FondoLab — Gran Fondo Fuelling Planner

Everything scales with duration. A 2-hour fondo needs no carb taper and barely any caffeine strategy; a 7-hour day in the mountains needs both. Include realistic time at feed stops — you fuel on the clock, not just while pedalling.

Up to ~60 g/h can run on a single sugar (glucose or maltodextrin) — fine for shorter or easier rides. But the gut's glucose transporter SGLT1 saturates near 60 g/h (~1 g/min): pour in more glucose alone and it just pools in your stomach. To go higher you must add fructose, which crosses on a separate transporter (GLUT5) worth another ~30–60 g/h. So above 60 g/h use a glucose : fructose mix (≈2 : 1); the top end of 90–120 g/h needs a ~1 : 0.8 ratio and a gut trained for it.

This planner gently reduces intake in the final third (down to about 80% of target). The evidence that "the stomach absorbs less when tired" is mixed, but in practice palatability and GI comfort fall over long efforts, so most riders naturally eat less late. Front-load the easy calories while you can stomach them.

Fuelling should begin at the very start — exogenous carbohydrate takes ~15–30 min to digest and reach your blood, so if you wait until you feel empty you're already behind, and you never claw it back. The plan's Start line is your opening feed.

One trap, though: a concentrated gel taken ~15–45 min before the gun can spike insulin, and the moment you start riding, insulin + exercise pull glucose from your blood together — some riders get a transient rebound (reactive) hypoglycemia dip in the first 20–30 min. So don't take it then. Instead take your first gel at the gun or in the final ~5 min before it (exercise onset blunts insulin release), or within the first 10–15 min of riding — washed down with a few sips, never a dry gel on an empty stomach. Net: fuel immediately, just skip the 15–45 min pre-start window.

Sweat rates run from about 0.4 L/h in the cold to over 2 L/h in the heat. We cap planned drinking at ~1 L/h — but that's a conservative ceiling, not a hard wall. The real limiter is usually gastric emptying (how fast fluid leaves your stomach), not intestinal absorption — your intestine can actually take up water faster than that. A typical carbohydrate drink empties at ~1–1.2 L/h, and that slows further with higher carb concentration, high intensity and a near-empty stomach. So packing lots of carbs into a bottle reduces the fluid it delivers — separating carbs (gels/solids) from a plain water bottle lets you drink more. Trained guts tolerate ~1.5 L/h.

The bigger reason to hold back, though, is safety: drinking beyond your losses risks exercise-associated hyponatremia (dangerously diluted blood sodium). So the accepted approach is drink to limit losses, not to erase them. This tool plans ~75% replacement, capped at ~1 L/h, keeping projected loss under about 2–3% of body weight — where performance starts to drop. On hot legs the cap bites and a planned deficit builds: start well-hydrated and don't chase it. Add electrolytes (≈300–800 mg sodium per litre) on hot days.

Performance benefit shows up around 3–6 mg per kg body weight; more rarely helps and brings jitters, GI upset and a poor finish-line crash. We cap total intake at 400 mg.

Why the finishing dose is timed at ~75 min before the line. Swallowed as a gel, drink or capsule, caffeine appears in your blood within ~15 min and keeps rising to a peak at ~30–60 min — and it's working the whole way up, not only at the peak. It then stays elevated for hours (half-life ~4–6 h). Take it only 45 min before the finish and it's still climbing as you cross the line — you get the front of the curve, not the plateau. Take it ~75 min before and it's risen and is sitting near peak across the entire closing stretch, covering the final hour where it counts. The long half-life means slightly earlier is no problem, so you don't have to nail the exact minute.

Collect, then take. Caffeine is tiny (a gum, tablet or gel), so you don't have to swallow it at a feed station. The plan tells you to pick it up at the last stop you pass before the optimal time, carry it, and take it at the noted minute. Need it even faster — e.g. you forgot to collect early? Caffeine gum absorbs through the cheek in ~10–15 min.

Strategy here: a moderate early dose (swallow ~45 min pre-start) plus a finishing dose taken ~75 min before the finish. Low sensitivity → toward 6 mg/kg with a bigger finishing hit. High sensitivity → toward 3 mg/kg, weighted earlier and gentler. Reference: espresso ≈ 75 mg, caffeinated gel ≈ 25–50 mg, caffeine gum ≈ 40–100 mg, caffeine tablet ≈ 50–100 mg.

Each row (and the pinned Start) is a place where you load up. The amount shown is what to take on there to cover the leg until the next stop — so you arrive at each aid station as you run dry. The leg temperature sets your sweat rate for that stretch via the table in step 3, so morning legs carry less fluid than the hot afternoon. Pack the Start amount before you roll out.