Pick a vehicle preset, enter annual highway miles, average cruise speed, and how much you plan to lower. See drag reduction, MPG gain, and kWh saved side by side.
Your setup
Preset: Sedan / Compact
Estimated savings
Highway drag reduction
—
Gasoline
MPG before—
MPG after—
Fuel saved—
Annual $—
Payback—
Electric
mi/kWh before—
mi/kWh after—
Energy saved—
Annual $—
Payback—
Practical tips & common mistakes
Speed matters more than drop
Drag savings scale with cruise speed. At 50 mph the same 1.25″ drop returns a fraction of the kWh or MPG gain you see at 75 mph.
SUV ≠ sedan gains
Taller bodies have more underbody turbulence — trucks and SUVs often see larger percent drag cuts but start from worse baseline efficiency.
EV range is kWh
A 3% drag cut on a 2.8 mi/kWh crossover saves more absolute kWh than the same cut on a 3.8 mi/kWh sedan — check both columns.
Highway-only model
City miles are held flat here. Mixed commuting lowers real-world payback — pair with tire pressure and alignment first.