Bicycle Mechanics - Bent frame...

Something went wrong with my bike after a hammock fell over it during a storm.

It pulls to the left when I am riding it, not much but still noticable.
I pulled a string from the dropouts to the headset and measured the distance from the seat tube to the string. Did it on both sides, and ended up with a deviation of 1-2 mm. 36-37 mm on the left side, 35 mm on the right side. My rear derailleur seems to be slightly damaged also.
Anyway, is this deviation enough to make the bike wanna go to the left or could the wheels (not seated properly in the dropouts or not aligned properly), head set (slight tendence towards index steering) or maybe cable routing (right side cables pass the stem on the left side, samt length as before though) have something to do with the problem?

And if it is the frame, what is the best technique to correct this. It is a steel frame.

If you do find excactly where the bend is a good welder can fix it for you.

Call up bike shops in your area and ask if they have frame alignment tools. They should be able to get it back into alignment. Since your frame's steel, it can be fixed by cold-setting; unless it's really tweaked. Your measurements don't sound too bad though. Another option is to have a frame builder realign it for you..

Some frames from the factory are 1-2mm off so I really really doubt that is enough to make a bike dogtrack. My Peugeot is about 1/4" off, maybe more, and it doesn't dogtrack.

Maybe it's the fork? Could be the fork got bent (more specifically, the legs). Perhaps one leg is bent out slightly causing the wheel to point to the side ever so slightly that you can't tell with the naked eye, but you can feel it when you ride?

Hmm, ok, so I will measure the fork. How do I do that?
If it is not the frame that is causing the dogtrack, then what else could it be?

Guess I could put the bike up in the repair stand and spin the front wheel to see if it lean over to any side? Is that a way to see if the fork is straight?

Aren't some dropouts asymmetrical? i.e. a different distance from centerline in order to accomodate the cogs?

I'd start with the basics before assuming bent frame. Like- slightly tweaked handlebars/stem, or wheels not properly set in dropouts.

Probably have to go to the LBS to check the fork. Park has a dropout alignment tool for checking this, but it's too expensive to just buy to have around.

http://www.parktool.com/repair_help/FFG.shtml