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I took my old, filthy bike apart to clean it up. I have never done this before!

When I took the front wheel bearings out, I ended up retrieving 9 from one side and 10 from the other.

It seems like logically there are a few explanations:

  1. There were actually 10 each side but I dropped one without noticing.
  2. It's designed to have a different number on each side.
  3. It's not designed to have a different number on each side, but the bike shop put it together wrong and I've somehow got away with it over the years.

I honestly think I was being super careful and that it's not (1), but I'm prepared to accept it could be that if the others are impossible!

And I guess in practical terms, what I really need to know is ... should I put it back together with 9 on one side, or should I buy some new bearings so I have 10 each side? I think I read somewhere that 10 each side is standard for a front wheel.

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  • If you put 9 back in one side, is there enough gap left to fit 1 more? I assume putting 10 in one side doesn't leave a lot of gap...
    – rally25rs
    Sep 8, 2011 at 23:51
  • Yeah, 10 seems like a perfect fit ... although 9 doesn't look too bad either ... hence the confusion :)
    – Luke Halliwell
    Sep 10, 2011 at 0:55
  • Another option is that there should be 10 a side, but one got munched to powder by the others and is now mixed with the grease acting as a grinding paste. I've also seen the retainer cages get chewed up in this manner.
    – Criggie ♦
    Nov 30, 2015 at 23:11

3 Answers 3

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It's not unusual for an asymmetric shaft (on some rear wheels or solid-crank bottom brackets, eg) to have different numbers of balls in one side vs the other. But it's a little unusual for a standard front hub. And if there's intentionally a difference then there would be a small but visible difference in the size of the races as well.

Likely the hub was serviced in the past and one ball was lost (or you lost one somehow). But it's not really terribly serious. It's often recommended (as a general rule for ball bearings) to have "a full race minus one" vs having the race completely full, and your typical 10-ball bearing can survive reasonably missing 2-3 balls (though that's not ideal).

However, since you have things apart it would be worthwhile to replace the balls. (Don't mix old and new balls.) See if ten fit comfortably. If they fit, and there's still room for a fingernail between them, then use ten, otherwise go with nine.

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  • Thanks for the info. It looks like I can fit ten, so I'll get some new ones.
    – Luke Halliwell
    Sep 10, 2011 at 1:01
  • Note that the new balls will be tighter, so make sure they aren't so tight that they'll bind.
    – Daniel R Hicks
    Sep 10, 2011 at 1:28
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    The full -1 formula is new to me... Can you please give more detail on it?
    – Jahaziel
    Sep 17, 2011 at 0:10
  • It may be new to you, but it's old mechanic's wisdom -- been a rule since the Model T, probably. Of course, it depends on the tolerances involved -- with many bearings it's probably the case that the "full" ball won't quite fit when races and balls are new, but will after some use, so the rule tends to work when rebuilding.
    – Daniel R Hicks
    Sep 17, 2011 at 0:47
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10 each side!

Invariably a bicycle has 10 3/16" balls on each side on the front and 9 1/4" balls on each side in the rear wheel.

You may want to read the Park Tool guide that confirms this and has plenty of tips for doing the job properly:

http://www.parktool.com/blog/repair-help/hub-overhaul-and-adjustment

You will need cone spanners, some clean grease and a new pack of 3/16" balls. The balls are cheap so replace all of them.

Important to get right is the bearing preload. Tighten the hub until it is running smoothly, then put a bit of extra on the locknuts to get everything really tight. If you are lucky then the bearing will feel slightly rough when you turn it, i.e. not as smooth as you set it up before the extra tightening. This will give a reasonable amount of preload on the bearing. Preload is important for carrying your weight properly and the longevity of the bearing. What you don't want is for the bearing to have play or be over-tight, the above technique should help you to get it right.

Hope that helps!

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  • Thanks (and yeah I have been following the Park guide ... seems brilliant)
    – Luke Halliwell
    Sep 10, 2011 at 0:56
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I would try to buy new bearing balls and fit 10 brand new balls properly greased in each side. I can't think of any reason for a front wheel to have more balls in one side.

I assume that your wheel uses rim brake, which being properly adjusted should put a fairly symmetrical load to the wheel assembly. Most modern hubs designed for Disc Brakes also use the same kind of bearing for each side. Even rear hubs, that clearly have a greater side to side load difference are commonly designed with identical bearings for both sides.

So, if there is no obvious difference in the left/right sides of the hub, the most reasonable answer is to use the same amount of bearing balls for each side.

Also, a personal tip: Some non-pro hubs use ball bearings consisting of a number of balls held together by some sort of cage. This cage keeps the balls separated. I use to buy a couple of extra bearings, take them apart and fit as many balls as possible, with also, as much grease as possible.

I do this based on the argument that the load will be spread among more balls, thus diminishing the load for each individual ball, with the positive effect of extending the time between hub maintenances. My results are that I have never had a case of cracked bearing balls in any hub that had this procedure performed.

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    I've never seen cracked bearing balls anywhere. Sounds like your procedure is keeping the elephants away.
    – Daniel R Hicks
    Sep 9, 2011 at 0:29
  • In fact wikipedia suggests that having a cage "avoids dents in the balls and has lower friction" en.wikipedia.org/wiki/Ball_bearing#Caged
    – Mac
    Sep 9, 2011 at 6:27
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    The cracked balls have happened to me when using low end hubs in very demanding situations, especially when water washes grease out of a non properly sealed hub. Obviously, I was using cheap balls too. The Wikipedia article also states that the cage can reduce load capacity and where designed for replaceable cup hubs. It just happens to be that in my country cheap balls are easy to find, whereas the store guy usually doesn't even know hub cups are replaceable. And yes, I really overloaded those bikes . . . 3 people instead of 1 ;)
    – Jahaziel
    Sep 9, 2011 at 21:54

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