The bonk is avoidable. The hollow legs, the heart-rate that won’t climb, the last 20 km that feel like riding through wet sand — almost always, that’s an empty tank, not a fitness ceiling. The fix is knowing how many carbs per hour your ride actually needs, and then training your body to take them on. Here’s the real number, and how to hit it.

Why carbs per hour is the question that matters

Your muscles run hard efforts on glycogen — stored carbohydrate — and you only carry 90 minutes to two hours of it at intensity. Once it’s gone, power falls off a cliff and no amount of grit brings it back. Eating carbs during the ride keeps your blood sugar up and spares that glycogen, which is why fuelling rate, not fitness, decides how strong you finish a long day.

The actual numbers

It scales with how long and how hard you’re going:

• Up to ~75 minutes: you likely don’t need to fuel mid-ride — water is enough, your stores cover it.
• 1 to 2.5 hours: aim for 30–60 g of carbs per hour. This is the bread-and-butter range for most rides.
• 2.5 hours and up, or racing hard: 60–90 g per hour — the high end of which only works with multiple transportable carbohydrates (a glucose-to-fructose blend, usually around 2:1). Your gut can only absorb so much glucose alone; adding fructose opens a second absorption pathway and lets you take on more without GI distress.

To put 60 g in context: that’s roughly two energy gels, or a bottle of carb drink plus a banana, every hour. It’s more than most riders eat — which is exactly why most riders fade.

Your gut is trainable — so train it

Here’s the part people miss: 90 g an hour will wreck you if you’ve never practised it. The gut adapts like any other system. If you want to fuel high on race day, rehearse it on your long training rides — nudge the rate up week by week until your stomach handles it comfortably. “Nothing new on race day” applies to fuelling more than anything else.

How to actually hit your number

Pick a rate before you roll out, then build the ride around it. Most gels land near 22–25 g, most carb mixes let you dial grams per bottle, and real food (bananas, rice cakes, dates) fills the gaps. The trap is winging it — eating when you remember, which is always too late. Set a timer, or fuel at fixed points, and treat it as non-negotiable as pedalling.

This is where guesswork quietly costs you. HELIOS counts the energy you actually burn on each ride and turns it into fuelling targets — how much to take on during the ride, and how to eat around it on the day. The numbers come from a real, USDA-backed food database, not an AI guess, and you log a meal in seconds by dictating it, snapping a photo, or scanning a barcode. Fuel that follows your training instead of the other way round.

Don’t forget after the ride

Mid-ride carbs keep you going; post-ride carbs decide how good tomorrow feels. The hour or two after a hard effort is when your muscles refill glycogen fastest, so getting carbs (and some protein) in early is part of the same fuelling job — and it’s how back-to-back hard days become possible instead of a slow dig into a hole.

The mistakes that cause the bonk

• Starting too late. Begin fuelling in the first hour, before you feel empty — once you’re hungry on the bike, you’re already behind.
• Under-fuelling the long ones. 30 g an hour on a five-hour ride is a guaranteed fade.
• Going big without practice. 90 g an hour on an untrained gut is a recipe for a roadside stop, not a PR.

The bottom line

Match your carbs to your ride: skip fuelling under ~75 minutes, take 30–60 g an hour for normal rides, and build toward 60–90 g (with a glucose-fructose blend) for the long and the hard — after you’ve trained your gut to handle it. Fuel early, fuel on a schedule, and refill after. Do that and the bonk stops being part of your ride.