How many carbs per hour for a 70.3: a rehearseable protocol

Spring in Australia means the long-course calendar is warming up. If you are building toward a late-year or early-summer 70.3, now is the window to lock a fueling plan you can actually rehearse, not invent on race morning.

The question athletes ask most is simple: how many carbs per hour? The useful answer is less a single number and more a protocol you can train, then race.

Start with the range, not a magic number

For a half-Ironman effort lasting roughly four to six hours, most well-trained athletes land somewhere between 60 and 90 grams of carbohydrate per hour once the bike is underway. Some tolerate toward the top of that band; others sit closer to 60-70 g/h and race cleaner for it.

What matters more than chasing the highest possible number is choosing a target you can absorb, then practising it until it feels ordinary.

Research on multiple transportable carbohydrates (glucose and fructose together) shows the gut can take up more carbohydrate when two pathways are used at once, which is why many modern race drinks sit around a 2:1 dual-carb ratio rather than a single sugar. That framing is about absorption and gut comfort, not about inventing a new rule for every athlete.

Sodium sits beside carbs. Long efforts in Australian heat pull a lot of salt through sweat. A fuel that also delivers meaningful sodium (think hundreds of milligrams per serve, not a token sprinkle) reduces the need to juggle gels, salt tabs, and bottles as separate systems.

Bike vs run: different intakes, same plan

Your 70.3 fueling plan should treat the bike and the run as two chapters of one story.

On the bike, you have time, bottle access, and a steadier gut. This is where you do most of the work. Aim for your full hourly target here, often 70-90 g/h if you have trained for it. A bottle of dual-carb drink mix every hour (or a measured scoop in ~700-1000 ml) is easier to execute than stacking gels while you are already managing watts and heat.

On the run, intake usually drops. Many athletes settle around 40-60 g/h once they are off the bike: enough to keep blood sugar stable without bouncing a full stomach. Use the same product family if you can, just smaller volumes or more dilute mixes. Familiar flavour and familiar osmolality beat a surprise gel at kilometre eight.

A practical split for a mid-pack 70.3 might look like:

Bike (~2.5-3 h): 75-90 g carb per hour, with sodium in the same bottle
Run (~1.5-2 h): 40-60 g carb per hour, sipping rather than gulping
Total race carbs: often in the 250-350 g ballpark, depending on duration and gut training

Those are starting points. Adjust for body size, heat, and how hard you plan to race, then write the numbers on your bike computer or race belt so you are not doing maths in the heat.

Gut training is the real protocol

Carb targets fail when the gut has never seen them. Treat fueling like a fourth discipline.

Over six to eight weeks of spring build:

Pick one primary drink mix and stick with it for long rides and bricks.
Start conservative (e.g. 60 g/h) for two long sessions.
Step up by ~10 g/h each week if comfort holds.
Rehearse race volume and dilution: same scoop, same bottle size, same timing.
Do at least two full-length bricks with race-day carb targets, not "easy long ride" fueling.

If you feel sloshing, nausea, or urgent bathroom stops, back off the rate before you blame the product category. Often the fix is slower sipping, cooler fluid, or one fewer scoop, not abandoning carbs altogether.

Gut training also means practising sodium with carbs. Separating "fuel" and "electrolytes" into five different packets works on paper and falls apart when you are tired. One bottle that carries both is simpler under stress.

For a personalised race-day sketch once you know your event and sweat rate, use the HYDRAX Fuelling Strategy Engine, then gut-train the numbers on long bricks.

A rehearseable hourly template

Here is a template you can copy into a training note and refine.

Two weeks out from race day (final dress rehearsal):

Pre-ride: light carb meal you already trust; optional small primer drink if that is part of your routine
Hour 0-1 bike: first bottle with ~70-85 g carb and high sodium; start early, do not wait until hungry
Hour 1-2 / 2-3 bike: same cadence: bottle per hour, or measured scoop into aero bottle
Run: switch to smaller sips aiming ~50 g/h; keep the same dual-carb base if possible
Aid stations: only take what matches your plan; curiosity gels are how protocols break

HYDRAX CORE is built around this kind of hour: 85 g carbohydrate and ~980 mg sodium per serve, dual-carb at about 2:1, mixed in ~700-1000 ml. That is one clear bottle for a solid bike hour, useful if you want fewer moving parts.

You do not need a lab to use the template. You need repeated long sessions where the bottle plan is non-negotiable.

Why spring AU racing makes this urgent

September through November is when Queensland and east-coast athletes load volume for summer 70.3s and late-season halfs. Heat and humidity climb. Sweat rates rise. Gut mistakes that were forgiveable in a cool winter century become race-enders in a December run.

Locking carb-per-hour now means:

Your long Sunday rides become dress rehearsals, not experiments
You learn your personal ceiling before taper week
Race morning becomes "execute the plan," not "hope the aid station has what I like"

If your A-race is still eight to twelve weeks away, you have time for a full gut-training block. If it is sooner, simplify: one product, one hourly rate on the bike, a reduced rate on the run, and two hard practice days. Perfect is optional. Rehearsed is not.

Keep the plan boring on purpose

The athletes who finish strong on the run are rarely the ones with the most exotic stack. They are the ones who:

Knew their grams per hour before the gun
Practised those grams in training heat
Used dual-carb drinks they could stomach for hours
Did not invent a new sodium strategy at T2

Write your numbers. Stick them on the stem. Rehearse until they are dull.

When the protocol is dull, it is ready.

If you want to rehearse this with one bottle system, try the hourly template with HYDRAX CORE (85 g carb / ~980 mg sodium per serve). Pair it with the Fueling Strategy Engine so your race plan matches what you actually practise. Orders over $95 ship free within Australia.