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Is hub weight in a wheel really improtant?

9K views 47 replies 26 participants last post by  Mr.SJ 
#1 ·
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?
 
#2 ·
You need a brain adjustment on rotational weight

fasteddy001 said:
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 ·
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.
 
#4 ·
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 ·
fasteddy001 said:
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.
 
#6 ·
I'm curious about your prior perception regards rotational weight

fasteddy001 said:
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 ·
Chris King hubs make you feel less tired

mtb_biker said:
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 ·
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.
 
#9 ·
Perhaps an expert will post something....re-rotational weight

fasteddy001 said:
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 ·
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 ·
STOP.....Read this January 04 thread first....

I'll look around over the next 24 hours to see what I see....(when I get some time)[/QUOTE said:
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......
 
#12 ·
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 · (Edited)
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.
 
#15 ·
Well, think about it this way.......

fasteddy001 said:
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 ·
Chester said:
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?
 
#17 ·
Chester said:
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!
 
#19 ·
Homebrew said:
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!!
 
#21 ·
This product puts Chris King hubs to shame..

Fett said:
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 ·
It's rotational and unsprung weight

nino said:
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.
 
#23 ·
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 ·
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.
 
#25 ·
Homebrew said:
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?
 
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