MTB Race Fueling 101: Carbs, Gels, and Timing

Why fueling matters in mountain bike racing

XC mountain bike races run at high intensity for 45 to 90 minutes. At that effort level your body burns through carbohydrates fast: muscle glycogen can last roughly 60 to 90 minutes at race pace, and once it runs low you slow down sharply. Riders call it "bonking" or "hitting the wall." It is one of the most avoidable mistakes in racing.

The fix is simple in concept: start fueling early, fuel consistently, and practice your plan before race day so your gut is ready. The numbers below give you a starting point. The race fueling calculator will build a personalized plan from your race length, body weight, and intensity.

How many carbs per hour

The starting target for most junior racers is 30 to 45 grams of carbohydrates per hour. This is conservative enough that most athletes can handle it without GI issues, even without a lot of gut training.

As a rough guide by race length:

• Under 45 minutes: fueling is optional; a small amount (15 to 20 g) can help but many athletes race fine on pre-race carbs alone.
• 45 to 75 minutes: aim for 30 to 45 g/hr. One gel early in the race is usually enough.
• 75 to 90 minutes: aim for 45 to 60 g/hr. Plan for 2 gels timed at roughly 20 and 55 minutes.
• Over 90 minutes: 60 g/hr or more. Multiple gels or chews plus a sports drink. Gut training becomes more important at this range.

Athletes who have done gut training over several weeks of riding with fuel can push toward 75 to 90 g/hr using a mix of glucose and fructose sources (many gels combine maltodextrin and fructose for this reason). But start conservative: race day is not the time to find out your limit.

How many gels to carry

Most energy gels contain 20 to 25 grams of carbohydrates. Use that to work backwards from your per-hour target:

• 30 g/hr for 60 min = 30 g total = 1 to 2 gels
• 45 g/hr for 75 min = ~56 g total = 2 to 3 gels
• 60 g/hr for 90 min = 90 g total = 3 to 4 gels

Always carry one extra gel beyond what your plan calls for. Mechanical delays, wrong turns, or a longer race than expected can stretch your fuel window, and an unused gel weighs almost nothing.

When to take your first gel

The most common mistake junior racers make with fueling is starting too late. If you wait until you feel hungry or tired, your blood sugar is already dropping and you are chasing a deficit that is hard to recover from at race pace.

Take your first gel 15 to 20 minutes into the race, before you feel the need. After that, set a rhythm: one gel every 30 to 40 minutes. If your race has feed zones, that is a natural trigger. If not, use trail landmarks or a watch alarm.

Wash every gel down with a few sips of water. Gels taken without water absorb more slowly and can cause stomach issues.

Gut training: practice your plan before race day

Taking gels while riding hard is a skill your digestive system has to learn. On an easy training ride it feels fine. At race pace, with your heart rate in Zone 4, your gut blood flow is reduced and digestion slows. Athletes who fuel in races without ever practicing it in training frequently report nausea, cramping, or the urge to stop.

The fix is gut training: bring gels on training rides and practice the timing, the chewing, and the water-chase routine. Start with lower amounts (30 g/hr) and build up over several weeks of training. By the time race day arrives, your body should be comfortable with the fuel plan on auto-pilot.

Water vs. sports drinks

For races under 60 minutes in mild temperatures, plain water is usually fine if you are fueling with gels or chews. For longer races or hot conditions, a sports drink that combines carbohydrates and electrolytes (sodium especially) helps you absorb fluid faster and replace what you lose through sweat.

Never try a new drink for the first time on race day. Taste test it on a training ride at race intensity first.

Build your personalized fuel plan

The MTB race fueling calculator takes your race duration, intensity, and body weight and returns your per-hour carb target, how many gels per hour, and a timed feeding schedule you can memorize before the gun goes off. No sign-in required.