Cyclists who ride for more than 2 hours a day need to eat at least 60% of calories from carbs to perform at their best or 5-8g/kg of body weight per day. For cyclists who ride less than 2 hours per day, about 45-55% of calories should come from carbs, which equates to 3-8 g/kg body weight per day [ 1]
Adequate carbohydrate is important for cycling because carbohydrate is the preferred fuel of working muscles, and depleting carbohydrate stores can lead to fatigue and poor performance 
. Carb needs vary based on training intensity and duration, so experiment with different amounts to figure out what works for you.
 Kerksick, C.M., Wilborn, C.D., Roberts, M.D. et al. ISSN exercise & sports nutrition review update: research & recommendations. J Int Soc Sports Nutr 15, 38 (2018). https://doi.org/10.1186/s12970-018-0242-y