On the flip side, if your gears are too small then your engine would be too high revving, and that will also affect fuel economy. These days auto makers lean more toward the taller gears because consumers want better fuel economy, but the second you apply any type of load to the vehicle like taller tires, steep grade, or towing/hauling then you will lose a ton of power. Usually the transmission is the first to suffer any kind of catastrophic failure.