Triathlon race-day fuel plan
Triathlon has three variables others don't: the strategy changes completely between Sprint (60-90 min) and Ironman (8h+), the GI stress of the aero position on the bike, and the transition where blood abruptly returns to the legs.
g/h by distance
Sprint (under 90 min): 30-45 g/h, focus on hydration. Olympic (1h30-2h30): 45-60 g/h. 70.3 (4-7h): 60-90 g/h with a mandatory 2:1 blend. Full Ironman (9-16h): 70-100 g/h with prior gut training. The bike leg is where most carbs go in, the run accepts less.
Hydration by temperature
In mild conditions, 500-700 ml/h works. In heat (above 25°C), step up to 700-1000 ml/h and add 500-800 mg sodium per hour (Veniamakis 2022, IJERPH). Athletes who have weighed before/after training know their real sweat rate, without it, drink at first sign of thirst but avoid gaining weight during the race (sign of over-hydration and hyponatremia risk).
The bike-to-run transition
The last 15-20 min on the bike is critical: keep ingesting carbs but cut fluid volume and avoid a large gel in the last 10 min (stomach has no time to empty before the run). On the run, the first 15 min is small sips of sodium drink only. First gel at km 3-5. In Ironman, alternate gel + drink + real food (banana, fig newtons) to vary osmolality.
Detailed strategy by distance
Sprint (60-90 min): 30-45 g/h, 1 pre-swim gel, 1 mid-bike gel, sips on the run. Olympic (1h30-2h30): 45-60 g/h, gel + 1 carb-drink bottle on the bike, gel at km 3 of the run. 70.3 (4-7h): 60-90 g/h, 3-4 gels + 2-3 drink bottles + 1 bar on the bike, gels every 30 min on the run with small sips. Ironman (9-16h): 70-100 g/h, gel every 30 min on the bike + continuous drink + real food in the last 30 km of bike to avoid sweet saturation; then gels and drink only on the marathon. Weigh yourself before and after your longest training session to calibrate real fluid losses and adjust.
3 mistakes that cost the Ironman year after year
Mistake 1: skipping breakfast because "the stomach is closed". Results in hypoglycaemia at km 60 of the bike. Fix: oatmeal in water 3 hours before even without appetite (liquid texture tricks the stomach). Mistake 2: trying a new drink from the race expo. 50% chance of GI distress in the first hour. Fix: 4-week gut training with the exact drink you will use. Mistake 3: ignoring sodium in warm climates. Muscle cramps at km 25 of the run. Fix: 500-800 mg/h in over-25-degree weather, monitor by perception (dark or absent urine), not by thirst.