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Does rotating weight really matter?

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Road Cycling ďIt is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.Ē -- Ernest Hemingway

Does rotating weight really matter?

Old 05-01-21, 11:29 PM
  #26  
Racing Dan
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Originally Posted by sfrider View Post
It matters for acceleration since you not only have to accelerate the wheel mass forward with the rest of the bicycle, but you also have to add rotational energy to the wheels. And the rotational (angular) energy grows with the square of the rotational speed (angular velocity). (For the technical people, there is an w^2 factor where w=omega.) Forward kinetic energy only grows linearly with speed.
No, forward kinetic energy also increases at the square of the speed.
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Old 05-01-21, 11:42 PM
  #27  
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Originally Posted by Koyote View Post
In other words, a guy who makes heavy aero wheels is trying to convince us that rotating mass doesn't matter very much.

Sure, yeah, I trust him.
True :-)

In racing and all else equal, lighter IS better. At the same power you accelerate and ascend faster. Period. However the penalty for adding a few hundred grams or even a kg is small and nothing that will spoil your Sunday ride. And saving a few aero watts is arguably more beneficial than saving a pound of weight, for most riding at least.
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Old 05-02-21, 12:20 AM
  #28  
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Originally Posted by Atlas Shrugged View Post
People use the rotating mass argument as a justification tool when trying to explain why they are riding multiple thousand dollar wheel sets while they are 20 or 30 lbs overweight.
Or marketing encourages misconceptions that make ppl believe a 200g lighter wheelset is much faster than the stock wheels, even if it likely isn't.

The basic difference between added weight or added rolling and wind resistance is analogue to the difference between a capacitor and a resistor. The former (weight) stores energy, but releases it again, whereas the latter (rolling and wind resistance) convert energy into heat and looses it.
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Old 05-02-21, 01:57 AM
  #29  
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When I drop weight and train, the rotational weight is far less, and matters far less than when I don't. Riding the same wheels.
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Old 05-02-21, 02:52 AM
  #30  
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Originally Posted by Seattle Forrest View Post
Having more than one road bike?
Without question.
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Old 05-02-21, 02:56 AM
  #31  
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Originally Posted by Koyote View Post
In other words, a guy who makes heavy aero wheels is trying to convince us that rotating mass doesn't matter very much.

Sure, yeah, I trust him.
I don't "trust" anyone. But, I am interested in the science.
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Old 05-02-21, 01:02 PM
  #32  
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Originally Posted by bruce19 View Post
I don't "trust" anyone. But, I am interested in the science.
If you're interested in science, learn to ask a proper question. Of course rotating weight makes a difference, but then again everything makes some difference. The question is either how much of a difference does it make, or is the difference greater than some specified threshold.
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Old 05-02-21, 01:10 PM
  #33  
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Let's talk about cassettes.. I don't think they qualify as rotating weight, since they only rotate when pedaling, correct? There'd be no stored kinetic energy, or is there? Same for cranks?
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Old 05-02-21, 01:19 PM
  #34  
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Originally Posted by Sy Reene View Post
Let's talk about cassettes.. I don't think they qualify as rotating weight, since they only rotate when pedaling, correct? There'd be no stored kinetic energy, or is there? Same for cranks?
There is some stored kinetic energy there, but (unlike the energy stored in wheels) it gets "thrown away" when you stop pedalling.
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Old 05-02-21, 01:42 PM
  #35  
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Rotating weight matters to me, regardless of what an "engineer" or "scientist" says.
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Old 05-02-21, 01:51 PM
  #36  
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Originally Posted by nomadmax View Post
Rotating weight matters to me, regardless of what an "engineer" or "scientist" says.
Well, as Daniel Patrick Moynihan said, “you’re entitled to your own opinion… .”

Last edited by asgelle; 05-02-21 at 06:52 PM.
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Old 05-02-21, 04:56 PM
  #37  
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Originally Posted by Atlas Shrugged View Post
People use the rotating mass argument as a justification tool when trying to explain why they are riding multiple thousand dollar wheel sets while they are 20 or 30 lbs overweight.
My justification is what a weapon my treadly feels like with a kilo wheelset.
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Old 05-02-21, 06:47 PM
  #38  
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Originally Posted by bruce19 View Post
My take away thus far is that there has been a lot of money spent for not much gain. I am willing to be convinced otherwise but so far that's where I am.
I tried a lighter carbon wheel set a couple of years ago, and found no gain. They felt different but in the end, no noticeable speed gain. For me, at least, a total waste. I'll stick with my Roval SLX 24 wheels.
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Old 05-03-21, 12:34 AM
  #39  
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Originally Posted by Racing Dan View Post
True :-)

In racing and all else equal, lighter IS better. At the same power you accelerate and ascend faster. Period. However the penalty for adding a few hundred grams or even a kg is small and nothing that will spoil your Sunday ride. And saving a few aero watts is arguably more beneficial than saving a pound of weight, for most riding at least.
​​​​​​No need to argue. 🙂 There's math to understand exactly how much time you'll save with less weight and with less aerodynamic resistance, so you can know which is more beneficial and by how much. We all have so much ride data we can break down how hilly our riding is, what % of our miles are on different steepness ranges, etc, to help with the "for most riding" part. You can even do that for just got favorites. We live in a golden age of cycling.
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Old 05-03-21, 12:42 AM
  #40  
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Originally Posted by bruce19 View Post
My take away thus far is that there has been a lot of money spent for not much gain. I am willing to be convinced otherwise but so far that's where I am.
Why do roadies have this myopic idea that anything that doesn't make you faster isn't worth doing? Having sex with my girlfriend doesn't affect my average speed on the bike, I wouldn't call it "no gain." Light weight bikes are more fun to ride, people gain more enjoyment of the time they spend cycling, anyone who thinks that's a whole lot of nothing needs to spend some time contemplating the meaning of life. When it's coming to an end none of us will care what kind of average speeds we did, most of us will care how much joy and misery we experienced when we look back.
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Old 05-03-21, 02:48 AM
  #41  
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Originally Posted by Seattle Forrest View Post
Why do roadies have this myopic idea that anything that doesn't make you faster isn't worth doing? Having sex with my girlfriend doesn't affect my average speed on the bike, I wouldn't call it "no gain." Light weight bikes are more fun to ride, people gain more enjoyment of the time they spend cycling, anyone who thinks that's a whole lot of nothing needs to spend some time contemplating the meaning of life. When it's coming to an end none of us will care what kind of average speeds we did, most of us will care how much joy and misery we experienced when we look back.
I'm not crazed about average speed. I do, however like it when what is advertised is what is delivered. And, at age 75 I know full well it''s the journey and not the destination.
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Old 05-03-21, 05:05 AM
  #42  
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Originally Posted by bruce19 View Post
I'm not crazed about average speed. I do, however like it when what is advertised is what is delivered. And, at age 75 I know full well it''s the journey and not the destination.
What benefits are being advertised as a direct result of wheel weight?
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Old 05-03-21, 05:25 AM
  #43  
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Originally Posted by Seattle Forrest View Post
Why do roadies have this myopic idea that anything that doesn't make you faster isn't worth doing? Having sex with my girlfriend doesn't affect my average speed on the bike, I wouldn't call it "no gain." Light weight bikes are more fun to ride, people gain more enjoyment of the time they spend cycling, anyone who thinks that's a whole lot of nothing needs to spend some time contemplating the meaning of life. When it's coming to an end none of us will care what kind of average speeds we did, most of us will care how much joy and misery we experienced when we look back.
but I think generally folks are looking for a tangible benefit when they decide to shell out cash on wheels and higher priced bikes. So itís fair to temper peopleís expectations. Iíve seen videos where the time savings of nice carbon wheels vs basic aluminum wheels is about 1min per hour, I certainly canít justify spending that much.

I have the most basic of bikes, a base model allez with Claris and axis sport branded wheels and I get lots of enjoyment on the bike, the only limiter is me. And I go way faster than a lot of folks because Iíve put in the work on myself. I think a lot of people buy into hype and then come up with nebulous things to justify spending way too much in absence of any tangible benefits they may have been looking for. Yeah itís all about fun, but I think most folks have priorities outside of cycling and helping people make smart purchases is just as important as getting enjoyment.
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Old 05-03-21, 06:18 AM
  #44  
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Originally Posted by Kimmo View Post
My justification is what a weapon my treadly feels like with a kilo wheelset.
Whoops, I meant to say, 50mm kilo wheelset...

Aero >≥ weight
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Old 05-03-21, 06:33 AM
  #45  
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Riding a heavier / less efficient bike has merits
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Old 05-03-21, 06:38 AM
  #46  
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There are things called flywheels that rely on the effect of rotating weight - yes it matters

does it matter in your specific case? Probably
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Old 05-03-21, 07:17 AM
  #47  
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Originally Posted by sced View Post
Riding a heavier / less efficient bike has merits
No, not really.
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Old 05-03-21, 08:14 AM
  #48  
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Once again GCN does stupid science.
Motorcycle world knows all too well about rotating weight, yes it matters both during acceleration and constant motion.

Reminds when GCN does "keto diet" a few years back. What a bunch of hacks.
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Old 05-03-21, 08:29 AM
  #49  
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Originally Posted by aclinjury View Post
Once again GCN does stupid science.
Motorcycle world knows all too well about rotating weight, yes it matters both during acceleration and constant motion.
To say it matters is a value judgement. Everyone will have their own value system. There is no blanket answer as to what matters. As to making a difference, any change by definition makes a difference cf. my post above.

p.s. bicycles are not motorcycles.
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Old 05-03-21, 10:35 AM
  #50  
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Originally Posted by sced View Post
Riding a heavier / less efficient bike has merits
Not for me.
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