Fuel Calculator

Your body stores roughly 60 to 90 minutes of hard effort as carbs. That's the whole tank. Burn through it and the lights go out: legs turn to concrete, your pace falls off a cliff, and your brain starts begging you to walk. Runners call it the wall. Cyclists call it the bonk. Same empty tank.

The fix is almost embarrassingly simple. Top the tank up from the outside, before it runs dry. That is all fuelling is.

Carbs per hour. That's it. Not brands, not magic powders, just grams of carbs going in for every hour you're working. Here's the rough guide:

• Under an hour, easy. You're fine on what's already in the tank. Water does the job.
• 1 to 2.5 hours. Aim for 30 to 60 grams an hour.
• 2.5 hours or more, or going hard. Push toward 60 to 90 grams an hour. Seasoned racers go higher.

Start at the low end and build. Your gut decides the rest, more on that below.

Don't wait until you're empty. By the time you feel the dip, you're already too late, and clawing it back mid-race is miserable. Start fuelling in the first 30 to 45 minutes, while everything still works, and keep topping up little and often.

A small amount every 15 to 20 minutes beats one big hit every hour. Steady in, steady out.

Here's the part nobody tells you: your stomach is trainable, exactly like your legs. Taking in 80 grams an hour feels grim the first time and completely normal by the tenth. So practise your race fuelling on your long training days. Same products, same amounts, same timing.

The golden rule, and the one that ruins the most races: nothing new on race day. Ever.

To go past about 60 grams an hour, you need more than one type of sugar. Your body takes in glucose and fructose through different doors, so using both lets you absorb more without your stomach staging a protest. That's why every GONNA carb runs a 2:1 glucose-to-fructose ratio.

In practice: a Drink Mix in the bottle for a steady drip, a Chew or a Shot when you want a quick hit. Mix and match to hit your number. The calculator above does the maths for you.