Every cyclist who has ridden long enough has a bonk story. Mine came about 130km into a 160km loop through the Borders — legs suddenly empty, speed dropping off a cliff, and that strange foggy-headed feeling where even simple decisions like "should I turn left here?" become genuinely difficult. The bonk, or hitting the wall, is not a fitness problem. It is a fuelling problem, and it is almost entirely preventable.
This guide covers what actually happens in your body when you bonk, the numbers you need to hit to stay ahead of it, and a practical plan for how to avoid bonking cycling long distances — whether that is your first 100km sportive or a full day in the saddle.
Quick answer: to avoid bonking, start the ride well fuelled and begin eating within the first 30–45 minutes. Aim for 30–60g of carbohydrate per hour on rides up to 3 hours and 60–90g per hour beyond that, drip-fed every 20–30 minutes rather than in big, infrequent lumps.
What Bonking Actually Is
Your body stores carbohydrate as glycogen — roughly 400–500g in your muscles and another 80–100g in your liver. That works out at around 1,600–2,000 kcal of readily available carbohydrate energy. Riding at a moderate endurance pace, most cyclists burn 600–900 kcal per hour, and a significant chunk of that comes from carbohydrate. Do the maths and the problem is obvious: ride hard for two to three hours without eating and your glycogen stores run dry.
When muscle glycogen empties, your power drops sharply because fat oxidation alone cannot supply energy fast enough to hold a decent pace. When liver glycogen empties, your blood glucose falls — and because your brain runs almost exclusively on glucose, that is when the dizziness, irritability and mental fog arrive. A proper bonk is both at once, which is why it feels so catastrophic.
The Numbers: How Much to Eat and When
The current sports science consensus is clear on intake targets:
- Rides under 90 minutes: you can get away with water and whatever is already stored, assuming you started fuelled.
- 90 minutes to 3 hours: aim for 30–60g of carbohydrate per hour.
- 3 hours and beyond: aim for 60–90g per hour. Above roughly 60g/hour you need mixed carbohydrate sources (glucose plus fructose), because glucose absorption alone caps out at about 60g per hour.
The single biggest mistake riders make is starting too late. Glycogen you burn in hour one is not available in hour four, so begin eating within the first 30–45 minutes of a long ride and keep drip-feeding carbohydrate every 20–30 minutes rather than eating in big, infrequent lumps. Little and often keeps blood glucose stable and is far kinder to your gut.
How to Avoid Bonking Cycling: A Practical Ride Plan
Here is a simple framework for a five-hour ride that keeps you comfortably ahead of the wall:
- The night before: a carbohydrate-rich dinner — pasta, rice or potatoes. No need for extreme carb-loading unless you are racing, but do not start a big ride half-empty.
- Breakfast (2–3 hours before): 100–150g of carbohydrate. Porridge with banana and honey is the classic for good reason.
- Hour 1: start eating at 30–40 minutes. Around 40g of carbs in the first hour is plenty.
- Hours 2–5: 60–80g per hour, split into portions every 20–30 minutes. Set a timer on your head unit if you are the type who forgets.
- Fluids: 500–750ml per hour depending on heat, with electrolytes on warm days or anything over three hours.
Practise this in training, not on event day. Your gut is trainable — riders who consistently fuel at 60g+ per hour in training absorb carbohydrate noticeably better than those who only attempt it at a sportive with unfamiliar feed-station food.
Fuel every 20 minutes, straight from the pocket
Tart Cherry Energy Pastilles — 2 pastilles ≈ 30g of carbs, with recovery-supporting anthocyanins built in.
Warning Signs You Are Heading for the Wall
The bonk rarely arrives without notice. Learn the early signals and you can usually rescue the ride:
- Your perceived effort creeps up while your power or speed stays flat — the same pace suddenly feels harder.
- You become unusually negative or irritable. The "why am I even doing this?" thoughts are frequently low blood sugar talking.
- You stop feeling hungry. Counterintuitively, appetite often disappears just when you need food most.
- Small climbs that should be trivial start feeling like walls.
If you catch these signs, take 40–50g of fast-acting carbohydrate immediately, ease the pace for 20 minutes, and keep eating on schedule afterwards. Caught early, you can usually ride through it. Caught late, you are managing damage — soft pedal home, keep eating small amounts, and accept the average speed is gone.
| Warning sign | What to do |
| Same pace suddenly feels harder | Eat 40–50g of fast-acting carbs now and ease the pace for 20 minutes |
| Unusually negative or irritable | Treat it as low blood sugar — fuel immediately, do not argue with yourself first |
| Appetite disappears mid-ride | Eat by the clock anyway — hunger is an unreliable signal late in a ride |
| Trivial climbs feel like walls (caught late) | Soft pedal home, keep eating small amounts, accept the average speed is gone |
What We Use at FTP Endurance Fuel
Everything above shaped how we designed our own products. We wanted fuelling that is easy to portion into that 20–30 minute rhythm, gentle on the stomach at hour four, and genuinely pleasant to eat — because the best fuelling plan in the world fails if you cannot face another sickly gel.
Our energy pastilles deliver carbohydrate in small, chewable portions, so hitting 60–80g per hour is as simple as a couple of pastilles every 20 minutes from a jersey pocket. On big rides we carry the Tart Cherry Energy Pastilles — the tart cherry is not just for flavour, as its natural anthocyanins are associated with reduced oxidative stress and better recovery, which matters when you are backing up long rides on consecutive weekends. If you prefer variety over a long day, the Mixed Fruit Pastilles solve the flavour fatigue problem that hits most riders after hour three.
Frequently Asked Questions
What does bonking feel like?
A proper bonk is muscle glycogen and liver glycogen running out at once: your power drops sharply, your speed falls off a cliff, and because your brain runs almost exclusively on glucose you get dizziness, irritability and mental fog — even simple decisions become genuinely difficult.
How do I recover from a bonk mid-ride?
Take 40–50g of fast-acting carbohydrate immediately, ease the pace for 20 minutes, and keep eating on schedule afterwards. Caught early, you can usually ride through it; caught late, soft pedal home and keep eating small amounts.
How many carbs per hour do I need to avoid bonking?
Aim for 30–60g of carbohydrate per hour on rides between 90 minutes and 3 hours, and 60–90g per hour beyond that. Above roughly 60g per hour you need mixed glucose and fructose sources, because glucose absorption alone caps out at about 60g per hour.
Can you bonk on a short ride?
It is unlikely. On rides under 90 minutes you can get away with water and stored glycogen, provided you started properly fuelled — a carbohydrate-rich dinner the night before and a decent breakfast cover it.
The Bottom Line
Bonking is not a rite of passage and it is not inevitable — it is arithmetic. Start fuelled, begin eating early, hit 60–90g of carbohydrate per hour on long rides, and practise your fuelling in training so your gut is ready on the day. Get those pieces right and the wall simply never appears.
If you want fuelling that makes the little-and-often approach effortless, have a look at our bundles — built for riders who would rather think about the road ahead than the maths in their back pocket.
Mixed Fruit Pastilles 1kg
Beat flavour fatigue on all-day rides — several flavours in one bag.
£44.99
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Electrolyte Tablets
Cherry-flavour electrolytes for warm days and rides over three hours.
£5.99
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