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  1. #1
    Senior Member ken cummings's Avatar
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    Total system efficiency bike vs car?

    I got into a discussion with a non-cyclist on a bus recently. I alleged that a cyclist crossing the country would only use the equivalent of 1.5 gallons of gas while a motorist would take 200 gallons or more. He countered with "How much fuel would be needed to produce and deliver the 3 weeks to three months of food you would be using? A car can cross in a week or less." Good point. A buddy and I crossed coast to coast in 50 hours in a van with a bed in it. Has anyone worked out the total energy costs of cycling, not just the energy loss in wind and rolling resistance?
    This space open

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    No longer in Wimbledon... womble's Avatar
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    The scenario proposed is way too vague for a meaningful answer. For instance, why assume that food has to be delivered from some arbitrary point to the cyclist? A tourer typically buys food from wherever he stops off. That food is sourced either locally, or as part of a national/international supply chain. So where do you draw the line of 'cycling' and 'everything else'?

    If you want to be neat about it, then total energy cost really is just the energy inputs of riding. One might argue that other inputs should also be considered- welding, tube manufacture, raw materials transportation, mining and ore refining. But once you get into that kind of territory, measurement becomes so difuses as to be meaningless.

  3. #3
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    Idk sounds like a similar discussion I had with a coworker today. I was thinking wow biking this last month I've put 230 miles on my bike I bet a save a ton of gas. Yeah ... with my suburban I saved 60 bucks at 12mpg, with his little car getting 30mpg it's more like 20..not as much as I hoped.

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    Feral Member Nicodemus's Avatar
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    I don't have detailed numbers so hopefully someone will respond with solid info for you, but I'm positive that driving is much more energy intensive. The BTUs available in gasoline are very very high. To use that equivalent in person-fuel would take a lot. Many people don't seem to appreciate how much energy is in gasoline or how inefficient cars are (even the "super" high mileage ones). There's just no comparison.

    Plus, for a fair comparision the driver needs to go without food for the whole time the cyclist is crossing the country.
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    CRIKEY!!!!!!! Cyclaholic's Avatar
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    Did he assume that the driver of the car doesn't eat when he's not driving across the country? sure the cyclist eats while cycling for a month but so does the driver after he's finished his drive, but the ammount of energy in the food is insignificant to the evergy differential in moving a couple of tonnes of steel at 50+ mph compared to a cyclist at 15 - 18 mph.

    From a total energy efficiency viewpoint cycling is significantly more energy efficient per unit of distance travelled, even taking things like food for the cyclint into account. I don't have the numbers at hand but I did go through the exercise of analysing it a while back.
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    http://auto.howstuffworks.com/question527.htm

    "If you look at a page like this calorie chart, you will find that a person riding a bicycle at 15 miles per hour (24 km per hour) burns 0.049 calories per pound per minute. So a 175-pound (77-kg) person burns 515 calories in an hour, or about 34 calories per mile (about 21 calories per km).

    A gallon of gasoline (about 4 liters) contains about 31,000 calories. If a person could drink gasoline, then a person could ride about 912 miles on a gallon of gas (about 360 km per liter). Considering that a normal car gets about 30 miles per gallon, that's pretty impressive!

    The people riding in a race like the Tour de France are riding more like 25 mph. Because air resistance rises very quickly with speed, they are burning about three times more calories -- something like 100 calories per mile. In a 100-mile stage of the tour, a racer might burn something like 8,000 to 10,000 calories in one day! So they are getting only about 300 miles per gallon."

    I think that for the last paragraph, a distinction has to be made between flat stages versus mountain stages. In a flat stage, unless the rider is in a small or solo breakaway, or working to pull the peleton to catch a breakaway, they'll be protected by the draft most of the way. On a mountain stage, the energy expenditure will be much higher per mile on a climb.
    Last edited by Mach42; 07-10-07 at 02:07 AM.

  7. #7
    Cycle Year Round CB HI's Avatar
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    Tell him since he does not count the food he eats, he cannot eat for the 3 weeks to 3 months the cyclist is riding across country.
    Also, does someone have to deliver his gasoline to stations across the country, or does he have a 200 gallon tank?

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    The real question is what resources are needed to be expended to maintain the smooth road surface a long distance ride would require. Additionally cyclists probably make more use of lodging, food, and rest areas. My guess is the most efficient way cross country is either jumbo jet or high speed rail.
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    This subject came up in the Car Free forum recently. Here's the link. There are some good posts and some links to articles on the subject. miles/gallon bad measure of efficiency
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  10. #10
    Senior Member maddyfish's Avatar
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    It doesn't matter. You eat whether you are cycling or not. What do you think is going to happen, you're not going to eat when you're not on your bike? sure you'll eat more when on a long ride, but I'd guess still less than the average fat-#ss who doesn't ride.
    Not too much to say here

  11. #11
    Senior Member mlh122's Avatar
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    When i'm not riding aggressively like in the winter, i might ride 5 to 10 miles per week running errands, but my longer commutes i'll do by car. I eat about 1000 to 1500 calories a day. If I'm riding a lot, like daily 95% bike commuting or a 4 day MTB trip i'll eat 3000 to 3500 calories. Some of the heavier people at my work will have a 2500 calorie lunch to go with their 100% sedentary lifestyle.

    Also, i read somewhere that a human uses 30 to 60 calories to ride 1 mile on flat land, depending on bike efficiency and the rider's weight and fitness. A typical car consumes 1400 to 1500 calories to drive 1 mile.

  12. #12
    Cries on hills supton's Avatar
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    I dunno. I've traveled with my family in the car. 4 people, enough luggage for a weekend trip, so say 400lb of people, and 50lb luggage. Going my "let's get there" speeds, I could probably get 42mpg; but diesel has about 10% btu's (or calories) than gasoline.

    In what terms of efficency do you wish to determine? Classical power out / power consumed doesn't quite work properly here, as car mpg doesn't go down (much) with number of people; but obviously, it's more "efficent" if I carpool. Anyhow, if a gallon of diesel has about 34,100 calories per gallon, I would consume 812 calories per mile, while moving 4 people and 50lbs luggage. Compared to the cyclist(s), 0.049 cal/min/lb x 450lb x 60min/hr / 15mph = 88.2 cal/mile.

    Now, that appears to be 9x worse for the car. Of course, my average speed is about 4x that 15mph of the cycles. I'm not sure what I'd get for cal/mile had I driven 15mph; but I doubt it'd go through the roof. OTOH, if wind drag goes up by the square of velocity, the the cyclist (if they could go that fast) should be consuming 16x the cal/mile, for a clear win for the car!

    [And yes, I know, I drive my car by myself to work, bad me. I'm just adding light in a different perspective. Although, instead of diesel I could be burning biodiesel, so maybe it's not that far off of a comparasion...]
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  13. #13
    You need a new bike supcom's Avatar
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    If you are comparing total energy cost, then you need to be careful to include only the energy required to perform the two tasks. Since, as has been pointed out, the cyclist eats everyday, you would calculate only the total energy used to power the bike during the trip. Let's say, that's 34 cal/mile. To that, you need to factor in the energy cost of the production and distribution of those calories. This is probably 2-3 times the energy value of the food. Let's take 3x for the sake of argument.

    We can ignore food for basic metabolism, and energy costs of other living activities such as lighting, air conditioning, etc. since these are required regardless of the activity.

    So, for a 3000 mile trip across the country, it would require 34 x 3000 x 3 = 306,000 calories.

    Now, consider the automobile. Let's say the auto gets 35 mpg (highway driving) for the same distance and assume that a gallon of gasoline has 31,000 calories. Gasoline production and distribution only requires about 15% of the energy delivered (very efficient).

    So the total energy required to drive across the country would be: 3000 / 35 * 31,000 *1.15 = 3,055,714

    From this analysis, unless we are very far off on our estimates, there is no question that riding a bicycle across the country would be far more energy efficient that driving a car. In the case of multiple people travelling together, this analysis would indicate that for 3 people sharing one car, the energy cost would be about the same as for those three to ride bikes.

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    If you want to get technical the driver of the car also burn calories just from driving, so that should be included in the total expenditure of the system. This site lists driving a car as expending 125 calories an hour. Assuming the cross country trip is NY to LA, the distance (according to Mapquest) is about 2793 miles, at 65 mph, you would need to drive about 43 hours, getting a total of 5375 calories just to keep the driver driving.

  15. #15
    Videre non videri
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    Quote Originally Posted by fuerein
    If you want to get technical the driver of the car also burn calories just from driving, so that should be included in the total expenditure of the system. This site lists driving a car as expending 125 calories an hour. Assuming the cross country trip is NY to LA, the distance (according to Mapquest) is about 2793 miles, at 65 mph, you would need to drive about 43 hours, getting a total of 5375 calories just to keep the driver driving.
    No, supcom excluded the energy required in excess of the energy required for riding, so forget about the driver's energy usage.

    But if we want to get really technical, we would have to look at the true total system efficiency. That includes not only the efficiency of the fuels, but also the total energy spent during the production of the vehicles, and the energy spent manufacturing and transporting "wear and spare" parts. Here, we have to include the projected energy needs for the full life of each vehicle, divided by the total distance they end up travelling at the end of their usefulness. This extra energy needs to be added to the distance in the example supcom provided.

    A typical car probably weighs around 100 times what a typical bike weighs. If we assume that that also means it requires 100 times more energy, the bike would have only 1/100 of the unit distance cost of the car. But if the bike travels 1/100 of the distance the car does during their respective lives, the unit distance cost becomes identical for both vehicles.

    What the actual figures are, I don't know...

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    Quote Originally Posted by CdCf
    No, supcom excluded the energy required in excess of the energy required for riding, so forget about the driver's energy usage.

    But if we want to get really technical, we would have to look at the true total system efficiency. That includes not only the efficiency of the fuels, but also the total energy spent during the production of the vehicles, and the energy spent manufacturing and transporting "wear and spare" parts. Here, we have to include the projected energy needs for the full life of each vehicle, divided by the total distance they end up travelling at the end of their usefulness. This extra energy needs to be added to the distance in the example supcom provided.

    A typical car probably weighs around 100 times what a typical bike weighs. If we assume that that also means it requires 100 times more energy, the bike would have only 1/100 of the unit distance cost of the car. But if the bike travels 1/100 of the distance the car does during their respective lives, the unit distance cost becomes identical for both vehicles.

    What the actual figures are, I don't know...
    However, the car cannot drive itself. I agree that not counting passengers is fair. However the car requires a driver and the driver burns energy. Thus it is fair to include the driver's energy expenditure in total energy usage required to perform the task. The passengers are not adding anything to the task, the driver is.

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    But we've already excluded the energy cost for staying alive from both the driver and the rider. If you didn't understand it the first time, read through supcom's post again.

  18. #18
    Senior Member edp773's Avatar
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    Quote Originally Posted by CdCf
    But we've already excluded the energy cost for staying alive from both the driver and the rider. If you didn't understand it the first time, read through supcom's post again.
    Quote Originally Posted by supcom
    Let's say, that's 34 cal/mile. To that, you need to factor in the energy cost of the production and distribution of those calories. This is probably 2-3 times the energy value of the food. Let's take 3x for the sake of argument.

    We can ignore food for basic metabolism, and energy costs of other living activities such as lighting, air conditioning, etc. since these are required regardless of the activity.
    Quote Originally Posted by fuerein
    If you want to get technical the driver of the car also burn calories just from driving, so that should be included in the total expenditure of the system. This site lists driving a car as expending 125 calories an hour. Assuming the cross country trip is NY to LA, the distance (according to Mapquest) is about 2793 miles, at 65 mph, you would need to drive about 43 hours, getting a total of 5375 calories just to keep the driver driving.
    Sorry CdCf, it may be semantics, but he is comparing apples to apples. The riders burns 34 calories per mile above sustenance and the driver burns 145 calories per hour above sustenance. 145/65 = 2.23, therefore, the driver burns 2.23 calories per mile by driving.

    But, you can also argue that is not comparing burning calories to burning petroleum directly.
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    Videre non videri
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    You mean that sitting on your butt and moving your arms and feet once every couple of minutes takes that much extra energy? No way...

  20. #20
    Prefers Cicero cooker's Avatar
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    Quote Originally Posted by maddyfish
    sure you'll eat more when on a long ride, but I'd guess still less than the average fat-#ss who doesn't ride.
    You'd guess wrong.

  21. #21
    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by supcom
    If you are comparing total energy cost, then you need to be careful to include only the energy required to perform the two tasks. Since, as has been pointed out, the cyclist eats everyday, you would calculate only the total energy used to power the bike during the trip. Let's say, that's 34 cal/mile. To that, you need to factor in the energy cost of the production and distribution of those calories. This is probably 2-3 times the energy value of the food. Let's take 3x for the sake of argument.

    We can ignore food for basic metabolism, and energy costs of other living activities such as lighting, air conditioning, etc. since these are required regardless of the activity.

    So, for a 3000 mile trip across the country, it would require 34 x 3000 x 3 = 306,000 calories.

    Now, consider the automobile. Let's say the auto gets 35 mpg (highway driving) for the same distance and assume that a gallon of gasoline has 31,000 calories. Gasoline production and distribution only requires about 15% of the energy delivered (very efficient).

    So the total energy required to drive across the country would be: 3000 / 35 * 31,000 *1.15 = 3,055,714

    From this analysis, unless we are very far off on our estimates, there is no question that riding a bicycle across the country would be far more energy efficient that driving a car. In the case of multiple people travelling together, this analysis would indicate that for 3 people sharing one car, the energy cost would be about the same as for those three to ride bikes.
    Your estimate of the fuel economy is off. Current US fleet average fuel economy is 27 mpg so the kcal needed is closer to 4,000,000 (rounding for clarity).
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  22. #22
    Senior Member edp773's Avatar
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    Quote Originally Posted by CdCf
    You mean that sitting on your butt and moving your arms and feet once every couple of minutes takes that much extra energy? No way...
    The link says 125 calories per 1.5 hours, so 125/97.5 = 1.28 calories per mile. I have no idea about the sites accuracy. I find it hard to keep a 65 MPH average counting stops for fuel and bathroom breaks.
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  23. #23
    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by cyccommute
    Your estimate of the fuel economy is off. Current US fleet average fuel economy is 27 mpg so the kcal needed is closer to 4,000,000 (rounding for clarity).
    I meant to get back to this but I got off to other things. If you consider that the average fuel economy is based on the EPA dyno test which only includes a short period at 65 mph and an average of 48 and doesn't take windage into account (other then by calculation) the average fuel economy is going to be even lower.

    Additionally, most people don't do cross country trips in compact cars but are more likely to use a larger lower mileage vehicle so the fuel usage would be even higher. If you use a 17 mpg van, the energy usage is going to be closer to 6,250,000 kcal. If a 14 mpg SUV is used, the kcals are 7.6 million. If you do it in an RV, you're looking at an incredible 20 million kcal

    Another way to look at it is to consider that for the caloric usage of even a high mileage car, the cyclist could cross the country 9 times, for the median mileage car it's around 11 times, for the van it's 20 times and for the SUV it's a whopping 25 times and for the RV it's a positively astounding 67 crossings

    So of course a bicycle is more energy efficient
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  24. #24
    Footballus vita est iamlucky13's Avatar
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    Totally apples and oranges. Not worth getting in anything more than a drinking argument over.

    There's some pretty good economies of scale in the US agricultural and commercial transportation industries. A semi-truck could easily haul 20 tons worth of food.
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  25. #25
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    Quote Originally Posted by Mach42
    On a mountain stage, the energy expenditure will be much higher per mile on a climb.
    Yes, but it will be 0 on the descent! WHEEEEEEEEEEEEEEEEEEEE!!!!!!!!!!!!!!!!!

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