[Carbon Fiber] Would this bike scare you?
#176
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Well no, energy is not lost, it's just turned into heat. But we were talking about rims (I thought). There's a little bit of energy lost due to atmospheric resistance on the surface of a rotating rim, and the deeper the rim, the more is lost, but that's a very small amount of loss that's only due to rotation. Vastly more is lost to the spokes just from rotation. What you're saying is true, but it has nothing to do with rim weight. In all the cases you point out, less energy is lost to an aero rim, no matter its weight. Though one must also point out that next to the losses due to the bike and its rider, the contribution of the rims is quite small.
....if you go back to the beginning, and read this thread (something I would not expect you to do, because a lot of it is extraneous trolling, that contributes little to the discussion), you will discover that I have never said otherwise, and in fact got into this topic from simply recommending to the OP that in her particular event, a modern, aero wheelset might be the best way to improve her performance times. I even went out of my way to provide a link to a guy's blog that said exactly that.
Then the hoard appeared.
Later on:
. Everyone, beginner or self styled expert, rides on wheels. And with the advent of newer materials tech and the R+D guys assigned to find a way to make an essentially un-aerodynamic package more aero. wheels have been all aero'd up for about the past 20 years, dating back to the exploding Spinergy wheels that damaged a few people. All the aero wheel designs add some weight at the rim, so suddenly the discussion boards were full of this.
It's been a very long time since I bothered to calculate something like this, because aero wheels are all the rage, and they do seem to work, even if I don't use them. Offsetting advantages and disadvantages with them make them the obvious choice, when permitted in the rules for your event, and there is no drafting or quick maneuvering involved.
But all other things being equal (and they are not in this case), putting a pound of additional weight onto your bike by using tires that weigh that much more on your rims, will slow you down quite a bit more than sticking it in your pockets. Try it yourself, if you don't believe me.
It's been a very long time since I bothered to calculate something like this, because aero wheels are all the rage, and they do seem to work, even if I don't use them. Offsetting advantages and disadvantages with them make them the obvious choice, when permitted in the rules for your event, and there is no drafting or quick maneuvering involved.
But all other things being equal (and they are not in this case), putting a pound of additional weight onto your bike by using tires that weigh that much more on your rims, will slow you down quite a bit more than sticking it in your pockets. Try it yourself, if you don't believe me.
It's odd how things get twisted in a discussion like this on teh Beikforooms. I think there's something in the water here. It's a pack mentality that contributes little to actual exchange of ideas. nttaawwt, it reminds me of the glory days in the road forum.
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#177
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All depends of what kind of money you are ready to invest in a good pair of wheels, if you want to gain weight ,then tubulars are recommended and if you better puncture resistance and more solidity of the rim then clinchers or/and tubeless clinchers are recommended
#178
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But does it matter where this mass is located? Does it take more energy to increase speed if you put the mass on the wheel? Yes. First, let's look at mass on the frame of the bike. If I add something to the frame the total mass increases. This means that I would need more work to increase the kinetic energy. That's pretty straight forward.
What if the extra mass is on the wheel? In that case, I must do two things to increase speed: increase the kinetic energy and increase the rotational kinetic energy of the wheel. If all of the mass on the wheel is located at the rim, I can write the rotational kinetic energy as:
In this expression, mw is the mass of the wheel, R is the radius of the wheel and ω is the angular velocity of the wheel. But if the wheel is rolling and not slipping then there is a relationship between the angular speed of the wheel and the linear speed of the bike (this is how a car speedometer works---or at least the way it used to work).
If I substitute in for ω, I can write the following for the total kinetic energy of the bike (translational plus rotational).
In the translational kinetic energy, mb is the total mass of the bike (including the wheels) but the rotational kinetic energy only depends on the mass of the wheels.
So let's say I add 100 grams to the frame. This would increase the value of mb but not increase the mass of the wheel. The translational kinetic energy would increase by some amount and it would require more energy to accelerate (increase the kinetic energy).
Now let's add 100 grams to the wheel (increasing mw). Since the wheel is part of the bike, this means that the total mass also increases (mb). Both translational and rotational kinetic energy terms will have a 100 gram increase in mass. You will have double the increase in energy by adding mass to the wheel.
So yes, adding mass to the wheel is worse than adding mass to the frame---but only when accelerating. Still, every little bit helps.
What if the extra mass is on the wheel? In that case, I must do two things to increase speed: increase the kinetic energy and increase the rotational kinetic energy of the wheel. If all of the mass on the wheel is located at the rim, I can write the rotational kinetic energy as:
In this expression, mw is the mass of the wheel, R is the radius of the wheel and ω is the angular velocity of the wheel. But if the wheel is rolling and not slipping then there is a relationship between the angular speed of the wheel and the linear speed of the bike (this is how a car speedometer works---or at least the way it used to work).
If I substitute in for ω, I can write the following for the total kinetic energy of the bike (translational plus rotational).
In the translational kinetic energy, mb is the total mass of the bike (including the wheels) but the rotational kinetic energy only depends on the mass of the wheels.
So let's say I add 100 grams to the frame. This would increase the value of mb but not increase the mass of the wheel. The translational kinetic energy would increase by some amount and it would require more energy to accelerate (increase the kinetic energy).
Now let's add 100 grams to the wheel (increasing mw). Since the wheel is part of the bike, this means that the total mass also increases (mb). Both translational and rotational kinetic energy terms will have a 100 gram increase in mass. You will have double the increase in energy by adding mass to the wheel.
So yes, adding mass to the wheel is worse than adding mass to the frame---but only when accelerating. Still, every little bit helps.
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#179
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..
...but hey. let's talk more about mountain bike wheels.
...but hey. let's talk more about mountain bike wheels.
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Anyway, I test rode a couple of 29ers and was not impressed by their handling. The difference in handling to me was quite significant.
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#181
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...that's very interesting, and much more detailed a calculation than any I've seen put forth elsewhere.
One question, if you will permit me. Your first graph (above), there seems to be no difference at all in the two wheelsets, even accelerating from low speed.
I'm not questioning either your expertise (I don't know you), or your mathematics. But this seems to fly in the face real world experience, even of the staunchest "wheel weight doesn't matter" folks here. All of them have argued that it does, at least, matter in accelerating from a standing start. In fact, a couple of them took great offense at my suggestion we go back to steel as a wheel rim material. Am I reading your graph wrong, or is there some other explanation ? If I am going to be wrong about something, I'd at least like to learn from it. And I freely admit, I learned little about pendulums here.
Is 6 or 7 MPH the magic number where this weight difference no longer matters ? There seem to be no blue line values below that.
One question, if you will permit me. Your first graph (above), there seems to be no difference at all in the two wheelsets, even accelerating from low speed.
I'm not questioning either your expertise (I don't know you), or your mathematics. But this seems to fly in the face real world experience, even of the staunchest "wheel weight doesn't matter" folks here. All of them have argued that it does, at least, matter in accelerating from a standing start. In fact, a couple of them took great offense at my suggestion we go back to steel as a wheel rim material. Am I reading your graph wrong, or is there some other explanation ? If I am going to be wrong about something, I'd at least like to learn from it. And I freely admit, I learned little about pendulums here.
Is 6 or 7 MPH the magic number where this weight difference no longer matters ? There seem to be no blue line values below that.
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#182
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....if you go back to the beginning, and read this thread (something I would not expect you to do, because a lot of it is extraneous trolling, that contributes little to the discussion), you will discover that I have never said otherwise, and in fact got into this topic from simply recommending to the OP that in her particular event, a modern, aero wheelset might be the best way to improve her performance times. I even went out of my way to provide a link to a guy's blog that said exactly that.
<snip>
It's odd how things get twisted in a discussion like this on teh Beikforooms. I think there's something in the water here. It's a pack mentality that contributes little to actual exchange of ideas. nttaawwt, it reminds me of the glory days in the road forum.
<snip>
It's odd how things get twisted in a discussion like this on teh Beikforooms. I think there's something in the water here. It's a pack mentality that contributes little to actual exchange of ideas. nttaawwt, it reminds me of the glory days in the road forum.
But beyond that, IMO you are incorrect in that bolded assertion. If you go back to her earlier threads in the dreaded Road Bike forum, there are photos of her on her current bike. It's pretty obvious that a real TT or tri bike will reduce her wind drag vastly more (IDK, by a factor of 100?) than the drag reduction offered by more aero wheels.
From what I've seen from coasting races during many mountain group rides is that aero wheels are probably the last place to look for lower drag. Meaning that with my crappy V-section rims and 23 BMI, my coasting speed, at ~40 mph, has only been matched by two riders, both of them with better positions than mine, regardless of wheel type. My position is pretty good, but could be better with a smaller frame. I beat most riders down a 2000' descent by a couple minutes. It can't just be my phenomenal courage.
Wring everything you can out of the bike before spending money. The best way is with coasting races. Experiment with position. Every little thing makes a difference. As another poster said above, get low and buy an aero helmet if you have to spend money. And of course, if you have to buy new wheels, go aero. I've had a set in my Amazon saved cart for a couple years. Haven't been able to justify them. Doesn't look like I'll live long enough to wear out my current set.
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#183
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There's some differences, but nothing I have to think about or plan differently when I'm riding. I was expecting it to be more significant that it turned out to be. This has been my experience, anyway.
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In the first graph, it's hard to see because of the scale. The second graph is just a zoomed in section of the first. I think that 250g per wheel just isn't enough to see much difference when considering the low relative mass of the wheels as compared to the whole system. Below is a zoomed in plot of distance vs time at around 20 seconds. The lighter wheels show a gain of about 1 meter - would definitely be worth something in a sprint event on a track. The second plot shows a more zoomed in part of the speed vs time with a bigger weight difference (1kg and 2kg).
...thank you very much.
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#185
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...I think I covered that idea that I'm "complaining" with the "nttawwt" comment. I never complain about anything, because it could always be so much worse.
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That's your own perception, not reality.
Last edited by Lombard; 12-02-22 at 05:17 PM.
#187
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What can I say? Difference strokes for different folks. I just happen to like being able to turn tighter on mountain bike trails and even on carriage trails.
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In the first graph, it's hard to see because of the scale. The second graph is just a zoomed in section of the first. I think that 250g per wheel just isn't enough to see much difference when considering the low relative mass of the wheels as compared to the whole system. Below is a zoomed in plot of distance vs time at around 20 seconds. The lighter wheels show a gain of about 1 meter - would definitely be worth something in a sprint event on a track. The second plot shows a more zoomed in part of the speed vs time with a bigger weight difference (1kg and 2kg).
#191
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...two more discussions on this same topic. One for bicycles, and one for cars (which is pretty much where I originally learned this stuff.)
...two more discussions on this same topic. One for bicycles, and one for cars (which is pretty much where I originally learned this stuff.)
...and here, for all the world to see, is the sort of writing that set me on the wrong path in this world of wheel weights.
We Can Prove Why Extra Mass on Bike Wheels Is Your Worst Enemy
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Looks pretty negligible. This isn't to 30 kph, but rather a 90kg bike/rider modeled with a constant 50N propulsive force (~828W at ~37mph) with CdA = 0.3. Rolling resistance not accounted for. Two wheel weights were considered: light set at 1500g, heavy set at 2000g. All weight concentrated at rim. EOMs used : dxdt(1) = x(2), dxdt(2) = (1/(m + 2*I/r^2))*(F - 0.5*rho*CdA*x(2)^2) with rho (air density) = 1.23 kg/m^2, r (wheel radius) = 0.343m, I (wheel moment of inertia) = mass_wheel*r^2, m (mass bike+rider) = 90kg, and F (propulsive force) = 50N. Many details were not included in this model, so it's not a highly accurate representation of reality.
#193
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What is also missing from what I can see is there is no comparable with the weight moved to the frame which would also slow acceleration. Frankly I find it strange that there no comparable with a simple model of 500 grams moved from 700c wheels to the frame to a reasonable speed such as 30kmh. I am sure lighter wheels feel more responsive and dynamic but I also am pretty sure that the actual power requirements is negligible. These types of forums become depositories of old myths and wives tales repeated ad nauseam.
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2. The divergence slows as aerodynamic drag becomes a factor. Once aerodynamic drag dominates, the gap between the curves barely changes.
3. The long time (30s) to get to 27mph is a consequence of using constant force (thrust) in the model. Even though the power peaks at 828 W, the power is really low at low speeds. (The power ramps up from zero to about 280 W during the first 10 seconds, and you've only reached 12.5 mph.) The time required to attain 27 mph would likely be quite a bit less if the model used constant power.
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I keep checking back to see if there's anything new about the question I asked. No new information, but this train wreck is just as entertaining.
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Entertaining for sure. It's always entertaining - and perplexing - to me how there are people who can't just make a point, disagree with another's point, and then just move on. What it is in a person's life that causes them to need to win a meaningless argument with strangers online? But what is it with me that causes me to read this irrelevant (to me) drivel, alone at a desk and shake my head at the computer? In case anyone thinks I'm trying to claim any high ground here.