John Buckley: Real-World Tire Testing and the Breakpoint Debate

**CORRECTION** John asked us to note that he gave incorrect figures for the wattage standard deviations during the episode. The best outdoor tests currently achieve standard deviations of approximately 0.8 W, while indoor testing has achieved a standard deviation of 0.3 W.

John Buckley of Streamlines returns to discuss the outdoor tire rolling resistance testing he conducted with cyclist and Escape Collective contributor Ronan Mc Laughlin — covering the methodology behind measuring CRR with an aero testing rig, the temperature sensitivity finding that nearly sank the dataset before it began, and what the data actually shows about tire pressure, width, and the widely-cited breakpoint theory.

Key Points

• Streamlines' method establishes CDA on baseline runs, then holds it fixed and solves for CRR as the energy remainder. Repeating baselines are the integrity gate for any outdoor tire test 
• Tire CRR sensitivity to temperature is approximately four times larger than published literature suggests, and the relationship is nonlinear at low temperatures. 
• Once vertical stiffness is equalized across widths, rolling resistance on smooth tarmac is nearly identical regardless of tire width. 
• John has never observed the pressure breakpoint in any of his field data. His critique is both theoretical — the mechanism requires a sudden onset of vibrational losses not supported by the data — and empirical: pressure sweeps consistently show gradual, small differences rather than a hockey-stick curve.

Links & Resources

• Streamlines: https://streamlines.aero
• Streamlines in the field — aero testing with Mattie Dodd: https://streamlines.aero/blogs/news-insights/position-data-and-a-blustery-november-aero-testing-with-mattie-dodd
• Contact / inquiries: [email protected]
• Ronan Mc Laughlin's Escape Collective tire testing article: https://escapecollective.com/introducing-escape-tyre-testing-get-ready-to-rethink-accepted-wisdom/
• BicycleRollingResistance.com — GP5000 multi-width comparison: https://www.bicyclerollingresistance.com/specials/grand-prix-5000-comparison
• John Buckley on Endurance Innovation (August 2022): https://zencastr.com/z/h0CqHZy5