Fuel Consumption in Different Gears of a Car

The relationship between car gears and fuel consumption is a critical factor for drivers aiming to optimize their vehicle's performance and reduce costs. Understanding this relationship helps in making informed decisions when driving to ensure minimal fuel use.

Understanding Fuel Consumption in Low Gears

The gears that consume more fuel are the low gears, specifically first and second gears. This is because these gears have larger diameters, resulting in the flywheel (connected to the clutch) and the first gear being almost the same size. Therefore, a single revolution of the flywheel corresponds to a single revolution of the first gear, which is essential for achieving high torque at low speeds.

As the number of gears increases, the gear set diameters decrease. For example, fourth gear has a smaller diameter gear set than third gear. This reduction in diameter typically results in higher engine efficiency as the engine is better able to manage the lower gear ratios. Additionally, the transmission becoming more efficient with a higher number of gears can be demonstrated by the concept of overdrive. In this scenario, when the flywheel's diameter is greater than a certain gear set, one revolution of the flywheel can lead to more than one revolution of the gear set, effectively realizing overdrive.

Fuel Consumption Examples and Considerations

Let's delve deeper into the fuel consumption aspects of different gears:

First Gear and Speed

First gear is particularly fuel-intensive when driving fast. As engine revs rise, more fuel is consumed. It's crucial not to lug the engine, meaning to avoid unnecessary high revs and substantial fuel consumption. However, alternating between high and low gears without proper coordination can increase fuel consumption.

High Gear and Optimal Speed

Driving in the highest possible gear at an optimum speed generally saves fuel. For instance, if you’re driving at 60 kmph in the fifth gear, the fuel consumption is lower compared to driving the same speed in a lower gear. This is because the engine operates more efficiently at higher gears where its speed and load are optimized.

Best Fuel Consumption Strategy

The best fuel consumption is achieved with the least number of cylinder firings per kilometre. Ideally, the vehicle should be in the highest gear most of the time, where the engine is operating close to its optimal speed. However, there are exceptions, such as when ascending a hill. In such scenarios, a lower gear helps to maintain traction and manageable engine load but increases fuel consumption.

Fuel Efficiency and Load/Torque

Fuel efficiency is completely tied to the load applied and the engine's throttle angle. There have been historical examples that illustrate this point effectively. For instance, a performance-loaded drag race involved traversing a flat and level stretch of land on a single gallon of gas. The last recorded winner achieved over a mile distance in around 13 hours, pulling a substantial load of around 500-1000 lbs.

More modern vehicles feature increasingly complex transmissions with more gears. In the 1950s, two popular mainstream transmissions were the two-speed Powerglide and the four-speed Hydra-matic. These transmissions were versatile and saw use in various vehicle weights, where the manual converter could be adjusted for optimal performance. More gears also allow for a lower final gear ratio, which can improve mileage.

By understanding these principles, drivers can make informed decisions to reduce fuel consumption and improve their driving experience.