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  1. #1
    CB2
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    240 grams rotational or 600 gram static

    Tax time is almost upon us which has given me a slight case of upgradenitis.
    Could swap out my rims and rim strips with Stan's Crests and yellow tape for a 240g savings, or my steel fork for a Niner carbon for a 600g savings.
    Rims would be cheaper but more work.
    Fork would be a quick swap, but a couple hundred dollars more, and also steepen the HT angle slightly.

    or
    I could just get over it, and leave well enough alone.

  2. #2
    ups and downs
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    You'd feel rotational weight changes instantly and everywhere, you'd likely only feel the fork weight difference in long climbs.
    I'm a member of NSMBA and IMBA Canada

  3. #3
    LMN
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    The rims will make a bigger difference, particularly on bigger hoops.

    The fork looks cooler.

  4. #4
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    And adding anything red is good for 2 seconds per lap.
    I'm a member of NSMBA and IMBA Canada

  5. #5
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    I would do the rims and in fact, I have a new Crest sitting at my LBS waiting for me to pick up. Adding to the lower rotational weight (but to a lesser degree), have you seen the ultra light Origin 8 branded rotors? A huge savings over the Avid BB7 stock rotors, like 1/2 the weight. For $20 retail . . . . . Niner Carbon fork, . . . . .meh.

    Oh, and thanks for the linkie. I did the same for you!
    Thanks to www.weavercycleworks.com for my awesome bike frames!

  6. #6
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    Why not both?

  7. #7
    mutaullyassuredsuffering
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    wheels

    Wheels no doubt. I hope the tax man is good to me!
    Free will is an illusion, people will always choose the perceived path of greatest pleasure.

  8. #8
    CB2
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    Quote Originally Posted by Gotta Know
    Why not both?
    You buying?

  9. #9
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    Mass at the very outside edge of the tire contributes 2x the inertia to the bike. So 240g savings on your rims will be less than 480g inertial mass. Losing 600g on the fork is better for both climbing (less weight) and acceleration (less inertia). No contest.

  10. #10
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    Quote Originally Posted by CB2
    Tax time is almost upon us which has given me a slight case of upgradenitis.
    Could swap out my rims and rim strips with Stan's Crests and yellow tape for a 240g savings, or my steel fork for a Niner carbon for a 600g savings.
    Rims would be cheaper but more work.
    Fork would be a quick swap, but a couple hundred dollars more, and also steepen the HT angle slightly.

    or
    I could just get over it, and leave well enough alone.
    get over it and buy gold and guns



  11. #11
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    Quote Originally Posted by spsoon
    Mass at the very outside edge of the tire contributes 2x the inertia to the bike. So 240g savings on your rims will be less than 480g inertial mass. Losing 600g on the fork is better for both climbing (less weight) and acceleration (less inertia). No contest.
    Ignoring that 2x is only a rule of thumb and is unlikely to be correct at MTB speeds, the fork weight loss does nothing to reduce rotating mass; angular momentum effects more than just climbing and accelerating. Simple arithmetic won't explain the handling improvements lighter wheels offer. Go for the lighter wheels unless you are unsatisfied with the performance of the fork.

  12. #12
    LMN
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    Quote Originally Posted by craigsj
    Ignoring that 2x is only a rule of thumb and is unlikely to be correct at MTB speeds, the fork weight loss does nothing to reduce rotating mass; angular momentum effects more than just climbing and accelerating. Simple arithmetic won't explain the handling improvements lighter wheels offer. Go for the lighter wheels unless you are unsatisfied with the performance of the fork.
    When I have tried different weight tires (200 grams) I came up with differences that can be measured on a power meter. When I have tried different weight frames (2lbs differt) I could not tell a difference with a power meter.

  13. #13
    CB2
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    I went with the rims. The fork was awfully tempting, but I really love the Singular fork.
    The rims weighed 370g each.
    I just swapped out the rims with my old rims (Sun EQ21's).
    Wheels weighed w/o skewers added up to 1530g.
    the total savings when I subtracted the rim strips, and velox tape was 290g.
    Here's the build:

    Front- Formula hub DT rev. 2.0/1.5/2.0, brass nipples
    Rear- DT 240SS, Wheelsmith 2.0/1.7/2.0, brass nipples.

    They built up quite nicely, and I was pleased with the quality of the rims

  14. #14
    LMN
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    Looks good.

    But why the brass nipples?

    I know shop rats don't like aluminum nipples but I have found with a bit of love they work quite well.

    The trick is to put grease on your spoke threads and then tension your wheel correctly when you build it. My Stans wheels are on their third season with alloys and I have had no problems (and yes I can still true the wheels).


    Quote Originally Posted by CB2
    I went with the rims. The fork was awfully tempting, but I really love the Singular fork.
    The rims weighed 370g each.
    I just swapped out the rims with my old rims (Sun EQ21's).
    Wheels weighed w/o skewers added up to 1530g.
    the total savings when I subtracted the rim strips, and velox tape was 290g.
    Here's the build:

    Front- Formula hub DT rev. 2.0/1.5/2.0, brass nipples
    Rear- DT 240SS, Wheelsmith 2.0/1.7/2.0, brass nipples.

    They built up quite nicely, and I was pleased with the quality of the rims

  15. #15
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    throw some racing ralphs on those rims -- i cant tell what tires you currently have on there, but i swapped my nevagals and saved 300 grams per wheel.

  16. #16
    CB2
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    Quote Originally Posted by LMN
    Looks good.

    But why the brass nipples?

    I know shop rats don't like aluminum nipples but I have found with a bit of love they work quite well.

    The trick is to put grease on your spoke threads and then tension your wheel correctly when you build it. My Stans wheels are on their third season with alloys and I have had no problems (and yes I can still true the wheels).
    I have some older road wheels built with alloy that are still fine and serviceable, but from my experience that isn't always the case. After 2 or 3 years on mtb wheels, nipples would seize or break, and with tubeless, there is just that much more to deal with to fix it.
    I used to always use alloy when building wheels for myself, but when every I would build a wheel for a customer with brass, I'd love the ease they took the tension.
    So ease in building and serviceability.

  17. #17
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    Quote Originally Posted by spsoon
    Mass at the very outside edge of the tire contributes 2x the inertia to the bike.
    Is this true?

    You have to accelerate the top part of the rim twice as fast, but the bottom part, not at all. Doesn't that balance out? Is there a definitive take on this subject?

  18. #18
    LMN
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    Quote Originally Posted by flargle
    Is this true?

    You have to accelerate the top part of the rim twice as fast, but the bottom part, not at all. Doesn't that balance out? Is there a definitive take on this subject?


    Once again your sense of humour kills me.

  19. #19
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    Quote Originally Posted by LMN


    Once again your sense of humour kills me.
    I wasn't joking (I think?). I've read various articles that talk about the "myth" of rotating weight, and that it's no more important than non-rotating, even when talking about accelerating the bike. I'm not distrusting your power data, just looking for a theoretical justification.

  20. #20
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    It is not true, it is simply an old rule of thumb.

    What you say is true, mass on the wheels averages out, but that's just linear momentum. Wheel mass also contributes angular momentum, though it turns out that the angular momentum is not as great as the linear momentum so the multiplier is not 2x.

  21. #21
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    Here is some online course material that addresses the subject directly:

    http://teacher.pas.rochester.edu/phy...Chapter12.html

    They work a specific example (12-1) using a solid disk where the multiplier is 1.5x. An ideal thin wheel would be 2x but a real-world wheel would be somewhere between those two.

    I once read a test where they empirically concluded that the multiplier was 1.4x. I believe they considered the hub weight in that estimation. Ignoring hub weight, it's clear that a disk wheel would be close to 1.5x and a normal wheel would be between 1.5x and 2x.

  22. #22
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    Brass nipples are defiantely the way to go here in New England. I'm pretty convinced that we get those rocks that "jump out at you" and hit those weal aluminum nipples...

    What where the wheels you replaced?

    Besides, wouldn't Singular have been a bit dissappointed if you changed their fork?

  23. #23
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    Quote Originally Posted by craigsj
    http://teacher.pas.rochester.edu/phy...Chapter12.html

    They work a specific example (12-1) using a solid disk where the multiplier is 1.5x.
    Excellent, thanks for the link.

  24. #24
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    I'm not quite convinced the physics lesson applies to the problem. Detectable difference from the power meter is pretty good evidence something is missing in the theory.
    Oh sh!+ just force upgraded to cat1. Now what?
    Best thing about an ultra marathon? I just get to ride my bike for X hours!

  25. #25
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    It's not a theory. The relationships between mass, velocity, momentum and kinetic energy are known facts. It is physically impossible for a real-world rolling wheel to have 2x the kinetic energy of a non-rolling one at the same speed. If power meter differences suggest otherwise, then subjectivity or inability to interpret the results are the cause.

    I did some back-of-the-napkin estimations yesterday of 3 wheels using real component weights. I did typical 26er, 29er, and 700c road wheel estimates and all came out between 1.72 and 1.74. Claiming 2x is a 30-40% overestimation of the angular momentum component.

    Incidentally, this also disproves the myth that 29er wheels have greater rolling momentum because of their size. 29ers have greater rolling momentum strictly due to their extra weight. Nowhere in the equation of the kinetic energy of a rolling wheel do you find the radius of the wheel as a term; only mass, velocity, and weight distribution.

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