Does weight affect downhill speed?
06-28-09 | 07:08 PM
#101
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From: Zang's Spur, CO
.
The bad news is those 15 mile descents on an 8% grade are pretty terrifying at the end after you have ground your brake pads off.
06-28-09 | 07:19 PM
#102
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Well, people are free to disagree, even with scientific laws. Someone not contributing to a thread, but rather, sticking their noses in and trying to insult people, seems to be the quintessence of trolling. Ipso facto, the guy is stupid.
06-28-09 | 07:26 PM
#103
You need to go back and actually read all the posts especially 13, 35 and 37 then go do your own real world test and report back till then I have no response for you. 
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It may not be fancy but it gets me were I need to go.
https://www.jtgraphics.net/cyclist_bicycles.htm
06-28-09 | 07:33 PM
#104
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Now it happens that while I don't ride a recumbent, I do have both an aerobelly and a degree in physics. I haven't used the physics degree lately and I'm lazy (which is why I haven't thought this through with any kind of rigor up to now), but this is the way I see it:
Let's say rider A weighs 220 and rider B weighs 110. The force due to gravity will vary depending on the slope, but it came be simplified as
F(g)(a) = 2x
F(g)(b) = x
where x is the weight of rider B times a factor to account for the incline. Now lets call the force from wind resistance y. For any given speed it will be about the same for both riders. So the net forces will be
F(net)(a) = 2x - y
F(net)(b) = x - y
Now for simplicity, let's consider the case where the gravitational force in for rider B is twice the force from wind resistance (x = 2y).
F(net)(a) = 4y - y = 3y
F(net)(b) = 2y - y = y
So at that speed (below terminal velocity), the rider with twice the weight will be experiencing three times the force, and therefore will be experiencing greater acceleration, even after you account for his greater weight.
Let's say rider A weighs 220 and rider B weighs 110. The force due to gravity will vary depending on the slope, but it came be simplified as
F(g)(a) = 2x
F(g)(b) = x
where x is the weight of rider B times a factor to account for the incline. Now lets call the force from wind resistance y. For any given speed it will be about the same for both riders. So the net forces will be
F(net)(a) = 2x - y
F(net)(b) = x - y
Now for simplicity, let's consider the case where the gravitational force in for rider B is twice the force from wind resistance (x = 2y).
F(net)(a) = 4y - y = 3y
F(net)(b) = 2y - y = y
So at that speed (below terminal velocity), the rider with twice the weight will be experiencing three times the force, and therefore will be experiencing greater acceleration, even after you account for his greater weight.
06-28-09 | 08:42 PM
#107
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06-28-09 | 09:01 PM
#108
Well when I said “This is getting old real fast” why did you think I was referring to you anyways?
I was referring to the thread going no where’s at this point.
So as I said this is going no place so no need to respond at least to me because I have nothing to say on this subject.
I was referring to the thread going no where’s at this point.
So as I said this is going no place so no need to respond at least to me because I have nothing to say on this subject.
__________________
It may not be fancy but it gets me were I need to go.
https://www.jtgraphics.net/cyclist_bicycles.htm
It may not be fancy but it gets me were I need to go.
https://www.jtgraphics.net/cyclist_bicycles.htm
06-28-09 | 09:30 PM
#109
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Well when I said “This is getting old real fast” why did you think I was referring to you anyways?
I was referring to the thread going no where’s at this point.
So as I said this is going no place so no need to respond at least to me because I have nothing to say on this subject.
I was referring to the thread going no where’s at this point.
So as I said this is going no place so no need to respond at least to me because I have nothing to say on this subject.
06-28-09 | 09:34 PM
#110
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Anyways, I'm going to bed. Bon soir.
06-28-09 | 11:17 PM
#111
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I would say that it always applies since at the speeds that most cyclists travel at, differences in wind resistance between fat and skinny riders are negligable (ie the vacuum vs not effects aren't an important distinction).
06-29-09 | 07:06 AM
#112
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Hope you slept well. I'm curious what you're trying to accomplish is this thread. Since the OP is talking about downhill bicycling speed where clearly air resistance is a major limiting factor, does repeating some abstract and incomplete statement like "the speed of falling objects is independent of their weight [in a vaccuum]" contribute in any way to the answer to the question? You're a fairly new poster with some helpful contributions in other threads, and not a smart alec teenager - what got you into such a feisty, oppositional mood in this thread?
06-29-09 | 07:10 AM
#113
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The OP was talking about downhill, where it's well established (and you can easily demonstrate it for yourself), that heavier riders coast faster than light ones. And it's for exactly the reason you mention - negligible differences in air resistance, but major differences in gravitational force.
Last edited by cooker; 06-29-09 at 09:24 AM.
06-29-09 | 07:26 AM
#114
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I rode downhill with another tourer. I had 4 loaded panniers, lots of gear and very heavy photo equipement (DSLR, lenses, tripod), 50mm Marathon XR. He had a small load, two rear panniers and maybe 28-32mm slicks. I had to pedal to keep up.
06-29-09 | 08:06 AM
#115
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Hope you slept well. I'm curious what you're trying to accomplish is this thread. Since the OP is talking about downhill bicycling speed where clearly air resistance is a major limiting factor, does repeating some abstract and incomplete statement like "the speed of falling objects is independent of their weight [in a vaccuum]" contribute in any way to the answer to the question? You're a fairly new poster with some helpful contributions in other threads, and not a smart alec teenager - what got you into such a feisty, oppositional mood in this thread?
I had a lovely sleep, thank you. My first post in this thread just stated a physical fact and an 'in spite of' (that physical fact) example. My greatest speed has been downhill with a heavy load. After stating the 'speed/weight' factoid, people countered with beliefs, as you have above in brackets, that were disproven hundreds of years ago. I'm just trying to clarify something, because I can't understand why some people are having so much difficulty wrapping their brains around a simple fact that's irrefutably proven in a vacuum, but applies always. You don't want me to repeat it, do you?
'Feisty' as in 'spirited', certainly, but the one's that are being difficult, are the one's that can't grasp a simple fact and seem to take insult when told they are in error.
06-29-09 | 08:15 AM
#116
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This is fairly bizarre. The majority of this thread has consisted of your "vacuum" principle being cited, somebody responding saying that wind resistance applies, followed by a counter response repeating the "vacuum" principle. I don't think anybody has disagreed with the principle. The only question is whether or not it directly applies to the original question without the need to consider air resistance.
06-29-09 | 08:26 AM
#117
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This is fairly bizarre. The majority of this thread has consisted of your "vacuum" principle being cited, somebody responding saying that wind resistance applies, followed by a counter response repeating the "vacuum" principle. I don't think anybody has disagreed with the principle. The only question is whether or not it directly applies to the original question without the need to consider air resistance.
06-29-09 | 08:27 AM
#118
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From: Zang's Spur, CO
Let me introduce you to John Kallend, Ph.D.
He is professor in the Dept of Mechanical, Materials, and Aerospace Engineering at the Illinois Institute of Technology.
He is also a pilot and a skydiver.
Here is a presentation he assembled on the physics of skydiving.
Note Slide 15:
https://www.usoe.k12.ut.us/curr/scien...cs/physics.ppt
Now you can go explain to him that he is wrong.
06-29-09 | 08:34 AM
#119
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06-29-09 | 08:40 AM
#121
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Andy_ K,
It's NOT a vacuum example. It's proven in a vacuum (with the feather/hammer or whatever). The air resistance is negligable with a penny and a 5 lb barbell plate. Drop them (same time and height) and they'll reach the ground at the same time.
It's NOT a vacuum example. It's proven in a vacuum (with the feather/hammer or whatever). The air resistance is negligable with a penny and a 5 lb barbell plate. Drop them (same time and height) and they'll reach the ground at the same time.
06-29-09 | 08:41 AM
#122
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06-29-09 | 08:42 AM
#123
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06-29-09 | 08:45 AM
#124
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06-29-09 | 09:21 AM
#125
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If the penny is wearing a skinsuit and an aero helmet it will reach the ground faster unless the hammer is using a disc wheel, shaved its legs, and put tape over its shoe laces. In that case it's too close to call.