What happens when larger tires are installed on a truck without adjusting the gear ratio?

When larger tires are installed on a truck without adjusting the gear ratio, the most significant effect is the reduction in engine performance and fuel economy. This occurs because larger tires have a greater circumference, which means that for each rotation of the tire, the vehicle travels a longer distance. Consequently, the engine has to work harder to maintain the same speed, effectively reducing the available power for acceleration and other performance metrics.

Furthermore, the original gear ratio is optimized for smaller tires. As a result, when larger tires are fitted, the truck's current gear ratio results in lower torque delivered to the wheels at lower speeds, which can make the vehicle feel sluggish. This increased load on the engine can lead to decreased fuel efficiency, as the engine consumes more fuel to compensate for the extra distance covered with each rotation of the larger tire. Therefore, without recalibrating or adjusting the gear ratio, installing bigger tires generally leads to reduced engine performance and lower fuel economy.