Why Under-Inflated Tires Burn More Fuel

Under-inflated tires increase rolling resistance—the energy lost as the tire deforms against the road. Here’s the physics:

Mechanism

1. Greater deformation: Low pressure allows more sidewall flex and tread squirm per revolution.
2. Hysteresis losses: Rubber’s viscoelastic nature converts deformation energy into heat instead of forward motion.
3. Larger contact patch: Increases friction (though slightly improves traction, the net energy cost rises).

Quantified Impact

• NHTSA/DOE data: Every 1 psi drop below placard pressure ≈ 0.2–0.3% fuel economy loss.
• Typical under-inflation (5–10 psi): 1–3% MPG penalty—~$50–$150/year per vehicle at current prices.
• Fleet scale: U.S. wastes ~1.2–2 billion gallons annually due to low tire pressure.

Secondary Costs

• Accelerated, uneven tread wear (shoulders wear faster).
• Reduced handling, longer braking distances.
• Higher blowout risk (heat buildup).

Solution

Check pressure monthly (cold tires) with a quality gauge. Inflate to the vehicle manufacturer’s placard (door jamb), not the tire sidewall max. TPMS (mandatory since 2007) warns only at 25% under-inflation—too late for optimal economy.