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Hub durability: more, smaller balls vs fewer, larger balls

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Hub durability: more, smaller balls vs fewer, larger balls

Old 04-12-13, 11:41 AM
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Metaluna
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Hub durability: more, smaller balls vs fewer, larger balls

Looking at Shimano freehub bearings, they have:

FH-7900 : 3/16" balls, 13 per side (I think)

FH-5600 (and many others, both road and MTB): 1/4", 9 per side

Would there be a noticeable difference in longevity between these for a heavy rider, all other things being equal? (Riding style, maintenance intervals, etc.) I assume the Dura-Ace hub uses smaller balls to allow more space for the over-sized axle?
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Old 04-12-13, 12:32 PM
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Quality is more important than quantity in this case. There probably will be no difference assuming thehubs are taken care of and lubed correctly. Roger
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Old 04-12-13, 01:25 PM
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Properly maintained hub bearings can last for decades with perhaps cone replacement, so unless you're worried about passing them down to grandchildren I would not worry about it. I'm sure that ball bearing size is one of the least significant factors in longevity.
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Old 04-12-13, 05:36 PM
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With proper maintenance it should last tens of thousands of miles.
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Old 04-12-13, 06:53 PM
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Originally Posted by Metaluna View Post
I assume the Dura-Ace hub uses smaller balls to allow more space for the over-sized axle?
And/or weight. Thirteen 3/16" balls weigh 39% less than nine 1/4" balls.
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Old 04-12-13, 07:14 PM
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13*3/16 = 39/16 or 2-7/16" of balls.
9*1/4 = 9/4 or 2-1/4" balls.
So the newer one has 3/16" more balls.

Does it matter********************
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Old 04-12-13, 07:23 PM
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About two years ago, a hub study suggested the grease was about 400 times as important as the type of bearings used in cup/cone systems.
I suspect bearing count has similar irrelevance.
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Old 04-12-13, 08:06 PM
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This is another example of where there is a technical difference, but it may not be relevant.

The choice in ball size and count in bike hubs is usually dictated by dimensional considerations rather than durability. As a rule larger bearings with higher load capacities will have larger balls, but the difference between 3/16 and 1/4 isn't enough to factor for bike hubs, since both have more than enough capacity.

OTOH- if you're really heavy and expect to subject these to max loads, and all other things are roughly equal, then go for the hub with the larger balls. It isn't the number of balls but the curvature that's more important.
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Old 04-12-13, 09:54 PM
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As the balls get smaller, more of them can be fit into place....

How about
Infinite number of infinitesimally small balls. -two bearing races riding on a thin film of grease.
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Old 04-12-13, 10:34 PM
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Originally Posted by xenologer View Post
As the balls get smaller, more of them can be fit into place....

How about
Infinite number of infinitesimally small balls. -two bearing races riding on a thin film of grease.
Grease containing buckyballs?
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Old 04-13-13, 12:24 AM
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Øk how do you propose this analysis be done ,. science and a controlled experiment, or anecdotal opinions?
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Old 04-13-13, 05:22 AM
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Originally Posted by xenologer View Post
As the balls get smaller, more of them can be fit into place....How about (an) Infinite number of infinitesimally small balls....
Wouldn't that basically be a bushing?
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Old 04-13-13, 05:55 AM
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Round balls will last longer because they will all carry the loads imposed on them.
I have re-balled hubs w/cheap balls and could not adjust them properly as they always felt lumpy unless set-up loose.

#25 is good enough... http://americandad.biz/gradechart.htm
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Old 04-13-13, 08:40 AM
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Originally Posted by Continuity View Post
Wouldn't that basically be a bushing?
I'll drag this further into the useless hypothetical territory. Disclaimer, I am neither a machinist, nor a an engineer.

Smaller bearings results in greater contact with the race surface. While this reduces the load on the individual contact points, wouldn't there be a point where the additional contact between bearings and races will result in increased friction? Especially when the viscosity of the lubrication overcomes the "leverage" (for lack of a better term) of the tiny bearings rolling against the races? At this point, the bearings do effectively become a bushing, correct? Therefore, when factoring in the lateral forces (i.e. weight) of the axel against the hub in combination with wheel size, etc..., there ought to be an ideal combination of bearings & races & lube that results in a perfectly calibrated bicycle wheel with a minimal amount of rolling resistance at the hub.

Once this feat of engineering is achieved, we need to locate a perfectly symmetrical cyclist who can ride in a vacuum to perform tests of this bike.

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Old 04-13-13, 08:49 AM
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Service your hubs regularly and they should last nearly forever. In my opinion that is all one really needs to know.
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Old 04-13-13, 09:35 AM
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It isn't necessary to rehash all this, or do any experiments. Bearing design is highly refined, and the folks who make bearings have been doing this kind of analysis for over a century.

The reason large balls are better for high loads is that the larger curvature allows for less local deflection of the contact surface before deforming enough to carry the load. Less deformation means less heat, and less stress on the surface. It's the same reason wider tires have lower rolling resistance for heavier riders, and why trucks use bigger wider tires than sports cars.

If you look at bikes in general you'll find that ball size is selected in proportion to the loads involved. But there's some latitude, especially since heat isn't a factor, and the component makers might let the dimensional constraints tip the decision one way or another for any bearing.
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Old 04-13-13, 09:45 AM
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Originally Posted by FBinNY View Post
The reason large balls are better for high loads is that the larger curvature allows for less local deflection of the contact surface before deforming enough to carry the load. Less deformation means less heat, and less fretting wear on the surface. It's the same reason wider tires have lower rolling resistance for heavier riders, and why trucks use bigger wider tires than sports cars.
Though I don't pretend to fully grasp the nuances, this makes more sense than my poor understanding. Its funny how often, for better or worse, ignorance will encourage someone to reinvent the wheel.
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Old 04-13-13, 10:10 AM
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Originally Posted by Ferrous Bueller View Post
About two years ago, a hub study suggested the grease was about 400 times as important as the type of bearings used in cup/cone systems.
I suspect bearing count has similar irrelevance.
All I know is I have a set of Superbe hubs with the grease ports, and I greased them twice a year unless I ran into lots of rain then I did it again. Those hubs have over 160,000 miles on them and the bearings are the original. So I kind of think clean grease may be a factor in longevity.

And I would thing more bearing would be better then less since you would be spreading out the weigh load over more surface area, but I'm not that scientifically minded so maybe that's incorrect.
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Old 04-13-13, 11:16 AM
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^The test was a friction one, not longevity. I didn't express that very well.
They repacked with different greases and different bearings and measured variances in drag.
Can't find it online. Was in Dutch.
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Old 04-13-13, 11:29 AM
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Originally Posted by Ferrous Bueller View Post
^The test was a friction one, not longevity. I didn't express that very well.
They repacked with different greases and different bearings and measured variances in drag.
Can't find it online. Was in Dutch.
Parasitic drag from the viscosity of the lubricant is a well documented phenomenon. More viscous lubricants have higher film strengths and are less likely to spin out of bearings, especially when heated, but create more parasitic drag.

Choosing the right lube is a matter of finding the one with the least drag, that will still do the job required. That's one reason there are so many choices in lubricants, running from very thin clock oils, to very thick axle greases. But in the scheme of things it barely matters on a bike, because even the worst bearing drag (from all causes) is near zero compared to the total resistance of a moving bicycle.

Unless you're racing a time trial where a second or two at the end of 30 miles may be a factor, bearing life is far more important than a minor change in bearing drag.
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Old 04-13-13, 12:04 PM
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Old 04-13-13, 12:07 PM
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lots of tiny balls, and the odds of one ball chipping is increased , just because there are more of them.
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Old 04-13-13, 01:24 PM
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Originally Posted by fietsbob View Post
lots of tiny balls, and the odds of one ball chipping is increased , just because there are more of them.
What would cause a ball to chip? I've never seen that unless there was some sort of failure internally. I've seen blue balls (no jokes please) from lack of lube, but never saw a chipped ball from nothing happening internally. Of course I haven't seen all the balls in the world either...nor do I want to!!!!
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Old 04-13-13, 01:38 PM
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This thread has pulled my mind firmly into the gutter....
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Old 04-13-13, 01:51 PM
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Balls occasionally chip or fracture because of dirt or contamination. Some bearing makers prevent this by including a single ceramic ball into the complement of balls. This is the crusher who's job is to pulverize grit that enters and might damage the bearing. However this is a special purpose application, and not common.

Bearing wear is normally on the races themselves which spall from the constant flexing as the balls pass by. This causes microspopic bits to break off over time until the hardened skin breaks through giving you the classic pitted appearance. Usually the cones wear faster because the track is half the length of the cup's.
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