Shimano SIS rear hub offset question I'm a beginner bike mechanic and am working on a used project bike I got cheap. I was just switching out the rear tire and tube for some new 700x25c Gatorskins and when I went to go put the wheel back, I found a really perplexing issue that I hadn't noticed. Namely, the derailleur side of the rear hub had this very strange offset to it, while the opposite hub had no offset.
When I went to put the wheel back on, I struggled with putting the derailleur side hub in, and with getting the right alignment on the non-offset hub.
This is the first time I've encountered this type of derailleur and I'm not sure what to do. Is it possible to get an offset of the same length, on the other side? Any advice?
Yes that's normal for an 80s style bike.  Notice the rear of the dropout slot goes back the same distance, but the drive side has the derailleur hanger there.
You can fit a block in the non-drive side, but having the slot open allows adjustment both ways.  Getting the rear wheel aligned right can be easier if you clamp on the rear brake while doing up the axle nuts, and holding the wheel in the middle of the chainstays while doing the nut up with your third hand.