Track end alignment.
 

Track dropout alignment (or track end)

I'll admit that I'm a bit obsessive when it comes to mechanics. Bicycles included.

This is about my 2010 Schwinn Madison fixed gear/single speed road bike. I notice that when I slide my rear wheel into the dropouts (or track end) it doesn't sit perfectly centered between the stays (both chain and seat). I can get it centered if I move it about a bit and hold it as I carefully tighten the axle nuts. I measured the frame alignment as per Sheldon's string method, and I get 31mm on the button from the seat tube on each side.

The bike rides just fine. I can ride straight with no hands, and it doesn't show any other symptoms of misalignment other than the wheel not centering in the dropouts without a little tweaking.

Anyone else have this issue? It bugs me a bit, but that's because I'm obsessive and I really appreciate accurate manufacturing.

that's pretty common.

Because the width of the slot is a bit wider than the axle, there's some vertical play in the dropout which allows the top of the wheel to rock a bit to either side.

If you want consistent results learn to install the wheel with the bike standing on the ground. This will ensure that the top side of both dropouts are resting on the axle, and keep the wheel in the same position every time.

This is excellent advice. One should always install the wheels and tighten the bolts/skewers with the bike standing on the ground. It's astounding how many customers stop in with problems which are solved by simply doing what I said.

checking with Dropout alignment tools is often in order.
get them square to the axles ,
and parallel to the center line.

Will give this a shot.

Also, perhaps I could use a file to correct this problem?