On a fixed bike, chainline is more important than how equidistant the wheel sits between the rear track ends. A bad chainline can cause a slew of problems, including friction, noise, and possibly even the chain to drop (which can be hazardous). Having messed with my fixed Swift for over a year, my advice to you is to get it to where the chainring and the rear cog are as close to alignment as possible.
This involves:
1.) Getting a measurement of your front chainline.
- Hold a ruler against the seat tube and measure the distance to the middle of the chainring teeth. Add 20mm to the result. This is your front chainline.
2.) Getting a measurement of your rear chainline.
- I suggest first re-spacing the axle to match your Swift's rear spacing. If you have an older Swift with 132.5mm spacing, then simply add 1 x 1mm axle spacers to each side of the axle. If you have a newer Swift with 135mm rear spacing, then add 2 x 1mm spacers to each side of the axle.
- Measure the distance from the inside of the rear fork end (or the outside of the axle locknut) to the middle of the sprocket. Double this, subtract it from 132mm (older Swift) or 134mm (newer Swift). This is your rear chainline.
Now the challenge is getting the 2 measurements as close as possible. If your chainline is off by more than 4mm, then you'll most likely need to change your bottom bracket and/or move the chainring to the inside position of the crank spider (or vice versa). You could also adjust using chainring spacers.
If you plan to move the rear axle spacers around, keep in mind that adding 2 mm of spacers to any one side of the axle will push the chainline 1 mm in the opposite direction.