My bicycle currently has poor chainring/rear sprocket alignment (as in the chain at the front is more than a chain's width from the chain at the rear). I'm wondering what the procedure is to correct this alignment, because currently riding the bike damages the chain. (I have already moved the wheel as far across as i can using washers)
To adjust chainline, you can:
At the back
- use spacers between the hub and cog
At the front
- use a longer/shorter bb spindle (as Kibbee says)
- use spacers on the bb cups (as Mark W says)
- use chainring washers (and likely different bolts) to adjust the position of the chainring on the crank
I'm struggling to think of any more options.
The only other thing I could think of is that if you do end up with an imperfect chainline, despite your every effort, then a 3/32" chain will be more forgiving than a 1/8" chain. 3/32" chains are designed to be able to traverse cassettes so have a little more flexibility in them.
You won't like the price tag on this solution, but to get my single speed bike with a perfect chainline, I used the Surly Single-Speed Kit which has 6 spacers of different widths that let you get things exactly right. The kits run about $40, but you also need a rear hub with the Shimano style cassette mount, such as for a 5-cog cassette on a 10-speed bike.
Based on my experience, determining the chainline based on specifications of the components (BB and Crankset) and a simple math calculation is the best approach. This is because I was having a hard time to ballpark the chainline. I then found out that the manufacturer of the crankset I use provides a specification document which describes the recommended spindle length of the BB and the chainline measurement.
To get the spacers adjustment correct, I use a table provided by Surly: surlybikes.com/files/SS_Spacer_Kit.pdf . The table isn't really specific for Surly spacers but it only works with Shimano hubs. Surly SS kits are expensive, so I recommend to purchase ones from a Taiwanese company which can be found on Ebay.
Rather than eyeballing, ballparking, or relying on tables, I have found that a ruler is the simplest and most accurate tool for this job. Put the ruler with the zero mark in the middle of the seat tube, and measure the distance to the teeth on the chainring. Then measure the inside diameter of the frame at the rear dropouts where the rear axle goes. Divide that by two, and put a piece of tape on the rear hub right at that distance from the inside of the rear drop out. That's the midline. Now measure from that line to the chain on the rear cog. That's how I used the Single Speed Kit to get the rear cog right on the chain line.