I have a 16' steel Stanley garage door with a broken torsion spring. The spring (it is the right hand spring as viewed from inside the garage) is 1 3/4' ID and 24" in length. The only 1 3/4" springs available in the DYI website are 32' in length. Will it be all right to replace the broken spring with a longer spring, or should I replace both sides with 32" springs to keep it balanced.

 

I don't understand how you can determine the ID of a torsion spring. A torsion spring runs along the top of the door and has a large rod going through it.
The other type of spring is a extension spring. It runs along the door tracks.
A DIY can replace the extension springs but not the torsion springs. Door springs must be the same size to pull the door up at the same rate. You should always replace both of the springs at the same time. If you go to a place like Lowes they have a chart to tell you what springs you will need. They sould be about the same size as the old springs.

 

You are probably not going to find you spring at a DYI store. They make 136 different kinds of springs and probably 1/3 of those are the same diameter as yours. If you do not have the correct springs you door will not work properly. My advice is to call a garage door pro. They have ways to get you your exact set of springs for your door. It has to do with how much your door weighs. They will have to insatll it anyway, so you might as well do it right. You will have to replace both springs, as they come in pairs. If you don't replace both, the other one will break very shortly. Good Luck