Tire Pressure
06-09-22, 02:12 PM
#126
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It's a shame that a single datum can disprove the most carefully constructed hypothesis. Only in this case there are reams of data validating the Martin model starting with what's included in the paper itself.
06-09-22, 02:38 PM
#127
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06-09-22, 03:08 PM
#128
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Actually, I was hoping to get an idea if your lived experience may have included heavy vs light wheels in a competition setting.
I agree that a person's cycling experience does not influence the laws of physics. But we're not talking about the laws of physics. We're talking about the accuracy of a model, loaded with assumptions. If it contradicts decades, no, generations of lived experience and wisdom, then it is to be questioned. Models are not 'authorities'. I think those who parrot so-called 'scientists' going against such lived experience might not have that lived experience as a common-sense check on their opinions. When they assert "facts" as "proven", it looks really dumb, frankly. It reminds me of people on an audio forum who judge equipment by test results, quite literally without any listening. Their opinions are worthless.
When a current racer tells me he thinks his aero wheels make more difference than light ones in a criterium, I'll credit that opinion highly. However, my own explanation for his opinion is that he has not tried competing on heavy wheels, so has no experience to really make the comparison.
The model is too crude, with too many simplifying assumptions. That it can be used to "prove" that weight off the wheels is no better than weight off of anywhere else is evidence of its need for refinement, rather than evidence of its accuracy.
https://www.youtube.com/watch?v=m3dZl3yfGpc
I agree that a person's cycling experience does not influence the laws of physics. But we're not talking about the laws of physics. We're talking about the accuracy of a model, loaded with assumptions. If it contradicts decades, no, generations of lived experience and wisdom, then it is to be questioned. Models are not 'authorities'. I think those who parrot so-called 'scientists' going against such lived experience might not have that lived experience as a common-sense check on their opinions. When they assert "facts" as "proven", it looks really dumb, frankly. It reminds me of people on an audio forum who judge equipment by test results, quite literally without any listening. Their opinions are worthless.
When a current racer tells me he thinks his aero wheels make more difference than light ones in a criterium, I'll credit that opinion highly. However, my own explanation for his opinion is that he has not tried competing on heavy wheels, so has no experience to really make the comparison.
The model is too crude, with too many simplifying assumptions. That it can be used to "prove" that weight off the wheels is no better than weight off of anywhere else is evidence of its need for refinement, rather than evidence of its accuracy.
https://www.youtube.com/watch?v=m3dZl3yfGpc
This part is especially funny, as you're stating that you value your own personal and anecdotal judgment above other people's personal and anecdotal judgments:
When a current racer tells me he thinks his aero wheels make more difference than light ones in a criterium, I'll credit that opinion highly. However, my own explanation for his opinion is that he has not tried competing on heavy wheels, so has no experience to really make the comparison.
06-09-22, 04:02 PM
#130
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Not that there's anything wrong with that, but... actually I'm trying to hypothesize why his might be different. Such a hypothesis in an audio analogy, for example, would be that people actually hear differently. I'm just guessing that the rider may not have experience with heavier wheels, and that if such a rider lost two pounds of weight himself, and then was given a bike identical except for an extra pound on each wheel because of heavier rims and tires, he would prefer to gain a couple of pounds, and get his old bike back, if that was the choice. Just a guess.
06-09-22, 04:50 PM
#131
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06-09-22, 05:00 PM
#132
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“In general, with all of those variables [like weather and riders’ personal preference], that tire pressure is 8 to 8.5 bar for the road stages, and then 9.5 to 10 bar for the time-trial stages. Around 115 psi in the front and 125 psi in the back for the road stages and 130-135 psi for time-trial stages.
https://www.bicycling.com/racing/g20...trial%20stages.
https://www.bicycling.com/racing/g20...trial%20stages.
06-09-22, 05:04 PM
#133
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The surface of a neutron star is like fresh asphalt, so you'll want to use 23mm tires at a pretty high pressure. But, of course, that's all common knowledge.
06-09-22, 05:06 PM
#134
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“In general, with all of those variables [like weather and riders’ personal preference], that tire pressure is 8 to 8.5 bar for the road stages, and then 9.5 to 10 bar for the time-trial stages. Around 115 psi in the front and 125 psi in the back for the road stages and 130-135 psi for time-trial stages.
https://www.bicycling.com/racing/g20...trial%20stages.
https://www.bicycling.com/racing/g20...trial%20stages.
06-09-22, 05:23 PM
#135
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Not that there's anything wrong with that, but... actually I'm trying to hypothesize why his might be different. Such a hypothesis in an audio analogy, for example, would be that people actually hear differently. I'm just guessing that the rider may not have experience with heavier wheels, and that if such a rider lost two pounds of weight himself, and then was given a bike identical except for an extra pound on each wheel because of heavier rims and tires, he would prefer to gain a couple of pounds, and get his old bike back, if that was the choice. Just a guess.
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06-09-22, 05:28 PM
#136
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“In general, with all of those variables [like weather and riders’ personal preference], that tire pressure is 8 to 8.5 bar for the road stages, and then 9.5 to 10 bar for the time-trial stages. Around 115 psi in the front and 125 psi in the back for the road stages and 130-135 psi for time-trial stages.
https://www.bicycling.com/racing/g20...trial%20stages.
https://www.bicycling.com/racing/g20...trial%20stages.
06-09-22, 05:47 PM
#137
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You've picked a poor example. The relative effect of rotational mass vs static mass on acceleration is very well understood in physics. It doesn't require any anecdotal rider experience to validate at this point in time. In case you missed it earlier, mass added on the wheel rim is equivalent to twice that mass added on the frame, but only when the bike is accelerating. When the bike is not accelerating (e.g. climbing a hill at a steady speed) then mass added onto the wheel is the same as mass added anywhere else. The only subjective element in this is how the bike might "feel" to the rider with lighter vs heavier wheels.
06-09-22, 05:59 PM
#138
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I just don't get how they get from 'makes a difference during acceleration', with or without an 'only', to 'makes no difference'. I'll need to watch the video again - ugh. It may be as simple as what a 'difference' is. If it is something as simple as expenditure of energy, I won't be interested in arguing. If it's getting dropped or not, it's wrong.
06-09-22, 06:45 PM
#139
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Aren't bikes always in a state of acceleration and deceleration? Full power is applied from about 1 o'clock until 5 o'clock with dead spots at the bottom and top of the stroke. We are never really in a steady state when riding or at least that has been my assumption
A pound in the wheels or two on the whole bike for a criterium rider? I think it could be significant. Average Fondue rider? Hard to see any meaningful difference. Hillclimb TT? 1% less weight on an hour climb should get you about a minute, whether in the wheels, you, or elsewhere on the bike. Extra weight on a climb is probably a larger effect than incorrect tire pressure.
A pound in the wheels or two on the whole bike for a criterium rider? I think it could be significant. Average Fondue rider? Hard to see any meaningful difference. Hillclimb TT? 1% less weight on an hour climb should get you about a minute, whether in the wheels, you, or elsewhere on the bike. Extra weight on a climb is probably a larger effect than incorrect tire pressure.
06-09-22, 06:48 PM
#140
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Aren't bikes always in a state of acceleration and deceleration? Full power is applied from about 1 o'clock until 5 o'clock with dead spots at the bottom and top of the stroke. We are never really in a steady state when riding or at least that has been my assumption
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06-09-22, 06:53 PM
#141
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06-09-22, 10:33 PM
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You've picked a poor example. The relative effect of rotational mass vs static mass on acceleration is very well understood in physics. It doesn't require any anecdotal rider experience to validate at this point in time. In case you missed it earlier, mass added on the wheel rim is equivalent to twice that mass added on the frame, but only when the bike is accelerating. When the bike is not accelerating (e.g. climbing a hill at a steady speed) then mass added onto the wheel is the same as mass added anywhere else. The only subjective element in this is how the bike might "feel" to the rider with lighter vs heavier wheels.
https://openstax.org/books/physics/p...ational-motion
the radius of the wheel comes into play. Basically the larger the wheel the more pronounced effect of the rim weight.
06-09-22, 11:02 PM
#143
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Basically the larger the wheel the more pronounced effect of the rim weight.
06-10-22, 02:49 AM
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Aren't bikes always in a state of acceleration and deceleration? Full power is applied from about 1 o'clock until 5 o'clock with dead spots at the bottom and top of the stroke. We are never really in a steady state when riding or at least that has been my assumption
A pound in the wheels or two on the whole bike for a criterium rider? I think it could be significant. Average Fondue rider? Hard to see any meaningful difference. Hillclimb TT? 1% less weight on an hour climb should get you about a minute, whether in the wheels, you, or elsewhere on the bike. Extra weight on a climb is probably a larger effect than incorrect tire pressure.
A pound in the wheels or two on the whole bike for a criterium rider? I think it could be significant. Average Fondue rider? Hard to see any meaningful difference. Hillclimb TT? 1% less weight on an hour climb should get you about a minute, whether in the wheels, you, or elsewhere on the bike. Extra weight on a climb is probably a larger effect than incorrect tire pressure.
When you are actually accelerating the bike during a sprint or out of a corner, then an extra pound on the wheels will be equivalent to 2 extra pounds on the frame in terms of calculating the time it would take to accelerate from v1 to v2.
Extra weight on a steady climb has the same effect regardless of where you save it. So a pound saved on the wheels is the same as a pound saved on the frame. Lighter is just faster when climbing against gravity, but wheel mass is not to be treated as a special case because you are not adding in any rotational acceleration in this scenario.
06-10-22, 03:03 AM
#145
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Not clear why exactly "twice"? According to rotational physics:
https://openstax.org/books/physics/p...ational-motion
the radius of the wheel comes into play. Basically the larger the wheel the more pronounced effect of the rim weight.
https://openstax.org/books/physics/p...ational-motion
the radius of the wheel comes into play. Basically the larger the wheel the more pronounced effect of the rim weight.
So the kinetic energy stored in a small wheel is identical to that stored in a larger wheel at the same road speed. The smaller wheel just rotates faster with its smaller radius.
Last edited by PeteHski; 06-10-22 at 03:07 AM.
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06-10-22, 07:38 AM
#146
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No, bikes are not always in a state of acceleration/deceleration. Regardless of our lumpy power output, a bike can and does travel at a steady speed (there is too much inertia to slow down in-between pedal stroke dead-spots). So you really want to drop that "micro-acceleration" assumption as it is a fallacy that has no meaningful effect on calculations related to how fast the bike accelerates.
When you are actually accelerating the bike during a sprint or out of a corner, then an extra pound on the wheels will be equivalent to 2 extra pounds on the frame in terms of calculating the time it would take to accelerate from v1 to v2.
Extra weight on a steady climb has the same effect regardless of where you save it. So a pound saved on the wheels is the same as a pound saved on the frame. Lighter is just faster when climbing against gravity, but wheel mass is not to be treated as a special case because you are not adding in any rotational acceleration in this scenario.
When you are actually accelerating the bike during a sprint or out of a corner, then an extra pound on the wheels will be equivalent to 2 extra pounds on the frame in terms of calculating the time it would take to accelerate from v1 to v2.
Extra weight on a steady climb has the same effect regardless of where you save it. So a pound saved on the wheels is the same as a pound saved on the frame. Lighter is just faster when climbing against gravity, but wheel mass is not to be treated as a special case because you are not adding in any rotational acceleration in this scenario.
I can.
This is an interesting study, more about loads and gross efficiency but they measured acceleration and deceleration (speed change). You can find it with google
"Crank inertial load affects freely chosen pedal rate during cycling" Ernst Albin Hansen
Note: I always chose reliability and then aerodynamics WAY over light weight in my decision matrix
06-10-22, 09:16 AM
#147
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You can't feel that constant change in speed on a climb?
I can.
This is an interesting study, more about loads and gross efficiency but they measured acceleration and deceleration (speed change). You can find it with google
"Crank inertial load affects freely chosen pedal rate during cycling" Ernst Albin Hansen
Note: I always chose reliability and then aerodynamics WAY over light weight in my decision matrix
I can.
This is an interesting study, more about loads and gross efficiency but they measured acceleration and deceleration (speed change). You can find it with google
"Crank inertial load affects freely chosen pedal rate during cycling" Ernst Albin Hansen
Note: I always chose reliability and then aerodynamics WAY over light weight in my decision matrix
06-10-22, 11:28 AM
#148
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The big thing to remember is that if you are the person that has to have your tires at the absolute max on the sidewall, temperature will change it a lot. Your say 120 pounds in your garage, will go a lot higher in the summer riding on black top roads. Black top roads can get burning hot, and then if hilly, add extra heat from riding your brakes down hills. On a 100 degree day, riding down a long hill riding the brakes can cause the tire to go bang. And that would happen probably at a good speed. You would actually be "bleeding" off speed with your hip and arm.
06-10-22, 01:29 PM
#149
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Bro ride your own ride... I work with physicists all day (im at a national laboratory in group looking for dark matter), there are too many variables to math out the fastest tires. The only reliable test is one done in real world conditions. Some people enjoy thin hard tires.
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06-10-22, 01:38 PM
#150
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Again, I'm not a racer. I'm a casual rider. I guess I just opt for a bike that "feels" faster instead of one that "feels" slower. My actual time means little to me. But, feel free to keep on trying to convince me.
Now if I could just find some 700 x 20C clinchers that went to 140.
Now if I could just find some 700 x 20C clinchers that went to 140.
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