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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
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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
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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
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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
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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
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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.

  26. #26
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    Quote Originally Posted by craigsj
    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.
    I think you have a serious misunderstanding of the situation here. Given equal weight, a larger radius hoop will have greater moment of inertia.
    http://en.wikipedia.org/wiki/Moment_of_inertia

  27. #27
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    Yes it does, but moment of inertia and inertia are not the same thing. A larger wheel spins slower at a given bike speed and this offsets the greater moment of inertia. Plug your equation for moment if inertia into the inertia equation and you'll see the radius terms cancel out.

  28. #28
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    Quote Originally Posted by craigsj
    A larger wheel spins slower at a given bike speed and this offsets the greater moment of inertia.
    Oops my bad. *slinks away*

  29. #29
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    Quote Originally Posted by craigsj
    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.
    I intentionally used 2x to overestimate the inertia reduction he would get from lighter rims. That's why I said the inertia reduction would be less than 480g equivalent non-rotating mass. Even being generous to the rims, the fork has greater benefit.

    Now, if you are talking about handling characteristics of the bike instead of just mass and inertia, then I am not qualified to comment

  30. #30
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    Quote Originally Posted by craigsj
    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.
    Over flat ground yes but what about the lower angle of attack over rocks and roots?

  31. #31
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    I think you are confusing that with rolling resistance.

  32. #32
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    Quote Originally Posted by craigsj
    I think you are confusing that with rolling resistance.
    I guess I am questioning your idea that there is a pervasive "myth that 29er wheels have greater rolling momentum because of their size." People do talk about 29ers "rolling better," due in part to their larger diameter and smaller attack angle.

  33. #33
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    Quote Originally Posted by flargle
    I guess I am questioning your idea that there is a pervasive "myth that 29er wheels have greater rolling momentum because of their size." People do talk about 29ers "rolling better," due in part to their larger diameter and smaller attack angle.
    This is true, but apparently according to the physics the radius of a 29er vs 26er has a very insignificant effect toward 29ers rolling better from increased rotational inertia. The greater rotational inertia the harder it would be to slow the bike down (even on a paved road). The physics claim that the greater rotational inertia of a 29er is from its increased mass rather than its increased radius. This has nothing to do with its angle of attack.

  34. #34
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    The bigger wheels also have a greater gyroscopic effect which gives more stability.

    I feel the 29er wheel adds a lot of confidence to the rider because its stability once you get the wheels moving...

    Large wheels maintain momentum better - the higher the speed, the easier it becomes to maintain momentum.

    Large wheels accelerate slower.

    29” wheels have more gyroscopic effect than their 26” wheeled little brothers, keeping the bike stable at speeds.

    ...the larger the wheel, the harder it is to get up to speed if looked at scientifically.

    Once up to speed, the 29” wheel maintains its momentum much better than a 26” wheel.

    The larger wheel offers increased centrifugal force, which in turn improves the bike’s stability.

    He [Willits] sees 26 inch wheels as inferior on the trail because they require handlebars and cranks that are too long to make up for the momentum disadvantage of the smaller wheels.

    These are some examples that I've found in a few minutes of searching and some may require some context to see why I chose them. Searching for this takes time. There was a classic smoking gun on this but I couldn't find it.

    Don't get me wrong, I like my 29er I just don't like the misinformation about it. I REALLY hate the "larger contact patch" claims. It's seems more and more people are getting that correct, though. Conrad Stoltz didn't.

    Quote Originally Posted by flargle
    I guess I am questioning your idea that there is a pervasive "myth that 29er wheels have greater rolling momentum because of their size." People do talk about 29ers "rolling better," due in part to their larger diameter and smaller attack angle.
    I'm fine with people believing that if they want to. I'm not sold personally on the smaller attack angle idea. I believe the wheels roll better, perhaps because of noticably better rolling resistance but I'm not sure it's 10% like some say.

    What EthanDM said is right.

    An interesting thing to think about: consider that you have two bike identical except for 26" vs. 29" and the wheelsets weigh exactly the same because the 26" wheels use slightly heavier stuff throughout. We know that the wheels will contribute the same momentum yet the bike will ride different. Momentum isn't what gives 29ers their characteristic ride.

  35. #35
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    Quote Originally Posted by craigsj

    I'm fine with people believing that if they want to. I'm not sold personally on the smaller attack angle idea. I believe the wheels roll better, perhaps because of noticably better rolling resistance but I'm not sure it's 10% like some say.

    What EthanDM said is right.

    An interesting thing to think about: consider that you have two bike identical except for 26" vs. 29" and the wheelsets weigh exactly the same because the 26" wheels use slightly heavier stuff throughout. We know that the wheels will contribute the same momentum yet the bike will ride different. Momentum isn't what gives 29ers their characteristic ride.
    nice googling
    29ers still suck

  36. #36
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    Quote Originally Posted by Gotta Know
    nice googling
    29ers still suck
    And so does your mom.

  37. #37
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    Quote Originally Posted by craigsj View Post

    ...

    I'm fine with people believing that if they want to. I'm not sold personally on the smaller attack angle idea. I believe the wheels roll better, perhaps because of noticably better rolling resistance but I'm not sure it's 10% like some say.

    What EthanDM said is right.

    An interesting thing to think about: consider that you have two bike identical except for 26" vs. 29" and the wheelsets weigh exactly the same because the 26" wheels use slightly heavier stuff throughout. We know that the wheels will contribute the same momentum yet the bike will ride different. Momentum isn't what gives 29ers their characteristic ride.
    OK. I’m curious.

    I always thought it was the attack angle that reduced the angle of the square edge bump that contributed significantly to the 29 wheel ride efficiency . I have worked it out once – it wasn’t a big number though – but I guess I just assumed it was significant to the ride. So going with your idea that maybe it is not the attack angle… what is it?

    Sooo...
    In your consideration of a 26 and 29 wheel of equal mass where the wheels will carry the same momentum.... Could it be tyre volume that gives some efficiency advantage to 29s? My scratch pad figures returned a 29x2.25 tyre is appox 5935cm^3 and a 26x2.25 is approx 5309cm^3… this would contribute to better rolling resistance as the German (http://www.mtbonline.co.za/downloads...llustrated.pdf ) study showed.
    Is it only rolling resistance that would give the 29 the efficiency advantage in that situation?

    OK so the next step is… if you kept the same weight but took away this volume advantage would you get a less efficient ride?

    For example: in WC XCO where (according to our fave XCO coach and apologies if I haven’t got the quote exactly) most – but not all – teams racing 29s set up the wheels to be as light as or sometimes even lighter than the 26 wheel next to them. They do this by using super light wheelsets (an acquaintance wrenched on WC team and related that by using less spokes, ti spokes, specially picked carbon rims these teams were getting the 29 wheelsets down to the 1200s and lower – however they were rebuilding them after most races) and super light skinny tyres at high pressures. It is the tyres that make it interesting. A 29x1.9 tyre has a volume of approx 4232cm^3 – significantly less than the 5309cm^3 of a 26x2.25 which is the predominant (but not all) sized tyre of the riders using 26in bike at WC XCO.

    Question. Are these guys kidding themselves? Are they actually less efficient? Is Maja W, Vogel et al who ride 29s but with larger volume, though heavier, tubular tyres on the right/better track?

    It would seem, on the face of it, the 26 bikes can have the best of both worlds – light wheelset - yet still ride a big bagged, low pressure tyre.

  38. #38
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    Quote Originally Posted by Electric Panda View Post
    In your consideration of a 26 and 29 wheel of equal mass where the wheels will carry the same momentum.... Could it be tyre volume that gives some efficiency advantage to 29s? My scratch pad figures returned a 29x2.25 tyre is appox 5935cm^3 and a 26x2.25 is approx 5309cm^3… this would contribute to better rolling resistance as the German (http://www.mtbonline.co.za/downloads...llustrated.pdf ) study showed.
    Is it only rolling resistance that would give the 29 the efficiency advantage in that situation?
    That's an interesting article, thanks for sharing it.

    Quote Originally Posted by LMN View Post
    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.
    Yeah, tires don't count. There's a lot more than just weight going on there.

  39. #39
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    Quote Originally Posted by litany View Post

    ....

    Yeah, tires don't count. There's a lot more than just weight going on there.
    I think you misread or miscomprehended LMN's post.

    An increase in tyre weight he could measure using a powermeter. It was frame weight that was far less important.

    My question/wondering is that tyre volume may be a very important factor (along with increased mass) of a 29 wheel ability to 'hold speed/momentum'. If that is so then at World Cup level XCO where many of the 29 bikes are set up with light wheels/tyres and skinny tyres do they loose this and is it better to go with the tubulars (which many do) which are a higher volume tyre even though it is more weight?

  40. #40
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    Quote Originally Posted by Electric Panda View Post
    I think you misread or miscomprehended LMN's post.

    An increase in tyre weight he could measure using a powermeter. It was frame weight that was far less important.

    My question/wondering is that tyre volume may be a very important factor (along with increased mass) of a 29 wheel ability to 'hold speed/momentum'. If that is so then at World Cup level XCO where many of the 29 bikes are set up with light wheels/tyres and skinny tyres do they loose this and is it better to go with the tubulars (which many do) which are a higher volume tyre even though it is more weight?
    My point was that when you switch tires to lose 200g you don't just lose weight, you may see huge changes in aerodynamics and rolling resistance (along with lower rotational inertia, lower unsprung weight, ride characteristics etc.) so to attribute all that to just weight, and say 200g in tires is better than 2lbs in a frame is a huge oversimplification.

    Go ride something like a 2.35" nevegal (~200g heavier) after riding some xc tires like race kings and tell me you don't notice a huge difference right away. With something like nevegals just coasting along it's as if you have a brake dragging quite badly--and keep in mind that while coasting, the increased weight of the tire means all things being equal it should take more time to coast down as ultimately more energy is stored in the heavier tire. If you can't notice that on a power meter I'd say your power meter is broken.

    As far as who is doing it right with the tire choices that article shows it would really depend on the course. Is there a lot of smooth hard pack that may roll much like a road (you'd want the skinny high pressure tires then) or is it really rough? Are the rough sections maybe only in the downhills where the extra rolling resistance won't hurt you as you're braking anyway? You may have to do a slightly different setup for each course to strike the best balance.

    At the same time that article didn't entirely make sense to me. The article talked about how the meadow provided much higher rolling resistance than gravel or road (and showed that in the figure on page 6) however on page 7 they are showing much higher resistance on gravel almost as if they accidentally swapped the labels for gravel and meadow on that figure. Additionally it appeared that on road the resistance peaked with the middle width tire. Why did it go back down? This is surprising to me and the article doesn't seem to address this at all.

    Also because of the much smaller effect that differences in the tires seemed to make on gravel vs road it would seem that perhaps it's not a huge overall difference. However the article did a bad job of showing the data for anything but meadow so it's pretty hard to tell.

    Personally I'll continue riding my fat tires at low pressures because I feel that gives me better grip and comfort and so far I haven't seen any reason not to. Considering how little actual testing people seem to do with bicycles and the pressure sponsors probably apply I'm not really surprised if pro racers don't get ideal setups.

  41. #41
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    Quote Originally Posted by litany View Post
    My point was that when you switch tires to lose 200g you don't just lose weight, you may see huge changes in aerodynamics and rolling resistance (along with lower rotational inertia, lower unsprung weight, ride characteristics etc.) so to attribute all that to just weight, and say 200g in tires is better than 2lbs in a frame is a huge oversimplification.
    oh sorry... yes absolutely...


    Quote Originally Posted by litany View Post

    As far as who is doing it right with the tire choices that article shows it would seem to really depend on the course. ...

    At the same time that article didn't entirely make sense to me.

    ...

    ...

    Personally I'll continue riding my fat tires at low pressures because I feel that gives me better grip and comfort and so far I haven't seen any reason not to. Considering how little actual testing people seem to do with bicycles and the pressure sponsors may apply I'm not really surprised if pro racers don't get ideal setups.
    re the article and the testing. From experience one off tests can be fraut with danger sometimes... but the general gist of it seems to back up current thinking...

    I would be interested to know the reasoning as to why the skinnys at high pressures are preferred in some race camps though... it may well be that the extra weight is a big thing...

    and yes I agree I am sure the race course would determine the final choice of pressures etc


    yes I am sold on fat tyres... currently running a 2.4 on the front and I am keen to put another on the rear.

  42. #42
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    I see where you are coming from.

    I actually used identical tires. One was a CrossMark UST 2.1 (700 grams) the other was a converted CrossMark 2.1 (500 grams). Both run at the same pressure.

    Yes, casing is going to effect things, but not a lot.

    Quote Originally Posted by litany View Post
    My point was that when you switch tires to lose 200g you don't just lose weight, you may see huge changes in aerodynamics and rolling resistance (along with lower rotational inertia, lower unsprung weight, ride characteristics etc.) so to attribute all that to just weight, and say 200g in tires is better than 2lbs in a frame is a huge oversimplification.

    Go ride something like a 2.35" nevegal (~200g heavier) after riding some xc tires like race kings and tell me you don't notice a huge difference right away. With something like nevegals just coasting along it's as if you have a brake dragging quite badly--and keep in mind that while coasting, the increased weight of the tire means all things being equal it should take more time to coast down as ultimately more energy is stored in the heavier tire. If you can't notice that on a power meter I'd say your power meter is broken.

    As far as who is doing it right with the tire choices that article shows it would really depend on the course. Is there a lot of smooth hard pack that may roll much like a road (you'd want the skinny high pressure tires then) or is it really rough? Are the rough sections maybe only in the downhills where the extra rolling resistance won't hurt you as you're braking anyway? You may have to do a slightly different setup for each course to strike the best balance.

    At the same time that article didn't entirely make sense to me. The article talked about how the meadow provided much higher rolling resistance than gravel or road (and showed that in the figure on page 6) however on page 7 they are showing much higher resistance on gravel almost as if they accidentally swapped the labels for gravel and meadow on that figure. Additionally it appeared that on road the resistance peaked with the middle width tire. Why did it go back down? This is surprising to me and the article doesn't seem to address this at all.

    Also because of the much smaller effect that differences in the tires seemed to make on gravel vs road it would seem that perhaps it's not a huge overall difference. However the article did a bad job of showing the data for anything but meadow so it's pretty hard to tell.

    Personally I'll continue riding my fat tires at low pressures because I feel that gives me better grip and comfort and so far I haven't seen any reason not to. Considering how little actual testing people seem to do with bicycles and the pressure sponsors probably apply I'm not really surprised if pro racers don't get ideal setups.
    "The best pace is suicide pace, and today is a good day to die." Steve Prefontaine

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