How many ball bearings to put in an axis?

Question

I'm cleaning out most of the axes on my new (second hand) bike.

I'm replacing the grease inside the pedal axes and I was wondering.

How many ball bearings should be inside? I thought there had to be just enough to fill the full circle, but a friend of mine told me I should fill the circle to it's fullest and then remove one ball.

The reason, he said, is that else there is to much pressure on the bearings.

Is this true? And is it true for all the axes (say, the ones in my wheels' hubs)?

And also, I'm putting vaseline (the yellow heavy duty variant) inside the axes, is that a good idea?

Answer 1

The reason behind the "full less one" is that you need at least half the race full (rounded up) for it to work and performance improves with more balls past that point, but if it's too full you get a dramatic loss in performance. So "full less one" is an easy guide.

In practice most bearings spread a little as you tighten the cones so "full" when you're adding balls is not actually full in use. You can usually see this - when you're adding balls they generally sit in against the axle, then when you add the cone it spreads the bearings slightly. So filling the race is almost always fine.

Don't be tempted to add one more to fill in the extra space created when you tighten it up, this is exactly the situation the "full less one" guide is trying to avoid. That "full plus one" means all the load is on one bearing (and one section of the cone), plus the bearings are really grnding against each other as the wheel rotates. If you're lucky the wheel won't rotate in this situation, but if you're unlucky you're wreck the cups and have to replace the cups (or hub, if the cups are not replaceable).

Answer 2

The general rule is a full race minus one ball. But if the race holds, say, 20.5 balls (ie, has space for more than 1/2 additional ball but not a full additional ball) then you can use as many as will fit (without forcing).

There probably is a (very small) rolling resistance advantage in using fewer balls (down to perhaps 3/4 full) but it would be at the expense of increased wear on the cones and races.

Do note that you should try to use all new balls or all balls that are originally from the same axle. The balls wear slightly over time and adding a new ball to a bunch of used ones will mean the new ball is slightly larger and will create additional wear and resistance.

You should use a good bicycle bearing grease for the bearings. This will resemble your standard black/brown/gray automotive grease but is better formulated for the conditions in a bicycle hub. At the very least use the automotive grease -- I would not expect petroleum jelly to hold up very well in a bike axle.

Answer 3

Did you not count the ones you removed? That's basic...

Also, be sure to take a couple of the old ones to the shop so that they can match the size; most are standard but some bikes have odd-ball sizes. And be sure to buy new bearings; they are cheap and most authorities recommend that old ones not be re-used.