New rider needs help with Mavic ES "Inertia" question

Discussion in 'Cycling Equipment' started by gregerson13, Jan 18, 2007.

  1. gregerson13

    gregerson13 New Member

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    I am looking at a new pair of Mavic ES wheels and when I was at the shop I spun the wheel and it turned for a while but seemed to slow somewhat fast at the end. The owner of the store said that they have "very low inertia" and that this is "good" for starts, braking, hills and control. The current wheels I have (very cheap) want to spin forever and I assumed that was a good thing. Does it sound like this guy knows what he is talking about because I definately don't.

    Thanks in advance for helping a newbie. . . .
     
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  2. sogood

    sogood New Member

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    I am aware of this observation. Initially I thought there was an issue with my bearing adjustment but it turned out to be not the case.

    But I bet there'll be a bunch of posts suggesting you away from that overpriced K-ES wheelset soon... :D
     
  3. dhk2

    dhk2 Active Member

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    Since all our current alloy-rimmed wheels have "low inertia", this sounds like typical salesman talk to me. Clever though, as he's claimed that the difference in inertia is so great that you'll notice it, even when just spinning the wheel by hand.

    Would guess the new seals and bearings on the ES wheels are a bit tight, that's all. After break-in, they should spin as well as your current wheels.

    One of the LBS here is a Mavic dealer, and he loves to push the SLs on everyone. Can understand why: no doubt the profits are huge at $875 USD, and he has a wife and kids to support. As sogood said, there are lots of other choices in wheels.
     
  4. bobbyOCR

    bobbyOCR New Member

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    Your LBS would tell you they gently fan you while you were riding, while being aerodynamic with low inertia....If you were gonna buy them. He is doing what salesmen do. If you get a bit of knowledge about them and walk in there and basically rattle it off talking about them, they will cange their attitude (maybe, works for me)
     
  5. sogood

    sogood New Member

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    I can't explain it as this observation is present on both the front and rear wheels. So the bushing bearing of the freewheel isn't the reason. I'd like to see how it compares with a wheel of similar weight spec but haven't had an opportunity.
     
  6. 531Aussie

    531Aussie Well-Known Member

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  7. sogood

    sogood New Member

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    Buy that doesn't answer this post's original question. Inertia may be small when taken the rider/bike as a whole, but when the wheel is isolated, the question of whether the lower mass is the explanation for present observation isn't confirmed.
     
  8. dhk2

    dhk2 Active Member

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    531's links were very interesting, but agree they don't answer the OPs question.

    My reason for answering that "it's not the inertia" is based on the fact that inertia couldn't vary enough to cause a huge difference in the time to come to rest. Consider that the difference between the ES (660 grams) and a "heavy" front wheel (eg, up to 1000 grams) is a max of 33%. Spun at the same speeds then, the ES wheel would come to a stop 33% sooner. If I read the OP correctly, this is not enough to explain what he saw as "slowing somewhat fast at the end vs "want to spin forever".

    Only thing left then is the conclusion that hub drag is higher on the new ES he saw. Clever the way the salesman changed this to an advantage for ES, but I don't buy it.
     
  9. alienator

    alienator Well-Known Member

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    The likely difference is in seal drag, the amount of grease in one hub vs. another, or any number of other factors.

    What the OP needs to know is there is nothing of value that can be gleaned from spinning a wheel in your hand about how that wheel will perform on the road.....unless it's a rear wheel, then you might be able to tell whether or not the rear hub's noise is irritating when it's freewheeling. The wheel isn't loaded so there's nothing to be learned about the bearings. Seal drag doesn't increase with speed so it's a non-factor in wheel performance. And as dhk2 said, the wheel spinning in a shop guy's hand is spinning way to slow for differences in moment of inertia to manifest. Hell, moment of inertia makes almost no difference in performance on the road, so the amount it'll make in a wheel spinning in someone's hand is much less than almost none.
     
  10. ScienceIsCool

    ScienceIsCool New Member

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    From the measurements I took, the ES has a moment of inertia similar to a lot of other wheels (0.039 kgm^2), but it had terrible bearing seal drag (coefficient = 0.013 or ~10 times worse than wheels with good seals) . I'd say that is why the wheel came to a halt quickly.

    John Swanson
    www.bikephysics.com
     
  11. sogood

    sogood New Member

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    This is a good answer to the observation. Thanks.
     
  12. dhk2

    dhk2 Active Member

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    Just went back and reread your paper. The results table is most helpful as it puts the various parameters you measured in context of overall power losses at speed.

    But, more questions (as always): Do the ES hubs use axle seals, like the "standard" cup and cone hubs? Would guess the hubs with lowest drag use no axle seals, but just rubber shields on cartridge bearings. How do you think a new Shimano DA or Ultegra hub would compare on seal and bearing drag to the old 105 hub you tested?

    Based on my limited experience with "no-axle seal" hubs, there may be a trade-off of low-drag vs effective sealing for durability in real-world conditions.
     
  13. ScienceIsCool

    ScienceIsCool New Member

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    I don't know the answer to your questions, but I do think you're right about the tradeoffs. The seals on cartridge bearings make for very low maintenace, but they do cause extra drag. I remember a time in the early 90's when people were removing all the seals and grease from their hubs, and lubricating with sewing machine oil. Very low friction, but you had to clean and relube after every ride/race.

    John Swanson
    www.bikephysics.com
     
  14. dhk2

    dhk2 Active Member

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    In my limited experience with Ultegra (axle-seal) hubs vs Velomax Circuit (cartridge bearings), the Ultegra hubs do a better job of sealing out rain and grit. After the first big rain ride on the Circuits, found the front bearings had corroded due to moisture getting past the (unsealed) end caps where it contacted the "sealed" bearings.

    A call to company Tech support was helpful, with the recommendation after rainy rides, the axle end caps should be pulled off and any moisture sitting on the bearings be removed. This is an easy two minute job, but probably not something I'd want to do often on a long rainy tour ride either.

    Note, searching for replacement bearings, I recall that they are listed as "2-RS", meaning they have "non-contact" rubber-coated seals on each side of the bearings. They aren't real lip seals, but just coated alloy washers; really "shields" is probably the better term. Have found the shields can be pried out and replaced for clean/relube.
     
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