Wheels - lighter weight vs aero
02-13-23, 11:01 PM
#151
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My whole argument was about climbing on a 7% grade being faster on aero wheels. The work in the link is referring to a climb with a 16.8 mph average speed, and 1/100th of a watt? Probably beyond the resolution of the instrumentation.
Almost everybody knows this. Merckx was furious, he had never lost a time trial to Moser:
The lenticular carbon-fibre disc wheels weighed 4.6kg between them and were intended to work like flywheels, allowing Moser to maintain a constant pace once up to speed. The total weight of Moser’s bike was 9.6kg — nearly twice the 5.75kg of Merckx’s machine.
Good luck on a real climb with these wheels, you would be hating life.
Almost everybody knows this. Merckx was furious, he had never lost a time trial to Moser:
The lenticular carbon-fibre disc wheels weighed 4.6kg between them and were intended to work like flywheels, allowing Moser to maintain a constant pace once up to speed. The total weight of Moser’s bike was 9.6kg — nearly twice the 5.75kg of Merckx’s machine.
Good luck on a real climb with these wheels, you would be hating life.
It climbs fine. I have a really hard time imagining wheel inertia makes that big of a difference as then I'd have real trouble making those explosive accelerations on 7% climbs you'd need to hop a fallen tree etc. And those sorts of things don't really pose a challenge, mainly because the added weight on the wheel compared to my overall weight is so small.
The only place wheel inertia begins to maje itself known is at 50kph+ speeds where you need to start thinking steering a little bit differently.
02-14-23, 09:44 AM
#152
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I disagree. You are assuming the rider's output is a mathematically perfect model. In reality there is a pulsating nature of power output, twice each crank revolution, from beginning to end of the climb. With a cadence of 80 rpm, 160 times a minute the rider is trying to accelerate upwards. "Micro accelerations" do not simply cancel each other out.
Take two identical riders and bikes. Have the first climb a steep 3 mile hill at 6 mph (30 minutes). Have the second climb the same hill in 30 minutes, but have him coast (no brakes) to a stop every 100 feet. Your argument says they do the same energy expenditure, perhaps mathematically they do, but we all know that's just not how cycling uphill works.
Take two identical riders and bikes. Have the first climb a steep 3 mile hill at 6 mph (30 minutes). Have the second climb the same hill in 30 minutes, but have him coast (no brakes) to a stop every 100 feet. Your argument says they do the same energy expenditure, perhaps mathematically they do, but we all know that's just not how cycling uphill works.
02-14-23, 11:14 AM
#153
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I've given this a fair amount of thought, and I suspect there may be a feature of climbing where wheel inertia matters.
Let's call it "micro decelerations-accelerations". Whenever the grade goes up even slightly, the speed drops quickly, and the rider must put extra force on the pedals to get back to speed. These very short bursts of acceleration add up, and if the wheels have more inertia, that effort requires more peak pedal force and total power.
One might reply that the heavier wheels also decelerate less quickly. Sure, but they require more power (and force) to bring back up to speed, and that's the part that causes leg fatigue.
I've climbed with light wheels and heavy wheels, and the heavy wheels definitely were more fatiguing.
Just a thought.
Let's call it "micro decelerations-accelerations". Whenever the grade goes up even slightly, the speed drops quickly, and the rider must put extra force on the pedals to get back to speed. These very short bursts of acceleration add up, and if the wheels have more inertia, that effort requires more peak pedal force and total power.
One might reply that the heavier wheels also decelerate less quickly. Sure, but they require more power (and force) to bring back up to speed, and that's the part that causes leg fatigue.
I've climbed with light wheels and heavy wheels, and the heavy wheels definitely were more fatiguing.
Just a thought.
"Because...PHYSICS!!" is every bit as lame as "Because...COMPUTERS!!"
I'm not ignoring the laws of inertia at all. I'm just saying that you can ignore wheel inertia when there is little or no acceleration involved e.g. steady state climb. For changes in inertia to matter, you need to be measuring significant accelerations. Any "micro-accelerations" during your pedal stroke are by definition "micro" i.e. approx. zero. And for every one of these micro-accelerations, there will be a micro-deceleration where the energy is recovered. It's one of the fallacies that persists in this type of discussion. I've heard it before and no doubt someone will mention it again next time. But the amount of power you need to climb a hill at an average speed can be predicted accurately from total mass, rolling resistance and aerodynamic drag. You don't need to know wheel inertia and it will make zero difference to the prediction, except maybe a tiny fraction of time while you initially accelerate from 0-15 kph or whatever on the climb.
Why don't you just admit that you were wrong, learn a little and move on? I'm a professional mechanical engineer, so I get paid to know this kind of stuff and I see a lot of people get confused about the importance of all these various parameters. I probably would if I did something else for a living. There is only shame in denial.
Can we all agree that the physics does say that the effect on acceleration of rotating weight at the radius is twice that of static weight, but only when accelerating? That is my understanding of the model.
02-14-23, 11:38 AM
#154
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If wheel A weighs more than wheel B, the extra mass is almost certainly not located at the full radius of the tire, which would be required for a doubling of the effect on acceleration. A more realistic distribution of the extra mass, and the radius-squared factor in rotational inertia, means the effect on acceleration will be much less than a doubling.
02-14-23, 11:45 AM
#155
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I think that what people are saying here is that things like the slight differences in power through a pedal stroke and the slight differences in rotating mass when doing the slight accelerations (because no one climbs at a perfectly steady pace, and no road is a perfectly smooth, steady grade) are Not Significant.
There was a thread many years back about bike weight, where people were arguing some nonsense about removing the weight of a molecule made a real, measurable difference in performance ... mathematically. People were really arguing such stuff!! It was hilarious.
If people can show real, experimentally derived figures illustrating exactly how many watts a rider loses while climbing with lighter wheels versus heavier wheels, balanced against similarly experimentally-derived numbers showing the gains and loses made to aerodynamics ... please do.
Perhaps in racing situations, there are more significant accelerations as riders attack on hills .... so show the numbers there. Wouldn't the aero benefit go up as speed went up, though?
So, the experiments would have to measure watts lost to aero and watts lost moving weight at a variety of speed and grades, steady-state and under different degrees of acceleration (not Micro-acceleration ... I think it seems obvious that the 2.5 pulses per second of a rider climbing with a cadence of 80 are too tiny to be deemed "significant"---there is neither enough time to lose much speed nor to gain much. Even at a cadence of 40, where you can much more feel the power pulses, the actual time spent accelerating vs. decelerating ... 1.2 pulses per second so peak accelerations for less than half a second? Go ahead and measure the watts lost and gained based on wheel weight, if you can.)
This is like the scraped-paint debate. If two identical riders on two identical bikes set off, but just before starting one scratches off a thumbnail's worth of paint from the frame, he has the advantage. Mathematically, sure ... but we don't ride mathematical models. Show Significant gains or losses ..... if the measurable losses and gains are not greater than the noise, the margins of measuring error, then they are not real.
Show me the numbers on how much is gained and lost due to cadence on a bike with lighter, less aero wheels versus heavier, more aero wheels.
Theoretically, the rotation of distant galaxies affect us all the time, but because the effects are so tiny as to be only calculable, not measurable ......
There was a thread many years back about bike weight, where people were arguing some nonsense about removing the weight of a molecule made a real, measurable difference in performance ... mathematically. People were really arguing such stuff!! It was hilarious.
If people can show real, experimentally derived figures illustrating exactly how many watts a rider loses while climbing with lighter wheels versus heavier wheels, balanced against similarly experimentally-derived numbers showing the gains and loses made to aerodynamics ... please do.
Perhaps in racing situations, there are more significant accelerations as riders attack on hills .... so show the numbers there. Wouldn't the aero benefit go up as speed went up, though?
So, the experiments would have to measure watts lost to aero and watts lost moving weight at a variety of speed and grades, steady-state and under different degrees of acceleration (not Micro-acceleration ... I think it seems obvious that the 2.5 pulses per second of a rider climbing with a cadence of 80 are too tiny to be deemed "significant"---there is neither enough time to lose much speed nor to gain much. Even at a cadence of 40, where you can much more feel the power pulses, the actual time spent accelerating vs. decelerating ... 1.2 pulses per second so peak accelerations for less than half a second? Go ahead and measure the watts lost and gained based on wheel weight, if you can.)
This is like the scraped-paint debate. If two identical riders on two identical bikes set off, but just before starting one scratches off a thumbnail's worth of paint from the frame, he has the advantage. Mathematically, sure ... but we don't ride mathematical models. Show Significant gains or losses ..... if the measurable losses and gains are not greater than the noise, the margins of measuring error, then they are not real.
Show me the numbers on how much is gained and lost due to cadence on a bike with lighter, less aero wheels versus heavier, more aero wheels.
Theoretically, the rotation of distant galaxies affect us all the time, but because the effects are so tiny as to be only calculable, not measurable ......
02-14-23, 11:59 AM
#156
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At this point I’m pretty sure they will continue to believe in the importance of wheel rotational inertia regardless of any data or mathematical modelling.
What they won’te able to do is quantify it or explain it to anyone with a basic understanding of the physics. It is classic BF pseudo-science.
Kudos to RChung for being so polite, but I expect he’s been through this pointless exercise so many times that he realised long ago that some people won’t listen to any explanation that isn’t in line with their original view of the world.
What they won’te able to do is quantify it or explain it to anyone with a basic understanding of the physics. It is classic BF pseudo-science.
Kudos to RChung for being so polite, but I expect he’s been through this pointless exercise so many times that he realised long ago that some people won’t listen to any explanation that isn’t in line with their original view of the world.
Last edited by PeteHski; 02-14-23 at 12:02 PM.
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02-14-23, 12:07 PM
#158
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02-14-23, 12:09 PM
#160
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If people can show real, experimentally derived figures illustrating exactly how many watts a rider loses while climbing with lighter wheels versus heavier wheels, balanced against similarly experimentally-derived numbers showing the gains and loses made to aerodynamics ... please do.
[...]
So, the experiments would have to measure watts lost to aero and watts lost moving weight at a variety of speed and grades, steady-state and under different degrees of acceleration (not Micro-acceleration ... I think it seems obvious that the 2.5 pulses per second of a rider climbing with a cadence of 80 are too tiny to be deemed "significant"---there is neither enough time to lose much speed nor to gain much. Even at a cadence of 40, where you can much more feel the power pulses, the actual time spent accelerating vs. decelerating ... 1.2 pulses per second so peak accelerations for less than half a second? Go ahead and measure the watts lost and gained based on wheel weight, if you can.)
Show me the numbers on how much is gained and lost due to cadence on a bike with lighter, less aero wheels versus heavier, more aero wheels.
[...]
So, the experiments would have to measure watts lost to aero and watts lost moving weight at a variety of speed and grades, steady-state and under different degrees of acceleration (not Micro-acceleration ... I think it seems obvious that the 2.5 pulses per second of a rider climbing with a cadence of 80 are too tiny to be deemed "significant"---there is neither enough time to lose much speed nor to gain much. Even at a cadence of 40, where you can much more feel the power pulses, the actual time spent accelerating vs. decelerating ... 1.2 pulses per second so peak accelerations for less than half a second? Go ahead and measure the watts lost and gained based on wheel weight, if you can.)
Show me the numbers on how much is gained and lost due to cadence on a bike with lighter, less aero wheels versus heavier, more aero wheels.
02-14-23, 12:30 PM
#161
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I was not arguing with you, sir. I have seen you here long enough, and gotten lost enough in your various postings .... You imprss me as being a very real and practical engineer who does the work, the experimentation and the calculation, and you know your stuff .... IMO.
Sorry I did not make it clear. I was talking about the people who do not accept your science.
The only question I had about your explanation was the issue of acceleration, which you explained to me (and explaining math and physics to me is a tough row to hoe, I know.)
I was addressing the people who did Not do the work you did and did not produce actual numbers as you did, and still argued againsnt the actual ... well, science.
Sorry I was not clear.
Sorry I did not make it clear. I was talking about the people who do not accept your science.
The only question I had about your explanation was the issue of acceleration, which you explained to me (and explaining math and physics to me is a tough row to hoe, I know.)
I was addressing the people who did Not do the work you did and did not produce actual numbers as you did, and still argued againsnt the actual ... well, science.
Sorry I was not clear.
02-14-23, 12:35 PM
#162
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02-14-23, 12:46 PM
#163
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My brother was trained as an engineer. He once declared, "The difference between engineers and physicists is that engineers think an equation is an approximation of reality and physicists think reality is the approximation of an equation." I was trained as a mathematician so he waited two beats while I was pondering that before he finished, "mathematicians haven't yet realized there's any connection."
02-14-23, 12:54 PM
#164
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I don't know if this is sloppy wording or truly a lack of understanding, but there are no simplifying assumptions in the Martin model with regard to acceleration. If the model results you've looked at haven't treated accelerations (micro or otherwise) to your liking, that isn't the fault of the model but how those people have chosen to apply it. If you're that interested, it would be straightforward to solve the equation with a time-varying input power to see the impact of micro accelerations, wheel weight, moments of inertia, or whatever parameter(s) you choose.
02-14-23, 12:58 PM
#165
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My brother was trained as an engineer. He once declared, "The difference between engineers and physicists is that engineers think an equation is an approximation of reality and physicists think reality is the approximation of an equation." I was trained as a mathematician so he waited two beats while I was pondering that before he finished, "mathematicians haven't yet realized there's any connection."
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02-14-23, 01:00 PM
#167
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If people can show real, experimentally derived figures illustrating exactly how many watts a rider loses while climbing with lighter wheels versus heavier wheels, balanced against similarly experimentally-derived numbers showing the gains and loses made to aerodynamics ... please do.
(by the way, no experiment can produce an exact result.)
02-14-23, 01:00 PM
#168
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02-14-23, 01:02 PM
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02-14-23, 01:15 PM
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So does anyone with a degree in engineering, physics or mathematics agree with the importance of "micro accelerations" during the pedal stroke or believe that wheel mass is equivalent to approx double static mass when climbing?
02-14-23, 01:25 PM
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02-14-23, 01:36 PM
#172
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The value of aerodynamics is a function of speed and it is completely different for a pro time trial where rides are averaging over 30 mph for this distance as compared to a pro hill climb at lesser speeds. One does not see effort to make bike wheels more aerodynamic on the non time trial stages of the various pro tour races.
On climbs what is important is how much power from the rider is effectively transferred to forward motion of the bike and that primarily affects frame geometry and to a lesser degree the gears available. All things being equal a lighter bike provides some advantage although how much is real and how much is psychological is another matter.
A friend who used to go on long rides with me had insisted that his bike was faster on the downhill sections than mine. At the top of one steep grade we switched bike and coasted to the bottom. He was faster on my bike and it was due to his extra 20 lbs of body weight. He was at a disadvantage going up the grades but compensated to some degree on the downhill sections. After I changed out my large chainring for a 60-tooth one he lost his advantage on the downhills as I could continue to pedal.
On climbs what is important is how much power from the rider is effectively transferred to forward motion of the bike and that primarily affects frame geometry and to a lesser degree the gears available. All things being equal a lighter bike provides some advantage although how much is real and how much is psychological is another matter.
A friend who used to go on long rides with me had insisted that his bike was faster on the downhill sections than mine. At the top of one steep grade we switched bike and coasted to the bottom. He was faster on my bike and it was due to his extra 20 lbs of body weight. He was at a disadvantage going up the grades but compensated to some degree on the downhill sections. After I changed out my large chainring for a 60-tooth one he lost his advantage on the downhills as I could continue to pedal.
02-14-23, 02:06 PM
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Last edited by Koyote; 02-14-23 at 02:11 PM.
02-14-23, 02:18 PM
#174
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As is mentioned here, (https://www.cyclist.co.uk/in-depth/w...tweight-wheels) even on climbs except at walking pace aero generally saves more watts than lighter weight. if you are riding multiple high-degree switchbacks and accelerating out of the corners, at low speeds, light wheels are marginally better. if you are doing anything steadily ten mph or more (they claim,) you save a tiny bit more with aero.
I think this is all in the Sky Racing "Marginal Gains" category ... the 0.1 percent advantage which only matters if you have a bunch of such advantages .... or if you just like one or the other .....
Ultimately everyone is just going to pick a position, buy a product, and consider it the best for that person's use. And no one is going to do a bunch of measurements to see if that person is right or wrong. it only matters as much as it matters to each individual .... no one else much cares.
A mathematician, a physicist, and an engineer went to a bike race ......
I think this is all in the Sky Racing "Marginal Gains" category ... the 0.1 percent advantage which only matters if you have a bunch of such advantages .... or if you just like one or the other .....
Ultimately everyone is just going to pick a position, buy a product, and consider it the best for that person's use. And no one is going to do a bunch of measurements to see if that person is right or wrong. it only matters as much as it matters to each individual .... no one else much cares.
A mathematician, a physicist, and an engineer went to a bike race ......
02-14-23, 02:28 PM
#175
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Honestly, I think the psychology of it (and "knowing" your way is right and that you are on the "best" possible setup for your situation) provides more benefit than the very marginal gain provided by lightweight or aero wheels as long as the wheels are appropriate to the frame, are (mostly) true and don't rub anywhere.
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