Upping Miles on Bike -- Change Weight Training?

I ride and lift twice a week, sometimes 3 times a week. But I'm not lifting to failure and not lifting heavy weights. I think since you're only lifting once a week you will be ok. How often are you riding per week? I would suggest 25 miles 3 times a week which should be easy enough. Or do 2 rides of 15-20 and then a long ride to make up the difference on the weekend. most cyclist do something similar with shorter rides during the week and a long ride on the weekend.

Ride the bike more. No weightlifting can replace the actual riding of the bike and the muscle endurance required.

I would say one hour spin classes would be more valuable than additional weights as well.

Gotcha, I think it will be more psychological than physical being on the bike longer. And with the heat right now it makes it doubly tough. Good luck!

I ride a Peloton mostly, but occasionally get out on my real bike. Nothing can replace miles ridden for that endurance. I still do leg day once a week, but it is typically squats/lunges/deadlifts with dumbbells, and not going super heavy or to failure. Pick a day, maybe a couple of days after a long ride, and do a quick weight session for your legs and you'll be fine. You still want that muscular strength, but riding uses muscles in a different way on long rides. I would focus more on glutes/hips/quads/hamstrings. Your calves will get enough ancillary work by biking. Also focus on stretching at least 2-3 days a week. Your hips will tighten up riding that much.