Factors that Influence Fuel Economy:
Ambient air temperature drop from 77* to 22*: -5.3% avg, -13% max
20mph headwind: -2.3% avg, -6% max
7% road grade: -1.9% avg, -25% max
27mph vs 20mph stop and go driving pattern: -10.6% avg, -15% max
Aggressive vs. easy acceleration: -11.8% avg, -20% max
Tire pressure of 15psi vs. 26psi: -3.3% avg, -6% max
A 10% ethanol mixture in fuel contains 3.4% less energy than pure dino fuel and is roughly proportional to mpg loss.
Winter-grade fuels also have less energy (up to 7.26% less) than summer-grade fuels, which will affect mileage.
Summer-grade Btu: 113,000-117,000
Winter-grade Btu: 108,500-114,000