Friction: The Price Paid by Every Meter of Transmission
Nothing moves forward without resistance. Every machine pays a price. The Stribeck curve decides how much.
F_f: total friction force. μ_b: boundary friction coefficient (Coulomb). N: normal force. φ: fraction of area with fluid film (0=dry, 1=full hydrodynamic). η: dynamic lubricant viscosity. dv/dy: velocity gradient. A: contact area. Stribeck mixed regime.
SCIENTIFIC NOIR — FRICTION
"Nothing moves forward without resistance. Every machine pays a price."
A bicycle chain with correct lubricant operates in the Stribeck mixed regime: part of the loads are borne by asperities in direct contact (Coulomb), part by the fluid film of the lubricant (hydrodynamic). Transmission efficiency depends on keeping φ — the hydrodynamic fraction — as high as possible.
Laboratory measurements of power losses in bicycle transmissions report 3-5W loss with clean, correctly lubricated chain at 250W pedal power. With dirty chain and degraded lubricant, losses scale to 8-15W. At 300W output, that represents up to 5% efficiency lost — approximately 1 km/h less in sustained average.
The Stribeck curve shows a friction minimum at intermediate viscosities under characteristic speeds. In bicycle bearings operating at normal rotational speeds, the optimal point corresponds to lubricants with kinematic viscosity between 15-30 cSt. Excessively viscous lubricants — thick greases poorly applied — raise the hydrostatic component without performance improvement.
MEASURED POWER LOSSES — TRANSMISSION
Clean 11s chain + correct dry lube: 3.2W at 250W. Same chain with Trujillo sand contamination (300 km without cleaning): 11.4W. New sealed bearings vs. bearings with 5000 km without service: difference of ~2W additional at bottom bracket.
La Libertad's coastal quartz dust has Mohs hardness 7 — greater than common steel. When it penetrates the chain-sprocket interface with lubricant acting as carrier, each link under load applies abrasive grinding on tooth flanks. φ drops, μ_b rises, total F_f increases, and the useful life of sprockets and chainrings shortens by a factor of 2-4×.
Lubrication is not just friction reduction: it is control of the φ parameter in the Stribeck equation. A lubricant that displaces abrasive dust from the contact interface — with high affinity for the metal surface — keeps φ high despite the environment. Lubricant selection in Trujillo is not preference: it is tribological engineering.
FIELD NOTE — BIKELAB
In dynamometer measurements before and after full transmission service on bicycles with 1500+ km of use in Trujillo conditions: average reduction of friction losses of 7.2W. The service pays for itself in power returned to the system.