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PostPosted: Tue Mar 04, 2014 1:12 am 
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Tubbie Guru

Joined: Tue May 03, 2005 2:20 am
Posts: 5786
Location: Belgium
Hi,

Quote:
I'd choose the lighter wheel - or lowest Moment of Inertia - for racing - always.


I wouldn't. Not always anyway. The are times were having more flywheel effect can be an advantage all else kept equal.

Having low inertia isn't a big factor in the grand scheme of things. Aerodynamics, total moving mass for instance are far more important.

Ciao, ;)

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PostPosted: Tue Mar 04, 2014 1:38 am 
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Joined: Wed Oct 30, 2013 12:52 am
Posts: 235
fdegrove wrote:
Hi,

Quote:
I'd choose the lighter wheel - or lowest Moment of Inertia - for racing - always.


I wouldn't. Not always anyway. The are times were having more flywheel effect can be an advantage all else kept equal.

Having low inertia isn't a big factor in the grand scheme of things. Aerodynamics, total moving mass for instance are far more important.

Ciao, ;)
As I posted " - equal in all but weight -" - so those other things are already considered.
Knowing it only added weight and nothing else - where would you add weight to a wheel to make the bike faster?

This site has posts on alloy water bottle bolts. Freewheel friction at high speeds with gear limits is a more significant factor.


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Posted: Tue Mar 04, 2014 1:38 am 


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PostPosted: Tue Mar 04, 2014 1:52 am 
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Tubbie Guru

Joined: Tue May 03, 2005 2:20 am
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Location: Belgium
Hi,

Time trial stage on flat or reasonably flat stretches, track races for instance.
It would have the most impact on the wheels periphery: rim and tyre. That is provided the tyre still has low enough RR not to have a negative impact on overall performance.

Ciao, ;)

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PostPosted: Tue Mar 04, 2014 3:55 am 
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fdegrove wrote:
Hi,

Time trial stage on flat or reasonably flat stretches, track races for instance.
It would have the most impact on the wheels periphery: rim and tyre. That is provided the tyre still has low enough RR not to have a negative impact on overall performance.

Ciao, ;)
Being everything else is equal (so no increased RR), and on a Track - How much weight would you add? 200g or 20kg? Assume there is no added aero drag - everything else is equal (per my post). How does added weight help?


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PostPosted: Tue Mar 04, 2014 6:33 am 
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Posts: 327
.


Last edited by Causidicus on Wed Jun 18, 2014 12:16 am, edited 1 time in total.

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PostPosted: Tue Mar 04, 2014 1:58 pm 
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Joined: Tue Apr 18, 2006 3:03 am
Posts: 1873
Location: Islip, NY
Spinning in a stand with no weight on the axle will net different results than out on the road. The fastest system you can get would be the Alchemy hub with the least amount of unsupported axle. If it were me, I would take my hub, remove all the seals on the and remove all grease in the hub. Then replace with motor oil. That will make the hubs spin forever and most importantly, still spin as free under load. Unfortunately, Alchemy hubs can't by purchased for a while. They are restructuring their business.

I think the next best option would be Dura Ace hubs. The bearings are outboard and the freehub is a load bearing structure. Again, strip it of grease and use light oil. You can even remove the rubber seals. This is what track cyclists have done for the longest time.

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PostPosted: Tue Mar 04, 2014 2:52 pm 
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Joined: Fri May 25, 2007 6:43 pm
Posts: 1938
Strip the grease out, use a light oil, remove seals that aren't "outward" facing i.e. anything facing into the body.

Be prepared to exchange bearings on a more regular basis.

Fastest feeling hub i ever had was a goldtec SAM which ran on an oversize axle with a nitrided surface, then a combination of needle rollers and deep groove cartridges. All running with no seals and a total loss lubrication system.
Used to roll for ages, but left me with a filthy cassette after every race (as that's where the oil ended up!)

Unfortunately, long since discontinued :(


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PostPosted: Tue Mar 04, 2014 4:09 pm 
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Tubbie Guru

Joined: Tue May 03, 2005 2:20 am
Posts: 5786
Location: Belgium
Hi,

Quote:
Being everything else is equal (so no increased RR), and on a Track - How much weight would you add? 200g or 20kg? Assume there is no added aero drag - everything else is equal (per my post). How does added weight help?


Much depends on the rider but I'd add at least 200 to 350g per wheel. it helps to sustain a steady cadence due to the flywheel effect .
Stored energy being return but delayed.

Ciao, ;)

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PostPosted: Tue Mar 04, 2014 5:47 pm 
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Location: Islip, NY
On 40+mph long descents I would favor aerodynamics over weight every time.

When pedaling isn't an option, do this.

Image

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PostPosted: Tue Mar 04, 2014 6:03 pm 
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As much as I am a weight weenie, it seems there is something to the flywheel effect of a heavy wheel, as long as there is not so much climbing that the disadvantages outweigh the advantages. As evidence, I cite Ondřej Sosenka, who used 3.2 kg rear wheel to break the hour record in 05'. I have tried to find more info on this setup, but most references on the web only mention it in passing.

Also, there was that spoke weight device that was making the rounds several years back. A guy in Boulder had developed it and Taylor Phinney tested it as a junior if memory serves. It had weights that slid on the spokes, and had some sort of springs that would hold them in toward the hub, until centrifugal force overcame the springs and moved them outward. This was supposed to offer the benefits of the flywheel effect at higher speed, when they weights would ride outboard, but reduce the rotational inertia at low speeds for climbing. Obviously total weight would remain the same, so you would still have to drag that mass uphill, just with lower rotational inertia.

I have heard a few explanations for the flywheel effect being helpful, and the commonality of them all is that they suggest that it is advantageous to store energy in one condition in order to receive it back in another condition. This has been suggested to help, as Causidicus suggested above, during the dead spots in the pedal stroke, helping to reduce the micro decelerations that would occur twice per pedal stroke. I have also seen it suggested that the flywheel effect helps on a slightly longer time scale. We have all had the experience of the "zone"/strength or whatever you want to call "feeling good" coming and going within a single effort. One minute you are ripping like Cancellara, and then you start to feel less good for a bit, only to have your good form return a minute later. The reasons don't really matter, as the point is that it is suggested that they heavier wheel will help to carry you through those weak period with more speed. Last, but related to the above two, it has been suggested that the flywheel will help on SHORT climbs, as it will store energy on the flat leading up the climb, and help carry you up the hill at a higher speed. Obviously, if the hill is long enough that you slow to your standard climbing speed, then the wheel will become dead weight, but for shorter hills, the wheel can carry you up and over, and then you can "recharge" the wheel on the following flat or descent.

From my understanding, the main reason that this is advantageous, rather than being a zero sum situation, is that the wheel will store and redistribute your power output to points in the effort when you are going slower, thereby reducing losses to aerodynamic drag, while boosting overall speed for the effort as a whole.

Back to the OP's original question regarding freewheels though, I had forgotten to mention this (unscientific) spin down test I saw a while ago on those crazy Gokiso hubs vs DT240s (http://cyclingtips.com.au/2014/02/gokis ... bs-review/). My interpretation of the chart is that freewheel drag is a great equalizer, at least between these two hubs, because as soon as it comes into play (the "chain on" condition), they are fairly closely matched. Also, within 240s results, it looks like freewheel drag adds (very roughly) about 20% to the drag when compared to the "chain off" condition. This was less of an increase than I anticipated, but on further reflection, I guess it may be due to the increased number of axle bearings engaged in the "chain off" condition, which partially offsets the drag of the freewheel mechanism itself.


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PostPosted: Tue Mar 04, 2014 10:02 pm 
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Joined: Wed Oct 30, 2013 12:52 am
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ergott wrote:
On 40+mph long descents I would favor aerodynamics over weight every time.

When pedaling isn't an option, do this.

Image

If you were doing that for 10+ min, how significant do you think the freewheel drag would be? (all else being equal)


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PostPosted: Tue Mar 04, 2014 10:23 pm 
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Joined: Wed Oct 30, 2013 12:52 am
Posts: 235
TheKaiser wrote:
As much as I am a weight weenie, it seems there is something to the flywheel effect of a heavy wheel, as long as there is not so much climbing that the disadvantages outweigh the advantages. As evidence, I cite Ondřej Sosenka, who used 3.2 kg rear wheel to break the hour record in 05'. I have tried to find more info on this setup, but most references on the web only mention it in passing...
I did nor mean for this to be a wheel weight discussion, but a freewheel drag discussion. Particularly on BRAND / type that offers lower resistance. But, as the wheel weight has become an interesting off track discussion...

I do agree there may be something to humans doing burst efforts, then allowing momentum to carry them on while they rest. This is the TT method my kid uses over trying to pedal 160 RPM, but he is using the mass of his body and bike, not the wheel. As I just ran over my Zipp 900 with my car last week, I soon have to make the choice between a 950g disc and a 1300g disk. Hmmm...

I do not follow track and hour record, but Ondřej Sosenka - did he add weight to the wheel? Moser had a huge wheel when he broke the record - but it was heavy because it was big. I would like to also know of any pro TDF teams that choose to add weight to their wheels in any stage. So - take wheel A - and add weight to wheel A and go faster. Not wheel A is faster than wheel B and wheel A is also heavier (I buy that). I understand the TFinney example, but I have not seen it actually used in any RR situation. Any stored energy to be legal must be put into the system during the race, meaning to get that momentum, the rider had to expend energy to put it there. consider also that actual racers spend lots of time with side to side movement. Its not near the straight line physics problem we think it is.

Long time ago I did pine wood derby racing. We used a car with jewel watch bearings and weighted wheels and while it started slowly it just carried a lot of speed through the hump on the track. We also had a car where we took the old Hot-wheel car axils and made light wheels. That thing just was much much faster.

In bike racing I have not seen anyone adding weight for the adding weight purpose. As most UCI bikes are underweight, I would think that weight would then be added to the wheels, yet most add to the BB, seat tubes.


Last edited by Zoro on Tue Mar 04, 2014 11:54 pm, edited 1 time in total.

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PostPosted: Tue Mar 04, 2014 11:42 pm 
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Joined: Wed Sep 20, 2006 1:03 am
Posts: 300
Location: Phoenix, AZ
I don't mean to be too blunt, but this talk of the "flywheel effect" somehow increasing speed on a flat course is a bit silly.

One poster suggested that heavy wheels "help to sustain a steady cadence." The masses he suggests are much too small compared to that of the bike/rider system to have any effect. But even if they weren't, why would a very slightly more steady cadence be an advantage? Do you ever get dropped because the cadence of your group varied by 0.01 RPM from moment to moment? I've explored all sorts of ways to get dropped, but usually it has more to do with insufficient power.

This is an old myth that pops up every once in a while. Even major manufacturers get sucked in. For example, Mavic used to make a Comete disk with removable weights. To wit:

http://velobase.com/ViewComponent.aspx? ... 1&AbsPos=3

You'll notice that Mavic no longer makes this wheel. If it provided a measurable advantage on the flat, why would they stop?

TheKaiser wrote:
From my understanding, the main reason that this is advantageous, rather than being a zero sum situation, is that the wheel will store and redistribute your power output to points in the effort when you are going slower, thereby reducing losses to aerodynamic drag, while boosting overall speed for the effort as a whole.


Although this belief is popular, it's not actually true. This is a zero-sum situation for two reasons: (1) There is no mechanism for a higher inertia to reduce aerodynamic losses, and, even if there were, (2) the changes in speed due power variation over the pedal stroke are unmeasurably small on the road (but not on, say, a wind trainer).

For steady-state riding on the flat (or on a velodrome) wheel mass has essentially zero effect. It does slow you down as you accelerate to your steady-state speed. One could argue that a pair of high-moment-of-inertia wheels are a hindrance on the track due to the fact that you're essentially taking two large gyroscopes through 360 degrees of rotation (which they resist) every lap. The losses would be very small, of course.

Sosenka broke the hour record with a heavy wheel, it's true But he did so in spite of its mass, not because of it. If the heavy wheels faction wants to ride 3-kilo disks on the flat, they certainly can...it makes no difference to me or the clock.

Cheers,

Jason

(For what it's worth, I'm a mechanical engineer).


Edit: I spelled "too" as "to." Fixed.


Last edited by youngs_modulus on Wed Mar 05, 2014 1:43 am, edited 1 time in total.

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PostPosted: Wed Mar 05, 2014 12:03 am 
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Joined: Wed Oct 30, 2013 12:52 am
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youngs_modulus wrote:
...For steady-state riding on the flat (or on a velodrome) wheel mass has essentially zero effect.
I can see we agree on wheel weight. However I am not a believer in there being steady-state riding.
youngs_modulus wrote:
(For what it's worth, I'm a mechanical engineer).

I was an electro mechanical engineer (solenoids and stepper motors in the 80s) - before I became a software guy.
Still I found the wheel one of the most fascinating things in my physics classes, yet put a person on their bike and its as easy as calculating where all the pool balls will go.


Last edited by Zoro on Wed Mar 05, 2014 2:14 am, edited 1 time in total.

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PostPosted: Wed Mar 05, 2014 12:03 am 
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Joined: Wed Oct 30, 2013 12:52 am
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Duplicate


Last edited by Zoro on Wed Mar 05, 2014 2:15 am, edited 1 time in total.

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Posted: Wed Mar 05, 2014 12:03 am 


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