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Author Topic: What is the weight of a bicycle?  (Read 8517 times)

Offline Geezer

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What is the weight of a bicycle?
« on: 19/03/2012 06:46:55 »
My bicycle weighs exactly 16kg, but that's when I'm not pedaling it. What does it weigh when I'm zipping along on it at 30km/hour?


 

Offline CliffordK

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Re: What is the weight of a bicycle?
« Reply #1 on: 19/03/2012 07:35:01 »
16 Kilos?
What is it made out of?  Cast Iron?

It will all depend on whether you are riding North, South, East, or West.
As well as depending on whether you are cresting a hill, or entering a valley.

My guess is that the biggest difference you will experience will be the different gravitational constants experienced in different locales, but you may in fact experience a significant difference based on the arc in which you are travelling. 
 

Offline RD

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Re: What is the weight of a bicycle?
« Reply #2 on: 19/03/2012 09:46:22 »
it's not clear to me whether airflow hitting the cyclist will have a net lifting effect:
the air hitting the torso in the posture below will lift, but will be cancelled out to some degree by airflow hitting arms and thighs which will produce down-force ...



[ If you are wearing a duvet cover that's a different matter ].
« Last Edit: 19/03/2012 10:13:44 by RD »
 

Offline Geezer

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Re: What is the weight of a bicycle?
« Reply #3 on: 19/03/2012 18:51:20 »
Maybe I should have said
 
"ignoring any aerodynamic effects and assuming the bicycle is traveling on a level surface"
 

Offline CliffordK

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Re: What is the weight of a bicycle?
« Reply #4 on: 19/03/2012 21:01:25 »
It still is very much direction and location dependent.

The Earth rotates at about 1670 kph at the equator.

Going eastward at 30 kph at the equator, your actual velocity is about 1700 kph, so you should feel slightly lighter due to centrifugal force.
Going westward at 30 kph at the equator, your actual velocity is about 1640 kph, so you should feel slightly heavier due to less centrifugal force.


 

Offline Geezer

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Re: What is the weight of a bicycle?
« Reply #5 on: 20/03/2012 02:47:45 »
Sounds reasonable. I suppose it does weigh a bit more in the opposite direction. However, it's centripetal, not centrifugal.
 

Offline RD

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Re: What is the weight of a bicycle?
« Reply #6 on: 20/03/2012 07:09:52 »
gonna have to crank those pedals hard for an increase in mass ... http://www.phy.olemiss.edu/HEP/QuarkNet/mass.html
 

Offline Geezer

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Re: What is the weight of a bicycle?
« Reply #7 on: 20/03/2012 08:02:26 »
gonna have to crank those pedals hard for an increase in mass ... http://www.phy.olemiss.edu/HEP/QuarkNet/mass.html


Not so much for weight though.
 

Offline RD

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Re: What is the weight of a bicycle?
« Reply #8 on: 20/03/2012 09:01:57 »
I still don't see how travelling at (constant) speed will make the bike weight different from when it is at rest,
neither does this guy ...
Quote
There is no reason for the moving bicycle to exert more force down ... when it is still compared to when it is moving (as long as it is not at the top of a curving trajectory).
http://www.newton.dep.anl.gov/askasci/phy00/phy00196.htm
« Last Edit: 20/03/2012 09:05:24 by RD »
 

Offline Geezer

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Re: What is the weight of a bicycle?
« Reply #9 on: 20/03/2012 17:46:59 »
I still don't see how travelling at (constant) speed will make the bike weight different from when it is at rest,
neither does this guy ...
Quote
There is no reason for the moving bicycle to exert more force down ... when it is still compared to when it is moving (as long as it is not at the top of a curving trajectory).
http://www.newton.dep.anl.gov/askasci/phy00/phy00196.htm

He actually explains it when he says "unless it's at the top of a curving trajectory".
 
A bike travelling on a level surface is on a curved trajectory because it is believed that the Earth is not flat. If you go fast enough you eventually achieve escape velocity, at which point the bike doesn't weigh anything at all (at al at all, in Ireland).
 
As Clifford points out, you do have to take direction into account, because you might also get a bit heavier before you start to get lighter.
 

Offline wolfekeeper

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Re: What is the weight of a bicycle?
« Reply #10 on: 06/04/2012 23:35:58 »
Sounds reasonable. I suppose it does weigh a bit more in the opposite direction. However, it's centripetal, not centrifugal.
Actually if you're doing the calculation in the reference frame of the (rotating) Earth it's coriolis, not centripetal or centrifugal.
 

Offline acecharly

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Re: What is the weight of a bicycle?
« Reply #11 on: 07/04/2012 16:01:03 »
If you were to put the cycle on a set of scales inside a van traveling at 30k/hr it would weigh no different to the van standing still. A difference in its weight could only be down to outside influences. The weight of the material the cycle was made of would be no different just the forces acting upon it.
 

Offline wolfekeeper

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Re: What is the weight of a bicycle?
« Reply #12 on: 07/04/2012 16:09:30 »
But there's curvature of the Earth as well as the rotation of the Earth.

In Concorde apparently the weight of the passengers reduced by 1% when flying west. Flying east, it made little difference because the two effects happened to cancel.
 

Offline Airthumbs

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Re: What is the weight of a bicycle?
« Reply #13 on: 08/04/2012 19:14:51 »
This thread has given me a great idea, but first I need to test it on some engineers on here........

One cycle made from cast iron weighing in at 16kg.   
Some small wings attached to the frame...... (you know where I'm going with this don't you)!

Lets say you generated 10% lift at 30km/h.  (I did say small wings)

So now your cycle is 10% lighter effectively then it was before. 

As I don't see the tour de france cyclists donning little wings to their bikes I can only assume  no one has thought this before.  The riders can clock upto 80km/h!! Factors such as wind resistance probably render the idea useless unless you can gain energy efficiency instead of loosing it somehow?

I know that traction is sometimes a problem when cornering at speed so adjustable wings to create negative lift increasing traction would be another use.  Just before a hill on the flat you could build up speed and then hit the positive lift setting at the base of the hill and fly up it....... :)
« Last Edit: 08/04/2012 19:40:19 by Airthumbs »
 

Offline imatfaal

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Re: What is the weight of a bicycle?
« Reply #14 on: 10/04/2012 10:02:22 »
This thread has given me a great idea, but first I need to test it on some engineers on here........

One cycle made from cast iron weighing in at 16kg.   
Some small wings attached to the frame...... (you know where I'm going with this don't you)!

Lets say you generated 10% lift at 30km/h.  (I did say small wings)

So now your cycle is 10% lighter effectively then it was before. 

As I don't see the tour de france cyclists donning little wings to their bikes I can only assume  no one has thought this before.  The riders can clock upto 80km/h!! Factors such as wind resistance probably render the idea useless unless you can gain energy efficiency instead of loosing it somehow?

I know that traction is sometimes a problem when cornering at speed so adjustable wings to create negative lift increasing traction would be another use.  Just before a hill on the flat you could build up speed and then hit the positive lift setting at the base of the hill and fly up it....... :)


Unfo Tour de France rules are pretty strict on bicycle design (especially for normal stages) - I heard it summed up as, if it doesnt look like Eddie Merckx would have ridden it, it aint allowed (ie two triangles, front forks, saddle and handle bars in the right place).  Just like F1 motor racing there is actually a minimum weight (15lb from memory) - and although you could walk out and buy a lighter bike on the highstreet, you wouldn't be allowed to race it.

And even if they did - the huge amount of effort needed on the flat stages is largely due to the air resistance - which your wings would only be adding to.  Weight just doesn't really matter once you are rolling, except for acceleration - and the main point of the team system is to avoid sudden accelerations apart from the very end of each stage.  And at the end of each stage in the mass sprint the best speedsters are actually quite close to spinning their rear tyre such is the massive forces they are trying to put through a few square inches of rubber.  TdF racers would go much faster if they were allowed silly lie flat bikes which minimize air resistance - however they would look a little silly trying to get round some of the corners and cobbled streets of france and esp belgium.

On the hilly stages (on which weight matters)  - your bike weighs about 10% of the average riders weight, and if you could take ten percent of that weight it is basically less than 1% of total mass.  It is considerably less than a full water bottle .  If you could get wings that would make a 5-10% saving of total mass at 15-20kph then it might be worth it - but they would have to be huge.

On the downhills professional cyclists have been rumoured to hit 115kph - any loss of grip are those silly speeds would literally be fatal
 

Offline Geezer

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Re: What is the weight of a bicycle?
« Reply #15 on: 10/04/2012 16:49:44 »
Even if the wings could produce lift without producing any drag (wind resistance), they would not help.
 
The energy you consume while cycling is lifting and accelerating your mass and the bike's mass, not their weight.
 

Offline evan_au

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Re: What is the weight of a bicycle?
« Reply #16 on: 15/04/2012 00:02:43 »
It is true that the equator is moving faster than higher latitudes, so centrifugal/centripetal forces would reduce weight. However, this same effect means that the equator bulges out.
The ocean responds to this effect, and will flow from an area of high surface weight to lower surface weight. So if you are cycling at average sea level, the bike should weigh the same at all latitudes (ignoring ocean gyres, which affect local sea level).
 

Offline Bored chemist

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Re: What is the weight of a bicycle?
« Reply #17 on: 15/04/2012 19:56:25 »
I'm shocked that there wan't a chorus of complaints about the units
"My bicycle weighs exactly 16kg"
No it doesn't.
 

Offline Guthers

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Re: What is the weight of a bicycle?
« Reply #18 on: 25/04/2012 13:16:12 »
I'm shocked that there wan't a chorus of complaints about the units
"My bicycle weighs exactly 16kg"
No it doesn't.
For Pete's sake!
 

Offline wolfekeeper

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Re: What is the weight of a bicycle?
« Reply #19 on: 25/04/2012 13:50:08 »
Even if the wings could produce lift without producing any drag (wind resistance), they would not help.
 
The energy you consume while cycling is lifting and accelerating your mass and the bike's mass, not their weight.
Actually it would help slightly if the lift doesn't produce any drag, since reducing the weight would reduce the load on the wheel bearings, which would reduce the bearing drag.
 

Offline Airthumbs

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Re: What is the weight of a bicycle?
« Reply #20 on: 25/04/2012 19:27:53 »
I get the feeling that the naked scientists might be able to make a whole programme on testing some of these ideas.  I can imagine MikeS on a small winged bike pedaling for England.
 

Offline Geezer

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Re: What is the weight of a bicycle?
« Reply #21 on: 25/04/2012 19:51:52 »
I'm shocked that there wan't a chorus of complaints about the units
"My bicycle weighs exactly 16kg"
No it doesn't.

No, see, I just stuck it on the bathroom scales again, and that's what they say it is.
 

Offline Bored chemist

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Re: What is the weight of a bicycle?
« Reply #22 on: 25/04/2012 21:22:34 »
I'm shocked that there wan't a chorus of complaints about the units
"My bicycle weighs exactly 16kg"
No it doesn't.

No, see, I just stuck it on the bathroom scales again, and that's what they say it is.

My bathroom scales tell lies too.
 

Offline Geezer

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Re: What is the weight of a bicycle?
« Reply #23 on: 25/04/2012 21:48:24 »
I'm shocked that there wan't a chorus of complaints about the units
"My bicycle weighs exactly 16kg"
No it doesn't.

No, see, I just stuck it on the bathroom scales again, and that's what they say it is.

My bathroom scales tell lies too.

But I had them calibrated to a guaranteed accuracy of 0.0000001%
 

Offline Bored chemist

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Re: What is the weight of a bicycle?
« Reply #24 on: 26/04/2012 19:49:30 »
By whom?
 

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Re: What is the weight of a bicycle?
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