What's the story with the rear bearings?

[GreasyC]

Why are the the rear bearings different sizes? The axle is obviously the same size at both ends, so why the bigger bearing at one end?

 

[weekendrider]

The spacer for that bearing not only corrects diameter but length.
It butts against the tube. Do you have yours? The spacer?
Sometimes they get thrown away with the old bearings. And that will make you sad.

 

[mrriggs]

I assume that the drive side has a larger bearing since it deals with a greater load (chain pulling on it).

 

[GreasyC]

Just seems odd to use a bearing with the wrong ID then correct it with a bushing. It didn't HAVE to correct the length of the middle spacer right? They could have just made that the right length in the first place. Reason I ask is I want to mount an XS rear wheel on a 17 mm axle and either way I go (replace bearings or bush them by necking in new spacers) the weirdness at the left side makes it more complicated. Just wondering if there's a good reason it has to stay complicated.