How Many Carbs Per Hour? A Numbers-First Guide to Fuelling Long Rides Without Bonking

If you've bonked, you don't need it described. The legs go to wood, the head fogs, and a flat road suddenly rides like a 6% drag. The good news: it's almost entirely your choice. Avoiding it is a numbers problem. This guide hands you the grams of carbohydrate, milliliters of fluid, and milligrams of sodium to take per hour, plus the one bit of physiology that lets a trained rider absorb twice the carbohydrate everyone used to say was the limit.

The bonk, explained: why glycogen runs out and what it feels like before it does

You store carbohydrate as glycogen in two tanks: your muscles and your liver. Together, a trained cyclist holds roughly 400-500 g of glycogen — about 1,600-2,000 kcal of fuel you can actually reach. Ride at a solid tempo-to-hard effort and you'll burn through it in around 90-120 minutes. When liver glycogen drops far enough, blood glucose falls with it, and since your brain runs almost entirely on glucose, you get the classic bonk (hitting the wall): deep fatigue, dizziness, a short fuse, and an effort that just stops obeying you.

Fat isn't the problem. Even a lean rider carries tens of thousands of calories of it — far more than any ride asks for. The problem is rate. Fat burns slowly, so above easy pace you lean on carbohydrate to hold the speed. Once glycogen's gone and you haven't been eating, your power is capped by how fast you can burn fat — and that ceiling sits well below your tempo or race pace.

The bonk isn't a failure of willpower or fitness. It's a fuel-logistics failure: you let the tank run dry instead of topping it up while you rode.

• Glycogen stores
• Without fuelling
• The bonk
• With fuelling
• Hours riding
• Carbs per hour
• 0
• 90 g
• Empty before the finish — you bonk
• Fuelled to the finish
• Ride intensity
• Easy
• Hard

What it feels like before the wall

The full bonk announces itself first, and the signs are easy to wave off: a creeping heaviness in the legs, less and less willingness to hold the pace on a climb, a flicker of irritability or unusual negativity, and a vague hunger that turns up too late to fix mid-effort. The physiology gives you a blunt rule: if you wait until you feel hungry to eat, you've already waited too long. Fuelling starts early and stays steady, because your gut absorbs carbohydrate at a fixed rate — you can't speed it up by shovelling in a big hit all at once.

How much carbohydrate per hour: from 30 g to 120 g and what determines your number

Your target rides on two things: how long you're out, and how hard you're going. Under an hour, you don't need to eat at all — glycogen covers it. As the ride stretches, the target climbs, until on the really long or hard days you're chasing the top end of what the gut can physically take in.

Two ceilings set the numbers. The first is the single-transporter limit: glucose crosses the small intestine via a transporter called SGLT1, which saturates at about 1 g per minute, or roughly 60 g per hour. Take in more glucose than that and the surplus just sits in your gut, pulling in water and serving up the bloating, cramping, and diarrhea riders call "gut rot." The second ceiling is the one you break by mixing sugars, which is the next section.

Ride duration	Easy / endurance	Tempo / threshold	Race intensity
<60 min	0-30 g/hr	0-30 g/hr	0-30 g/hr (often none needed)
1-2.5 hr	30-60 g/hr	30-60 g/hr	60 g/hr (single transporter, SGLT1)
2.5-3 hr	60-90 g/hr	60-90 g/hr	90 g/hr (dual transporter)
>3 hr / ultra	60-90 g/hr	90-120 g/hr	90-120 g/hr (dual transporter, trained gut)

The role of pre-ride fueling

What you eat before you clip in sets your starting glycogen. Aim for 1-4 g of carbohydrate per kilogram of body weight in the 1-4 hours before a long ride — the bigger the dose, the more time you need to digest it. A 70 kg rider eating 2 g/kg takes in 140 g, topping off liver glycogen and buying time before on-the-bike fuelling has to carry everything. Starting full doesn't change your per-hour target, but it gives you a cushion for the moments when eating gets awkward — a fast descent, a hard pull, a technical stretch.

The glucose:fructose trick: beating the 60 g/hr single-transporter ceiling

For decades the line was that 60 g/hr was the hard ceiling — and for glucose alone, that was right. The breakthrough was spotting that fructose uses a completely different intestinal transporter, GLUT5, running in parallel with the glucose transporter SGLT1. Take glucose and fructose together and you open a second lane. The glucose lane delivers up to ~60 g/hr; the fructose lane adds another ~30 g/hr on top, lifting total usable carbohydrate oxidation to about 90 g/hr at the well-studied 2:1 glucose:fructose ratio.

Push the ratio toward 1:0.8 (closer to equal parts) and trained athletes can oxidize 100-120 g/hr, because the fructose lane is being worked closer to its capacity. That's why every modern sports-nutrition product shouts its glucose-to-fructose ratio: it's the single most important spec for high-rate fuelling. A glucose-only product physically cannot give you more than ~60 g/hr, no matter how much you choke down.

Glucose:fructose ratio versus maximum carbohydrate oxidation rate. Mixing sugars is the only way to exceed the single-transporter ceiling.

Glucose:fructose ratio	Max carb oxidation	Transporter pathway	Typical GI tolerance
Glucose only (1:0)	60 g/hr	SGLT1 only	Good up to 60 g/hr; gut rot above it
2:1	90 g/hr	SGLT1 + GLUT5	Well tolerated; the proven workhorse ratio
1:0.8	110 g/hr	SGLT1 + GLUT5 (fructose lane near capacity)	Needs a trained gut; favored for 100-120 g/hr

• SGLT1 · glucose
• GLUT5 · fructose
• Glucose only
• Glucose + fructose
• g/hr absorbed
• Carbs per hour
• 0
• 120 g
• Both doors keep up
• Glucose maxed — fructose adds the rest
• Both maxed — the rest is wasted
• Fructose mix
• Glucose only
• 2:1 mix

• The gut's fixed rate
• Absorbed
• Backing up — gut rot
• Carbs per hour
• 0
• 120 g
• All absorbed
• At the limit
• Overflowing — gut rot
• Gut training
• Untrained
• Trained

The practical version: if you're chasing more than 60 g/hr, every carbohydrate source in your pockets should carry both glucose (or maltodextrin, which digests down to glucose) and fructose. Reading the label for that ratio tells you more than the brand name ever will.

Training the gut: why fueling tolerance is adaptable, not fixed

Here's the part most riders miss: your maximum fuelling rate isn't a fixed personal constant. The intestinal transporters — GLUT5 for fructose especially — are upregulated by repeated exposure. Riders who never take more than a gel an hour feel sick the first time they try 90 g/hr, then conclude that high-rate fuelling "doesn't work for them." It does. Their gut is just untrained.

Gut training is progressive overload like anything else. The protocol:

1. Start where you are. If 40 g/hr sits fine, begin there, not at 90.
2. Add ~10 g/hr every week or two on your long rides, always from a mixed glucose:fructose source.
3. Practice at race intensity, not just easy pace. Blood flow shifts away from the gut as the effort climbs, so tolerance you proved on a Zone 2 spin may not hold at threshold.
4. Rehearse your exact race-day products. The gut adapts to specific carbohydrate types and concentrations; don't surprise it with something new on event morning.

Over a few weeks, that's how riders go from a 60 g/hr ceiling to comfortably putting away 100-120 g/hr. The transporters are trainable — you just have to train them on purpose, the same way you build any other capacity in the legs.

Hydration and sodium: estimating sweat rate and replacing what you lose

Carbohydrate keeps the legs turning; fluid and sodium keep the rest of you working. Sweat rates for cyclists run from about 0.5 to 2.0 liters per hour depending on heat, intensity, and how you're built. You generally can't — and shouldn't try to — replace all of it in real time, because the gut takes in fluid at a limited rate too. Sensible target: replace roughly 0.4-0.8 L/hr, accept a small deficit on hot days, and top up afterward.

Measure your own sweat rate

The number that matters most is yours. Measure it: weigh yourself naked before a one-hour ride and again straight after, accounting for anything you drank along the way. Every kilogram of body mass lost is roughly 1 liter of sweat. Do it across a few conditions — cool, moderate, hot — and you'll have a personal map instead of a population average to guess from.

Temperature	Typical sweat rate	Fluid target	Sweat sodium	Sodium to replace
Cool (<15°C)	~500 mL/hr	400-500 mL/hr	~500 mg/L	~300 mg/hr
Moderate (15-25°C)	750-1,000 mL/hr	500-700 mL/hr	~500-1,000 mg/L	~400-600 mg/hr
Hot (>25°C)	1,000-1,500+ mL/hr	600-800 mL/hr	~1,000-1,500 mg/L	~500-700+ mg/hr

Sodium earns its place for two reasons: it drives the absorption of both water and glucose (SGLT1 is a sodium-glucose cotransporter — that's where the name comes from), and it replaces what you lose in sweat. Sweat sodium swings hugely between riders, from roughly 200 mg/L in low-salt sweaters to 1,500+ mg/L in heavy salt-losers, and a reasonable replacement target is 300-700 mg/hr, skewing higher in the heat and for known salty sweaters. You don't need to match losses gram-for-gram on shorter rides, but on long, hot efforts, under-replacing sodium feeds the cramps and that hollow, hyponatremic flatness that ambushes you late.

• Drink
• Gel
• Solid
• fast · hydrates
• fast · portable
• slow · filling
• Gut tolerance
• Intensity
• Easy
• Threshold
• Easy pace — anything goes, solids spare your gels
• Tempo — gels and drink, go easy on solids
• Threshold — liquid and gels only, solids won't clear

Building a real-world fueling plan: a worked example for a 4-hour ride

Numbers are useless until they turn into a packing list. Take a 70 kg rider doing a hard 4-hour endurance ride in moderate weather, targeting 90 g/hr of carbohydrate, 600 mL/hr of fluid, and 500 mg/hr of sodium.

The totals to hit

• Carbohydrate: 90 g/hr × 4 hr = 360 g total (all from mixed glucose:fructose sources)
• Fluid: 600 mL/hr × 4 hr = 2.4 L total
• Sodium: 500 mg/hr × 4 hr = 2,000 mg total

A workable per-hour pattern

1. Pre-ride (1-3 h before): ~140 g carbohydrate (2 g/kg) to roll out topped off.
2. One 750 mL bottle per hour of drink mix delivering ~40 g carbohydrate and ~400 mg sodium. Across four hours that's ~160 g carbohydrate and most of your sodium from fluid alone.
3. One gel every ~40 minutes (~25 g carbohydrate each, ~6 gels) adds ~150 g carbohydrate.
4. One real-food item (a rice cake or banana) around halfway, for palate relief and the last of the carbohydrate.

That stacks to roughly 360 g of carbohydrate, ~2.4 L of fluid, and ~2,000 mg of sodium — all three targets hit. The habit that makes it work is the schedule: eat and drink on a timer, not on feel. Set a 15-20 minute alert and take a sip or a bite every time it goes off. Steady small inputs match your absorption rate; sporadic big hits overwhelm the gut and leave you under-fuelled in between.

Source	Carbs per serving	Glucose:fructose	Fluid needed to digest	Practical notes
Energy gel	~25 g	~2:1 (check label)	~150-250 mL with each	Fast, packable; needs water or it sits heavy
Drink mix (per bottle)	~40-60 g	~2:1 to 1:0.8	Self-contained (it is the fluid)	Best backbone; delivers carbs, fluid, sodium together
Banana	~25-30 g	Glucose + fructose + some sucrose	Modest; eat with water	Real-food relief; bulky, can bruise in a pocket
Energy chews	~20-25 g (per pack portion)	~2:1 (check label)	~150-250 mL	Easy to dose in small bites; chewing at intensity is harder
Real-food rice cake	~30-40 g	Mostly glucose (rice) + add fruit/honey for fructose	Modest; eat with water	Gentle on the gut for ultra-distance; bulky to carry

• Bottle — every hour
• Gel — every ~40 min
• Real food — at halfway
• Hours
• Carbs per hour
• Gut's limit

Common fueling mistakes and how to fix them

• Starting too late. Wait until you feel hungry and you're already behind your absorption rate. Fix: start fuelling within the first 20-30 minutes and stay on a timer.
• Glucose-only at high rates. Trying to pull 90 g/hr from a glucose-only product is a guaranteed gut ache, because SGLT1 caps glucose at ~60 g/hr. Fix: use mixed glucose:fructose (2:1 or 1:0.8) sources for anything above 60 g/hr.
• Never training the gut. Attempting race-day fuelling rates for the first time on race day. Fix: build tolerance over weeks, adding ~10 g/hr at a time at race intensity.
• Ignoring sodium and fluid. Carbohydrate without fluid digests poorly, and under-replacing sodium invites cramps and late-ride flatness. Fix: pair gels with water, and target 300-700 mg sodium per hour, higher in heat.
• Eating in big, infrequent batches. A single large feed can't be absorbed faster than ~1.5-2 g/min total even with mixed sugars; the surplus just bloats you. Fix: small inputs every 15-20 minutes.
• Trying new products on event day. Your gut is adapted to specific carbohydrate types. Fix: rehearse your exact race-day nutrition on training rides first.

Fuelling a long ride isn't guesswork. Pick your per-hour carbohydrate target off the duration-and-intensity table, make sure your sources are mixed glucose:fructose if you're going above 60 g/hr, measure your own sweat rate to set fluid and sodium, train your gut to take the load, then execute on a timer. Do that and the bonk stops being a risk you fear and becomes a problem you solved before you rolled out.

FAQ

How many grams of carbs per hour should I aim for on a long ride?

It depends on how long you're out and how hard you're going. Under an hour, glycogen covers it and you don't need to eat; from 1 to 2.5 hours aim for 30-60 g/hr, and on the really long or hard days push toward 90-120 g/hr. That top end is only reachable with mixed sugars and a trained gut.

Why can't I just take more of a glucose-only gel to hit 90 g/hr?

Glucose crosses your gut through a single transporter, SGLT1, which saturates around 60 g/hr — pile on more and the surplus just sits there pulling in water and handing you gut rot. To go higher you need fructose alongside it, since it uses a separate transporter (GLUT5); a 2:1 glucose:fructose mix gets you to about 90 g/hr.

When should I start eating on a ride, and how often?

Start early — within the first 20-30 minutes — and stay on a timer, because if you wait until you feel hungry you're already behind your absorption rate. Small inputs every 15-20 minutes match how fast your gut works; sporadic big hits just overwhelm it and leave you under-fuelled in between.