Climbing Power-to-Weight Ratio (W/kg) vs Absolute Power: When to Look at Which

One of the most common sayings in cycling: “Look at W/kg for climbs, look at absolute watts on the flats.” This isn’t wrong, but it’s overly simplified. In reality, how steep the grade is, how heavy the rider is, and what the aerodynamic conditions are all change the relative importance of W/kg versus absolute watts.

1. Why W/kg Matters on Climbs

When climbing, the primary resistance is gravity:

Gravity resistance = m × g × sin(grade)

So weight directly multiplies resistance. Two riders both putting out 300W:

• A: 60kg → 5.0 W/kg
• B: 80kg → 3.75 W/kg

On an 8% grade, A rides at about 19 km/h, while B rides at about 14 km/h. A is 36% faster than B.

2. But How Steep Does a “Climb” Need to Be?

The key: the crossover point between aerodynamic resistance and gravity resistance.

At different grades and speeds, here’s the ratio (assuming CdA = 0.30, rider + bike = 80kg):

Conclusions:

• Grade < 3%: Aero accounts for over 40% of resistance; both absolute watts and W/kg matter
• Grade 3–6%: Gravity dominates; W/kg is primary, absolute watts secondary
• Grade > 6%: Almost purely a W/kg comparison

3. Real-World Case: A Head-to-Head Between Two Riders

Rider A: 60kg, FTP 270W (4.5 W/kg), CdA 0.28
Rider B: 80kg, FTP 360W (4.5 W/kg), CdA 0.34

Both have the same W/kg, but their absolute watts differ greatly. Speeds at each grade:

Conclusions:

• On pure climbs (> 6%), A wins slightly (thanks to smaller aero drag)
• On shallow grades (< 4%), B wins (because absolute watts push through greater aero drag)
• On most real-world courses (mixed grades), B actually comes out slightly ahead overall

4. When Should You Look Only at W/kg?

In these situations, look purely at W/kg:

• The latter half of Wuling, Siyuan Pass: sustained grades > 6%
• Short, steep climbs (grade > 10%): almost no aero involvement
• Tour de France HC climbs: average grade of 8–10% over the final 10K before the summit

5. When Should You Look at Absolute Power?

In these situations, absolute watts are equally important or more important:

• Long, shallow climbs (< 4%): Beiyi Highway, the early section of the East Route up Wuling
• Rolling terrain (mixed 0–5%): Shiding Outer Loop, North Coast
• Flat time trials, team time trials, group riding

6. Training Recommendations

Light riders (< 65kg):

• Training focus: maintain W/kg; absolute watts just need to be “good enough”
• Flats: draft, lower CdA, don’t fight to match absolute watts
• Climbs: build sustainable FTP and VO2

Heavy riders (> 75kg):

• Training focus: build absolute watts, keep weight from ballooning
• Flats: leverage the advantage of absolute watts, take pulls
• Climbs: don’t try to follow light riders; pace yourself

7. Conclusion

W/kg versus absolute watts isn’t an either-or choice—it’s about “weighting the two based on the grade.” Most climbing races in Taiwan (Wuling, KOM Challenge) average around 6% grade, so W/kg is indeed the dominant factor. But for the full 105K KOM course, the first 70K is a shallow climb, and the influence of absolute watts can’t be ignored either. Understanding this trade-off is how you design a training strategy that truly fits your body type.

Related Reading

• Power and Weight: A Complete Breakdown of the Physics of Cycling Climbing Performance
• Weight Management for Climbers: The Relationship Between W/kg Ratio and Climbing Speed
• Climbing Weight Management: The Truth About W/kg and Healthy Weight Loss Strategies
• Optimizing Power Output: How w/kg Determines Climbing Rankings