If you want to improve cycle specific adaptations you have to do do cycle specific training ie on bike.
However, you can supplement this if you have time with certain weight training which targets specific areas like the quads, hamstrings, glutes, lower back and shoulders which can prove to be problem areas for cyclists for a variety of reasons.
So, stuff like squats, lunges, hamstring raises, lever raises / trunk extensions, shoulder presses or extensions would be good.
If you want to avoid adding mass then don't work within the hypertrophy range (around 8-12 reps per set) and high volume training (so multiple sets.)
You can either go really heavy to work neuromuscular adaptations (so 3-5 reps) or light to work endurance (15-20). I favour really heavy myself.
I also think weights are great for bony injury prevention as it improves bone mineral density.