"What should my race weight be?" is a question I get asked a lot, and it is rarely only about performance. It sits right next to a lot of people's insecurities, so it deserves handling carefully.
Let me be clear about the position before anything else.
BLUF: body composition genuinely affects performance in some situations. Chasing a number for its own sake damages performance in nearly all of them. Those two things are both true.
Where weight actually matters
The physics is not controversial. When you ride uphill, your speed is governed largely by power to weight: the watts you can hold for every kilo you are carrying up the road. Same power, less mass, and you go up faster.
Running has a similar, smaller effect, roughly in the region of a 0.5 to 1% pace change per 1% of body mass, all else being equal.
So, what that means is: on a hilly course, composition is a real lever. On a flat, windy course, aerodynamics, pacing discipline and fuelling matter far more.
For example: our race guides model this directly. A course with 1,200m of climbing and a pancake-flat one will give you very different answers about what a few kilos are worth on the day. That is deliberate, because a generic "lighter is faster" claim is not honest.
Where it goes wrong
Here is what I see in practice, and why I am cautious about the subject.
- Under-fuelling to lose weight while training hard. This is the big one. You cannot meaningfully diet and train hard at the same time without something giving.
- Losing muscle, not fat. Aggressive deficits take both, and muscle is the thing producing your power.
- Low energy availability. Persistently eating less than your training demands is associated with hormonal disruption, bone loss, poor recovery and increased injury and illness risk. In women it can disrupt or stop menstrual cycles, and it affects men too.
- Race week crash attempts. Arriving at the start line under-fuelled and dehydrated, which reliably costs more time than the weight ever saved.
The key message here is: the fastest version of you is well fed. Not lighter at any cost.
A more useful way to think about it
Rather than a target weight, think about it in this order:
- Fuel the training first. Enough carbohydrate to complete your sessions properly, enough protein to hold onto muscle (roughly 1.6 to 2.2g per kg of body mass a day is a sensible working range), enough overall energy to recover.
- Change composition in the off-season, slowly. Away from your key races, a modest deficit and continued strength work is where this belongs. Somewhere around 0.25 to 0.5% of body mass a week is gentle enough to keep performance intact.
- Protect the race block. When training volume rises, that is the time to eat, not restrict.
- Judge it by performance and health markers, not the number on the scale. Are sessions improving? Sleeping well? Recovering? Cycle regular? Bloods fine? Those tell you more than a morning weigh-in.
What about the numbers people quote?
You will see recommended "race weights" and body fat percentages online. Treat them with real caution.
Those figures usually come from elite populations, they vary enormously between individuals, and the maths cannot tell how much of your weight is muscle, bone or hydration. A single number cannot know whether losing weight would help you or harm you.
That being said, if you carry a meaningful amount of excess fat mass and you have a hilly race coming up, there is a genuine performance and health opportunity there. It just needs doing gradually, with the training protected, and ideally with someone keeping an eye on it.
How our tools handle it
Every one of our race guides includes a power-to-weight section. It uses your height and weight in the background to give a sense of whether composition is a genuine lever for you on that particular course, and it deliberately frames a healthy range as "no big weight-loss push needed, small gains available".
If you want to understand your energy needs first, the TDEE calculator is the better starting point. Most people who think they need to lose weight are actually under-fuelling their training and over-eating around it.
The bottom line
Power to weight is real, and on hilly courses it matters. But it is one lever among several, and it is the one most likely to do harm if you pull it too hard.
Fuel the work. Build the engine. Keep the strength. Let composition change slowly, in the right season, as a by-product of training well rather than the goal itself.
If you are wondering whether this applies to you, or how to approach it safely, don't sit on it, let me know.