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Does rotating weight really matter?

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Does rotating weight really matter?

Old 05-05-21, 09:28 AM
  #101  
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Originally Posted by terrymorse View Post
Not, it isn't. Climbing is all about power-to-weight ratio.
Rest assured if one rider has 3.5 w/kg and another has 3 w/kg it won't matter who has the lighter wheels 3.5 w/kg will be faster. If both riders had the same w/kg saying the rider with lighter wheels would be noticeably faster is doubtful at best.
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Old 05-05-21, 09:53 AM
  #102  
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Originally Posted by aclinjury View Post
I see that you want to look at this from a value judgement angle. That's fair enough.

But I can tell that you have never ridden or jumped a bmx bike vs a downhill bike either.. Bmx bike spins and gyrates differently compared to the downhill bike, and it not just because of bike size either. Rotating weight. Forget bmx, just take a road bike and put some 50mm deep wheels and sprint, now do it with 80mm wheels. Tell me if you don't sprint quicker in the 50mm. Climbing is just a series of mini accleration. Does it matter now? up to the rider to judge, but if rider cares about performance, then it matters.
Track sprinters basic set up is a five spoke up front and a disc in the back. When accelerating, aero matters. Some guys even use a disc front and rear for their 200TT.
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Old 05-05-21, 09:57 AM
  #103  
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Looking at the pie plate size cassette sprockets that are appearing on bikes now, it must not matter much.
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Old 05-05-21, 10:15 AM
  #104  
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Answer to OP question: no. There was a good market demonstration of this ~25 years ago: Helium wheels They were the lightest wheels on the market at the time. They were also dead flat box section rims. Many of the good climbers went out and bought them. They made no difference. 2 years later, they had disappeared from the bikes I was riding with. Aero trumps weight, even climbing. Red anodized, they were quite striking in appearance.
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Old 05-05-21, 10:30 AM
  #105  
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Originally Posted by Carbonfiberboy View Post
Aero trumps weight, even climbing.
Nope.

When it comes to climbing anything above a shallow grade, weight trumps everything else.
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Old 05-05-21, 11:02 AM
  #106  
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Old 05-05-21, 11:48 AM
  #107  
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Originally Posted by terrymorse View Post
Nope.

When it comes to climbing anything above a shallow grade, weight trumps everything else.
Grade is not the determining factor, speed is. If you climbing speed is above around 12mph Zipp 404 depth wheel will be faster.
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Old 05-05-21, 11:48 AM
  #108  
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Originally Posted by aclinjury View Post
Forget bmx, just take a road bike and put some 50mm deep wheels and sprint, now do it with 80mm wheels. Tell me if you don't sprint quicker in the 50mm.
You could be right if you're sprinting from a standing start in a parking lot. In a more realistic sprint under race conditions you would be starting your sprint at 55+kph and the actual accelerations involved are much lower than the parking lot sprint. The aero benefits from a deeper profile wheel can easily outweigh the small penalty from increased inertia of the deeper wheels.
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Old 05-05-21, 11:51 AM
  #109  
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Originally Posted by gregf83 View Post
You could be right if you're sprinting from a standing start in a parking lot. In a more realistic sprint under race conditions you would be starting your sprint at 55+kph and the actual accelerations involved are much lower than the parking lot sprint. The aero benefits from a deeper profile wheel can easily outweigh the small penalty from increased inertia of the deeper wheels.
He is still wrong. Kilo riders use disc wheels and five spoke wheels.
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Old 05-05-21, 12:05 PM
  #110  
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Originally Posted by colnago62 View Post
Grade is not the determining factor, speed is. If you climbing speed is above around 12mph Zipp 404 depth wheel will be faster.
OK, although may I suggest that for us non-mutant climbers, climbing above 12 mph means that we're on a shallow grade?
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Old 05-05-21, 12:11 PM
  #111  
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Originally Posted by colnago62 View Post
Grade is not the determining factor, speed is.
It's both. Aerodynamic drag is the same when you're doing 12mph on a 3% grade as on a 10% grade, but in the latter case, rolling resistance and weight offer much larger contributions.

Overall it's a pretty complex problem.
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Old 05-05-21, 12:15 PM
  #112  
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Originally Posted by terrymorse View Post
OK, although may I suggest that for us non-mutant climbers, climbing above 12 mph means that we're on a shallow grade?
In my case, climbing at above 12 mph is an enjoyable but fleeting experience which is only preceded by a steeper descent.
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Old 05-05-21, 01:22 PM
  #113  
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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.

Money for gainz? None of the people I've ever met that buy expensive carbon rims mention "rotating weight", "mass", or the Harmonic Motion principle. Each person buys them for two reasons:

1. They look spectacular.
2. They make a "whooooosshhhhhhhh" sound when you pedal fast.

The rest is flapdoodle.
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Old 05-05-21, 01:23 PM
  #114  
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Originally Posted by aplcr0331 View Post
Money for gainz? None of the people I've ever met that buy expensive carbon rims mention "rotating weight", "mass", or the Harmonic Motion principle. Each person buys them for two reasons:

1. They look spectacular.
2. They make a "whooooosshhhhhhhh" sound when you pedal fast.

The rest is flapdoodle.
You need to get out and meet more people.
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Old 05-05-21, 01:40 PM
  #115  
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Originally Posted by asgelle View Post
You need to get out and meet more people.
I need to meet more people who are into the marginal gains from their LARP'ing hobbies?

Ok, oddly weird but sure...next time I'm passing some carbon-fiber-roadie-in-a-lycra-skinsuit on my 50lb upright cantilever braked Fuji Hybrid I'll ask him about his rotational mass and whether he thinks that air pressure/density plays any role in their aero'ness. "Pardon me Lance Armstrong, but do you ride faster at sea level than you do when you're riding the Col du Tourmalet?"
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Old 05-05-21, 01:41 PM
  #116  
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Originally Posted by terrymorse View Post
When it comes to climbing anything above a shallow grade, weight trumps everything else.
Um, nope. It's not 1999 anymore.

Aerodynamic analysis of uphill drafting in cycling - https://link.springer.com/article/10...83-021-00345-2
Check out the research above they have a decent video in there analysis too.

But maybe you have some analysis you've read through. I'd love to see the research/analysis that shows weight trumps aero when climbing above a shallow grade.

Also, this author has some other fascinating stuff on the effects of Aerodynamics in the peloton...

Aerodynamic drag in cycling pelotons: New insights by CFD simulation and wind tunnel testing - https://www.sciencedirect.com/scienc...67610518303751

https://ars.els-cdn.com/content/imag...03751-gr22.jpg
https://ars.els-cdn.com/content/imag...03751-gr23.jpg

Last edited by aplcr0331; 05-05-21 at 01:58 PM. Reason: link fix
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Old 05-05-21, 01:42 PM
  #117  
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Originally Posted by aplcr0331 View Post
Ok, oddly weird but sure...next time I'm passing some carbon-fiber-roadie-in-a-lycra-skinsuit on my 50lb upright cantilever braked Fuji Hybrid I'll ask him about his rotational mass and whether he thinks that air pressure/density plays any role in their aero'ness. "Pardon me Lance Armstrong, but do you ride faster at sea level than you do when you're riding the Col du Tourmalet?"
Make fun if you like, but willful ignorance isn't something I'd go bragging about.
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Old 05-05-21, 01:46 PM
  #118  
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Originally Posted by terrymorse View Post
From the usenet archives:

So there's been no changes in equipment, knowledge, or testing of said equipment within the cycling realm in the last say....21 years since this comment was made?

Wow...TIL.

And major kudos for that picture of the guy checking his watch to see if his ride was fun. I'm stealing that for sure....lol PERFECT!
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Old 05-05-21, 01:52 PM
  #119  
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Originally Posted by asgelle View Post
Make fun if you like, but willful ignorance isn't something I'd go bragging about.
Oh damn you sure told me Professor! I hadn't realized the fact that we'd thusly entered the serious discussion zone. I'll try to measure up to your lofty standards. Please be patient with me Einstein, I'm a bit slow on the uptake.

It's willfully ignorant of me that of the (admittedly) small sample size of people I ride with who have carbon rims, bought them because they look cool and make a neato sound? Or it's willfully ignorant of me that I don't know anyone (other than the fine scholars of the hallowed halls of BF academia) who care so deeply about aero, rotational mass, and the rest?

I'll try to search out the serious cyclists out there and ask them to be my frenz, so as to avoid being ignorant.
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Old 05-05-21, 03:21 PM
  #120  
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Originally Posted by bruce19 View Post
As to this statement that I made....."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." What I was trying to say is that I see a lot of money being spent on wheels because lighter wheels reduce rotational weight. That supposedly has a major benefit. However,when I do a search about rotational weight, I get results that say that this "attribute" is largely a myth. If there is some science that says that rotational weight is what we have been told it is, I would like to see it. And, thus, I am willing to be convinced. This ignores the fact that some people "feel" a difference. I have no problem with that. We all spend our money on what we like. I'm just trying to sort out the objective science of it all.


Can we agree "a benefit" or "a difference" are things that can show up on the clock but they aren't things that have to? (Like a non scale victory during weight loss. )

Example: a bike handling the way you expect it to increases confidence in high speed corners. That might even show up on the clock, personally it's all about the sweet, sweet Gs. Just like skiing. Another example is when buying better gear made me feel more inspired to ride harder and take on more hills, and I got fitter as a side effect.

The science is: your speed on a bike comes down to (1) the power you're making, (2) how much of that power you're spending on overcoming things like rolling resistance, gravity, air resistance, and (3) the line you take and how much you use your brakes. Things like wheels, frames, etc, can help with #2, if you spend fewer watts fighting gravity, you have more left over to make you faster. It's really not a matter of opinion, how weight and aero affect your watt budget for a situation. Rotational weight is a real, very small contributor to that. Even the weight difference between a carbon or alloy frame isn't that big a deal unless the hill is pretty steep. That's all just math. The science is also: it affects the way the bike "behaves" in a way that some people really like. When a bike responds to your input the way you expect it to, you ride it better. 🙂

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Old 05-05-21, 03:24 PM
  #121  
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Originally Posted by bruce19 View Post
My comment about losing weight is meant to address the issue of rotational weight vs weight generally. If rotational weight's importance is basically inconsequential, that doesn't mean that a lighter wheel weight is unimportant. It only means that it's the reduction in overall weight that may have a significant impact. In that case, if I lose 10 lbs the overall weight of bike and rider would be reduced by 10 lbs without me spending $2-3K for a wheel set that might reduce the weight of bike and rider by a lb or so. Anecdotally, last year I lost almost 15 lbs and my climbing was so much easier and better. My bike's weight of 17+ lbs as ridden did not change. The point I was trying to make is that it is more cost effective for me to lose 10 lbs than to spend a lot of money to lose a lb of bike/rider weight. I was speaking for myself and not trying to say that other people should avoid whatever wheels they want.
It's also true the bike will never eat too many tacos.

Congratulations on losing 15 pounds, that's awesome, and I learned it's also not easy, it takes a lot of long term discipline but it pays off too.
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Old 05-05-21, 03:50 PM
  #122  
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Originally Posted by aplcr0331 View Post
Aerodynamic analysis of uphill drafting in cycling - https://link.springer.com/article/10...83-021-00345-2
Check out the research above they have a decent video in there analysis too.
Thanks, that's a very interesting analysis. It identifies a savings for drafting behind team members at speeds as low as 11 mph, which is a bit different than a weight vs aero component benefit analysis.

I found this chart from wheelscience.com that compares the weight savings needed to match the benefit of their aero wheels, at various climbing grades:



wheelscience.com weight saving needed to get same benefit as aero wheels for various climbing grades

According to wheelscience.com (a company that wants you to buy their aero wheels), at a 7% grade, the equivalent weight savings is 400 grams.
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Old 05-05-21, 03:54 PM
  #123  
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Originally Posted by aplcr0331 View Post
So there's been no changes in equipment, knowledge, or testing of said equipment within the cycling realm in the last say....21 years since this comment was made?
I'm pretty sure Newton's laws of motion haven't changed for quite a while.
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Old 05-05-21, 05:21 PM
  #124  
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Originally Posted by terrymorse View Post
Thanks, that's a very interesting analysis. It identifies a savings for drafting behind team members at speeds as low as 11 mph, which is a bit different than a weight vs aero component benefit analysis.

I found this chart from wheelscience.com that compares the weight savings needed to match the benefit of their aero wheels, at various climbing grades:



wheelscience.com weight saving needed to get same benefit as aero wheels for various climbing grades

According to wheelscience.com (a company that wants you to buy their aero wheels), at a 7% grade, the equivalent weight savings is 400 grams.
So if you already have lightened your bike as much as possible(or legal), wheels are the only other equipment change one could make to improve climbing performance. I wonder how those numbers would change with a less deep wheel, as those rims are used mostly for time trials. To lose 400 grams can be pricey. Either way, you will spend some money.

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Old 05-05-21, 10:10 PM
  #125  
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Originally Posted by terrymorse View Post
From the usenet archives:
Although it may seem daunting, when another rider pulls away on a hill
or in a bike race on the flat, these accelerations, except in standing
starts, are so small as to make the rotating mass story a hoax. Sure,
the mass counts twice as much when accelerating but two times zero is
still zero, and how long does a rider accelerate. Weight of bicycle
components for climbing is the main consideration, not acceleration.
The rotating mass story is a fable that sounds good and has just
enough technical truth to be one that will probably sustain itself
indefinitely
. Making equipment choices by it are a matter of faith,
not fact. — Jobst Brandt, 26-Mar-2000
I call B.S. on this. (Jobst Brandt knows way more about bikes and engineering than I do, but I think this old usenet post should be challenged.)

I think minute differences in acceleration can make or break competitors at the end of the race. If someone wants to say "it doesn't matter very much" it should be quantified.

I know the basic physics of aero being more important than mass, and rotational mass, but rotational mass is still a factor. We can't call it insignificant because most people can feel it, so if someone wants to claim it's so small it's meaningless they need to back up that claim with data.
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