So by now you should know there is no bottom limit if you are motivated. You will have to learn for yourself how motivated you are and part of that learning process will be to learn how to dress at various temps. My wife and I also keep a winter chart of temps and clothing layers that work at those temps. +1 on lenny866. Every 10F or so requires some change to your layering system. Pogies become very helpful for the hands at some point (we ride to about -10F when we feel tough. Rarely but occasionally below that and regularly to +10F). Cycling shoes give way to lightweight boots and hand-warmer packets become very useful inside gloves/pogies/boots when it gets seriously cold. Panniers are important to carry extra clothing. Changing a tire at +10F when you are sweaty is a serious problem if you can't add some layers. Winter riding takes time to learn. Good questions. Keep that up and with the right clothing and equipment it can be a lot of fun. PS. My forum pic was after an hour or two ride at -20F. My breath collects on my beard and makes a pretty well encrusted beardcycle.