The basic text in our FAQ describing what's on topic comes from the original Area 51 proposal for our site. In the first few months of our beta, we added a bit referring people to on-off-topic on meta and reference on the site, but haven't otherwise changed it.
I think that instead of referring people to some meta threads, we should spell out what is and is not on-topic right there in the FAQ. I also think it's long enough since we had any real changes to defining what is on and off topic that we can safely put it in the FAQ.
I've gotten a bit of inspiration from:
Here is the current text from the FAQ that we can change (the rest isn't ours to touch):
Bicycles - Stack Exchange is for people who build and repair bicycles, people who train cycling, or commute on bicycles.
If you're not quite sure if your question is on topic, consider looking at meta questions tagged [on-off-topic] where the community has discussed what questions are appropriate for this site.
If your question is fairly basic, you might find the answer in one of our growing reference pages. Also, feel free to link to these in your questions and answers, particularly the entries in the terminology index if you'd rather not re-invent the two-wheeler.