Inspect suspension and chassis parts for occasional misalignment. Bent wheels, axles, bad shocks, broken springs, etc. create engine drag and are unsafe at high traveling speeds. Inflate all tires to maximum limit. When shopping for new tires, get large diameter tires for rear wheels. Remove vinyl tops - they cause air drag.
Rough surfaces disturb otherwise smooth air flow around a car's body.
Remove excess weight from trunk or inside of car - extra tires, back seats, unnecessary heavy parts. Extra weight reduces mileage, especially when driving up inclines. Car pools reduce travel monotony and gas expense - all riders chip in to help you buy. Conversation helps to keep the driver alert. For best results, distribute passenger weight evenly throughout car.