Theoretically a smaller tent can be warmer, all things being equal. All things are never equal in real life. You have a smaller space to warm up with your body heat, but of course you lose heat in al tents, so eventually it is probably a moot point. I do find my 1 person tent a bit warmer than my 3 person tent, but they have never been set up at the same time in the same place.
As others have said your pad, and bag will be more important than the size tent you choose. One issue than can occur with a 1 person tent in the cold, is more condensation building up inside, if it doesn't vent well, and I have found my 1 person tend doesn't seem to vent as well as my larger tent. Of course the larger tent is a 3 person tent.
I do use a one person tent quite a bit. I like it. It is larger than most 1 person tents though, and has four right angled corners so it isn't tapered at one end. As a result, I can bring in my bags if I want, though when bike touring I generally don't. On a motorcycle trip a couple years ago I took the one person tent and my hammock. I ended up using the tent, and was able to bring my large tank bag, and a 40 liter Ortleib duffle bag inside with me. As I said, the one person tent I have is a bit wider than most. It is an REI Passage 1 tent. I bought it on a whim when it was marked down, and I am glad I did. I really like it. It also has a vestibule where I can put things, keeping them out of the weather. The poles fit perfectly attached under the top tube of my LHT, so I can pack the tent smaller. It's a great little tent. They no longer offer it, but they have the Trailmade 1 tent which seems to be its replacement.
Last edited by phughes; 04-06-24 at 08:01 PM.