Search sheldonbrown.com and sheldonbrown.org
Your bicycle's chainwheels should run perfectly straight and true, with no side-to-side wobble. This is especially true if you have a newer bicycle with indexed front shifting. With front indexing, it is difficult or impossible to make fine adjustments to the front derailer while riding. While perfection is not attainable in this Vale of Tears, it should be possible to get your chainwheels to run true to within 1 mm or less.
If your chainwheels are not running straight, you could, of course, replace them, but it might be possible to straighten them instead.
There are three things that could be bent, and if you "straighten" the wrong one, you are bending a good part to make it fit a bad part, thus compounding the problem.
The bottom-bracket axle may be bent. This is not very likely, but you should still check it first:
The spider may be bent. To check this, you need to:
The chainrings may be bent. If steps 1 and 2 come up negative, the chainrings themselves are bent.
I have had the best success straightening them on the bicycle, so I would say to bolt them back on to the spider.
Bent chainrings can sometimes be straightened by using a screwdriver as a prybar. A special bending tool made by Bicycle Research sometimes will fit, but not usually on modern chainsets.
If you have the guts to try it, a large rubber mallet will often do the trick.
If only the teeth are bent, they can often be straightened with an adjustable wrench, and the edges filed smooth.
Last Updated: by Harriet Fell