Is hub weight in a wheel really improtant?- Mtbr.com
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  1. #1
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    Is hub weight in a wheel really improtant?

    I was thinking of getting a light wheelset using chris king hubs. I noticed the weight of a rear XT hub disc is only about 60-70 grams more than CK ISO disc hub. Given that the rims (mavic 317) and spokes(DB 14/15 g) for both wheels would be the same, isn't the rotational mass thing mean that the using lighter weight hubs doesn't really help in acceleration (since the difference in weight is centered around the axel and not out at the rim)?

    I realize the quality of hubs for CK is great, but I'm looking for a lightweight disc wheelset so I'm not draggin tons of weigh on the few occasions that I race. I assume my best bang for the buck is on lightweight tubes, light but good tires and light rims.Once i get to the hubs,does weight matter very much?

    On a separate note, in the FAQ section of this forum, they mention a good bang for the buck is spending money on light skewers, but since they don't rotate and are at the center of the wheel, I wouldn't think that is true. Any insight?

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    You need a brain adjustment on rotational weight

    Quote Originally Posted by fasteddy001
    I was thinking of getting a light wheelset using chris king hubs. I noticed the weight of a rear XT hub disc is only about 60-70 grams more than CK ISO disc hub. Given that the rims (mavic 317) and spokes(DB 14/15 g) for both wheels would be the same, isn't the rotational mass thing mean that the using lighter weight hubs doesn't really help in acceleration (since the difference in weight is centered around the axel and not out at the rim)?

    I realize the quality of hubs for CK is great, but I'm looking for a lightweight disc wheelset so I'm not draggin tons of weigh on the few occasions that I race. I assume my best bang for the buck is on lightweight tubes, light but good tires and light rims.Once i get to the hubs,does weight matter very much?

    On a separate note, in the FAQ section of this forum, they mention a good bang for the buck is spending money on light skewers, but since they don't rotate and are at the center of the wheel, I wouldn't think that is true. Any insight?
    Sounds like you have been spending too much time listening to someone blabber on about "rotational weight".... The way you talk, one would think that somehow...someway a pound of rotational weight is equal to 2 or more pounds of core weight (hub, skewers etc). This is a myth when taken to the degree you seem to be operating under.
    Perhaps under constant acceleration during the most technical climbing or racing a pound of rotational weight may equal 1.25 pounds of core weight......but even that amount is questionable. You would be better off when thinking about an entire race, to be thinking in terms of "at most" 1 gram of hub weight equaling 1.1 grams if put out in rotational weight areas. So perhaps a 10% extra amount of energy needed during a race for the different kinds of weight.....and I REALLY doubt it is even that much. Very little difference over an entire race where most of the time you are riding at a fairly steady rate of speed. Remembering also that the amount of weight we are talking about is only a small fraction of the weight of the bike.......and an even smaller amount of the bike+rider.

    Buy the CK hubs because they are lighter.....not dependent on where the weight is.
    Spend far more of you analysis on subjects like the rolling resistance of your tires, which will have far more impact on your race times than some rotational weight concerns.

    Which tires you running and why did you choose them....? Because of weight?

  3. #3
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    So are you saying rotational weight is a myth- that losing weight on wheel is the same as losing weight on the frame ? I think many here would have an argument with you. The rotational weight thing is the reason why discussion of light weight wheels is so prevalent on this board. My question was not does rotational weigh matter, but does it matter as much when talking about the hub where the weight is centered around the axle vs when the weight is far out from the center of the wheel (rim and tires).

    I understand that tire choice is key and rolling resistance may matter than weigh for tires. I never really got why tubeless offer less rolling resistance, not that I doubt it, but just don't understand why. Not sure I understand you condescending attitude either.

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    60-70g is actually quite much...

    60-70g is really quite much BUT you are right that it won't change the outcome of your races as much as a 70g heavier rim for example.

    XT hubs are "anchors" by weight-weenie standards.you say you want "light" wheels so you definitely want to stay away from them.

    with skewers it's real easy and cheap to save some weight.your usual steel QRs weigh around 120g.some 15$ steel bolt-on axles weigh 65g and increase stiffness too. 60g for 15$...that's what we call good bang for the buck.


    now if that still sounds strange to you:
    60g here, 60g there...that adds up and that's what finally makes the difference wheter it be rotational weight or not.

  5. #5
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    Quote Originally Posted by fasteddy001
    I was thinking of getting a light wheelset using chris king hubs. I noticed the weight of a rear XT hub disc is only about 60-70 grams more than CK ISO disc hub. Given that the rims (mavic 317) and spokes(DB 14/15 g) for both wheels would be the same, isn't the rotational mass thing mean that the using lighter weight hubs doesn't really help in acceleration (since the difference in weight is centered around the axel and not out at the rim)?

    I realize the quality of hubs for CK is great, but I'm looking for a lightweight disc wheelset so I'm not draggin tons of weigh on the few occasions that I race. I assume my best bang for the buck is on lightweight tubes, light but good tires and light rims.Once i get to the hubs,does weight matter very much?

    On a separate note, in the FAQ section of this forum, they mention a good bang for the buck is spending money on light skewers, but since they don't rotate and are at the center of the wheel, I wouldn't think that is true. Any insight?
    The reason kings are so popular isn't necessarily that they're light. Theres a ton of other ligter hubs , hugi, american classic, etc. With the king you're getting a top notch part that will probably outlast your bike. twice the engagement points that most all hubs is something i love.. No slop here. You'll appreciate it on a super slow climb, or when you want responsive acceleration. King headsets/hubs are something you can put on your bike and forget about it.

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    I'm curious about your prior perception regards rotational weight

    Quote Originally Posted by fasteddy001
    So are you saying rotational weight is a myth- that losing weight on wheel is the same as losing weight on the frame ? I think many here would have an argument with you. The rotational weight thing is the reason why discussion of light weight wheels is so prevalent on this board. My question was not does rotational weigh matter, but does it matter as much when talking about the hub where the weight is centered around the axle vs when the weight is far out from the center of the wheel (rim and tires).

    I understand that tire choice is key and rolling resistance may matter than weigh for tires. I never really got why tubeless offer less rolling resistance, not that I doubt it, but just don't understand why. Not sure I understand you condescending attitude either.
    Well, all things being equal, the weight at the hub is less important than the weight at the rim, tube or tire.....BUT........I think you still are thinking in terms of some multiple which is in excess of reality when actual measurements are taken.....such as the impact on one's time over a hour long cross country race. All in all, during a cross country race you aren't doing such an amount of accelertion that it greatly impacts your time whether the weight is at the hub or at the rim. Now, it may be the impression that it is so, but from the times I've seen someone examine the math/physics it doesn't pan out.

    But there is some difference.....
    So I guess my question for you is what is your thinking being based upon. I don't mean the source of your thinking about this, but rather the magnitude of the ratio.
    In your thinking prior to this thread what was the ratio of your sense of the situation.
    Core (hub, skewer) weight------> taken out to the rim/tire.
    Was your general impression it was something like 4 to 1 or ...2 to 1 or .....1.5 to 1
    or even 1.1 to 1.....when you take that 100 grams out to the rim/tire
    I'm actually very curious what the general thinking/mindset is for those thinking about this as part of their performance analysis.

    In other words, I am curious as to what the general perception is among riders about this aspect of weight. How much does 100 grams at the frame-core-hub equal when its out on the rim/tire with regards to energy needs? Does it require double the energy needs or does it require triple the energy needs to take that rotating 100 grams around the cross country course versus taking 100 grams of hub or frame weight.

    Prior to this thread, what was your perception?

    Didnt' mean to sound condecending in my orginal thread.....its just the internet attitude which ends up like some locker room back and forth sometimes....

    I'll let Nino try to explain the tubes vs tubeless........On that I depend on the German magazine tests for my belief. However, one way to think about it is that the tube at pressure just creates an extra thickness layer of tire and friction and needed deformation (energy) as opposed to having nothing there except some goop. Obviously with 5 tubes in one tire there would be extra friction and deformation even it they didn't weigh more, so even one tire has some effect.

  7. #7

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    Chris King hubs make you feel less tired

    Quote Originally Posted by mtb_biker
    The reason kings are so popular isn't necessarily that they're light. Theres a ton of other ligter hubs , hugi, american classic, etc. With the king you're getting a top notch part that will probably outlast your bike. twice the engagement points that most all hubs is something i love.. No slop here. You'll appreciate it on a super slow climb, or when you want responsive acceleration. King headsets/hubs are something you can put on your bike and forget about it.
    The real secret to Chris King hubs is that your mind only has so much space for sensory imput.....
    Now with the noise generated by the Chris King hubs.....one of your senses, your hearing, is so overwhelmed by the noise, that it kind of uses up all the pain/sensation brain areas, and as such effectively blocks out a significant portion of the other pain sensations. As such, your feeling of muscle fatigue and being out of breath are greatly reduced. Thus you can push yourself even harder without "feeling" tired....
    Granted, the noise comes into effect when coasting downhill but there is a time lapse after the noise has stopped before the brain sensation areas are returned to normal.
    During that time, on the next climb, you are typically almost to the top of the next climb before you once again begin to feel the "true" level of pain and fatigue....Then it just a short time until you crest and begin another onslaught of the brain numbing noise from the Chris King hubs...
    Science has proved all of this and revealed it in German magazine testing.

  8. #8
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    My understanding on rotational weight is/was

    and this has all been gathered from MTBr and MB periodicals, that rotational weight (wheels, cranks, etc) was worth about 3X more than stationary weight. What I mean by that is saving 30 grams on your rims was the same as saving 90 grams on your frame. Don't know if that is true but seen it said many times.

    Wasn't sure if that same formula applied when the weight was at the center of the wheel though. Seen it written that the further out the weight (on the wheel) the greater the impact on the rider. I thought the hub/skewer weight savings might be similar to frame weight savings.

    Of course I realize that any weight saved on a bike will help, but that saving weight on the wheelset is better and saving weight on the rim/tire is best.

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    Perhaps an expert will post something....re-rotational weight

    Quote Originally Posted by fasteddy001
    and this has all been gathered from MTBr and MB periodicals, that rotational weight (wheels, cranks, etc) was worth about 3X more than stationary weight. What I mean by that is saving 30 grams on your rims was the same as saving 90 grams on your frame. Don't know if that is true but seen it said many times.

    Wasn't sure if that same formula applied when the weight was at the center of the wheel though. Seen it written that the further out the weight (on the wheel) the greater the impact on the rider. I thought the hub/skewer weight savings might be similar to frame weight savings.

    Of course I realize that any weight saved on a bike will help, but that saving weight on the wheelset is better and saving weight on the rim/tire is best.
    OK, thanks for your perception....3 times more for rotational weight versus frame/hub weight.
    I wish I could remember the sources where I read lengthly discussions about this previously....Hopefully someone will point us in the right direction.
    My "perception" is that over a typical hour long cross country race loop, that the ratio would be no more than 1.1 to 1..... meaning 100 grams on the rim would only be the same as about 110 grams on the frame.. Perhaps not even that much.

    So one of our perceptions is way off.......perhaps both of our perceptions....

    This dicussion has been gone over many times.....several times regarding climbing a fixed hill. One thing I can tell you that seems to be agreed (mostly) is that if you are climbing a steady climb, the weight on the rim will be equal to the weight on the frame, although there are some folks who claim that every pedal stroke has mini acceleration within itself. But some of those folks are the same ones shaving their legs for lower wind resistance.
    I'll look around over the next 24 hours to see what I see....(when I get some time)

  10. #10
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    Same here

    Dong the same thing. I decided on a CK/DT XR 4.1d wheelset. When i researched the weight of my XT 756 disc hubs i was surprised to find that i was going to same almost 3/4 of a pound in hub weight alone by switching hubs. However the difference in the rims im using 317's vs. those that im getting XR 4.1d will offset some of that reduction in weight.

    I figure that while the weight reducton may be marginal the wheels will roll easier given the higher tolerances, machining and sealed bearings. Not to mention that by choosing a stronger and slightly heavier rim the rim will spend less time being deflected off objects and more time rolling forward. This may result in less drag climbing, better carrying of momentum, better control & tracking Also, the CK hubs are bulletproof and pretty much trouble free which i cant sday of the other hub options.

  11. #11

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    STOP.....Read this January 04 thread first....

    [QUOTE=
    I'll look around over the next 24 hours to see what I see....(when I get some time)[/QUOTE]

    OK......found something......Look at the following thread, especially the posts by Boj
    Then read the rest of the thread and see what you think.

    Also be especially aware of the typical speeds you are riding at during over 90% of your cross country race. Most of it you are grinding up a hill at a steady pace or coasting down a hill where weight is not the important criteria. How much the rotational weight affects the other 10% of the ride is questionalble...

    http://forums.mtbr.com/showthread.php?t=1460

    Extensive thread......

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    Hey Chester-thanks for the link!

    I found many answers at that link including the hub vs rim issue. Many post-ers seem to think wheels weigh vs frame weigh is a big difference, but of course everyone has there opinion. Some also think the issue is overblown, I guess it depends on the situation. In my world, my speed is constantly changing when in a race so I think it would make a big difference- I mean each person has to define what acceleration is. If your speed varying at all even by 1/4 to 1/2 mph, which mine is, you're constantly accelerating or decelerating. I think it may be a mistake to think of acceleration only in terms of what you do at a drag strip or waht happend at the start of a race. IN MTB world I think its any time your pace changes even by a minor degree

    Seriously, thanks for all the help!

  13. #13
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    I think it's more than that.

    I'm too lazy to look now, but isn't an King ISO rear hub like 320 grams or so? The XT M756 rear disc hub (which I have) comes in around 500+ grams, IIRC. I can tell you, it's a total frickin boat anchor.

    They're solid, reliable, cheap and easy to service, but heavy as heck.

    I'll also add to that my opinion that rotational weight is important. I can fully feel it when I put heavier innertubes (+30 grams) on instead of the LunarLites I usually use. I mean, it really is noticable, at least to me.

    That said, the hub would have little impact on the feeling of rotational weight because its mass is so close to the center of the wheel. It behaves more like static unsprung weight.
    Last edited by pimpbot; 05-06-2004 at 10:39 AM.

  14. #14
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    2003/2004 xt disc hubs (not sure of model #) weig about 430 with skewers but only365-370 without . thats only about 60 g more than a king. the original XT disc hubs were about 500gs

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    Well, think about it this way.......

    Quote Originally Posted by fasteddy001
    I found many answers at that link including the hub vs rim issue. Many post-ers seem to think wheels weigh vs frame weigh is a big difference, but of course everyone has there opinion. Some also think the issue is overblown, I guess it depends on the situation. In my world, my speed is constantly changing when in a race so I think it would make a big difference- I mean each person has to define what acceleration is. If your speed varying at all even by 1/4 to 1/2 mph, which mine is, you're constantly accelerating or decelerating. I think it may be a mistake to think of acceleration only in terms of what you do at a drag strip or waht happend at the start of a race. IN MTB world I think its any time your pace changes even by a minor degree
    !
    Well, I think you had better think about it this way.......

    Boj said the following....
    Here are the actual numbers where a gram saved is worth this much on a particular part (and only for cases of acceleration):

    hub 1.0007
    spokes 1.2043
    rim 1.7006
    tube 1.8723
    tire 1.8723

    wheel overall

    front 1.563
    rear 1.467

    Now, he is good on the math part......but as he said those number are for only those time of acceleration...
    So look at your riding.. You think you are constantly going 1/4 or 1/2 mph faster or slower all the time..... But think about it. Do some real math. If you are even doing mini accelerations that also implys you are also doing mini decelerations and unless you are the most unusual rider, you are also having some time spent neither doing acceleration or deceleration. In the maximum case I doubt a rider is spending more than 1/3 of his time in acceleration, with another 1/3 in either deceleration or coasting and probably another riding at a steady state.. I think you would agree it would be almost impossible to get much beyond 33% in acceleration because you also must slow down or coast.....and if you take a good look at your riding on many flat sections you are doing neither.
    So just using that 1/3+1/3+1/3 =1 type of riding you then will have to take Boj's figures and devide by 3 for the weight ratio to use in your decision making process.

    Look at his figures for tubes, tires and rims and they go from 1.70 to 1 to 1.87 to 1 but only "during" acceleration. So if you are spending only 1/3 of your time in actual acceleration then you have to divide those figures by 3......ending up with about a range of 1.23 to 1 ....to 1.29 to1. Thus you are less than 1.3 to 1 under any circumstances.
    Nowhere near the 2 to 1 or even 3 to 1 you often hear cited.
    So maximum, the the 100 grams saved at the rim-tire-tube is equal to 130 grams at the hub...
    AND, in actual riding under scientifically measured conditions, I seriously doubt it it that high. I think it would be almost impossible to be accelerating 33% of the time....certainly anything beyond that is simply impossible... The theoretical maximum I am thinking would be 50%....and that is if you are never riding at a steady pace but instead only accelerating and then decelerating or coasting.
    Pay attention to how you really ride next time and I think you will see that even on lots of your climbs you speedo is just switching a tenth of a mph back and forth and much of that is just due to minor undulations in the terrain as well as a speedo that isn't precisely accurate... For all practical purposes going from 8.9 mph to 9.0 mph and back to 8.9 mph is not acceleration and hardly even counts as part of the 1/3 I am talking about. Even a little rock or rut can push the computer back and forth a tenth of a mph.

    I stick with my orginal estimation that the difference between rim-tire weight versus hub weight is only about 1.1 to 1 ...or maximum 1.25 to 1........over a typical cross country course.....AND remembering that the grams involved are only a very tiny part of not only the bike weight, but an even smaller part of the entire rider-bike weight.
    As I said, the rolling resistance of the tires probably is a 100 times more important consideration in final lap time.

  16. #16
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    Quote Originally Posted by Chester
    The real secret to Chris King hubs is that your mind only has so much space for sensory imput.....
    Now with the noise generated by the Chris King hubs.....one of your senses, your hearing, is so overwhelmed by the noise, that it kind of uses up all the pain/sensation brain areas, and as such effectively blocks out a significant portion of the other pain sensations. As such, your feeling of muscle fatigue and being out of breath are greatly reduced. Thus you can push yourself even harder without "feeling" tired....
    Granted, the noise comes into effect when coasting downhill but there is a time lapse after the noise has stopped before the brain sensation areas are returned to normal.
    During that time, on the next climb, you are typically almost to the top of the next climb before you once again begin to feel the "true" level of pain and fatigue....Then it just a short time until you crest and begin another onslaught of the brain numbing noise from the Chris King hubs...
    Science has proved all of this and revealed it in German magazine testing.
    So, if I put a card in the spokes of my cheapo wheels, it will be as effective as having Chris Kings?
    "Son, The world needs ditchdiggers, too"-Ted Knight, Caddyshack

  17. #17

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    Quote Originally Posted by Chester
    Well, all things being equal, the weight at the hub is less important than the weight at the rim, tube or tire.....BUT........I think you still are thinking in terms of some multiple which is in excess of reality when actual measurements are taken.....such as the impact on one's time over a hour long cross country race. All in all, during a cross country race you aren't doing such an amount of accelertion that it greatly impacts your time whether the weight is at the hub or at the rim. Now, it may be the impression that it is so, but from the times I've seen someone examine the math/physics it doesn't pan out.
    I think everyone is missing part of the overall picture here. It isn't a matter of "weight ratios"....or accelerating and decelerating in an XC race. When answering the question of rim weight vs. hub weight you really need to think of this scenereo:

    Tie a bucket of water to the end of a rope and trying to swing it in a circle. This is the same principal of spinning your wheel, just on a smaller scale.

    Part of a post earleir stated that it only matters when accelerating. That is not the case!! It matters the most when accelerating but you can imagine that even if you aren't accelerating that swinging bucket after you do it for an hour it gets tireing. We can all also agree that the more water in that bucket the more tired it is going to make you over time.

    That being said, this is why most people argue that it is worth more to shave weight off rim and tire weight then something that is not experiencing as much rotational acceleration and drag.

    So it isn't as important to shave weight in the hub as in the rim and tire, however my suggestion would still be to spend some good cash on hubs. More money equals less maintenance, less weight and probable better bearings which will save you rotational drag in the longrun.

    I hope I have helped... Good luck!

  18. #18
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    Quote Originally Posted by jgillam
    It isn't a matter of "weight ratios"....
    It's a simple question of weight ratios! A five ounce bird could not carry a one pound coconut.

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    Quote Originally Posted by Homebrew
    It's a simple question of weight ratios! A five ounce bird could not carry a one pound coconut.
    Did you totally miss the original thread topic?!?!

    It isn't a matter of rider to bike weight ratio!!!! i.e. your bird / coconut analogy. It is a matter off what bike components are the most valuable to replace weight wise!

    You can't say that it is 1.2 times better to replace a rim then a hub. Ratios like that are pathetically false and opinionated.

    Trying to apply mathematics to it in a small scenerio like this is impossible. It is a matter of dynamics and finite element analysis. Don't get into a debate like this with an Engineer.

    The simple fact is that it more benificial to get rid of rotational weight... i.e. THE RIMS, TUBES AND TIRES!!

  20. #20
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    My favorite part about King hubs is all the pretty colors like red, turquoise, navy, mango, green apple, pewter, mauve, fuchsia, salmon and burnt sienna.

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    This product puts Chris King hubs to shame..

    Quote Originally Posted by Fett
    So, if I put a card in the spokes of my cheapo wheels, it will be as effective as having Chris Kings?
    Well, yes a good "crisp" baseball card with clothespin attachment will indeed give you the same effect as the $265 Chris King hub, but of course, the Chris King hub will last much longer.
    I've actually done some calculations on this subject and found that if you are riding 1,350 miles or more per year, you will actually save money with the Chris King hub because those baseball cars only deliver full decible value for a fairly short time period.
    So there are a few ways to go. 1. Buy a Chris King hub 2. Buy a huge supply of baseball card.. 3. Use baseball cards ONLY during race situations
    OR.....4. Use my new secret bike component......

    Yes, there is a valuable and inexpensive alternative to the $265 rear Chris King hub

    For less than $35 you can get a long lasting, far more effective product that will greatly outperform either the Chris King hub or the baseball cards and will last for years...

    The fantastic new TURBOSPOKE !!!!!

    Yes, this product is great and will soon be showing up on trails everywhere.
    Not only does it supply the sensory numbing noise to mask the pain of those long climbs, but it also as a very very effectgive deterrent to mountain lion attacks which have been so prominent in the news... Take a look and "listen" for your self.....remembering this product works even when you are not coasting like the less-effective King hubs.

    http://www.turbospoke.com/global/products.asp

    Well, what do ya think? I've been using mine for a few days now and all the guys on the trails seem to be impressed. Everyone stops and looks at me as I come sceaming down the trail. I swear, even though it only costs $35 it will get you more attention than a top of the line $6,000 Blur.

    And as we discussed with this auditory imput overwhelming your senses, you'll hardly ever notice yourself getting tired........You simply fly around the typical cross country course. By next year, you be seeing these on half the bikes at Sea Otter.

  22. #22
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    It's rotational and unsprung weight

    Quote Originally Posted by nino
    60-70g is really quite much BUT you are right that it won't change the outcome of your races as much as a 70g heavier rim for example.

    XT hubs are "anchors" by weight-weenie standards.you say you want "light" wheels so you definitely want to stay away from them.

    with skewers it's real easy and cheap to save some weight.your usual steel QRs weigh around 120g.some 15$ steel bolt-on axles weigh 65g and increase stiffness too. 60g for 15$...that's what we call good bang for the buck.


    now if that still sounds strange to you:
    60g here, 60g there...that adds up and that's what finally makes the difference wheter it be rotational weight or not.
    I think a set King hubs are at least 200g less than XT 756 hubs. That is significant. Even if the rotational component is negligible, hub weight is unsprung which means that it hinders suspension action, plus it is at the extreme front and back of the bike which affects handling. You will definitely notice an improved bike with this upgrade.
    M

  23. #23
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    Some of you dudes are such homers about your King hubs. You pay no attention to fasteddy and try to compare the King's to the old XT hubs when he's talking about the rotor lock hubs. Excel lists them at 555 grams, they are not anchors. The price listed for both is $99 compared to $415 for the Kings. The Kings are listed at 474 without skewers but you guys know what your own hubs weigh. I think Shimano quality is good enough for almost everybody and King equipment is almost at the level of jewelry. Mounting that King product is like strapping on a fine Rolex watch, while the Shimano product is really all you need. I haven't blown a Shimano hub in 10 years of riding off-road so they look like a bargain to me. I'm sure King is the best from all of the testimonials, but they cost almost $300 more. And let's face it, a better rider on the XT hubs is still gonna clean your clock, quick engagement or not. Wading through all the rotational weight talk above I think money would be better spent out at the rim and tire, and maybe on the shoes, pedals, and cranks.

  24. #24
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    with xt hubs, he's looking at a 1700g+ wheelset. Not light by any means. By using the new xt disc hubs means he also has to use the center lock rotors. Alot of weight savings can be had by using a lighter rotor(hayes 110g, hope 107g). He's stuck with using a shimano splined rotor (140-150g). If he ever wanted to upgrade to a 170mm rotor, he'd be outa luck.

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    Quote Originally Posted by Homebrew
    It's a simple question of weight ratios! A five ounce bird could not carry a one pound coconut.

    but if it were two swallows using a strand of creeper held under the dorsal guiding feather... well, why not?

  26. #26
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    Quote Originally Posted by Homebrew
    It's a simple question of weight ratios! A five ounce bird could not carry a one pound coconut.
    An African swallow, or a European swallow?
    Herro prease

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    I am all for light wheels, but..

    the 3 to 1 ratio or anything in that neighborhood is B.S. That might hold true if you were just accelerating the wheel while your bike is in the stand, but while riding your wheels are attached to the ground making making the weight of the whole bike just about as important as the wheels. Think about it for a moment.

  28. #28
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    Quote Originally Posted by Fett
    So, if I put a card in the spokes of my cheapo wheels, it will be as effective as having Chris Kings?
    As long as that card is marketed by Specialized as the new revolution in cycling, then yes.

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    All I can say is $300 to save 80 grams. If you're not building up a $5000 bike you can use that $300 to save yourself a pound or two somewhere else. Since those hubs and rotors are close to the axle they aren't your best bet as far as saving rotational weight. What you really have to do is ride this stuff out on the trail. Then you can cut through the hype and figure out if there is any difference. It's too bad demo days don't usually include stuff like King hubs, I would definitely be there. I'm sure the King hubs are the best but they won't magically make you good. There is no product that can make you good, you've gotta put in the training.

  30. #30
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    Quote Originally Posted by jgillam
    Did you totally miss the original thread topic?!?!

    It isn't a matter of rider to bike weight ratio!!!! i.e. your bird / coconut analogy. It is a matter off what bike components are the most valuable to replace weight wise!

    You can't say that it is 1.2 times better to replace a rim then a hub. Ratios like that are pathetically false and opinionated.

    Trying to apply mathematics to it in a small scenerio like this is impossible. It is a matter of dynamics and finite element analysis. Don't get into a debate like this with an Engineer.

    The simple fact is that it more benificial to get rid of rotational weight... i.e. THE RIMS, TUBES AND TIRES!!
    Hey, before we go off on another epic debate about this (seeing as you're new here) may I direct you to read the thread in the link posted by Chester (Thank you, btw). It has mention of the bucket too.

    Swinging bucket is not applicable to a bicycle wheel for so many reasons that it is easier just to identify that only similarity is that they are bolt rotating. Everything else is different. In any case the argument is not if the bucket would be harder to spin with more weight - of course it will. The argument is weather the equivalent increase of weight in case of bicycle wheels will produce any additional detrimental performance purely because its 'rotational' weight. It will, but very insignificant additional detriment - certainly not enough to justify as being important, at least in case of MTBing.

    Anyway to add more confusion to the guy who originally asked the question I would suggest to shave weight off your wheelset (or bike) anywhere that will give you the best weight saved for buck. Rims, hubs, spokes, frame and all alike. If you feel like saving money and extra 70 g (or whatever) with XT hubs that's fine, but don't then blow money saved to trim 40 g on the spokers or rims because they are 'rotational' weight. It would have been better to save more weight in hubs than lesser weight in rims if you're going to spend the money anyway.

    You've read all of my arguments from the other post so no need to repeat them here but consider just that wheel inertia is only helping you when accelerating. And even though you may think that upon carving that hairpin and putting the foot down on the other side you are 'accelerating' very hard its only a sensation of your effort from the legs. Actual acceleration (change of the speed over time) is quite low in the order of 0.1 to 0.2 g (g being acceleration of a freefalling object, 9.81 m/s^2) and not enough to justify the hype of 'rotational' mass in wheels.

  31. #31
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    Quote Originally Posted by Go Kart Motzart
    the 3 to 1 ratio or anything in that neighborhood is B.S. That might hold true if you were just accelerating the wheel while your bike is in the stand, but while riding your wheels are attached to the ground making making the weight of the whole bike just about as important as the wheels. Think about it for a moment.
    Ditto and well put. Probably could add that besides the bike you are also moving your entire body mass so considering just how insignificant wheel mass is comparing to the mass of bike + you, it makes it easier to see my point.

  32. #32
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    Quote Originally Posted by Chester
    Well, I think you had better think about it this way.......

    Boj said the following....
    Here are the actual numbers where a gram saved is worth this much on a particular part (and only for cases of acceleration):

    hub 1.0007
    spokes 1.2043
    rim 1.7006
    tube 1.8723
    tire 1.8723

    wheel overall

    front 1.563
    rear 1.467
    MTB Race is always an acceleration.

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    Always exhilaration perhaps, Always accerleration....NO

    Quote Originally Posted by dot
    MTB Race is always an acceleration.
    I suppose you are just trying to be funny.....At least I hope so....

    Other wise you are riding on a very unusual course...
    Suppose you began on a 1 hour cross country course and started your constant ("always") acceleration...
    So you begin your acceleration at only .5 mph/ per minute....
    "Always an acceleration" leaves you at 15 mph at the 30 minute mark and still accelerating... At the 45 minute mark you are doing 22.5 mph and still picking up speed...Hope you are approaching a downhill section because you are still in the "always an accerleration" mode. Certainly by this point you are begining a long downhill because you are still accerlerting.....and as you cross the finish line of the 1 hour loop you are clocking 30 mph and on the verge of spinning out with your legs going like a sewing machine.

    I'd like to ride that course.......Very very steep at the begining......slowly getting a bit more level until the last 15 minutes where you begin a long steeper and steeper downhill.
    Actually I supppose it is in theory possible, its just that I've never seen a course quite like that.

    Normally a course riden by a typical rider will have about 1/3 climbing, 1/3 level, and about 1/3 downhill........though some do have very little level, leaving perhaps 45% uphill and 45% downhill.
    Anyway, weight dependent acceleration limitations on the downhill sections are very few and mostly insignificant... So that eliminates 33 to 45 percent of your riding right there.
    Then you have level areas with at most about 50% acceleration.. though normally you have large sections of steady-state riding.
    Lastly you have, the 33 to 45 percent climbing during which some would think you are accelerating. But the reality is that even during the climbing, most riders are doing most of it at a steady-state of speed, with very minor fluxuations...
    Thus when you add it all up, most of a typical riders time is spent NOT acceleratiing, but rather decelerating or at a steady-state of speed.

    The almost mythical standards that have been attributed to "rotational weight" are very hard to eliminate, especially with high-end companies trying to sell ever lower weight "rotational" products. Many riders continue to believe the myths because it "seems" to make sense even though one seldom sees any science to give actual quantification to the reality. Only with actual data will it make any reasonable sense.

    Perhaps some day some research group will present a clearer picture.

  34. #34

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    Quote Originally Posted by TheRedMantra
    An African swallow, or a European swallow?
    Can't be an african swallow... african swallows are non "mi--graye-tor--ee"

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    Chester I think he means in a race most people are constantly makingadjustments to their speed. You pedal, you coast for a 1/2second, then you pedal to get over a rock, past a rider, because or you're coming out of turn etc. I really don't know anyone who rides mtb that is not constantly slowing down and then speeding up. Road rider may keep a certain speed but most mtbr don't.

    As fars as your 1/3 up, 1/3 level, 1/3 down theory- from a distance stand point you are probably right. But that assumes the effort expended over each is the same which I don't think is true. From a time standpoint alone, it might take 20 minutes to climb a hill and only 4 or 5 minutes to come down. It that instance 80% of time/effort is expensed on the uphill and 20% on the downhill. This is not even taking into account that the effort (calorie expenditure) on the DH is probably far less per minute than on the climb. So while distance my be equally divided among up/ level/down, effort is most likely expended in the fllowing manner 70% to get up hills, 20% on level, 10% on down. All racers know that, excluding mechancials, races are won on the climbs.

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    Perhaps Boj can help us here with our thinking

    Quote Originally Posted by fasteddy001
    Chester I think he means in a race most people are constantly makingadjustments to their speed. You pedal, you coast for a 1/2second, then you pedal to get over a rock, past a rider, because or you're coming out of turn etc. I really don't know anyone who rides mtb that is not constnatly slowing down, speeding up, charging harder then slowing down to set up for tehcnical section, then speeding up then coasting, the slowing down. its the constant changes in cadence and speed(in new england our races usuall have some technical elements ). Think about you pedal to certain speed, you might then coast for a milisecond to neogitate a rock, rut or whatever, when you pedal again you are basically acelerating. Yo are moving items with mass at a speed (chainm, cranks, casette and wheel unless you can perfrectly match the previous speed). Becuase friction is slowing you down constantly

    Now while you may be right about your 1/3 up, 1/3 level, 1/3 down theory from a distance stand point- from a time standpoint you might take 20 minutes to climb a hill and only 4 or 5 minutes to come down. It that instance 80% of time effort is expensed on the uphill and 20% on the downhill, not to mention you probably are barely pedal on DH section.
    Your "logical" "reasonable" "common-sense" is fooling you...... What seems like it makes sense to you, is I believe, wrong. Perhaps a more scientifically versed reader will put his take on it.......

    1. It doesn't matter if the split-up of acceleration, steady-speed, and deceleration take place in 20 min + 20 min + 20 min single segments of a one hour loop or that they take place in 5 second + 5 second + 5second mini 15 second segments. Its still 1/3 + 1/3 + 1/3.......so you are not doing any more acceleration than I said....That being a maximum of 33% using our above example...
    As such you would have to take those previously discussed rotating-weight maximums of about 1.75 to 1 and divide by 3 to give you an over all max of about 1.25 to 1....certainly far less than most folks are taking in their common sense judgements.
    Even if you break it down to 1 sec + 1 sec + 1 sec, you still get the same result.

    NOW......as to your suggestion that this thinking is overcome because you may divide the course in thirds....1/3+1/3+1/3 and that each section might include a 20 minute climb followed by only 5 minutes of downhill....(no level ground for our thinking in this theoretical example).....
    I am no math or science whiz but I am almost certain you are still fooling yourself with that 20 min + 5 min example.....
    Hopefully Boj will give us some math/science to counter your theory..........but here is why I , in my simple way think you are still very very confused by your "common sense"

    1st.......Even you will agree that the 5 minute downhill section will not benefit by having less rotating weight.....Right?

    2nd......During your 20 minute climb you, once you get up to the initial 6 to 12 mph in the first 30 seconds, you will the go through a series of mini accelerations, steady-state, and decelerations the rest of the climb.... They may only be 5 sec + 5 sec + 5 sec series but they will repeat over and over......and you will also have lots time spent at a steady speed like 8.4 mph with very minor terrain induced (not power output induced) fluxuations in speed.....8.4....8.3.......8.5..........etc....dep ending on ruts, roots and small rock...etc..

    When and if you could attach instruments to your ride, I firmly believe you would have no more than about 1/3 or your "climb" time in actual acceleration where the rotational weight would be of a greater value, being less, compared to hub weight or bike weight...with the exception being the every famous "flick-a-bility"

    Many climbs might actually be made with acceleration being present in less than 10% of the climbing time.......added to almost zero value on the flats and zero value on the downhills sections......

    Now, the only point I am uncertain about and I hope someone with more science gives us some thinking about......is the part as to whether you can fairly compare the 20 minutes climb directly with the 5 minutes downhill...... I mean, is it fair to comare time with time, as opposed to distance covered...
    So, in theory, is it even correct ( assuming the rider slowly increased speed--accelerated- during the entire 20 minute climb) to compare 20 minutes (80%) with the 5 minutes (20%) downhill given in your example....
    Off hand, I think it is NOT fair to do that kind of comparison.......Lets see what others say.

    Real world........I think you still end up with only a very small percentage of actual acceleration over a cross country course, given that it is not even a 50% proposition on the climbing sections.
    Last edited by Chester; 05-07-2004 at 12:44 PM. Reason: correction typo

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    One thing that no one has mentioned, and I don't know how significant it is in the real world (maybe not much at all), but unsprung mass affects suspension performance, and hubs are unsprung mass, along with the rest of the wheel, and the fork sliders & springs for the front and the swing arm & everything that is attached to it, for the rear.

  38. #38
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    wrapping an inner tube around your hub shell has less effect on the rotating wheel that getting 5 grams of dog poop stuck to one of the knobs of the tire.

    The only reason to care about hub weight is in the terms of the overall weight of the bike.

  39. #39
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    Quote Originally Posted by fasteddy001
    Chester I think he means in a race most people are constantly makingadjustments to their speed. You pedal, you coast for a 1/2second, then you pedal to get over a rock, past a rider, because or you're coming out of turn etc. I really don't know anyone who rides mtb that is not constantly slowing down and then speeding up. Road rider may keep a certain speed but most mtbr don't.

    As fars as your 1/3 up, 1/3 level, 1/3 down theory- from a distance stand point you are probably right. But that assumes the effort expended over each is the same which I don't think is true. From a time standpoint alone, it might take 20 minutes to climb a hill and only 4 or 5 minutes to come down. It that instance 80% of time/effort is expensed on the uphill and 20% on the downhill. This is not even taking into account that the effort (calorie expenditure) on the DH is probably far less per minute than on the climb. So while distance my be equally divided among up/ level/down, effort is most likely expended in the fllowing manner 70% to get up hills, 20% on level, 10% on down. All racers know that, excluding mechancials, races are won on the climbs.
    Hey,

    I didn't get to present this last time but I made a small Matlab simulation of an accelerating bike (which included accelerations due to pedalling mashing). Its basically does the same thing as analyticcycling.com application but with easier inputs.

    Anyway results presented here are for the case of 2 identical riders producing identical power, one having 500 g heavier rim and the other 500 g heavier frame. Ie both their bikes are therefore the same weight but one has rotational mass advantage. This way only 'rotational' mass advantage is investigated cause both bikes overall weigh the same. All runs are for offroad setting.

    Anyway first is the case for acceleration from 3 m/s (10.8 kph, 17.4 mph) at power of 300W for 10 seconds. Its like a hairpin turn and accelerating away from it. In first figure is the profile of both riders speeds over time (I know you can basically see only one line - thats cause their speeds are so indifferent). And second is snapshot of some relevant figures.



    Therefore at the end of this little race the two have covered 53.9 m and rider with lighter wheels is ahead by 7.3 cms or 0.011 seconds. Very little indeed for such a huge rotational mass advantage (500 g).

    Second case is constant speed pedalling - ie accelerations purely due to pedalling mashing. Its for a 1.5 hour flat offroad time trial at 300W (though first figure is just first 10 seconds of it).


    Anyway so at the conclusion of the time trial the two riders have covered ~46.5 kms (28.9 mi) and after that race the rider with a lighter wheelset is ahead by 0.7 of a meter or 0.08 seconds.

    These differences presented here are purely due to the rotational mass difference, and that was 500 g at the rims. That's why I say that its not so important to distinguish between rotational and static mass and such unless you are fighting in photo sprint finishes.

    In conclusion the 'rotational' mass phenomenon is overrated because:

    - Wheelset is such a small part of the bike + rider system
    - Advantages are only confined to cases of acceleration only
    - Acceleration in MTB is not prevalent to a degree that rotational mass effects would give distinguishable advantage

    This is not to say everyone should not bother saving weight at the wheels - on contrary save as much as you can, it will be making you significantly faster. BUT thats because you are carrying less mass and not all that much due to the fact it is 'rotational'.

  40. #40
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    you guys should go out and ride a little more...
    hey
    ho
    lets go!

  41. #41

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    Science VS "common sense"......guess who wins

    Quote Originally Posted by Boj
    Hey,


    In conclusion the 'rotational' mass phenomenon is overrated because:

    - Wheelset is such a small part of the bike + rider system
    - Advantages are only confined to cases of acceleration only
    - Acceleration in MTB is not prevalent to a degree that rotational mass effects would give distinguishable advantage

    This is not to say everyone should not bother saving weight at the wheels - on contrary save as much as you can, it will be making you significantly faster. BUT thats because you are carrying less mass and not all that much due to the fact it is 'rotational'.
    Oh my! They're not gonna like this one bit.....

    Who? All those people who have been brainwashed for years about the "Holy Grail" of rotational weight. I've seen figures from 1.5 to 1 all the way up to 7 to 1 for the value of rotational weight compared to frame weight.

    Now you come here and tell folks that even with a 500 gram heavier rim (or set of rims) versus a 500 gram heavier frame, that they are only going to slow down by about one seven hundreth (1/700).
    No, they simply will NOT believe it. Their "common sense" revolts against the idea.
    They'll shout you down and report you to the board administrator. "You should be banned for such heresy" And all the wheel companies will branding you as a complete lunatic. I wouldn't be surprised if Mavic hauls you into court.

    I know you put a lot of work into these calculations.....but think about it.
    Put 100 typical mtn bike riders or board readers into a room to listen to the two sides

    First, Boj gets up and gives his scientific presentation..........backed up by calculations, graphs, slides and formulas........Eyes begin to glaze over after the first 2 minutes.....but he gets a polite reception.

    Next, jgillam goes to the front of the room to give the other side.... He has no calculations, no graphs, nor slides, and certainly no formulas....
    Instead he brings a simple bucket half filled with water with a rope attached to the handle.... He begins to swing it around faster and faster as though he was a Olympic hammer thrower in a earlier life... Finally the rope snaps and crashes into a hapless audience member in the first row. As paramedics tend to him, jgillam allows two members from the audience to try the "bucket with water on a rope" experiment.
    After seeing the first bucket break loose, the audience is spell bound and very attentive.
    jgillam and the other two participants all agree that the faster they spin....the heavier the bucket became.......very very heavy...

    jgillam says.....".Boj stated that it only matters when accelerating. That is not the case!! It matters the most when accelerating but you can imagine that even if you aren't accelerating that swinging a bucket after you do it for an hour it gets tireing."
    Most members of the audience nod their heads in agreement.

    Now comes the time when the audience gets to vote...

    Vote yes......if you think rotational weight is extremely more important......and will affect your performance at least twice as much as frame weight....

    Vote no if you believe Boj and his.....so-called charts.....which show rotational weight has only a very small "greater affect" compared to frame weight.

    Votes are calculated........Yes (for the bucket) 89 .........No ( for science) 6
    Too confused to vote or injured by flying bucket....5

    Well, as you can see....."common sense" has prevailed once again :-)

    Science is just toooooo complicated....
    Never mind that Einstein once said "Things should
    be as simple as possible, but no simpler"

    Anyway......I'm sure most will remain unconvinced......
    But I liked it.....especially the two examples......The pure 10 sencond acceleration and also the often cited...pedal mashing.....which always comes up in these discussions, usually described as "you are always accelerating on every pedal stroke"

    With all the suspected acceleration we hear about in these discussions, I'm surprised the average cross country rider isn't averaging about 60 mph on a loop.

    Of course the guy with the lighter rims will be doing 60.0857 mph.....but only if both riders had been engaged in steady acceleration throughout the loop.....

  42. #42

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    Hub weight can be really important:
    For instance, some of the Formula hub bearings in their lightweight products (and other brand extra light hubs) may turn slick in the truing stand, but drag severely when supporting the weight of the cyclist. There are also flexy axles available (in many brands) that cause the cassette to tilt when under torque, which can also cause the bearings to drag (at the worst moment). And, there are terrible lightweight pawl systems (from Mavic and others) that can simply go "crunch" inside and not engage again afterwards (pedals spin but the bike doesn't go forwards). These sorts of hubs can make super-light wheels that are really exhausting!

    Saving weight at the hub does absolutely nothing beneficial by itself. This is like just one TI bolt or just one lightweight spoke.
    Saving weight at the hubs goes along with lots of other things, like Thompson's seatpost, Jagwire Kevlar-jacketed racer cables, lighter derailleurs and shifters, Sram's 990 cassette (red alloy spider), Kore steel quick release skewers, Kool Stop brake pads (or light rotors for the disc people), DT hardened alloy (looks frosty) spoke nips (in the front wheel), Truvativ/Sram chainring bolts, and FSA's alloy bolt headset compressor with carbon cap. These sorts of things go together as an approach. Just one light item by itself doesn't do that much.

    Therefore. . . if you already have all of the other lightweight items, then hub weight may be an important issue. Otherwise, just go for really good bearings and enjoy them.

  43. #43
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    Quote Originally Posted by Homebrew
    It's a simple question of weight ratios! A five ounce bird could not carry a one pound coconut.

    That depends: African or European swallow...
    A hardtail is forever

  44. #44
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    Man... That movie is the best. lol Have to see it again! Thanks for remind me. Excelent.

  45. #45
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    Daniel Haden you do know this conversation happened over 5 years ago right? Seriously what true weight weenie buys king hubs?

  46. #46
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    yeah but what happened to the bird and the coconut???

  47. #47
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    Don't lace Chris King ISO hubs to Mavic XM317 rims. That's like using SUV wheels in a Ferrari. You are better off getting sub-400 gram hoops like the Mavic XC717 disc, or Stan's Olympic. Yes, total wheel weight matters(hoops, hubs, spokes). Go bold...or go home.
    "This is a male-dominated forum... there will be lots of Testosterone sword-shaming here" ~ Kenfucius

  48. #48
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    I am still thinking about this topic and I tried to ask a few physicists, professional riders and engineers, because I am not an expert, but would like to get the best performance out of my bike. And I think it does not make sense for me as a hobby racer to spend too much money, I am definitely not the upcoming olympic champion.

    Meanwhile I was told that a few tests were done, and it seems, that the "system weight"
    ( = rider, clothes, shoes, bike, water bottles and so on) is the main factor in the game. Makes sense, I think: you accelerate not the wheel set itself, there is a rider ON the bike to be accelerated...

    Of course it makes sense to lower the weight of the wheel set / tires for having a more agile handling.

    But as I said: I am not an expert!

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