live311

That's what the Road Cycling Forum description claims. In terms of energy input and output, is there any machine more efficient than a dedicated road bicycle? If so, why doesn't it power our cars and household appliances or heat our homes? Would you consider another source of energy to be more efficient? Let's not limit the discussion to human-powered machines. This might require input from a real math geek, which I am not

Consider the fact that the average internal combustion engine operates at a peak efficiency of about 20%, in terms of turning the chemical energy in the fuel into mechanical energy to propel the vehicle/run the machine it's attached to. Most of the energy is lost to heat and friction. Solar powered electric motors require large panels and lots of space-age materials to make them light enough, and forget about using them at night without heavy batteries, so they are not feasible from an economic or practical standpoint for consumer use.

Hybrid vehicles use advanced technology to reclaim lost energy from the decelertion of the vehicle and store that energy in batteries. This is why hybrids get better mileage with city driving than with highway driving. A gasoline engine takes over when the electric motor can't handle the load.

A bicycle's efficiency would probably have to be calculated in terms of calories burned vs. wattage generated by the rider and speed. And what makes a road bike more efficient than a hybrid, a recumbent, or a mountain bike on slicks? Would you consider a time trial or triathlon bike to be more efficient than a road bike?

So I ask my fellow roadies: Is a road bicycle really the most efficient machine known to man, or is our mighty founder feeding us crow?

martin_j001

Didn't you see that old ESPN commercial where Lance provided power for the building?

Phantoj

What is a "machine"? A pair of pliers is a machine. A wedge is a machine.

I have seen a graph that showed km/kJ or some such measure of energy efficiency for different methods of passenger transportation, including walking. Cycling was the most efficient.

my58vw

The only true way to answer this question is to look at how many calories are used for the bodies other functions and those used to power the muscles that power the bike. Since 100% of the calories are not used to directly power the bike (some amount like 92% has been thrown around) the motor is not 100% efficient for pushing the bike. Now to live it is nearly 100% efficient. This is important in comparing to other "non human powered" devices as part of efficiency.

Now my understanding that as a "human powered insturment" the road bike is indeed the most efficient machene. Nearly 98% of the rotation motion applied to the pedals is directly translated to forward motion of the bike. The loss is attributed to friction (of the road, BB, chain, hubs, etc) and other issues. Wind resistance for the bike itself is also an interesting question.

Now looking at TT vs road bikes and speed, TT bikes are more efficient because the translate more pwoer to forward motion then to fighting the wind compared to a traditional road bike. Recumbants are also fast for simular reasons.

Speed per calorie burned then the road bike would not be the most efficient machiene, the others would be. We are spliting hairs at this point, so I would not worry about it too much.... just that we can go fast on a road bike...

live311

For the sake of discussion, let's exclude "simple machines," like wedges, levers, pulleys, etc. from our definition and limit it to more complex things that drive modern industry, improve the quality of life, don't fit in your pocket, and require fuel (i.e., an engine or motor of some sort, including humans) to power them.

Kennetht638

The trouble here is that you're defining efficiency differently in each case that you mention. For internal combustion engines, you're talking about how much of the gasoline's energy is turned into crankshaft rotation rather than heat, and then for solar vehicles, you mention weight, which does not affect the efficiency of the solar panels, but rather how much energy it takes to move the vehicle. Then, you mention regenerative braking in hybrids, which is sort of a lurking variable because it can't really be accounted for in a drivetrain/powerplant efficiency test.

What the forum description refers to is (probably) drivetrain efficiency, which is the amount of power put to the ground through your rear tire compared to the amount of power that is input into the pedals. From what I've read, a chain drive is 98-99% efficient, and after that, the only losses are flex in the wheel and tire, which are not all that great. I'm not sure if that actually makes it the most efficient machine known to man, but it is pretty ridiculously efficient. If anything, the track bike would be the most efficient machine, because there are no losses from imperfect chainline or tight bends around derailleur pulleys.

AndrewP

I think the transportation efficiency is expressed in terms of speed and payload moved for a given power input. In these terms the bicycle comes out as the best, and the slower it goes the more efficient it is because less energy is wasted overcoming wind resistance.

live311

Maybe I need to re-think my question. I originally wanted to take everything into account when trying to find an answer, such as fuel efficiency, power-to-weight ratio, power loss due to wind resistance, friction, heat, etc, and maintenance costs. In those terms, I think a road bike would be the most efficient simply due to the relatively low cost of maintenance.

Now that I think about it, if I take a car engine's fuel efficiency into account, I would need to take the human body's fuel efficiency into account, as well. And that opens a whole other can of worms with diet, metabolism, and waste disposal So let me ask it this way: Why does Joe Gardner or whoever wrote the forum description believe that a road bike is the most efficient machine known to man?

sparknote_s

Human powered machines will always be more efficient than things like cars, because ATP (adenosine triphosphate) production in our bodies is 38% efficient. That's the MOST efficient 'machine' if you can call it one.

Monument Man

recumbent bikes are much more efficient than road bikes for simple reasons of aerodynamics. the resistance of the tires along the road and into the wind eats up a tremendous amount of energy expendature and makes road bikes not-quite-as-efficient-as-you'd-think. To achieve a certain speed on a roadbike, you have to push SIGNIFICANTLY harder on the pedals just to counteract the negative forces of wind, air, etc. That means you're expending extra energy to achieve the same level of efficiency.

A solar powered car is an example of an extremely efficient machine, same with those crazy solar powered airplanes that circumnavigate the globe. Very little energy is required to power them for absolutely 1000s of miles, and very little energy is wasted.

If you were cycling in a vacuum you would get much higher levels of efficiency on a road bike. Honestly it's an efficient machine but "the most efficient" is just a gimmick slogan.

Lt.Gustl

newer compound engines are doing a pretty good job at gettting the most energy from fuel, long ago jet engines were super inefficient, but thanks to the jet industry they have gotten alot better as gas turbines power gensets in applications that were ruled by diesel cycle piston engines even boats are now being powered by GT engines, now they are using the super hot exhaust heat from gas turbines to heat water for use by steam turbines, this is very efficient.

https://www.power-technology.com/projects/sannicolas/

there's also helium charged extra fancy stirling cycle engines that get good numbers,

https://www.bekkoame.ne.jp/~khirata/

but from an energy in = energy out standpoint the simpler the better, a good old crowbar will win every time, I also feel that to truly compare efficiency you should include the energy put into building a machine over it's functional lifespan minus the work getting the recycleable materials, so for example you wouldn't include mining the lead for a battery every time it's made since it's always recycled. when you add this some of the super efficient solutions lose big since more energy was put into producing them than will be saved over time vs. the less sophisticated machine, it's the slow and steady wins the race sort of thing.

a bicycle isn't complete till you add the rider and I'm just guessing but I think a tiny diesel engine could outperform a human in terms of energy input=output, especially if you include the cost of the energy since lets say for renewable energy you use soy based biodiesel which is roughly $3 a gallon, a heavy ass india enfield motorcycle using 50 year old tooling that uses a cheap subaru robin diesel generator engine will go 200mpg

https://www.spheral.com/g+/uk/uk-pete.html

clearly it's pretty hard to try to go 200 miles as quickly a motorcycle but also to do it using only $3 of food and water is a tall order and imagine if purpose built for the task something like a super light diesel fully faired feet forward scooter



https://www.eurosoft-ind.demon.co.uk/ffbikes.htm

KevinF

I saw an article on this once a couple years ago, although I forget the source. Might have to do some Google'ing. Anyway, the author was comparing how much of the input energy was converted into forward motion of the vehicle. According to him, bikes were the second most efficient means of transportation ever devised. First place? Sailboats. I haven't spent a lot of time on sailboats, but it takes a surprisingly little amount of breeze to get one moving. It would definitely be an interesting comparison as to which one is more efficient in terms of harnassing all of the available input energy...

va_cyclist

In terms of energy in : energy out, it's tough to beat the efficiency of an atomic bomb. Tiny amount of energy/matter in, unbelievable amount of energy out.

cycleprincess

Not the way I ride. But it sure is fun!!

sparknote_s

For energy input to output, ATP production is THE MOST EFFICIENT cycle known to man.

EDIT: As a comparison, gas and electric motors are around 10 - 20% efficient.

Mr_Super_Socks

In college, I took a course in biomechanics. big mistake since I did it before I had the necessary background in physics and biology, but I remember one and only one thing from that course - and it was AndrewP's transportation efficiency point. Not only was a human on a bicycle the most efficient human transportation machine (that was a footnote in this textbook), it was the most efficient of any living thing in the animal kingdom pound for pound, distance for distance, calorie for calorie - by a longshot.

Mr_Super_Socks

Not sure that's right. aren't you dealing with a huge amount of energy stored over a really long time (even in geological terms) that is then mined and released in a relatively uncontrolled manner? if you only consider the energy to mine the material, you are missing massive amounts of geological energy that goes into its creation. In the same way, oil is very energy rich but it is the result of massive geological and biological forces exerted over long periods of time. thus the burning of oil and the exploding of nuclear material is just an inefficient release of stored energy. and anyway, I don't think bombs are machines , though a nuclear reactor I suppose would be. Others may be able to explain this better and I may have it wrong. Oh, and I think fusion might be a different matter, but someone else would have to explain that (but anyway, nobody has figured out how to do it.)

Mr_Super_Socks

This is only true if you ignore the energy of the wind. If you've ever driven through the wind farms in central CA you can get an inkling of the energy there. and putting a sail on a bike wouldn't make it more efficient, it would just let it take advantage of a massively inefficient, yet totally free, energy source.

Mr_Super_Socks

I think Kennetht638 is right - the "efficiency" not so clearly defined by the "mighty founder" at issue is the bicycle's efficiency at converting energy into forward motion. this is the bicycle's sole, elegant purpose which it does exceedingly well. The reason man on a bicycle is so efficient is for the reason sparknote mentions -- i.e. our bodies convert food into power better than gas engines convert oil into power.