If you’re cycling for 90 minutes or more, consume a small amount of energy gel every 15-30 minutes. After 60-90 minutes your body has used up most of its stored carbohydrate (glycogen) and research suggests that you need to replace that carbohydrate to maintain energy and maximize performance 
A good rule of thumb is to aim for roughly 30-90g/ hour if you’re cycling for more than 90 minutes 
. Most gels have about 20-30 grams of carbs, so that equates to 1-3 packets per hour. Bananas, sports drinks, sports chews, and honey sticks can also be used to meet carbohydrate needs during a ride. The longer and hard you cycle, the more carbohydrates you will need during a ride. Tolerance varies from cyclist to cyclist so don’t forget to experiment in training!
 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