Does weight really matter on flat roads?
#52
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Of course weight matters even on the flats... it doesn't keep moving all by itself without any input from the rider.
Try this exaggerated test: Pull an enclosed trailer while empty. (enclosed to maintain the same aerodynamics) Use an electric motor to get up to X speed. (to eliminate acceleration) Accurately measure speed and power output over a flat course.
Then repeat while adding weight inside the trailer. If weight really doesn't matter like some here are saying, you should be able to keep piling it on (hundreds of pounds!) and see no increase in power needed. Does anyone here really think that would happen?
Try this exaggerated test: Pull an enclosed trailer while empty. (enclosed to maintain the same aerodynamics) Use an electric motor to get up to X speed. (to eliminate acceleration) Accurately measure speed and power output over a flat course.
Then repeat while adding weight inside the trailer. If weight really doesn't matter like some here are saying, you should be able to keep piling it on (hundreds of pounds!) and see no increase in power needed. Does anyone here really think that would happen?
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Yes, as long as air resistance and rolling resistance would remain the same, it would indeed happen. Unfortunately, rolling resistance grows with added weight, as there are no absolutely hard wheels and roads in the real world. This is why railroads are the most effective means of transport over land: it takes quite a while for the locomotive to get the whole train rolling, but once it's moving, it is able to pull the thousands of tons quite easily, since the deflection in steel wheels and tracks is minimal.
It's funny you mentioned the train, because that was my first thought as a test. Place a smooth riding surface between the rails for a bike to ride on while towing a box car. Have locomotive push it up to 15 mph and release. Since (some believe) weight doesn't matter, it should be no problem for the cyclist to keep it rolling on a flat grade even after adding several tons, right?
Last edited by AlmostTrick; 07-08-19 at 06:55 AM.
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Since (some believe) weight doesn't matter, it should be no problem for the cyclist to keep it rolling on a flat grade even after adding several tons, right?
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Increasing tire pressure when running more weight will compensate by restoring tire deflection to the same amount as it was with a lighter weight. But even if the extra weight does still increase rolling resistance, so what? It would be attributed to the weight itself, not some other factor.
It's funny you mentioned the train, because that was my first thought as a test. Place a smooth riding surface between the rails for a bike to ride on while towing a box car. Have locomotive push it up to 15 mph and release. Since (some believe) weight doesn't matter, it should be no problem for the cyclist to keep it rolling on a flat grade even after adding several tons, right?
It's funny you mentioned the train, because that was my first thought as a test. Place a smooth riding surface between the rails for a bike to ride on while towing a box car. Have locomotive push it up to 15 mph and release. Since (some believe) weight doesn't matter, it should be no problem for the cyclist to keep it rolling on a flat grade even after adding several tons, right?
That's not as simple as one might think. If you could isolate the resistance the cyclist overcomes to merely rolling resistance, I think a strong cyclist could keep it rolling. Unfortunately you can't separate the inherent level track components of rolling resistance, track or flange resistance, and oscillatory and miscellaneous frictional resistance.
However, back in 1926 the total of these (and other components) were derived empirically resulting in the Davis Formula, and revised in 1970 for modern equipment.
R (pounds resistance per ton) = 0.6 + 20/weight. weight in tons. For just the components which include rolling resistance.
With this modified Davis formula, the resistance added per added ton would be 3.1 pounds for an 8 ton train with about 25 pounds total resistance. As mentioned, rolling resistance is only a portion of that. It would seem feasible, right?
(The Application of the Davis Formula to set Default Train Resistance in Open Rails, Coals to Newcastle 20/11/2017)
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So getting back to the OP's question, yes, weight does matter, even on a flat road.
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Increasing tire pressure when running more weight will compensate by restoring tire deflection to the same
It's funny you mentioned the train, because that was my first thought as a test. Place a smooth riding surface between the rails for a bike to ride on while towing a box car. Have locomotive push it up to 15 mph and release. Since (some believe) weight doesn't matter, it should be no problem for the cyclist to keep it rolling on a flat grade even after adding several tons, right?
It's funny you mentioned the train, because that was my first thought as a test. Place a smooth riding surface between the rails for a bike to ride on while towing a box car. Have locomotive push it up to 15 mph and release. Since (some believe) weight doesn't matter, it should be no problem for the cyclist to keep it rolling on a flat grade even after adding several tons, right?
Not sure if people don’t understand physics or just have no common sense...
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The problem with so many of these discussions is that the question of whether weight is a factor (undoubted) gets conflated with whether it's the main factor to focus on--my opinion is that marketing has placed way too much emphasis on weight because it fits people's intuitions and they can feel it in the show room, while the importance of aero and tires are much harder to understand and can't be demonstrated by just lifting the bike.
It doesn't help that really aero bikes look weird and require positions that make their use somewhat limited for the non-racing rider.
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Regarding the effort involved with the change in momentum to accelerate, it would seem energetically balanced with the extra momentum when decelerating provided you keep off the brakes. Although the metabolic efficiency (and cumulative fatigue from numerous accelerations) comes into question, you don't get that part back.
#62
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Weight matters insofar it increases rolling resistance (and in real world, it always does so) . The force that has to be applied for an object to keep moving at a constant speed acts solely to overcome the resistance, which, in this case, in broad terms falls under two categories - air friction and rolling resistance (not limited only to deflection of tire and track, as noted before). If there is no resistance, no force at all is needed to keep an object moving at a constant speed (that's inertia, Newton's first law). If the resistance is equal, the force needed to overcome it is equal as well.
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If your bike weighs over one ton weight matters. If you’re talking about adding a few pounds then, no, it doesn’t matter. Yes, it might take an extra Watt of power but it won’t make any difference to your enjoyment of riding.
Not sure if people don’t understand physics or just have no common sense...
Not sure if people don’t understand physics or just have no common sense...
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It's never a simple matter of weight alone, LOL! Too many other factors figure in. Today was a prime example. I took out the old SL tubed Ribble bike. It weighs 19.7 ozs and has on some 40mm deep and light carbon fiber tubular wheels. I did my normal base 25 mile route. I worked really hard today but the flex of this 1985 race built frame under my 175 lbs meant that no matter how hard I tried I couldn't hold the higher speed I wanted to. Ran 19.1 mph avg and it was work. It just wasn't there in this bike and it's current configuration. Yet two days ago I took out the PDG Series Paramount made with oversize Tange Prestige and rode the exact same route with another 3 mile diversion and finished with a 20.2 mph avg. Yet this bike is over 2 1/2 lbs heavier with a wheelset over a pound heavier and not as deep. Both bikes are 53/42T with identical 8 speed cassettes. The fit is the same in terms of saddle height, setback, crank arm length, reach, handlebar width, etc. The heavier bike is consistently one of my fastest. It also is one of my better climbers which totally goes against what the experts will say. A well designed bike can help offset a "weight penalty" IMHO.
I'm sorry, are you claiming IDENTICAL test conditions except for frame a that weighs 1 1/2 lbs more & built of different shaped tubes, with a wheelset that is heavier by a lb, and less aerodynamically efficient? And you attribute the 1.1 mph increase to different power transmission characteristics of the frames? Or are you saying that aerodynamic improvement in the frame alone, (not in your position on the bike) accounts for the difference? If you changed your position, absolutely, sure (LeMond/Fignon). Just the frame's power transmission and it's incremental aero improvement? Seems like there's a piece missing.
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Weight/mass does not, for the most part, matter in this case.
Newton’s law, F=MA, refers to the amount of force required to accelerate a given mass. The question as stated has to do with a body moving at constant speed (zero acceleration).
The amount of force required by you to keep you and your bike moving at constant speed exactly equals the sum of the resistance forces (air drag, rolling resistance, etc.).
If you were to somehow ingest a massive amount of food equal to your weight as you travelled along, you would not have to supply an increased force to the pedals (perhaps the rolling resistance would increase a bit, but nothing substantial). Of course, you might not feel so great, so you could end up applying less force to the pedals and attribute it to the increased weight, in which case you’d be wrong.
Newton’s law, F=MA, refers to the amount of force required to accelerate a given mass. The question as stated has to do with a body moving at constant speed (zero acceleration).
The amount of force required by you to keep you and your bike moving at constant speed exactly equals the sum of the resistance forces (air drag, rolling resistance, etc.).
If you were to somehow ingest a massive amount of food equal to your weight as you travelled along, you would not have to supply an increased force to the pedals (perhaps the rolling resistance would increase a bit, but nothing substantial). Of course, you might not feel so great, so you could end up applying less force to the pedals and attribute it to the increased weight, in which case you’d be wrong.
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The discussion above has mostly acknowledged that weight matters very little while running n the flat, but that acceleration is where it would make a difference. Most of the argument has been about how much that matters.
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I'm sorry, are you claiming IDENTICAL test conditions except for frame a that weighs 1 1/2 lbs more & built of different shaped tubes, with a wheelset that is heavier by a lb, and less aerodynamically efficient? And you attribute the 1.1 mph increase to different power transmission characteristics of the frames? Or are you saying that aerodynamic improvement in the frame alone, (not in your position on the bike) accounts for the difference? If you changed your position, absolutely, sure (LeMond/Fignon). Just the frame's power transmission and it's incremental aero improvement? Seems like there's a piece missing.
Now the faster bike is red, white and blue and we know red makes a bike faster so yeah that's why!
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Steel is real...and comfy.
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If you were to somehow ingest a massive amount of food equal to your weight as you travelled along, you would not have to supply an increased force to the pedals (perhaps the rolling resistance would increase a bit, but nothing substantial). Of course, you might not feel so great, so you could end up applying less force to the pedals and attribute it to the increased weight, in which case you’d be wrong.
Ah-oh, You've done it now. But yeah, fun!
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Basically, your straw man was kind of funny looking.
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You'll be a bit slow to accelerate, but be able to maintain speed better, and take longer to decelerate.
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All weight matters. Now, rotating weight matters more. Furthest weight from your axles matters more than a full water bottle if your tires and tubes equal weight of water bottle...
#74
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Really wasn't the point--the previous poster had pointed out that by increasing it to a few tons, you were obscuring the likelihood that a realistic change in bike weight wouldn't result in any PRACTICAL difference. My point was that the box car was not even a good example because the momentum is so great.
Basically, your straw man was kind of funny looking.
Basically, your straw man was kind of funny looking.
That a few pounds on the bike would require a much smaller amount of extra power to propel at X speed than the extreme examples, and may even be difficult for some to notice, was specified many times over by me.
I think you're being a bit disingenuous saying that equals a straw man.
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Atomic weight matters most.