November 24, 2025 · 3 min read

Body Weight and Cycling Performance — How Much Does It Really Give You?

"Drop a kilo, gain 2 watts on the climb." That's a simplification, but a fair one — body weight has a real effect on cycling performance, especially uphill. The question is: when does losing weight help, and when does it start to hurt?

Weight and power — W/kg

On the flat, absolute power (W) is what counts. Uphill, it's the power-to-weight ratio (W/kg) that counts. A rider with an FTP of 250 W and a weight of 75 kg has 3.33 W/kg. If they drop 5 kg: 250 ÷ 70 = 3.57 W/kg — a 7% increase with no extra training.

When does losing weight help?

• You're overweight — if your BMI is above 25, one kilo less is pure gain. Less weight to haul uphill, less load on your joints.
• You ride in hilly terrain — on the flat, a 2 kg difference costs a fraction of a watt. On an 8% climb lasting 30 minutes, it's 10–15 seconds.
• You want to improve W/kg without adding power — for riders who have plateaued in training, dropping weight can be easier than finding an extra 10 W.

When does losing weight hurt?

• You lose power — an aggressive diet lowers FTP. If you've dropped 3 kg but your FTP has fallen by 15 W, your W/kg may actually be worse.
• Body fat too low — men below 8%, women below 15% risk hormonal problems, weakened immunity and worse recovery.
• Eating disorders — cycling has a disproportionately high rate of eating disorders. If you're thinking about food and weight obsessively — that's no longer optimisation, it's a problem.

How to lose weight without losing power?

1. A small deficit — 200–300 kcal a day. Not 500+. Slow loss (0.3–0.5 kg/week) protects your muscle.
2. Protein high — 1.6–2.0 g/kg of body weight. It protects your muscle during a deficit.
3. Timing — don't ride the trainer fasted, don't do intervals while in a deficit. Eat before and after training, save your calories for the rest of the day.
4. Not in season — lose weight in the off-season or early base. In race season you need fuel.

Bike weight vs body weight

A lighter bike costs thousands of euros per kilogram. A lighter body is free (and even saves money on food). Before you spend €1,200 on carbon wheels, check whether you're not carrying 5 unnecessary kilos on yourself.

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