n00b question about sleeping bag temperature ratings
I've been going camping all my life (50+ years) and never paid much attention to sleeping bag ratings and we have a motley collection here of various bags. Now that I'm getting more into bikepacking, I'd like to get a higher quality sleeping bag that's less bulky / heavy.
If a bag is rated for 40° F, does that mean it'll be at the edge of comfortable at that temperature and going lower the bag just won't keep up? Also, does that mean that if it's maybe 60° F out, the bag will be sweltering and uncomfortable? What's the rating really mean?
These higher end lightweight sleeping bags are expensive and I'd like to just get ONE that is going to be suitable for the sort of camping I envision I'll be doing. I don't see myself going out in the deeper winter, so I'd say my experience will likely be in the 45° nights and upwards.
In advance, thanks for your advice, help, criticism, recommendations, and terrible jokes.