+1 I was gonna suggest it but d_D got here first.
I've contributed some to the wiki, but the thing really needs an outline first. For instance, the "How to fix a flat" section is applicable only to a narrow cross-section of bikes and assumes (e.g.) that it has Schrader valves. The problem with trying to enlarge it to cover most cases is that it almost of necessity turns into a tutorial about bicycle components - something that is covered pretty well in the main Wikipedia already. Someone needs to look at it from the point of view of general coverage, but limiting the scope at the same time. Not an easy job to do well.