Power Leakage on Cobbled Classics: Why Flat-Road FTP Doesn't Equal Roubaix Performance

Flat Power and Cobblestone Power Are Two Different Things

Many people assume Paris-Roubaix is simply “whoever has the highest FTP wins.” That is a serious misunderstanding. The cobblestone (pavé) surface introduces a variable that simply does not exist on a flat indoor trainer: mechanical energy leakage. Research and real-world testing both indicate that vibration on cobblestone sections causes roughly 5 to 10% of pedaling power output to fail to convert into forward kinetic energy, instead being absorbed by the frame, wheels, and the rider’s body.

Energy Budget Comparison: Cobblestones vs. Asphalt

Tire Pressure: Roubaix’s Most Underrated Adjustment

On asphalt, the low-rolling-resistance logic is “higher tire pressure equals more speed”; on cobblestones, this is completely reversed. Excessively high tire pressure causes the tires to bounce over the cobblestones, which actually increases rolling resistance and power leakage. Modern teams at Roubaix generally adopt wider tires, lower tire pressure, and tubeless systems, trading deformation-based shock absorption for preserved effective power.

Core Stiffness: The Human Body Is Part of the Drivetrain

Pedaling power must pass through three interfaces—the pelvis, the core, and the handlebars—before it reaches the bike. Cobblestone vibration causes this transmission chain to constantly loosen in tiny increments, and every loosening is energy leakage. This is why riders with a cyclocross background have a structural advantage at Roubaix—their core stabilizer muscles are trained to maintain rigid power transfer even under vibration.

Three Levers for Keeping Watts at the Rear Wheel

• Tire system: Wider tires + lower pressure + tubeless, reducing bounce and leakage
• Body stiffness: Core and handlebar training, reducing transmission chain slack
• Line choice: Picking the relatively smoother “crown” line on cobblestones rather than the gutters

Implications for Training Prescriptions

For Roubaix-specific preparation, simply stacking FTP is inefficient. A smarter approach is to move some training onto rough surfaces or deliberately introduce vibration disturbance, training the neuromuscular system to sustain output under instability. This is also why Roubaix specialists may not have top-tier flat time trial results, yet their efficiency at delivering watts into the cobblestones is unmatched.

The cruelest thing about Paris-Roubaix is that it discounts every impressive number you produce on the trainer. It doesn’t ask how much power you can generate, but how much of that power you can actually deliver to the ground under dozens of vibration impacts per second. FTP gets you through the gate; cobblestone efficiency is the ticket to the final.

Related Reading

• Cobblestones vs. Gravel: Two Kinds of Rough Roads, Two Completely Different Equipment Philosophies
• Wout van Aert’s 2026 Paris-Roubaix Victory Breakdown: How a Two-Up Sprint Defeated Pogačar
• Gravel Climbing Strategy: Gear Ratio Selection and Cadence Stability Technique on Gravel Surfaces
• Triathlon Hill Course Pacing: Uphill Power and Downhill Risk Management