You’ve gotten good advice re: what to do during the winter. When its “regular” riding season again try mixing up your rides. Not sure if you have a running background but its similar re: building up more stamina. If you’re doing the same rides over and over and getting faster thats great but you’re probably continuing to exert the same high-end effort. To build stamina work in 1-2 longer rides per week at a more moderate tempo. Read articles on training with a HR monitor. Once you understand and implement that you can really make measurable progress. You can do that over the winter using a trainer or stationary bike at a gym and make some progress…but nothing like the real thing.