Manual says letter side out, both sides of the bearings look identical, guess it doesn't matter, putting fresh bearings in rear wheel.

 

I just make sure the the part numbers are on the outside so that I can read them. A new roller bearing can turn in either direction. It don't care.

 

Ya, there must have been a reason for the manual to say that, maybe earlier bearings could take cornering thrust better installed like they say. Both sides have the same printing on current bearings

 

Id say it has something to do with the seal on the bearing, the external seal is probably more impervious to any foreign material than the inner seal.

 

I'm guessing it has something to do with the anti-lock brakes.

 

There are not numbers on letters/numbers on both sides. The black seal of the bearing has numbers on both sides, but the internal race of the bearing has letters/numbers on one side only. That is the side that faces out. In the attached pic, the red arrow points to where you will see the numbers.

 

Since they specify a direction it is probably because the bearings are a angular contact type bearing.

Standard ball bearings are only good at taking a load at a 90 degree angle to the axle.
And are very poor at taking side loads.

In applications where loading in both directions is important a angular contact bearing is used.
In this case it is a angular contact ball bearing. In a bearing without seals is is normally easy to tell the correct mounting because one face of the bearing is wider than the other.

In this application the wider outer race would be to the inside, and wider inner race to the outside.
The attached picture shows how a set of angular contact bearing would be mounted.
The only thing different on a wheel is that there is a spacer between the bearings.
The wheel hub itself is the outer spacer and the inner spacer is a sleeve.
The length of the inner sleeve can be changed to control the end play.

 

I believe the reason for the orientation is the numbered side will take more stress....for the installation of the bearing.

 

Or there might be a microscopic taper, similar to inner cam bearings supposedly, to make installation easier.

But that's 100% guessing on my part.

 

Anyone ever think that maybe they said numbers out is only so they can be read for future replacement?