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Old 09-24-12, 06:20 AM   #1
Winfried
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Energy spent to bring bike from full stop to full speed?

Hello

I'm curious to know how much energy an average cyclist spends to bring an average bicycle to an average speed in the city from a full stop. Does someone have some data?

The reason I ask, is to explain to motorists that the reason some cyclists would like to be allowed to slow down and make a right-turn or even go straight through in the absence of pedestrians and cars, is simply that, unlike cars, it takes physical efforts to get the bike rolling again, especially when going up-hill and/or when carrying stuff. Besides the fact that the rules of the road were written for motorized vehicules.

Thank you.
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Old 09-24-12, 06:55 AM   #2
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From Wiki:
For example, one would calculate the kinetic energy of an 80 kg mass (about 180 lbs) traveling at 18 metres per second (about 40 mph, or 65 km/h) as

E[SUB]k[/SUB] = (1/2) 80 18[SUP]2[/SUP] J = 12.96 kJ

I think the issue with stop signs is safety. It's safer to slow to 2-3 miles, look for cars and accelerate through the intersection than it is to come to a full stop. Starting from a foot-down position is much slower, more exposure time, that slowing down and a cyclist has much better visibility, is much closer to the front of the vehicle, than a driver so the issues are not the same. This is exacerbated on a tandem which is even harder to get going from a true stop.
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Old 09-24-12, 09:56 AM   #3
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Yes. I generally treat stop signs as yields and red lights as stop signs, and I do it with no apologies.

It's easy enough to calculate and express in terms of Joules, but I don't think there is any way to convey that in a meaningful way to a non-cycling public. You might say it's equivalent to the energy needed to power a 100W light bulb for 1 minute (to a 12 m/sec = 27 mph) or something, but that still pretty meaningless, and in fact may not seem like much.

Basically, motorists want you out of their way, preferably off the roads, and certainly not entitled to do anything they're not allowed to do. If it's going to change, it has to start with changing the laws and driver education.
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Old 09-24-12, 10:15 AM   #4
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Do report, if you have had a citation , for not coming to a full stop.
and what was your argument before the judge, that was successful?

Might not have been a conservation of momentum defense..
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Old 09-24-12, 11:05 AM   #5
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There are two ways of thinking about this. Obviously it takes more energy to stop motion and restart it than to maintain it. There are also the issues of the law and annoyance to motorists that end up passing you many times between the block only to be passed at the intersection. Conservation of energy is important if you want to get the most of your ride and ride greater distances. I often add energy on selected down hills when I know there is no stop at the bottom and use the free energy to help me up the next hill. One of the reasons for tall gears that might be too tall to ride in on level ground without mashing. There are no methods to store energy other than thru inertia or thru planning, when it’s output. (storing it in your body) if I’m coming up on a place I know at best I will have to do a momentary stop or almost stop. If I’m not in a hurry to get someplace I tend to stop outputting save the brake pads and coast to the point almost stopping. The little rest coasting will save some energy you can use for the takeoff.

The same method does apply to your car also. Riding bikes has made me a much better driver in terms of fuel usage. Timing lights, coasting up to a red, etc. can save a lot of fuel and wear.

The laws of physics don’t equal the laws of LEO.
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Old 09-24-12, 12:08 PM   #6
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It takes far more energy to get a car up to (and down from) speed. More mass. So by that argument cars should never be required to come to a full stop--and all cyclists and pedestrians should yeild to automobiles.

Instead I'd point out that the energy required by a driver to press down on a throttle or brake pedal is trivial as compared to the energy required by a bicyclist to get back up to speed. So much so that numbers aren't required, since it'd be hard to quantify anyhow (how much energy does it take to move your toe?).

You probably won't win an argument, but if you wanted to try, I'd take a different tack. I'd point out that if you were in a car, you'd be adding that much more to road congestion.
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Old 09-24-12, 12:43 PM   #7
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I think supton is on to something. All we need is to have the government mandate brake and gas pedal forces on all cars. If when the driver was allowing the car to slow itself and accelerate slowly little pedal force would be required as more aggressive driving habits were shown the force would go up and drivers being inherently lazy would soon grow tired and alter their habits thus saving gas.

That’s kind of where autos started now that I think about it.
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Old 09-24-12, 12:45 PM   #8
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The amount of energy is irrelevant. If you're worried about how much further another 10 kJ can take you on your ride, you're in over your head on a bicycle.
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Old 09-24-12, 08:44 PM   #9
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Quote:
Originally Posted by Winfried View Post
Hello

I'm curious to know how much energy an average cyclist spends to bring an average bicycle to an average speed in the city from a full stop. Does someone have some data?

The reason I ask, is to explain to motorists that the reason some cyclists would like to be allowed to slow down and make a right-turn or even go straight through in the absence of pedestrians and cars, is simply that, unlike cars, it takes physical efforts to get the bike rolling again, especially when going up-hill and/or when carrying stuff. Besides the fact that the rules of the road were written for motorized vehicules.

Thank you.

Before attempting to debate motorists on this topic, maybe you should start with a less lofty goal and try and explain the reasonining to me (a cyclists); why we shouldn't have to use stop signs?
My initial impression from the stop/go/effort argument is that it implies you are either lazy or don't know how to gear down as you approach stops -not a great foundation to stand on.
Are there more compelling reasons?

Car and bike collide at intersection because bike rolls stop; cyclist dies.
Car and bike collide at intersection because car rolls stop; cyclist dies.
....
Rather than tell motorists why cylists should be allowed to roll stops; I'd prefer to always obey them and instead insist that cars stop rolling them....
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Old 09-24-12, 10:07 PM   #10
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The amount of energy is irrelevant. If you're worried about how much further another 10 kJ can take you on your ride, you're in over your head on a bicycle.
Ok, now repeat the stop/start every 300 ft or so for 8 or 10 miles and let me know how you feel. I don't get the benefit of timed lights like motorists. There are several sections of my commute where stops signs are so close together such that if there are two or three cars queued, the next one will block the intersection. Now repeat for 1/2 mi.

Last edited by jsdavis; 09-24-12 at 10:11 PM.
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Old 09-24-12, 10:22 PM   #11
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Originally Posted by xenologer View Post
'''''
My initial impression from the stop/go/effort argument is that it implies you are either lazy or don't know how to gear down as you approach stops -not a great foundation to stand on.
........
Maybe you should think a bit beyond your initial impression. Try accelerating a tandem every 1/4-1/2 mile from a standstill on a long ride in an suburban environment. I can get my single up to speed in a few pedal strokes, not so the tandem.

50% of cars(or you pick a number) don't come to a full stop at stop signs. I'll stand by what I posted earlier: getting across intersections is a big hazard and coming to a full stop can greatly increase exposure time. The big difference between car and bicycle is that I'll proceed through a 4-way stop (after stopping, of course) on a car with an intersecting car approaching at speed assuming he'll stop; I won't do this on a bicycle unless I absolute know I can get through the intersection before he gets there.

Last edited by rdtompki; 09-26-12 at 10:09 AM. Reason: clarification
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Old 09-24-12, 10:24 PM   #12
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Besides the fact that the rules of the road were written for motorized vehicules.
Uhhh yeeeeah! Blow through a stop sign next time you see a cop eating a donut parked on the side of the road.
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Old 09-25-12, 05:22 AM   #13
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Thanks for rdtompki for how to compute the kinetic energy. I'll try and see if I can find how to translate this in terms of gas needed for a car to perform the same task so that it's meaningful for a motorist.

I didn't get fined but did get stopped a few times by the police because I went through a red light, although I always do this slowly, with no cars and pedestrians in sight. A friend of mine did get fined, though (90/US$117), and the fine is the same as if a car blew the red light since both are considered the same, legally. Stupid, but legal.

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Ok, now repeat the stop/start every 300 ft or so for 8 or 10 miles and let me know how you feel.
Exactly. I guess some of the contributions come from people who ride on week-ends, while I mostly ride to commute, in a big city with red lights very close to each other. Hence the need to explain to motorists in terms they can understand (read: gas/money) why cyclists would like to be allowed to ignore red lights when it's safe to.
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Old 09-25-12, 07:08 AM   #14
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It takes far more energy to get a car up to (and down from) speed. More mass. So by that argument cars should never be required to come to a full stop--and all cyclists and pedestrians should yeild to automobiles.
This argument is actually occasionally used in our local discussions regarding traffic laws. One can quickly point out that all small automobiles should then yield to larger automobiles etc. Once it gets to the point where SUVs should yield to buses, car advocates usually shut up.

It's a bit similar than the claim that fluid traffic flow means less stop/go, which means less fuel consumption, pollution and wear. Therefore, we should build more and wider roads to make our cities "greener". And get rid of all the traffic lights too, especially when they're on MY route.

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Old 09-25-12, 07:53 AM   #15
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The problem with all these arguments is that not everyone can accurately judge what is 'safe'. And the objective of making a stop is SUPPOSED to be to look both ways and make sure things are clear. Too many people think that after making that obligatory stop - they have the right to go. Without looking.

Some people are just dumb, or unlucky, or both:

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Old 09-25-12, 08:42 AM   #16
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Um, you are riding the bike to get exercise aren't you? What is a stop but a good chance to get exercise? Getting back up to speed again doesn't take THAT much effort.
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Old 09-25-12, 01:22 PM   #17
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Ok, now repeat the stop/start every 300 ft or so for 8 or 10 miles and let me know how you feel. I don't get the benefit of timed lights like motorists. There are several sections of my commute where stops signs are so close together such that if there are two or three cars queued, the next one will block the intersection. Now repeat for 1/2 mi.
If it's too hard for you, you're in over your head.
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Old 09-25-12, 03:03 PM   #18
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Quote:
Originally Posted by Juha View Post
This argument is actually occasionally used in our local discussions regarding traffic laws. One can quickly point out that all small automobiles should then yield to larger automobiles etc. Once it gets to the point where SUVs should yield to buses, car advocates usually shut up.

It's a bit similar than the claim that fluid traffic flow means less stop/go, which means less fuel consumption, pollution and wear. Therefore, we should build more and wider roads to make our cities "greener". And get rid of all the traffic lights too, especially when they're on MY route.
I think the way to make the point is that if you have to stop and go so many times during an average commute, you'll be so tired that the next day there'll be another car participating in the gridlock in front of them.
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Old 09-25-12, 05:49 PM   #19
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I think the way to make the point is that if you have to stop and go so many times during an average commute, you'll be so tired that the next day there'll be another car participating in the gridlock in front of them.
So its less frustrating to sit in a car for an extra hour than to stop at stop signs on a bicycle? So where do you draw the line? If its OK to roll through a stop sign - how fast? Or is it maybe OK to blast through stop signs since its OK to roll through them anyway. Or if its OK to roll through stop signs does that mean bicycles automatically have a right of way?

This is more than about stopping. The objective is to promote personal and public safety by defining acceptable behavior. Its a double edges sword because it also enables responsibility to be assigned in the event of an 'accident'. A stop sign is supposed to be accompanied by looking in all directions to make sure its safe to proceed. In the event of an accident, its much easier for witnesses and police to establish whether someone actually stopped than to prove that they did or didn't look both ways.

And if thats too much to handle - there's always the bus.
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Old 09-25-12, 08:59 PM   #20
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I'm one of those kooky riders that don't believe I'm entitled to special privileges outside of the law.

I also wouldn't feel entitled to run stop signs and lights if I was driving a 4 cyclinder car versus a big V8 for the same reason you cite for a bicycle.

But that not withstanding.....

What I'm really curious about is....exactly who are you going to "explain" this too? Random people stopped at intersections? Are you going to print the computations on the back of your t-shirt ? Exactly what do you expect to come of this?

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Old 09-26-12, 12:35 AM   #21
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I think the way to make the point is that if you have to stop and go so many times during an average commute, you'll be so tired that the next day there'll be another car participating in the gridlock in front of them.
Meh. Stopping and going is just traffic IMO. I do appreciate the fact that my commute is long enough to have both city riding (complete with repeated stops and all) and stretches of uninterrupted, grade separated MUP by the seaside. Maybe I'd feel different if I had to ride in city environment only.

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Old 09-26-12, 06:43 AM   #22
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Riding is different than driving a motorized vehicle. A car doesn't get tired. It can stop and go all day long. Maybe the spark plugs will foul up a bit in traffic like Manhattan and performance will start to drag.

It takes energy to power a bike and the more stop and go, the more a rider will lose that snap. It might take the same power to reach a certain speed, but the rider will tire out of the repeats.
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Old 09-26-12, 08:49 AM   #23
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Stopping and starting is good exercise. My cycling power has increased in large part due to all those red light->green light starts.
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Old 09-26-12, 01:25 PM   #24
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Ok, now repeat the stop/start every 300 ft or so for 8 or 10 miles and let me know how you feel. I don't get the benefit of timed lights like motorists. There are several sections of my commute where stops signs are so close together such that if there are two or three cars queued, the next one will block the intersection. Now repeat for 1/2 mi.
Where is it that you ride that you can even find roads like that? Even if there is a cross street, normally you don't get a light unless you hit another major cross street. You can't be getting a major cross street every 100 yards for 8 to 10 miles can you?

I would try to find another route.
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Old 09-26-12, 08:57 PM   #25
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Stopping and starting is good exercise. My cycling power has increased in large part due to all those red light->green light starts.
That's my general attitude, and stoplights give me a chance to practice low speed balancing.
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