallon of soybean oil contains 30800 calories. If a typical rider could sip that (yuck!) for extra energy, they could ride 684 miles. That’s somewhat similar to the 1000 mpg you sometimes see quoted for bicycle mileage.
As E-P points out though, a car is doing more work for each mile it drives than a bicyclist. Let’s ignore speed and just look at the weight issue for a moment. The bikemetro page assumes a rider weight of 160. Let’s add an arbitrary 30 pounds for bike, gear, and water. That means a bike rider is moving 190 pounds over 684 miles with each gallon, or 129,960 pound-miles/gallon. How does a car do?
The Volkswagen TDI is probably the most widely driven “efficient diesel” in America. Choosing an arbitrary model (I’ll probably get in trouble here because my pick isn’t a stellar performer on mpg), I find a curb weight of 3148 lb and an observed mileage of 32 mpg. That’s 100,736 pound-miles/gallon. Whoo-Hoo! The bicyclist wins by a hair.
Actually, I think the interesting thing is the similarity here. I think this supports my fuzzy idea that oil is oil, whether we drink it or feed it to our machines. This might allow us to independently compute an “ergamine” (the oil equivalent of a man-day of labor), ourselves.
[splitting this long post into two ...]
October 15th, 2005 at 1:49 pm
Interesting but I think you need to include the driver’s energy consumption as well as the car’s consumption. Even when sitting and not engaged in a lot of physical activity, the driver’s engergy consumption likely is a sizeable fraction of the cyclist’s.
October 15th, 2005 at 2:25 pm
Hmmm. I saw a huge list of activities and their associated “burn rates” somewhere … I’ll have to look for it again …
October 15th, 2005 at 2:34 pm
FWIW, this site rates driving as “very light”, one step up from resting ;-).
http://www.exrx.net/Calculators/CalRequire.html
We don’t know of course, but I assume the bikemetro calories are the increase over normal, non-strenuous activities like driving.
October 16th, 2005 at 5:23 pm
I did a similar calculation for a cycling newslist. However, I used the cargo capacity instead of total weight to factor in the efficiency of the design of the vehicle. I use your bicycle numbers. The semi weights I have seen on vehicles. The semi mileage I remember from an email from a tucking company dispatcher. The VW Jetta info I got from http://www.vw.com/vwcom/content/objects/pdf/vw_jetta_specs.pdf
Bicycle 190 – 30 = 160 * 684 miles per gallon = 109,440 cargo pound miles.
VW Jetta Diesel 4,302 – 3,197 = 1,105 * 30 mpg = 33,150 cpm.
Semi 80,000 – 32,000 = 50,000 * 7 mpg = 350,000 cpm.
November 2nd, 2005 at 12:55 pm
A fair comparison would be an engine hauling only itself and fuel, vs a man on a bike, which is in essence, an engine and fuel. But then, the bottom line is the bottom line….cost. If I spent no more per month on groceries than I do now, and was able to ride my bike to and from work instead of a car, then for me, that might equate to a savings of 40.00 a month in gasoline (320 miles a month, 25 mpg, 2.75$ a gal).
December 21st, 2005 at 9:19 am
A newer, related, article appers here
February 2nd, 2006 at 11:32 am
Figures from Bicycling Science 2nd ed., Whitt and Wilson, MIT Press 1994, p186:
Note that figures for human-powered transportation are in incremental consumption above the resting level.
Road bicycle plus rider
4mph 8.4 kcal/km 2440mpg
10mph 15.6 kcal/km 1310mpg
15mph 24.4 kcal/km 840mpg
Auto plus one rider
30mph 539kcal/km 38mpg
60mph 820kcal/km 25mpg
That calculator doesn’t seem to work very well. It determines that it takes more energy to travel on a bike at 5mph than at 18mph, but the wind resistance drag increases with the square of the speed, and wind resistance is the limiting force for cyclists on a flat road. You might ask them for their calculations so you can make better ones. Bicycling Science goes through the studies and calculations it uses to get to those results. Worth a read.
A more important point, which isn’t really a quibble with your result, is that if the purpose of a car is to one or more people, what is the point of comparing the mass moved? Put another way, your figures demonstrate that we can move one person 32 miles with 1440 calories by bike or the same person 32 miles with 30800 calories (or more than 21 times as much) by car.
To be complete, you should compare a 1/5 loaded passenger train WRT kcal/passenger/mile. Bicycling Science lists the loaded train as 183mpg @ 30mph and the 5 passenger car as 170mpg @ 30mph.
February 2nd, 2006 at 11:33 am
Terribly sorry, the first sentence of the second to last paragraph should say “… to move one or more people,…”
February 4th, 2006 at 5:59 am
Sorry to be slow on the comment approval … since I haven’t been posting I haven’t been checking the queue either.
As far as which to compare with which, I think it’s all just numeric play. As I ride my bike I mentally compare with the people I see in a larve SUV (one person, no observable cargo, on a beautiful road not ‘requiring’ a truck).
I left out the whole speed thing because I was thinking, in the speed domain a bicycle can easily achieve, how does a car compare? I kind of left it that machines can certainly more energy faster than a human on a bicycle ever could. I’m sure a dragster burns more in 5 sec than a bicyclist all day. And so on.
Best wishes.
July 4th, 2006 at 10:43 am
Hi!
Dropped in quite accidentally, while searching for information on biodiesel yields!! Yet liked the discussion in the blog article…let me take time to “drink” your argument – oil is oil whether used as food or as diesel….hmmm
Thoughts from http://www.castoroil.in
August 8th, 2006 at 4:38 am
Just a heads up: calories are gram calories, Calories are kilocalories
so a gallon of gasoline has 31,000,000 calories
and 31,000 Calories
August 8th, 2006 at 4:49 am
That’s true. I was taught the capitalization rule back when I got my old chem degree. I guess I’m lazy now and just use “calorie” in what I think is the public sense. I say “calorie” for what is on a food packaging label.
My thought at the time was that the audience would relate to food calories and that would simplify things.
Reading your post now, I see that I could have said food Calories and made more people happy ;-)