jakemoffatt

I'd like to see a breakdown by type of bicycle.

Can someone...

Figure out the MPG of a 150lb, 6' bike rider going 10mph, 15mph and 20mph average, on a road bike and a mountain bike.

How would you do this?

Figure out how much energy in calories it takes to travel 15mph and then figure out how many calories are in a gallon of gasoline?

Or is it harder than that?

Show your work!

You have 1 hour.

Go!

Boudicca

A gallon of gasoline probably has a lot fewer calories than a gallon of chocolate chip ice cream

Bikepacker67

Not even close!

A gallon of gas has about 30,000 calories.

Basically, if you could drink gas, a gallon would give you enough energy (in theory) to ride about a 1000 miles.

Eatadonut

well then I suppose it depends on the brand of chocolate chip ice cream

chroot

Energy in one gallon of gasoline: 28 399.6359 kilocalories / US gallon.

Sources:
https://www.uvi.edu/Physics/SCI3xxWeb...solineFAQ.html
https://en.wikipedia.org/wiki/Density
https://www.google.com/search?hl=en&l...on&btnG=Search

Calories expended by bicycle riders:

Racing bike, 20 mph: 30 kilocalories / mile = 947 miles per gallon equivalent
Racing bike, 15 mph: 20 kilocalories / mile = 1420 miles per gallon equivalent
Racing bike, 10 mph: 13 kilocalories / mile = 2185 miles per gallon equivalent

Mountain bike, 20 mph: 48 kilocalories / mile = 592 miles per gallon equivalent
Mountain bike, 15 mph: 31 kilocalories / mile = 916 miles per gallon equivalent
Mountain bike, 10 mph: 19 kilocalories / mile = 1495 miles per gallon equivalent

Sources:
https://www.kreuzotter.de/english/espeed.htm
https://www.google.com/search?hl=en&l...on&btnG=Search

- Warren

genec

Chroot... good answer... but you missed the 1 hour deadline. Sorry -10 points.

So basically 1000 MPG... good enough.

af895

Couple of things.

First, a "calorie" as is commonly used is usually refering to a "kilocalorie."

One "kilo-calorie" is the amount of energy required to raise the temperature of one liter of water by one degree celsius.

Not sure how relevant that is but if you think about trying to boil a liter of water (a quart being about 95% of a liter), let's say you start with the water at 15C, you have to raise it by 85 degrees C.

Gasoline has a lot more energy than, say, methanol but I've used a Trangia to boil a quart of water and it really doesn't take much fuel. That's to say, the small amount of fuel in the Trangia (if I just put enough in to boil the water) is about 85 kilo-calories.

*** *** ***
Of more relevance perhaps, here's a page I found last week when I was trying to figure out how many calories I'd burned on a 57km ride. (I'm 6'0" and 236lbs)

https://www.coolnurse.com/calories_burned.htm

There are other sites that actually let you specify weights, heights, body fat % etc which would produce more accurate results if you don't fit the criteria listed on the pre-made matrix.

I conservatively figured for that ride of about 3.5hours, 57km, I burned between 1500 and 1750 kcal as a bare minimum.

I'd have burned a gallon of fuel driving that in a car. I'd say the $1 Udon noodle bowl I ate for breakfast was a lot more "calorie economical" than the fuel! Those huge numbers figured by Chroot sound like they're in the ballpark.

NUTTY!

localtalent

Sadly, I should be getting more miles per gallon of beer I drink...

jakemoffatt

Thanks for the replies everyone (esp. Chroot, very nice breakdown!).

I was thinking about getting a shirt made that had the MPG I get on my bike on the back.

People could drive down the road and see 997 MPG and maybe it would get them thinking?

Thanks again,

Jake

TheKillerPenguin

Damn mountain bikes always wasting fuel. The suv's of the biking world

Lets all go to our LBS and set mountain bikes on fire.

cyccommute 

Pretty close (for the gas not the ice cream). At 12 mph we burn around 45 Calories per mile (around 550 Cal/hr) giving a "gas mileage" of around 670 mpg. Or, in Jelly Donuts, around 2 per hour. Your car gets 120 per gallon. Bummer!

Eatadonut

I like the idea of feeding my car jelly donuts more than drinking gasoline, even if it's not quite as efficient

cyccommute 

Works with WonderBread too. It just takes 18 feet of WonderBread to equal a gallon of gasoline.

NoRacer

Looks like we need restrictor plates on bikes set to 10 MPH for the highest "fuel" efficiency.

.

Eggplant Jeff

I dunno about you guys, but I don't think I can ride even ONE mile after drinking a gallon of gasoline. Maybe there's something wrong with me...

cyccommute 

One of the things that often gets overlooked in discussions of global warming is the heat created by burning a gallon of gasoline. You are correct in your definition of a kilocalorie. It is indeed the amount of heat needed to raise 1 kg of water one degree celsius. Therefore 1 gallon of gas will raise 1kg of water 30,000 C This of course couldn't happen but 1 gallon of gas will raise the temperature of 30,000 kg of water 1C (for the metrically challenged that's about 10,000 gallons of water raised around 2F). Multiply that 1 gallon of gas by millions and we are starting to talk about significant heat poured into our planet! That heat doesn't go anywhere (okay some is lost to space but not that much) but into the air and water. I think that's were the real problems lie. We have millions of heat pumps merrily pumping out heat and we don't have anywhere to put it.


It gets even better because all of that Udon noodle bowl doesn't get converted to energy. A lot of it can't be processed by mammalian guts so it gets "lost" and...um...excreted.

NoRacer

At 150 pounds and 7.5% bodyfat, I have enough fat to outclass a gallon of gasoline:

150 x .075 = 11.25 pounds
11.25 pounds x 3,500 kcals = 39,375 kcals / NoRacer

Once depleted, I'd need a couple McGriddles to top me off.

.

Eggplant Jeff

Actually that's an exhaggeration, cyccommute. A LOT of waste heat is generated, true, but some of that energy (something like 30% I think) is converted into work (I.E. moving the piston in the engine, which is what actually gets you going on your trip to the local donut shop). And then some of that energy is reconverted to heat again when you brake.

You also have to consider that some fraction of that gallon isn't burned anyway, and is just wasted. That's the HC in your emissions, and why you have to change your oil so often.

Still a good point, but it isn't 100% waste heat.

cyccommute 

I had this discussion with the motorhead engineers at the heavy duty vehicle test facility that I work at. They were making the same argument about the heat being converted to work but we all finally came to the conclusion that work ultimately still gets converted to heat anyway.

As for the unburned hydrocarbons, the amount coming out of the tailpipe of modern vehicles is so small as to be insignificant. The unburned HC gets converted to heat in the catalytic converter. That very small fraction that doesn't can be oxidized further in the atmosphere which is a heat process also.

chroot

I'm curious about the real impact of heat exhausted by cars into the environment. Let's see how much the ocean's temperature rises each year due to waste heat from US gasoline consumption.

The US uses about 20 million barrels a day of petroleum, 47% of which is refined into gasoline. This amounts to about 9.5 million barrels a day of gasoline, about 400 million gallons a day, consumed almost entirely in automobiles. That's a volume of about two cubic football fields burned every day. Annually, the volume of gasoline consumed by US automobile engines is almost enough to bury an area the size of Washington, DC's National Mall, from the Lincoln Memorial to the Capitol Building, 300 yards deep in gasoline.

Now, automobiles are roughly 15% efficient, so nearly 85% of the 30,000 kilocalories in each gallon of gasoline ends up in our air and water. (Of course, when the motorist comes to a stop at his or her destination, even the kinetic energy of their automobile is converted back into heat. As has been mentioned in this thread, it's a reasonable approximation that virtually all of the energy used by an automobile is turned into waste heat. The amount of work required to move a person across a flat surface in an unchanging gravitational field is zero.) Enough energy is wasted every year by automobile engines to light a 100W light bulb for five billion years, longer than the Earth has even existed.

The world's oceans have a combined volume of about 1.4 billion cubic kilometers. Dumping all that wasted heat directly into that water would raise its temperature by only about 0.00074 degrees Celsius, less than a thousandth of a degree.

This doesn't sound like much, but consider that transportation only accounts for about 27% of our energy use, and automobile exhaust contributes about half of our carbon dioxide output to the atmosphere. This may be leading to an increased greenhouse effect, which over centuries may dramatically increase the temperature of our planet.

If there's any lesson to be learned, it's that people's minds are boggled by big numbers. Sure, 400 million gallons a day is a big number, but the 1.4 billion cubic kilometers of ocean watter is a lot bigger still. Automobile waste heat is certainly not a positive topic, but, in my opinion, its effect on our planet pales in comparison to that of automobile pollution, environmental damage caused by oil collection, and the political ramifications of billions of dollars wasted in lining the pockets of corporate execs and oil shieks.

Sources:
https://en.wikipedia.org/wiki/Oceans
https://www.eia.doe.gov/mer/pdf/pages/sec11_6.pdf
https://tonto.eia.doe.gov/oog/info/tw...ne.html#demand
https://www.eia.doe.gov/kids/energyfa...nitsindex.html
https://en.wikipedia.org/wiki/New_York_City%2C_New_York
https://www.google.com/search?hl=en&l...29&btnG=Search

- Warren

Eggplant Jeff

Amen, brother!

cyccommute 

It really doesn't matter how efficient the automobile is because ultimately the heat produced gets pumped back into the system. Conservation of energy and all. Consider that all the work gets converted to kinetic energy which eventually will be bleed off by converting it to potential energy (stopping the car, lifting the car to a higher altitude, etc) it still gets converted to heat so where along the way.


But consider that the heat exacerbates the greenhouse effect. All that heat gets reflected and trapped in the atmosphere. Also rather than the heat being pumped into the oceans, which have a high heat capacity, the heat is pumped into the atmosphere which has a much lower heat capacity. The fact that we have large oceans are the only thing keeping our planet from looking like Venus (even before we started messing with the system).

I don't disagree with anything you've said. [edit] I sometimes find that large ridiculous numbers help make the point. That's why I use the Jelly Donut conversion. People don't think about how much energy they use on a regular basis. If you convert it to Jelly Donuts it's silly but it make 'em think!

chroot

I should also mention that my body consumes about a hundred watts of power even when I'm just sitting around the house. That's the equivalent of about 2,000 gallons of gasoline over my expected lifespan of 76 years! It all pretty much gets turned into waste heat, too, since the total intellectual effort I'll exert over 76 years is energetically worthless. I'm such an energy hog, aren't I? I disgust myself.

- Warren

cyccommute 

Don't be so hard on yourself. You are making food for other organisms! I mean you are just sitting there being a habitat for a whole host of icky things and excretin' stuff for other icky things (plus a little CO2 for pruty flowers). Finally, if you happen to get eaten by a bear sometime in that 76 years of worthlessness, you could be helping make little bears, as noble a cause as I've ever heard of

DannoXYZ 

yeah, cars are pretty inefficient, most of the heat generated by combustion goes into heating up the air with exhaust, very, very little of it gets converted into propelling the car down the road.

In dietary terms, calories are usually mistaken for kilocalories. It's often distinguished more correctly as a capitalized Calorie which is the same as a kilocalorie in lab terms.

cyccommute, we also have to account for heating effects of humans riding bikes as well. Body-heat being radiated off to the atmosphere is where the majority of food-stuff calories go. Also converting kinetic energy into heat under braking also occurs on bikes. I'd like to see someone do a PhD study on the effects of human flatulence on the environment and how biking affects that.