Which is best in wheels- weight or aerodynamics?

Discussion in 'Road Cycling' started by mcfc09, Jul 17, 2009.

  1. mcfc09

    mcfc09 New Member

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    Hi,
    I've been looking to get some new wheels in the price range of £750-£1500 but I can't decide which is better lightweight or aerodynamics can anyone help?
     
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  2. geerfree

    geerfree New Member

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    Depends on what sort of riding you do, aero wheels are good for flats, light weight for the hills.
     
  3. alienator

    alienator Well-Known Member

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    One of the biggest myths going is that lightweight wheels offer some significant performance advantage. They don't. Aero rules until the road grade exceeds 10% or so, after that weight--actually moment of inertia--starts to dominate wheel performance. Now before read too much into that, there's this: moment of inertia doesn't start to dominate because of its great effect. It starts to dominate because aero benefits fall of the table at slow speeds. Moment of inertia benefits just decrease more slowly. MOI is still tiny.

    What really matters is body weight.

    With that get aero wheels. I've got a set of wheels built with 55 mm rims and weigh 1345g that climb at least as well as the 880g wheel set I used to have.
     
  4. azdroptop

    azdroptop New Member

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  5. 25hz

    25hz New Member

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    Go aero, every time.
     
  6. Meek One

    Meek One New Member

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    +1

    You don't see pros climbing on 808s, but since you live in the UK. Go aero.

     
  7. alienator

    alienator Well-Known Member

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    But you see pros climbing on Boras, Zipp 303's, Zipp 404's, and so on. So much for the pros not climbing on aero wheels myth.

    It's time people get a reality check and realize this whole "rotating mass" thing with bicycles amounts to a whole lot of nothing. Do the math. Do the science. You'll see what's already been verified. FYI, the math and science show the best possible results, for a given set of conditions, for the rotating mass crowd, and those results are miniscule. In the world, the differences are even smaller.
     
  8. swampy1970

    swampy1970 Well-Known Member

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    You've obviously not climbed too many hills in the UK have you. They might be on the shorter side when compared to mainland Europe but they're generally fecking steep.
     
  9. alienator

    alienator Well-Known Member

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    Steep. Shallow. It's all the same: rotating mass isn't the issue cyclists think it is. It's a mental thing. Full stop. Even the weight of wheels isn't that great. The only problem I see with climbing with 808's is possibly dealing with fickle winds, after the climb, and on the descent.

    It be nice if one of these rotating mass believers could offer up proof of why their belief is true, but they can't: it's not in the math/science. It's that simple.

    It's time to grow up, move on, and blame the suffering on a climb on something else.
     
  10. Feltski

    Feltski New Member

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    Whenever im at the LBS and I hear someone talking about saving x amount of grams by paying and extra 500 or whatever, it always makes me laugh. Most of the time, the weight youre saving is the same weight you could lose by taking a piss before the ride. Also, as a rather large guy (220lbs) I cant warrant buying super lightweight stuff until im at a lighter "racing weight)

    My vote goes to aero. The time difference bw shallow and deep rimmed wheels has been well documented, regardless of the weight difference. theres a good reason companies like Zipp spend so many hours in the wind tunnel. I recently read that Giant teamed up with a Formula One racing team when designing the new trinity sl TT bike
     
  11. howardjd

    howardjd New Member

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    Your absolutely right about light weight wheels being a myth. I've tested water vrs air inflation over a 9mile gently rolling return to start course at 300watts and actually got about 15sec faster with the water. Enhanced gyroscopic stablity leading to straighter riding and energy storage are the reasons I've hypothesized for this result. Just think about Sosenka's 3.2kilo rear wheel and Mosers monsterous rear wheel. I'm pretty sure since these guys were riding for the hour the did some in field testing before hand. I personally have constructed a 7 and 12 pound disk wheels named the "Chunky Churner" and "Air Hammer". Once up to speed slower accelerations are actually a plus because you deccelerate slower. Heavy wheels also performed very well in windy conditions. I've road the 12 pound disk on a gusty day and found no problem riding straight, good old gyroscopic stability.
     
  12. alienator

    alienator Well-Known Member

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    Sorry, your test only shows a very limited result. It makes no over arching statement. In fact, the "water test" is one of the worst tests to be done of all wheel tests. Did you use a power meter? What variables did you account for? What variables did you hold constant?
     
  13. alienator

    alienator Well-Known Member

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    Double post.
     
  14. An old Guy

    An old Guy Member

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    Use the wheels you have. When you wear them out, get a wheel with a PowerTap hub. Much better investment. Might as well get one now. I prefer Mavic OpenPro rims - my preferred tires go on easily.

    ---

    Maybe you could tell us how fast you ride, alone or in groups, and what sort of terrain you ride on.

    ---

    Rotating mass is really neat. Some people claim it is enough to produce a gyroscopic effect. Some people claim it limits acceleration.

    Both are right, but not enough to matter in the real world.

    If in the real world rims weighed 6 or 12 pounds, then 2 of those wheels might change things enough to matter. (An extra 24 pounds on long up hills would make a boy into a man in short order.)
     
  15. howardjd

    howardjd New Member

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    I did use a power meter. Yes my testing is limited but I've been injured for a couple years and have not been able to do follow up testing. I controlled power, clothing, and cadence. Tire pressure was actually lower for the water at 90psi vrs 100 because of difficulties pumping it into the wheel. I've heard water should have a higher rolling resistance because it is incompressible but have not found any studies to verify this. If you would like I ask that you perform such test for yourself so you can feel the difference in how the bike rides. I also think different riders will respond differently. I would like other riders to try it so I can get a broad range of data as I am writing a paper on the subject and need in dependant studies to either verify or disprove my findings.
     
  16. alienator

    alienator Well-Known Member

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    I've no interest in doing a study with water in tires because it makes for a lousy model. One big unknown is the friction between the water inside and the rotating inner tube. Also unknown are the losses due to turbulence. Also the water doesn't really provide rotational motion. After all, to a first order approximation, it remains in one place. To that end, it does not behave at all like a wheel with a large moment of inertia. In essence, you'd have had similar results with weights taped to the frame. Better results would be had with attaching lead weights to a rim and/or spokes. In any case, aerodynamics dominate wheel performance until the road grade gets pretty steep. Then, weight takes over. Where that crossover is depends on a number of factors related to the wheelw, the specific bike/rider system in question, and the road quality. Note that when weight starts to dominate on steeper grades, it dominates strictly as weight (mass, actually), not in its distribution in the wheel (moment of inertia). For normal conditions, moment of inertia for bike wheels is not a big influence. You can of course take MOI to an extreme by significantly increasing it, and you can also make weight/mass significantly greater thus also significantly increasing a bike/rider system's inertia. In both cases, however, you will also start encountering significant penalties for those increases.
     
  17. howardjd

    howardjd New Member

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    Some problem with lead weights is getting enough mass to significantly increase the wheel inertia, it would effect aerodynamics, and the difficulty of actually attaching them. Beleive me I've though about all of this water was the most efficient way to test this. One aspect of increasing the wheel inertia of the bike is how it affects rideability and that you can test with using water. Well anyway I hope you change your mind and give it a go if you do you may be suprised. Thanks for the input by the way I had not considered the factor of the water moving around inside the tube. I did bleed and re pumped with water several times to unsure there was no air bubble but I guess there could still be currents generated inside the tube.

    The big difference between weight on the frame to weight on the wheel is that frame weight does not contribute to spin angular momentum.
     
  18. alienator

    alienator Well-Known Member

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    Not contributing to angular momentum means there no benefit to putting weight on the wheels. A specific problem with water in the tires/tubes is that not only does water not rotate, it changes the center of mass of the bike, the handling of the bike, and the stability characteristics, and it does so in very unrealistic fashion. In doing so, the test becomes meaningless since it is no longer an accurate representation of a bike/rider system. I don't see the need to put water in my tires/tubes and won't do so. A mathematical model of a bike is easy enough to create and has been done many times. In fact the model at the following link, generated by Mark McM, is very accurate and will easily show you the effects of different wheel MOI. Note that in his model the wheel MOI is given by mr^2 (this demands that the axis of rotation be coincident with the wheel axle's axis of symmetry). Here's the link: http://weightweenies.starbike.com/forum/viewtopic.php?f=3&t=6394&start=52 FYI, there's no need to be able to put huge amounts of mass on a wheel. It's easy enough to record data for several different wheel masses and do a best fit to that data. You'd be able to reduce the noise in the test by increasing the number of test runs done, both at a given wheel mass and in the number of different masses used. You can even use Excel to fit the data by having it fit a second power polynomial, i.e. it will fit to a+bx+cx^2, where a will be some offset, b will be inertial effects, rolling resistance, and bearing resistance, and c will be aero effects.
     
  19. alienator

    alienator Well-Known Member

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    Another fucking double post.
     
  20. mpre53

    mpre53 Well-Known Member

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    It's an inherent problem in the Huddler platform used to power the site. Almost every Huddler powered site suffers from it. /img/vbsmilies/smilies/rolleyes.gif
     
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