What is the most fuel-efficient speed for a car?

Fuel prices are rising, and every driver is looking for ways to cut costs. The engine's fuel consumption varies with different driving modes. Many drivers believe that higher speeds lead to increased fuel consumption, but this isn't always the case. We explain which speed is the most economical for a vehicle and what can help reduce gasoline or diesel expenses.

Is There an Optimal Driving Speed for Fuel Savings?

Standard passenger cars equipped with 1.6L naturally aspirated engines consume about 10-11 liters of fuel when driving in the city. Frequent drivers may see consumption rise to 13-15 liters. Meanwhile, most cars state in their manuals that the engine should burn no more than 7-8 liters in urban conditions.

It is a common misconception that the optimal speed for fuel consumption is 70 km/h. Some suggest even lower figures—50-60 km/h—implying that the slower you drive, the more you save. However, the reality is more complex. The fuel consumption depends not solely on speed but rather on the instantaneous load on the power unit.

Is Speed Important for Fuel Economy?

A car can operate at the same engine RPM at both 20 km/h and 125 km/h. If the instantaneous load remains below the engine's nominal torque in both scenarios, fuel consumption at higher speeds can actually be lower than at lower speeds. The key to economical driving is to avoid exceeding the RPM range where the engine achieves maximum efficiency.

Numerous studies indicate that for most vehicles, the difference in fuel consumption at speeds of 70-80 km/h, 90-100 km/h, and 110-120 km/h is minimal—often just a matter of percentages.

A Hack for Economical Driving

To achieve fuel consumption figures of 7-8 liters, you must adhere to a specific driving regime—accelerating to 50 km/h in 25 seconds with the minimal possible engine load. However, constantly monitoring this is extremely challenging, so there's another hack.

After starting, once you reach a speed of 50-60 km/h, you should shift to a higher gear and maintain this range of speeds from 45 to 80 km/h.

If driving a manual car, shift to a higher gear as soon as the tachometer reaches 1,500 RPM. In this case, a modern engine can produce up to 80% of its torque and maintain the necessary driving pace.

Is It Better to Drive Fast or Slow on the Highway?

While driving on the highway, energy is primarily expended overcoming air resistance. The higher the speed, the more energy is required, as air resistance increases proportionally with speed. An increase in speed by 30 km/h can lead to a nearly one-third rise in fuel consumption.

However, driving too slowly on the highway is not advisable for fuel savings. The optimal speed is between 80-90 km/h. Maintaining this speed allows you to drive in a higher gear for extended periods, avoiding sudden braking and frequent accelerations, thus saving fuel. The engine will rev up to 1,200-1,500 RPM, and the consumption of a 1.6L car will drop to 6-7 liters per 100 km. Further savings can be achieved by coasting, allowing the car to roll down hills.

Based on materials from “RBK-Ukraine” and Autostrike