Power-to-weight ratio is the metric cyclists live and die by. It's how we compare ourselves, how we set goals, and how we explain why that bloke up the road is faster on the climbs. But for triathletes, the relationship between W/kg and performance is more complicated than the cycling world makes it seem.
The truth is: for many triathlon courses, your power-to-weight ratio barely matters. And for the courses where it does, it's still not the whole story.
Olav Bu addressed this head-on when he came on the podcast. One of his core principles coaching Blummenfelt and Iden is: avoid chasing relative power by simply losing weight. Instead, focus on absolute improvements in fitness while maintaining caloric balance to support continued growth. As he told us: "You can't create and you can't destroy energy, you can only convert energy from one form to another form — and that's why I'm very careful about causing too large deficits over longer periods." The man who coaches the world's best triathletes is telling you to stop dieting and start building.
When Absolute Power Wins
On a flat Ironman course — think Ironman Florida, Western Australia, or any of the pancake-flat 70.3s — the dominant force slowing you down is aerodynamic drag, not gravity. And aerodynamic drag doesn't care how much you weigh. It cares how much power you produce and how aerodynamic your position is.
Dan Bigham, who accidentally became one of cycling's foremost aerodynamics experts while chasing the world hour record, explained this on our show. The human on the bicycle is 80% of the drag. You can find marginal gains around spokes and rim shapes, but that's all playing within the remaining 20%. The real gains are in the body, clothing, helmet, and position. Weight barely features in that equation on flat terrain.
A 90kg rider producing 210 watts in an aero position will often be faster on a flat course than a 70kg rider producing 200 watts, despite the heavier rider having a significantly lower W/kg. The extra mass has negligible effect on flat speed, but the extra 10 watts pushes them through the air faster.
This is why many successful Ironman athletes are bigger than you'd expect. They've optimised for absolute power and aerodynamics, not for climbing.
When W/kg Matters
Gravity enters the equation on hills. Every kilogram you carry uphill costs energy, and on sustained climbs of 5% or more, power-to-weight becomes the primary determinant of speed.
If your target race is Ironman Lanzarote, Challenge Roth, or any course with significant elevation, then W/kg becomes much more relevant. The maths are straightforward: on a 6% gradient, a 1kg reduction in body weight saves roughly the same amount of time as a 3-4 watt increase in power.
But here's the catch: most triathletes shouldn't try to lose weight to improve W/kg. The risks almost always outweigh the benefits.
The Weight Loss Trap
Dropping 3kg sounds attractive until you consider the downstream effects across three disciplines. Dr David Dunn, the World Tour nutritionist who's worked with INEOS, EF Education, and Uno-X, was devastating on this topic when he came on the podcast. His core message: "Your body works off this law of preservation. If we don't have enough energy to sustain what we're doing, we'll start to shut off other processes."
When we talk about cycling weight loss, the discussion needs to account for the unique demands of triathlon:
Power loss. Most age-group triathletes who aggressively cut weight lose power. A 5kg weight loss that costs 15 watts of FTP makes you slower on flat and rolling courses, even if you're marginally faster on climbs. Dr Dunn was clear: "Chronic underfueling over extended periods causes impaired performance, increased illness and injury risk, and poor recovery — not the lean fitness you're chasing."
Recovery compromise. Training three disciplines creates enormous recovery demands. A caloric deficit reduces your body's ability to repair and adapt. You might drop weight, but your training quality suffers — and with it, your fitness. Dr Dunn's framework is useful here: frame food as "appropriate" or "inappropriate" for your current situation, not "good" or "bad."
Run durability. Being lighter helps on hilly run courses, but being too lean compromises your muscular endurance. The marathon off the bike is a war of attrition, and the athletes who hold together are often those who haven't stripped themselves down to the bone.
Immune function. Under-fuelling across a triathlon training block is a recipe for illness. One lost week of training to a cold costs more fitness than 2kg of body weight ever will. Seiler's research is relevant here — he told us consistency and staying healthy enough to complete 300-600+ workouts per year trumps any single performance variable, including body weight.
What to Optimise Instead
For most triathletes, the hierarchy of bike leg improvements looks like this:
1. Aerodynamic position. A proper aero position is worth 15-30 watts of free speed at Ironman pace. That's the equivalent of months of FTP training, available immediately through a good bike fit. Dan Bigham told us: "Most people don't know what Q factor is and so they're like 'I can reduce my Q factor, what the hell is that?'" Even small geometry changes — a 10mm reduction in Q factor — can deliver 1-1.5% drag reduction, worth 2-4 watts depending on speed.
2. FTP and sustainable power. Raise your ceiling so you can race at higher absolute watts. Structured FTP training with proper periodisation is the fastest path. Dan Lorang's approach with Roglic is instructive: "It's not about the one key session. It's more about giving your body constantly a certain amount of load." Consistency, not breakthroughs.
3. Pacing discipline. Riding at the right intensity — 68-75% FTP for Ironman — preserves your run. This is free performance that requires zero physical improvement, just restraint.
4. Nutrition execution. Proper bike nutrition at 90-120g carbs per hour ensures you don't bonk. Another free performance gain.
5. Body composition. Only after the above four are dialled in should you consider optimising weight. And even then, only if your target race has meaningful climbing.
Brownlee made this point eloquently when he sat down with us: "The admin and marginal gains — aerodynamics, kit prep, course knowledge — matter, but training volume and your physiological engine remain the 95%. Don't sacrifice core training hours to chase the 1%." Weight obsession is exactly the kind of 1% distraction that steals from the 95%.
Practical Numbers for Age-Group Triathletes
Here's what realistic FTP and race power looks like across triathlon distances:
Competitive male age-grouper (80-85kg):
- FTP: 250-300W (3.0-3.5 W/kg)
- Ironman race power: 170-220W
- 70.3 race power: 200-245W
Competitive female age-grouper (60-65kg):
- FTP: 180-230W (2.8-3.5 W/kg)
- Ironman race power: 125-170W
- 70.3 race power: 145-190W
The range is wide because course profile, conditions, and individual strengths all factor in. But notice: the race power numbers are well below FTP. The limiter in triathlon is rarely peak power — it's sustainable power over hours while preserving capacity for the run.
Ben Hoffman summed it up perfectly: "The final frontier in athletics is unlocking the potential of the mind." Pacing discipline, nutritional execution, and race-day decision-making deliver far more than chasing a number on the scales.
Key Takeaways
- On flat courses, absolute power and aerodynamics matter more than power-to-weight
- W/kg becomes important on hilly courses with sustained climbs over 5%
- Most triathletes should not actively try to lose weight — the risks to power, recovery, and run durability outweigh the gains
- Optimise aero position, FTP, pacing, and nutrition before touching body composition
- Use the FTP Zone Calculator and Race Weight Calculator to understand where your biggest gains are
- Race power is 68-82% of FTP — the limiter is sustainability, not peak output
- Being lean enough matters, but being the lightest you can be doesn't
Frequently Asked Questions
What is a good power-to-weight ratio for a triathlete?
For competitive age-group triathletes, 2.5-3.5 W/kg is typical for FTP. However, the bike leg isn't raced at FTP — it's raced at 68-80% of FTP. What matters more is your absolute power at race intensity and your ability to sustain it for 2-5 hours. A heavier rider with 280W FTP may be faster on a flat course than a lighter rider at 3.5 W/kg.
Should triathletes try to lose weight to improve their power-to-weight ratio?
Only if the course is hilly and only if you can lose weight without sacrificing power or compromising recovery across three disciplines. For flat Ironman courses, absolute power matters more than W/kg. Losing weight at the cost of 10-15 watts of FTP often makes you slower overall, especially when factoring in the run where muscular endurance matters.
Does power-to-weight ratio affect the run in triathlon?
Yes — indirectly. A better power-to-weight ratio means you can produce the same bike split at lower absolute power, which reduces muscular fatigue going into the run. But being underweight can hurt run performance. The sweet spot is being lean enough for the hills without being so light that your run durability suffers.
