Fork Alignment

 Sometimes I come across a bike that doesn't track straight. If I try to ride with no hands, the bike will veer off in one direction. This is usually caused by a misaligned fork. I made a simple tool to check the alignment of the fork blades:

 

 This was an old curtain rod that I crushed flat in a vise. The round end goes into the steerer tube, and the flat end sits between the fork legs. The cross bar fits across the fork to hold tension on the tool and keep it in place while you measure. These two pieces are loosely bolted together with an M5 nut and bolt. You could also make something similar with two pieces of 3/4" by 1/16" steel or aluminum flat bar stock.

To use it, first unbolt the front brake and slide it out of the way:

  

Then, insert the tool into the steerer tube, and rotate the cross bar so it sits across the fork legs. The spring pressure from the backward bend in the middle bar will keep it centered in the steerer tube: 

 

 Now you can measure and compare the two sides:

     

This fork is misaligned by 1/8" of an inch. That was enough to affect the bike's handling. If your fork is steel, you can carefully bend it back into alignment by pulling or pushing on the fork legs while bracing the head tube with your foot. If it isn't steel, then you'll need a new fork.