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Are Fat People Faster?

Old 08-05-06, 02:17 PM
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Are Fat People Faster?

Mostly on the down hill I (the fat one 107- 108kg) pass my friends (not fat ones, sub 80kg), if we are both coasting or even if i coast and they pedal a bit, i still beat them to the bottom...

Any bike, we tried switching bikes around, same thing i whooped.

Also flats (not tested with diffrent bikes), like were crusing, and then one of the sub 80s decicing to mash away, i do the same (i dont stand) and i end up flying past...

And if were all pedaling downhill (again, no tested with diff bikes) its usless im so far gone i gota use brakes so i dont completly loose them.

This is all road riding, off road on the steep ups i can (not cant) keep up but i start to "pant" for a while lol...


Is the watermelon really faster than the egg?
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Old 08-05-06, 02:30 PM
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No, otherwise bikeracers would outweigh sumowrestlers. But If you, like me, are a big guy and have a physically active job or maybe walk a lot you will have stonger legs than your lighter counterparts. Down the hills you will naturally be faster since you have more mass to push you down.
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Old 08-05-06, 02:31 PM
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Yeah,
I am the charter member of Whales onWheels, and I descend like
a rocket. I don't do too bad on the flats, but I slow to a crawl on hills.
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Old 08-05-06, 02:55 PM
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Only on downhill. On flats & uphill people who weigh less then me kick my ass.
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Old 08-05-06, 03:16 PM
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I suggest an experiment. Take two people, fat and slim one, and throw them down from a high building. They will hit the ground at the same time.
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Old 08-05-06, 03:35 PM
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Originally Posted by CTAC
I suggest an experiment. Take two people, fat and slim one, and throw them down from a high building. They will hit the ground at the same time.
I suggest another experiment, take two bike riders, fat and slim one, and let them coast down a hill, The fat one will arive at the bottom first.
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Old 08-05-06, 03:47 PM
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They are faster on downhill. (The reason for that although they experience more air resistance, i.e. a greater slowing-down force, the force is acting on a much greater mass and thus having much less effect. For the same reason the fat biker will hit the ground first if thrown off a tall building simultaneously with a thin biker.)

Fat people also float better which makes swimming easier for them.

But I still take skinny, thank you very much.
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Old 08-05-06, 03:50 PM
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Yes, weight is a big advantage on descents, but a bigger liability on climbs.
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Old 08-05-06, 04:09 PM
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Originally Posted by chephy
They are faster on downhill. (The reason for that although they experience more air resistance, i.e. a greater slowing-down force, the force is acting on a much greater mass and thus having much less effect. For the same reason the fat biker will hit the ground first if thrown off a tall building simultaneously with a thin biker.)
That's one of the classic fallacies in physics...

If you simultaneously threw a fat biker and a skinny biker off the roof of a building, and if both have about the same air resistance (say they are in the straight diver's position), both should hit the ground at about the same time.

Galileo simultaneously dropped a small, lighter lead ball and a big, heavier lead ball off the top of the Tower of Pisa in his famous experiment. Both balls hit the ground pretty much simultaneously.

Ditto the hammer vs. feather experiment made famous by one of the Apollo missions to the moon.. I think it was Gene Cernan who conducted that experiment, who dropped both a feather and a hammer. Both hit the surface of the moon at the same time.

As far as a fat biker having a greater speed coasting downhill than a skinny biker... I'm not going to speculate on that because I'm no physicist and I'm not about to be called out by one.

Last edited by LongIslandTom; 08-05-06 at 04:14 PM.
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Old 08-05-06, 04:34 PM
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The rolling resistance and a heavier rider apply to gravity making the heavier rider on an equal sized wheel bike, roll faster making him go quicker. You can do a google to find that one. We aren't dealing with simple wind resistance and a common dropping of two different weights.

http://www.cptips.com/energy.htm

That site seems to have some good info and this paragraph, I believe would have it right.

What about descents and hilly terrain? How does weight factor into these riding conditions? You may have noticed that a heavier rider descends a hill faster (energy expenditures being applied to the pedals being equal) than a lighter one. This seems to fly in the face of a fact you learned in physics class about all objects falling at the same speed independent of their weight. But when going biking down a hill, the slope factor needs to be taken into account. The final speed down a long hill is the balance between the propulsive forces - total rider/bike weight x the sine {that's a trigonometric function} of the angle of the hill - and the resistive forces - wind resistance is the big one. And the heavier rider comes out ahead. If one does the exact calculations with twin brothers weighing 175 pounds, descending a medium slope hill, riding similar bikes, and in exactly the same aerodynamic positions, with one carrying 25 pounds of lead shot, the heavier one would go 26.73 mph while the lighter one would be slightly slower at 25 mph.
I am no physicist myself but it makes sense the inclusive of slope and resistance, the heavier rider goes down faster than the light rider. As a larger rider who rides with 170pnders often I find this to be true. In the end I also need a lot more force to stop me too.
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Old 08-05-06, 05:24 PM
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Originally Posted by LongIslandTom
That's one of the classic fallacies in physics...

If you simultaneously threw a fat biker and a skinny biker off the roof of a building, and if both have about the same air resistance (say they are in the straight diver's position), both should hit the ground at about the same time.
This is both wrong and imprecise. If two objects have the same air resistance but different mass, the heavier one will always fall faster than the lighter one. If they have "about the same air resistance" then they have different resistances, and in that case, if the drag on the heavier object is greater than on the lighter one, then the lighter one may fall faster.
The force equations (in a fluid) demonstrate this quite simply
F_g = mg : m = mass; g = gravitational acceleration
F_d = 1/2 rho Cd A v^2 : rho = fluid density; Cd = drag coefficient; A = frontal area; v = velocity
so at terminal velocity F=0 and v = Sqrt(mg/1/2 rho Cd A)

Terminal velocity increases with increasing mass or decreasing air resistance (CdA)

Grade of the road, rolling resistance, drivetrain losses, crosswinds, all complicate the analysis but don't change the ultimate conclusion.
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Old 08-05-06, 05:39 PM
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I think Maelstrom (and his web site) are correct. Once at the top of the hill, the heavier rider has more potential kinetic energy. On the downhill, the internal friction of the bike itself (bearings, chain, tires, etc.) and the external wind resistance are approximately equal regardless of rider weight.

Therefore, since it takes more energy to lift a heavier rider up a ramp or hill, the same amount of energy must be released going down that ramp or hill. The heavier rider has more energy to convert to motion on the downhill. That energy will manifest itself as either higher speed or longer coast distance if no pedaling is done.
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Old 08-05-06, 05:43 PM
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Originally Posted by FarHorizon
... the same amount of energy must be released going down that ramp or hill.
Only if A) the kinetic energy is the same at the bottom of the hill as at the top (i.e., same speed), and B) no energy was added (through pedaling).
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Old 08-05-06, 05:52 PM
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Originally Posted by asgelle
Only if A) the kinetic energy is the same at the bottom of the hill as at the top (i.e., same speed), and B) no energy was added (through pedaling).
OK, but you ignored my critical final sentance. Let's assume that the cyclists both coast down the hill. The heavier cyclist will coast faster (on the hill) and farther (once the pavement flattens) because of his greater kinetic energy.
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Old 08-05-06, 06:06 PM
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Well i guess it all makes sence. Now to race up hill... lol the BB cant take it much longer, when the ligheter people try my bike (ie lbs guy, + friends) they dont get this click click click, lol the second i get on, its CRUNCH click CRUNCH. Im waiting for it (the BB) to fail, then ill switch to a sealed 20eu shimano BB...
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Old 08-05-06, 06:34 PM
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Originally Posted by CTAC
I suggest an experiment. Take two people, fat and slim one, and throw them down from a high building. They will hit the ground at the same time.
What about a ping-pong ball and a golf ball?
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Old 08-05-06, 07:04 PM
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The problem with simplistic junior-high physics is that it doesn't take into account complex interactions in the real world. We have to deal with wind-resistance and most junior & high-school physics don't deal with that at all (try explaining CFD to teenager ). They have a hard time getting basic physics concepts across as it is.

Due to wind-resistance, big heavier riders WILL descend hills faster. That's becasue if you're twice as big, you'll block only 4x as much wind, but you'll have 8x the mass pushing aside that wind. So the increase in mass goes up quicker than the increase in wind-resistance.

Unfortunately, the about the only time extra size and mass helps is on the downhills. Might be a wash on the flats, but on the uphills, extra weight will certainly hurt you.

You can test this extra-weight on downhills yourself. Fill two large water-bottles with lead-weights for an extra 15-20 lbs. You'll find yourself gaining an extra 2-4mph on the dowhills easily.

Last edited by Mothra; 08-06-06 at 03:07 AM.
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Old 08-05-06, 07:25 PM
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Originally Posted by LongIslandTom
Galileo simultaneously dropped a small, lighter lead ball and a big, heavier lead ball off the top of the Tower of Pisa in his famous experiment. Both balls hit the ground pretty much simultaneously.
The historical Galileo rolled balls down ramps.
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Old 08-05-06, 08:23 PM
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Originally Posted by cooker
What about a ping-pong ball and a golf ball?
Don't know about how fast they descend but if they have testosterone patches applied they'll certainly climb back up heaps quicker
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Old 08-05-06, 08:28 PM
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[/QUOTE=Mothra]Due to wind-resistance, big heavier riders WILL descend hills faster. That's becasue if you're twice as big, you'll block only 4x as much wind, but you'll have 8x the mass pushing aside that wide. So the increase in mass goes up quicker than the increase in wind-resistance. [/QUOTE]
Only if you assume humans are spheres, which the last time I checked, they were not. Frontal area goes as weight anywhere from the 0.408 to 0.762 power, but there's also the change in drag coefficient, so drag scales as mass to the 1/3. See for example:
http://groups.google.com/group/rec.b...a6271724ddf228
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Old 08-05-06, 09:03 PM
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Originally Posted by LongIslandTom
That's one of the classic fallacies in physics...

If you simultaneously threw a fat biker and a skinny biker off the roof of a building, and if both have about the same air resistance (say they are in the straight diver's position), both should hit the ground at about the same time.
Nope. Air resistance is a force, trying to slow down the bikers' downward motion. Now consider a truck loaded with lead and a bicycle moving at the same speed, and applying the same force to stop them... The force that will stop a bicycle dead in its tracks will go unnoticed by the truck driver. Similarly air resistance will slow down the lighter biker more.

In the absence of air resistance the fat and the skinny biker will hit the ground at the same time precisely because DIFFERENT gravitational forces are applied to them (if one biker is twice the weight of the other, there is twice as much gravitational pull on him which causes the same acceleration and hence hitting the ground at the same time).

All of this is very simple physics actually. Basic high school stuff.

Last edited by chephy; 08-05-06 at 09:11 PM.
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Old 08-05-06, 09:10 PM
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Originally Posted by FarHorizon
Therefore, since it takes more energy to lift a heavier rider up a ramp or hill, the same amount of energy must be released going down that ramp or hill. The heavier rider has more energy to convert to motion on the downhill. That energy will manifest itself as either higher speed or longer coast distance if no pedaling is done.
No offence to anyone, but this tread is kind of funny...

If you're considering an air-resistance-free and friction-free situation... Yes, more energy is required to move the heavier rider up. And yes, more energy will be released going down the hill. But that energy will NOT be manifested as higher speed or longer coasting distance (coasting distance will actually be infinite if there is no friction). It's simply that a heavy object travelling at a certain speed has more kinetic energy than a lighter object travelling at the same speed (since KineticEnergy = 0.5 mv^2, where m is the mass of the object and v its speed).

Last edited by chephy; 08-05-06 at 09:17 PM.
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Old 08-05-06, 10:07 PM
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Originally Posted by asgelle
If two objects have the same air resistance but different mass, the heavier one will always fall faster than the lighter one.
The heavier one has the potential to reach a higher terminal velocity, but both will accelerate downwards equally at 9.81 m/s/s (assuming it is done on earth). The heavier one will just keep on accelerating a little longer than the lighter one, if the lighter one reaches its terminal velocity.
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Old 08-05-06, 10:33 PM
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Originally Posted by asgelle
[/QUOTE=Mothra]Due to wind-resistance, big heavier riders WILL descend hills faster. That's becasue if you're twice as big, you'll block only 4x as much wind, but you'll have 8x the mass pushing aside that wide. So the increase in mass goes up quicker than the increase in wind-resistance.
Only if you assume humans are spheres, which the last time I checked, they were not. Frontal area goes as weight anywhere from the 0.408 to 0.762 power, but there's also the change in drag coefficient, so drag scales as mass to the 1/3. See for example:
http://groups.google.com/group/rec.b...a6271724ddf228[/QUOTE]

Give it up. Heavier riders will go down faster than lighter riders. Nice try with the physics stuff, it's been tried before and failed.
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Old 08-05-06, 10:47 PM
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Originally Posted by CTAC
I suggest an experiment. Take two people, fat and slim one, and throw them down from a high building. They will hit the ground at the same time.


Dick Cheney &

Let's see...who do we get for the fat one?
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