Carbs, fluid and sodium - planned for your ride, start to finish.
How fuelling works
Where your energy comes from
A ride runs on two fuels - fat and carbohydrate. How they behave, and why one of them runs out, is the whole reason this calculator exists.
Every figure here - fuel stores, the crossover concept, the carbohydrate-feeding studies - is referenced in the research.
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FatCarbohydrate
Why it's worth getting it right
Fuelling well isn't only about dodging the bonk. The research points to a handful of everyday payoffs:
You hold your pace. Carbs keep your power and speed where you want them and push back the moment fatigue bites - the difference between finishing strong and crawling home.
Steadier energy, fewer cravings. A blood-sugar crash is one of the body's oldest hunger alarms - it sets off strong cravings on the bike and for hours afterwards. Eating little and often keeps blood sugar level, so you're not battling cravings.
A clearer head. Low blood sugar dulls concentration and judgement - the "foggy head" feeling. On a bike, in traffic or on a descent, staying sharp matters for safety, not just comfort.
Better recovery. Carbs taken during and after the ride start refilling your stores sooner - less next-day fatigue, and a better second ride if you're out again tomorrow.
None of this needs a number hit perfectly. It mostly rewards simply not skipping food on any ride longer than an hour or so.
01Two tanks, very different sizes
Endurance energy comes from fat and from carbohydrate, the latter stored as glycogen in your muscles and liver. Both bars below are drawn to the same scale.
Fat~50,000+ kcal
Slow to burn - it needs a steady, aerobic effort. For any ride here, effectively unlimited.
Carbohydrate muscle + liver glycogen~2,000 kcal
The fast fuel - the only one that sustains a hard pace. Small, and it empties within hours.
Fat is the huge, slow tank. Carbohydrate is the small, fast one - and it's the tank you can run dry.
02How hard you ride sets the mix
You always burn a blend of both fuels. The harder the effort, the more your body leans on carbohydrate - fat can't be burned fast enough to keep up. Sports scientists call this the crossover concept.
SocialMostly fat
EnduranceAn even mix
TempoMostly carbs
ThresholdNearly all carbs
A harder ride drains the small tank faster - which is why your carb target climbs with effort level.
03Fuel as you go, or hit the wall
Once the carbohydrate tank runs low, blood sugar falls and you're forced down to a pace fat alone can hold - the dreaded "bonk". Eating carbs as you ride keeps the tank topped up so it never gets there.
No carbs on the bikeHits the wall
Carbs every ~30 minFinishes strong
Start1 hr2 hr3 hr
You can't make the carbohydrate tank bigger - but you can keep refilling it. That's the job of the plan below: how much to eat, and when.
What about weight loss?
A fair question - and the popular answer gets it mostly wrong.
The myth
Ride easy to stay in the "fat-burning zone", and skip the carbs - that's how the weight comes off.
The weekly total is what counts. Fat loss comes from a sustained, modest energy deficit over weeks - not from the fuel you burn on any single ride. Easy pace does use a higher share of fat, but the body simply rebalances its stores afterwards.
Harder riding burns more. A bigger, well-fuelled ride burns more total energy than an easy crawl - and fuelling protects the muscle and recovery that make a deficit sustainable.
Skipping carbs rarely helps. With calories matched, riding fasted or low-carb hasn't been shown to beat normal fuelling for fat loss - and it invites the under-fuelling trap: cravings, lost muscle, poorer training.
Losing weight well is its own project. Fueller plans the ride, not a diet - for body-composition goals, a SENr-registered dietitian is the right guide.