Race Day Nutrition: How Many Carbs Per Hour Do You Actually Need?
You trained for months. Your FTP is dialed. Your pacing plan is solid. Then you bonk at km 100 because you ate two gels and called it a nutrition strategy.
Fueling is the most neglected performance lever in amateur endurance sports. Most cyclists know their FTP to the watt but have no idea how many grams of carbohydrate they need per hour.
The science is clear. The practice is where most athletes fail.
The basic math
During endurance exercise above moderate intensity, your body burns a mix of fat and carbohydrates. As intensity increases, the proportion shifts toward carbs. At threshold effort, you’re burning almost entirely carbs.
Your body stores roughly 400-500g of glycogen in muscles and liver. At moderate-to-high intensity, you burn through 60-90g per hour. Simple math: without exogenous fueling, you have 5-7 hours of moderate fuel and 3-4 hours at higher intensity.
But those reserves aren’t fully available. Your brain needs glucose. Your muscles can’t drain glycogen to zero and keep functioning. In practice, you start feeling the effects of depletion well before stores are empty.
The solution: replace as much as you can, as early as you can.
Current recommendations
The sports science consensus has evolved significantly in the last decade:
| Effort duration | Carbs per hour | What to use |
|---|---|---|
| Under 1 hour | Nothing needed | Water |
| 1-2 hours | 30-60g/hour | Single-source carbs (glucose) |
| 2-3 hours | 60-80g/hour | Dual-source (glucose + fructose) |
| 3+ hours | 80-120g/hour | Dual-source, practiced and tolerated |
The shift to 80-120g/hour for long events is relatively new. Five years ago, 60g/hour was considered the ceiling. Research on dual-source carbohydrates (2:1 glucose-to-fructose ratio) showed that the gut can absorb significantly more when using multiple transport pathways.
But here’s the critical caveat: gut tolerance is trainable. You can’t jump from 30g/hour to 90g/hour on race day. Your gut needs weeks of practice to handle high carb intake under exercise stress.
How to calculate your personal target
Step 1: Know your event
- Duration: How many hours will you be riding?
- Intensity: What percentage of FTP will you average?
- Conditions: Heat increases carb burn rate by 10-20%
Step 2: Estimate carb burn rate
At moderate intensity (60-75% FTP): ~60g/hour burned At high intensity (75-90% FTP): ~75-90g/hour burned At threshold (90%+ FTP): ~90-120g/hour burned
For a typical gran fondo averaging 70% FTP over 4-5 hours, you’re burning roughly 65-75g/hour.
Step 3: Set your intake target
Aim to replace 60-80% of what you burn. Perfect 1:1 replacement isn’t realistic during exercise — absorption has limits.
For that gran fondo example: 50-60g/hour minimum, 70-80g/hour ideal.
Step 4: Plan your sources
- Gels: Typically 20-25g carbs each
- Bars: Typically 30-45g carbs each
- Drink mix: Typically 30-60g carbs per bottle
- Real food: Banana ~25g, rice cake ~30g
A practical 70g/hour plan might be: 1 gel every 25 minutes + 1 bottle of carb drink per hour.
The timeline
Fueling isn’t just about the total — it’s about the timing.
Before the start (2-3 hours pre-race): A carb-rich meal. 100-150g of easily digestible carbs. Oatmeal, toast, banana, rice. Nothing new, nothing high-fiber.
First 30 minutes: Start drinking your carb mix. Don’t eat solid food yet — you don’t need it, and your stomach is still settling.
Every 20-25 minutes after that: Take a gel, a bite of bar, or a sip of concentrated drink. Set a timer on your watch. Don’t wait until you’re hungry — by then you’re already behind.
Last 30km of a long event: Increase to your maximum tolerable rate. Caffeine gel here if you use caffeine. This is where races are won or lost nutritionally.
The mistakes that ruin races
Starting too late
“I’ll eat when I’m hungry.” By the time you feel hunger during exercise, glycogen depletion is already advanced. Start fueling early, eat by the clock, not by feel.
Too much solid food early
Your gut diverts blood to digestion, but during hard exercise, blood is needed in muscles. Liquid and gel calories are absorbed faster and cause fewer GI issues. Save solid food for very long events (5+ hours) and lower-intensity sections.
Not practicing in training
Race day is not the time to discover that Brand X gels make you nauseous at 200W. Practice your exact fueling plan on training rides. Every gel brand, every drink mix, every timing interval.
Under-hydrating
Dehydration impairs gut absorption. If you’re not drinking enough water alongside your carbs, the carbs sit in your stomach. Aim for 500-750ml/hour depending on temperature and sweat rate.
All-or-nothing
Some athletes eat nothing for 2 hours, then slam 3 gels at once. This causes GI distress. Small, frequent doses are always better than large, infrequent ones.
Your metabolic profile changes the math
Here’s where it gets interesting: your VLaMax affects how many carbs you burn.
Athletes with high VLaMax burn carbs faster at any given intensity. They deplete glycogen sooner and need more exogenous fueling. Their “Zone 2” is more glycolytically demanding than someone with low VLaMax at the same relative intensity.
Athletes with low VLaMax are more fat-adapted. They burn more fat and less glycogen at moderate intensities, meaning their carb needs are lower — and their glycogen stores last longer.
This is why a personalized fuel plan based on your actual metabolic profile is more accurate than generic recommendations. The difference between 60g/hour and 85g/hour over a 5-hour race is massive — both in performance and in gut comfort.
A practical race-day fuel plan
Event: Gran Fondo, 140km, 4.5 hours estimated, average 68% FTP
Target: 65g carbs/hour = ~290g total
Execution:
- Pre-race breakfast: 120g carbs (oatmeal + banana + toast), 3 hours before
- Start to km 30: Water + 1 bottle carb drink (40g)
- Km 30-100: 1 gel every 25 min + carb drink per hour = ~70g/hour
- Km 100-130: Increase to 1 gel every 20 min + drink = ~80g/hour
- Km 130+: Caffeine gel, final push
Inventory: 8-10 gels, 3 bottles of carb drink, 2 bottles plain water
Practice this exact plan on a 3-4 hour training ride at least twice before race day.
The bottom line
Fueling is not a nice-to-have. For any event over 2 hours, it’s as important as your training. Under-fueling by even 20g/hour compounds over time — by hour 3, you’re 60g behind, and your body knows it.
Calculate your target. Practice it in training. Execute it by the clock on race day. The athletes who bonk are almost always the ones who didn’t have a plan.
Watts generates a personalized fuel plan based on your metabolic profile, event duration, and intensity targets. Carbs per hour, gel timing, hydration — all derived from your actual VO2max and VLaMax, not generic tables.