Part of the problem is your string analogy. The forces you're feeling when swinging the weights are the forces tended to by the spokes. And there's an equal amount of wheel on the oposite side generating an equal force in the opposite direction.

Can you push a stalled car? The force necessary to push something (a car or bike) on wheels is miniscule in relation to the weight of the object. Take a guess, how much force is needed to get several tons of car to roll? Clearly it's different, but the difference is really, really small when you're talking about the force needed to move a couple hundred grams of wheels.

Got an A in high school physics but I don't pretend to remember any of it...

I have felt the same sensations you are feeling, with lighter wheels. Then I remind myself that I'm accelerating a 70,000 gram object (me) on top of my bike!

It's kind of like strapping a brick to a hot wheels car and saying that the wheels should be lighter :)

-Physiojoe

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-Physiojoe
Instagram: @thephysiojoe
Cycling coach, Elite racer on Wooster Bikewerks p/b Wootown Bagels

I believe the term you're looking for could be moment of inertia. basically, moment of inertia of spinning objects is their resistance to a change in their motion. http://en.wikipedia.org/wiki/Moment_of_inertia
pretty cool when you're 1st year physics professor pulls out a big gyroscope for a demo and the whole class wakes up. here's a demo using a bicycle wheel at MIT
http://www.youtube.com/watch?v=8H98BgRzpOM

Inertia, I, is the sum of the mass*(the distance that mass is from the axis you want to evaluate)^2
so if everything is close to the center, inertia is less than if the same amount of stuff was further away.

for example:
the inertia of a solid disc is 1/2 *m*r^2.
the inertia of a hoop is m*r^2
so if the wheels have the same mass, and the mass is uniformly distributed among the volume of the rim or disk, a solid disk has the half the inertia of a rimmed wheel of the same mass.
Now of course I guess disk wheels weigh more? go figure that mess out.


But as you said, differences are small.

it does! The weight at the outer edge of your wheels DOES take more energy to get moving than the weight at the center. But your wheels weigh how much? and you weigh how much?

say you're really light. You weigh 66000 g with your bike frame etc.

Your wheels are pretty heavy. 1700 g.

I believe that after I'd done the math rim weight counts double. So overall wheels are 5% of your mass. Now say you have some really nice and light wheels. 1000g. That's a 2% change in equivalent mass. Now that's great if you're going from non-aero wheels to non-aero yet lighter wheels. But the fact of the matter is that if your wheels were aero in the heavy case and not in the light case you've almost certainly given something up.

The German is spot on. Moment of inertia is the principle working on the wheels.

You stated that it feels this way as you are accelerating and not when the wheels are at speed. That is when you are apply the most force (to accelerate) the wheel. When you are spinning at a constant speed, you are applying less force (you are only applying force to replace what is being lost (friction, drag, etc.).

The principle is at play in any rotating system and has two variables - Weight, and distance from center. Lets look at your cranks, for example. At first glance, cyclists should rush out and buy the longest cranks that they can find. When they actually try them out, however, they find that they can accelerate well (longer crank lever helps them), but they are really tough to keep spinning over long distances (larger moment of inertia hurts them). So they settle somewhere in the middle.

Ask a race-car mechanic - how do I get from 1,000 rpms to 10,000 rpms faster while not changing any horsepower? - reduce rotating weight (lighter flywheel, crank, etc.).

Hope that helps.

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G

If this doesn't answer your question, nothing will:

http://weightweenies.starbike.com/...t=runge+kutta#p60824

Love it. That is a great post.

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TriRig.com
The Triathlon Gear Guide

THAT GUY is the reason I dropped out of engineering school to become a cop :) Mark McM must be a MIT mathmatical prodigy.

A heavier (typo corrected, see posts below) wheel will take significantly more energy to accelerate, but it takes virtually no extra energy to keep it going at a constant speed (there is a little since rolling resistance increases with bike/rider weight....but what % of that total is your wheels?).

Since most riding is done at a relatively constant speed, wheel weight isn't that important. Even when you slow down going up hills or down the rate of acceleration/deceleration is quite small.

When climbing you are dragging the entire bike&rider weight up the hill. In that respect wheel weight is no different from weight in any other part of the system.

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

why not go to his website and buy something?
PS: don't say his name three times!

The first half of the sentence, really?

He meant heavier wheels take more energy to accelerate.

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TriRig.com
The Triathlon Gear Guide

I've got my own physicist ;-) and over a few beers and a bottle of scotch (with the help of a water cooled calculator) we came up with something like

Given 112 miles and an avg power output of 300watts and a net zero altitude delta the results are: we were too drunk to figure.

Given 100meters level, and a constant power of 500 watts, the difference of a system (rider and bike of equal drag) traveling over that 100m with the only variable being 483g of rotational inertia (the rim of the wheel) the time of acceleration of one system to the other over the 100m was about 2 meters.
We later sobered up to find that the lighter system accelerated faster by a very small amount and that once that moment of acceleration was ceased (the system reaching maximum speed for the 500 watts) the systems equilibralized and the math was pretty much the same.


Now, the equations work in a way that as watts go up the difference in acceleration goes down (something about the square or cube of something) so the stronger you are, the less it matters in a sprint. But of course the stronger you are in a sprint the more every advantage matters.


But in a Tri, on a flatish course, well, we like to drink more than that equation.

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This is your life, and it's ending one minute at a time. - Fight Club
Industry Brat.

Yes. Thanks for catching my typo (now fixed in my original post).

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

I think that the key of T'war's formula is that the reach of equilibralization is proportional to the epicness of the drinkage. I like that.

It seems no-one really adressed your question so I'll take a stab.

Yes, there is a difference in effort required to spin up a heavier wheel.
Yes, you can feel it.
Yes, this will be more pronounced during climbing.
(No, it won't matter squat in a tri)

The reason you feel it more when you ride slowly, like after a corner or climbing (or MTB-ing) is that for a given power you have more acceleration force and thus more acceleration. That's when a bigger proportion of what you put into the pedals goes into the inertial effects.

If we discard the aero, rolling and "slope" resistance and extract the phenomena you are feeling:
Power = Force x Velocity -> Force = Power/Velocity
at the same time:
Force = (inertial) Mass x Acceleration

so:
Power/Velocity = (inertial) Mass x Acceleration
or:
Acceleration = Power/(Velocity x (inertial) Mass)

For a given Power you feel the acceleration more if the Velocity or inertial Mass or both are low.

The velocity is low when you climb or exit a sharp corner.

Another factor is what happens when you stand up to accelerate. Then the "inertial mass" is somewhat separated into a "bike mass" and your mass. Now you can really feel the difference because the difference between heavy and light wheels is compared to ~6kg of bicycle + parts of your arms and feet/legs, say 15kg. It becomes more "lively" underneath you for each "stomp". You still have to accelerate the whole package though so it won't matter that much, it just feels like it.

So here is my part of the question:

If I had two sets of wheels, both the same teroidal profile, one set is Zipp 404, the other is made of concrete in the same mold as the 404's.......on a totally flat course, zero wind, same bike/rider, 40K TT, at 300 watts, will they come in at the same time.........the model on weightweenies suggests that the concrete set would be faster!?

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http://theworldthroumyeyes.tumblr.com/

Not to take anything away from jackmott or Tom A., they both have great insights and I have learned a good amount from both of them. But, anybody notice that when their adive is not specifically requested they are all over the post but when directly asked they are nowhere in sight? Just an observation.

Hey, I apologize for being in the middle of traveling while my input was requested.

why is it people love conspiracy theories so much? Same basic reason people can't accept that wheel weight doesn't matter appreciably more than frame weight or ass weight I imagine. people crazy =)

The link posted above says it all:

http://weightweenies.starbike.com/...t=runge+kutta#p60824

That people can feel the difference in a light set of wheels could be due to:

imagination
ability of the human body to perceive tiny differences when accelerating at slow speeds
lightweight wheels can sometimes save you a couple pounds of total weight, which is a lot. wheel or not. maybe you feel THAT
maybe you feel the better tires you have on your better wheels.

lighter is better, but not especially so on wheels.

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

What I'd like to see quantified then is how much time you lose on a dead stop with light versus heavy wheels, going from 0-20mph. I race on a lot of courses that are neither straight nor flat. One of my favorite local sprints has 8 dead stop turnarounds. How much time do I lose with heavy wheels during those turns?

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TriRig.com
The Triathlon Gear Guide

analyticcylcing.com has a whole tool for calculating exactly those sorts of things.

http://www.analyticcycling.com/WheelsSprint_Page.html

the default values compare a 32 spoke wheelset to specialized trispokes. but you can enter whatever you like

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

Can't do the numerical integration off my iPod so I'll have to do an energy anaysis instead.
If Zipp 404 is approximated with 20x60 mm you get ~5kg of rim weight, so that's 20 kg of inertial mass added.
Say your resistance numbers yields you 13m/s at 300W, you pass the finish line with an extra 20x13^2/2=1690J kinetic energy and that equals 1690/40000x13=0.5W.
But your rolling resistance will increase by 0.004x100x13=5.2W
Say you lose 6W total, that's 0.6x40=24 seconds down (+/-5s)

Perfect - thanks, Jack. I must be misunderstanding analytic cycling, because my inputs keep breaking the models. If you drop the wheel inertia below 0.7, the speed plots go negative. Happens in both the Sprint and Breakaway simulations. Hmph.

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TriRig.com
The Triathlon Gear Guide

Another energy analysis, 1kg extra total weight at the rim/tire will require 2x13^2/2=169J.
I'd say you lose 0.5s (wow, that's a lot!) everytime you accelerate to 46 km/h with your 340W...