Miles per gallon from bicycling

MichaelBluejay · 2013-07-03 11:11:21

“For instance, the bicycle is the most efficient machine ever created: Converting calories into gas, a bicycle gets the equivalent of three thousand miles per gallon.” - Bill Strickland, The Quotable Cyclist

Sorry, but that's not even remotely accurate. While the bicycle is very efficient, the human body is not. It's rather wasteful in converting food into work. On a typical American diet, a cyclist gets the equivalent of 63 mpg. A vegan gets double that (125 mpg), since more energy is required to produce livestock than crops. It's still way better than driving solo, but it's nowhere close to 3000 mpg. See my article on bicycling and gas for more.

dougmc · 2013-07-06 11:34:03

It's accurate enough for what it is, but the real problem with this comparison is that the human body doesn't run on gasoline. (MPGe has the same problem, but they run with it anyways.)

A gallon of gasoline contains about 31,000 kcal of usable energy. Given that a good cyclist can probably go 16 mph using 700 kcal/hour, that gives us 700 miles/gallon. Which is lower than what he said, but if our cyclist slows down to 10 mph we probably get close enough for government work.

Our muscles are roughly as efficient as a car engine at converting fuel to work -- around 20% -- but of course we also use a lot of energy just to live, and that muddies the waters there.

In any event, his statement is looking at different things than your page, so it's not really fair to say that it's wrong because he came up with a radically different figure. When we give the mpg rating of a car, we don't look at the fuel needed to create the fuel that goes into the car -- we look just at the fuel that went into the car.

We could easily do the same calculation based on food -- a gallon of potatoes probably has around 4000 kcal of energy that we can use -- but gasoline just has a much higher energy density than things we can actually eat.

Bicycles *are* extremely efficient, especially if we keep the speed low. This is why electric bikes are so much easier to make practical than electric cars.

MichaelBluejay · 2013-07-06 22:42:02

Sorry, I can't agree, and I still think the proper comparison means you have to count the energy used to make the cyclist's fuel.

We know how far a car goes on a gallon a fuel. The question then becomes, how much food could you create with a gallon of fuel, and then how far could the cyclist go on that? Either way, we're looking at the same starting amount of fossil energy:

(1) Fossil fuel >> Car

(2) Fossil fuel >> Food >> Bicyclist

Whatever fuel is used to procure the fuel that goes into the car, a similar amount is used to procure the fuel to produce the food. We don't need to know how much fuel is used to create the fossil fuel, because we'd count it on both sides.

So, the proper comparison is, how far does the car go on X amount of fossil fuel, and how far does the bicyclist go on the same amount? And again, the answer is 63 mpg for a bicyclist eating a typical American diet, and 125 mpg for a vegan.

dougmc · 2013-07-07 00:23:50

The question then becomes, how much food could you create with a gallon of fuel, and then how far could the cyclist go on that?

That's the question you answered. That's not the question he answered. You're asking/answering different questions.

Now, you've got a strong case for your question/answer being the more relevant one, but that doesn't make his wrong. He's just attempting to demonstrate 1) the greatly higher usable energy density in gasoline over food and 2) how much further a bicycle can go on a given amount of energy than a car.

Though he'd do better to leave out #1 entirely (as it muddies the point), and simply point out that a human on a bicycle can go 150 times as far as a car using the same amount of energy. (Though that's not as quotable as what he said.)

Though realistically, this is comparing a more efficient than average bicycle (going like 10 mph or so on flat ground with no wind) to an average car going at typical car speeds (assuming that 20 mpg is average). I suspect 150x is a bit on the high side if we really wanted to compare the average bicycle to the average car -- but either way, the difference is substantial.

MichaelBluejay · 2013-07-07 09:56:33

i'm sorry, I can't agree with this. Strickland is definitely wrong because he's comparing car mpg to bicycle mpg, and coming up with the wrong answer. The answer is wrong because he didn't do an apples-to-apples comparison. To give him credit for asking a different question, it would have to *look* like a different question, along with a big disclaimer that that question is actually irrelevant for a practical comparison of car to bicycle fuel consumption. He's giving an mpg figure, which suggests to the most readers that he's answering the relevant question, when in fact he's not.

The bottom line is, here in the real world, since a cyclist *can't* *actually* go anywhere close to 3000 miles on the equivalent of a gallon of gas, Strickland's answer is wrong.

Now let's say we take Strickland at his word and look at the efficiency of the *bicycle* rather than the cyclist. We can easily do this by seeing how far a gas-powered bicycle will go on a gallon of gasoline. And the answer is: 100-160mpg. So even by that metric, Strickland is wrong.

dougmc · 2013-07-07 12:30:03

MichaelBluejay wrote:

The bottom line is, here in the real world, since a cyclist *can't* *actually* go anywhere close to 3000 miles on the equivalent of a gallon of gas, Strickland's answer is wrong.
Now let's say we take Strickland at his word and look at the efficiency of the *bicycle* rather than the cyclist. We can easily do this by seeing how far a gas-powered bicycle will go on a gallon of gasoline. And the answer is: 100-160mpg. So even by that metric, Strickland is wrong.

The reason gasoline powered bikes go only 100-160 mpg on a gallon of gas is that they use very inefficient engines and people use them to go 30+ mph -- way faster than average human powered bicycles go (and the speed is key, more on this in a bit.)

If you made a tiny gasoline engine that was still as efficient as a car engine but only put out like 35 watts of power (and no cheating by pedalling), you could probably do around 3000 miles from one gallon of gas with a regular bike, without even things like farings. You'd be puttering around pretty slowly -- you probably wouldn't be going over 8 mph -- but you'd go a very long distance.

These folk got about 9000 mpg out of a car, and that's not even the record. The way they do this is 1) they go as slow as possible, 2) use an engine that is as efficient as possible and puts out only the tiny needed amount of energy, and 3) make the car as aerodynamic as possible, and 4) reduce all other losses as much as possible. A bicycle does a pretty good job of #4 already , and for our 3000 mpg purposes will probably be going even slower than this car (as the competition for these cars requires an average speed of at least 15 mph.) #3 would be cheating for our purposes, #2 is reasonable and #1 can be served by picking a realistic speed, but keep it on the low side (a leisurely cyclist.)

The key part of a bicycle's efficiency in all of this is that most of a bike's energy goes into overcoming air resistance, and the energy required to do that is proportional to speed cubed. Basically, what that means is that if we ignore other losses (which are very small on a bicycle anyways), it takes 1/4th as much energy to go a mile at 15 mph as it does at 7.5 mph. Certainly, this 3000 mpg figure would have a cyclist going like 8 mph rather than 20 mph.

Jessamine · 2013-07-07 13:33:57

Created a handle here just to post this.

It's a fascinating discussion, this conversion of gasoline to calories, but it doesn't have much real-world applicability. If we are using miles per gallon (of gasoline) as the point of comparison (rather than calories burned), then the gasoline (or gasoline equivalent as other refined forms of oil like nitrogen fertilizers) used to produce crops to feed cyclists is what cyclists' fuel efficiency should be measured by. It's silly to think we can get away without any environmental impact from our transportation, with the way most food is produced these days.

If a person grew all their own food using only locally-produced compost for fertilizer (had a closed-loop system of food production) and hauling all their materials via bike, then they would be getting infinite mpg and could feel really extra super good about how they were living their life.

As for everyone else, we're still indirectly using fossil fuels even when we ride.

MichaelBluejay wrote:

To greatly reduce your energy and pollution footprint, you should reduce or eliminate consumption of animal foods — no matter how you get around.

Hear hear.

MichaelBluejay · 2013-07-08 19:35:03

Thanks for the comments! So okay, I overhauled the calculator, and now it calculates MPG, gallons of fuel, and carbon, for cyclists, walkers, and drivers, for various speeds and numbers of passengers. It's pretty frickin' comprehensive:

http://bicycleuniverse.info/transpo/energy.html

rich00 · 2013-07-10 13:44:27

Don't forget that it takes a lot of electricity to produce the gallon of gasoline. From the oil well to the gas pump. Think of the energy involved. I heard that it takes about 7kwh of electricity to do this.

If you grow your own organic grains to fuel your bicycling, that is about the most efficient use of energy possible.

Next up is likely an electric bicycle which it's battery is charged by a small wind/water turbine. Then likely a solar panel.

On a cost basis, food for transportation fuel is awfully inefficient and very expensive. This is one reason I am not totally behind longer distance pedal cycle commuting. Any physical effort past the healthy required amount of about 30 minutes a day is wasteful in these terms. So if you pedal 35 miles a day for commuting, costing you the same money in food as you would be spending on gasoline for a 35mpg car.
5 gal x $4/gal = $20
100 miles of (extra) cycling requires about 4200 food calories or about $20 in groceries if you eat healthy/balanced.

Don't forget to add in the energy cost of any additional hot water used to take additional showers or extra laundry.

Now look at an electric bike - after the initial purchase, the operating expense is miniscule. 100 miles of not pedaling the bicycle will only cost about $0.25 in electricity. You get your healthy 50 miles of pedaling per week, and only a quarter to do the other 100 miles of transportation. You also likely don't sweat nearly as much, so no extra showers or laundry.

Yes, an ebike will take more energy to manufacture than a standard bicycle, but compared to a car it's negligible.

MichaelBluejay · 2013-07-10 18:53:24

rich00 wrote:

On a cost basis, food for transportation fuel is awfully inefficient and very expensive.

It greatly depends on what kind of food you eat. From this old post, I figured the "price per gallon" of biking (i.e., the cost of food to cycle the same distance that a gallon of gas would take a typical car) would be:

$8.94 salmon or catfish (farmed)
$6.56 Big Mac
$4.21 ground beef (85% lean)
$3.35 chicken breasts (boneless)
$2.88 cheese
$2.04 Cheerios
$1.17 potatoes
$0.79 peanut butter
$0.77 oats
$0.66 pinto beans
$0.58 rice (white or brown)

Those are 2008 prices, so it'll be a little more now.

Don't forget that it takes a lot of electricity to produce the gallon of gasoline.

It looks like you didn't actually read the article, since I covered it there. As I said there, do you think that the amount of electricity to make the gasoline is different somehow depending on whether the gas goes into a car or into a tractor?

And in the case of different kinds of energy inputs, perhaps you believe that only gasoline requires energy to produce, while mountains strip-mine themselves and beam the coal directly to the power plants?

Don't forget to add in the energy cost of any additional hot water used to take additional showers or extra laundry.

Also covered in the article, and also insignificant.

rich00 · 2013-07-25 18:05:29

You assume that a cyclist eats rice or beans to replace the calories burned. It's possible, but not likely nor a balanced diet. I got my figures from assuming that my typical healthy balance diet costs $10/day and I burn about 2500 calories a day. When you add in quality meats and produce, the cost is closer to $4/ per gallon of gas equivalent, at 20mpg. 35mpg cars are readily available and cheap, so that would be closer to $7/gal of gas equivalent. My old Civic gets 35mpg combined, is worth $1900. For me to bike 35 miles, I will need to eat around $7 in quality/balanced foods.

You think that hot water for a typical shower is insignificant? Have you measured it? What about the energy to cook your rice and beans? That ALONE is more energy than the food will provide you in miles compared to what an ebike will use. You can easily use double the electricity cooking your food and for the additional shower for cycling.

An ebike uses 0.4kwh in electricity to go 20 miles, (includes charger losses). That's about 4 cents. I've mentioned that I solar charge most of the time as well.

As for battery costs: I have a 440 watt hour a123 lifepo4 battery that has 8,000 miles on it. Capacity is 95% of original. These cells are rated for 2000 cycles before dropping to 80% capacity (of course, it's still useful, just not quite as far). It's fair to say this battery will provide 40,000 miles of transportation. Replacement cost is $500. That's $0.0125/mile.

Where is your reasoning that a 25lb bicycle is not pretty closely comparable to a 60lb ebike, and both are essentially neglible to a car which is 3000lbs+ ?

MichaelBluejay · 2015-12-14 00:48:53

rich00 wrote:

You assume that a cyclist eats rice or beans to replace the calories burned.

I don't see where I suggested any such assumption.

rich00 wrote:

You think that hot water for a typical shower is insignificant? Have you measured it?

Of course I measured it. And yet again, I mentioned the shower angle specifically in the article, which it doesn't seem you've read carefully.

Maybe you didn't know, but while I run this website, I'm better known for my work on documenting household energy use. Here's my dedicated page on figures related to water heating. As per that page, 8.33 BTU per 1°F rise x 45°F rise (59°F to 104°F) x 10 gallons ÷ 62% efficiency for the gas water heater is 6046 BTU. With 114k BTU in a gallon of gasoline, a shower is the equivalent of 0.05 gallons of gas. The average car uses five times that for a five-mile trip.

Maybe I should clarify what I mean by "insignificant". In this case, I mean that adding in the energy for extra showers doesn't change the conclusion for comparing biking to driving.

rich00 wrote:

What about the energy to cook your rice and beans? That ALONE is more energy than the food will provide you in miles compared to what an ebike will use.

Okay, two issues here:

(1) How significant is the energy used to cook food?
(2) How efficient are electric bicycles?

Let me take them in reverse order. First, yes, eBikes are crazy efficient, even more efficient than pedaled bikes. That is, an eBike uses less energy even without any pedaling, than a traditional bike uses once you count the energy needed to make the food. Anyone who thought that en eBike was “cheating” from an eco-perspective can rest easy.

Someday I should add ebikes to the transpo energy calculator, but until then here are some numbers in brief: human efficiency at turning food into work is only about 15%, while an electric bike (without pedaling) is about 54%. (78% for charging/discharging the battery, 75% efficiency for the motor, and 7.2% in transmission losses) So from those rough numbers, eBikes should be in the neighborhood of three times more efficient than human effort in biking. When I run the numbers a little more, I figured this many gallons of gasoline used per 100 miles:

eBike: 0.6 (no pedaling; includes the energy to make the battery)
Bicycling: 1.3 (1.0 vegetarian, 0.7 vegan)
Walking: 3.2 (2.4 vegetarian, 1.7 vegan)
Driving: 5.0 (U.S. avg. mpg)

Of course the caveat is that we can’t technically figure the energy used by the ebike in gallons of gas, because electricity isn’t produced by gasoline, so I figured the BTUs required to make the electricity using the U.S. average mix of fuels (e.g., ~50% coal, 22% natural gas) and then compared it to BTUs in gasoline, which will have to do. We *could* compare the CO2 emissions from the energy used, but we’ll save that for a different day.

In any event, the point is, less energy is used by using the eBike as a scooter than by actually pedaling a regular bike.

On the next issue, rich00 brings up a good point that we should consider the energy to cook the food, not just to produce and transport it. Of course, on one extreme, things like fruits and raw vegetables require no energy to cook. But on the opposite side, things like beans take quite a lot. I just calculated that the energy to cook the beans required for a five-mile bicycle ride is the same as the energy burned by a typical car for the same five miles. That’s disheartening, for sure. Now, that’s for the *most* energy-intensive cooked food, and most foods will take considerably less energy to cook, so biking will still beat driving in most cases on an energy basis. But not in all cases. And of course, cars cause problems way beyond the amount of energy they use and pollution they generate, even if they're slightly more efficient on *some* trips (almost certainly a minority of trips).

Anyway, I guess I should factor in cooking energy to the calculator someday, too. But between that, and putting multiple people in the car for the trip, and more efficient cars, cars are going to use less energy than biking in an increasing number of cases. I guess that's even more reason to add eBikes to the calculator also, since eBikes are even more efficient than pedaled biking.

For those who want to see my work on the cooking calc., especially since I might have erred:

• 0.05 therms per hour (estimate) on a burner x 60 minutes for a pot of beans is 3 therms.
• 4 cups of beans is 2679 calories.
• At 420 calories per hour for cycling at 9mph, a 5-mile trip would take 5/9 x 420 = 233 calories, or 0.09 of the pot of beans, or 0.27 therms.
• At 100k BTU per therm, that's 27k BTU to cook the food for five miles of cycling.
• At 114k BTU per gallon of gas, that 0.25 gallons, again with the caveat that natural gas ≠ gasoline, but we make do with what we have.

glockdoc · 2015-12-14 10:35:23

Long thread so am not sure if you take into account that electricity, for the most part, is produced by fossil fuels. The best I can remember is that the typical nat gas, oil, or coal fired power plant is roughly 33% efficient and during peak demands (usually a/c season) power plants actually use jet engines coupled to generators to fill the hole. Guess you can argue solar/wind/water but unless you are completely off the grid you could instead be selling it back to the power company thus reducing fossil fuel usage.

MichaelBluejay · 2015-12-14 14:36:23

Yes, I used the average U.S. mix of fuels for making electricity in my calculations. Here's a pretty chart showing that mix.

Bicycle Austin forum

#1 2013-07-03 11:11:21

Miles per gallon from bicycling

#2 2013-07-06 11:34:03

Re: Miles per gallon from bicycling

#3 2013-07-06 22:42:02

Re: Miles per gallon from bicycling

#4 2013-07-07 00:23:50

Re: Miles per gallon from bicycling

#5 2013-07-07 09:56:33

Re: Miles per gallon from bicycling

#6 2013-07-07 12:30:03

Re: Miles per gallon from bicycling

#7 2013-07-07 13:33:57

Re: Miles per gallon from bicycling

#8 2013-07-08 19:35:03

Re: Miles per gallon from bicycling

#9 2013-07-10 13:44:27

Re: Miles per gallon from bicycling

#10 2013-07-10 18:53:24

Re: Miles per gallon from bicycling

#11 2013-07-25 18:05:29

Re: Miles per gallon from bicycling

#12 2015-12-14 00:48:53

Re: Miles per gallon from bicycling

#13 2015-12-14 10:35:23

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#14 2015-12-14 14:36:23

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