I ate low carb for 6 months until I reached my ideal weight and have since added moderate amounts of carbs back in without gaining. I didn't have problems with rides even in ketosis (low, low carb) but my rides were generally in the 30 mile range. From readings, I take it you can perform in a very low carb status, but it takes some getting used to and thought. It might be better to simply eat some carb snacks prior to and during the ride. Lots of LCHF diets allow days off and most of us are not so carb sensitive that one day of higher carbs will kick off cravings. Keep in mind, in the long term you want to end up at a sustainable, eating lifestyle, not some forced diet. Depending on your constitution that might mean very low carb permanently or, like me (dropped from 195 to 163 and stayed going on 15 months), that could mean sandwiches with whole grain bread at lunch and a moderate amount of rice and potatoes with dinner.