What is the speed ratio of a car?
2 Answers
The speed ratio of a car varies depending on the model, and the specific model must be known to determine the speed ratio value. Automotive transmission ratio: Also known as the speed ratio, it refers to the ratio of the rotational speeds of the two transmission mechanisms before and after the gearbox in the automotive transmission system. There are two types of transmission ratios in an automotive transmission system: the speed ratio of the main reducer and the speed ratio of the gearbox. In the same car model, the speed ratio of the main reducer is a fixed value, while the speed ratio of the gearbox varies depending on the gear used. The speed ratio data for various types of cars can be found in the automotive performance data manual. Determination of the maximum transmission ratio: The maximum transmission ratio is the total transmission ratio of the transmission system when the car is in first gear. Since the transmission ratio of the main reducer is a fixed value, and usually, the car does not have a transfer case or wheel-side reducer, only the first gear transmission ratio needs to be determined.
The gear ratio of a car actually refers to the gear ratio in the rear differential, which determines how many times the engine turns for each rotation of the wheels. From a technical perspective, the standard gear ratio for compact cars typically ranges between 3.5:1 and 4.5:1. For example, economy cars like the Honda Fit often have a ratio around 3.7:1, prioritizing fuel efficiency, low engine RPM during highway cruising, and reduced noise. However, if you frequently drive uphill or tow loads, opting for a higher ratio like 4.2:1 can enhance initial acceleration force. I believe this ratio directly impacts overall performance—higher values provide more torque but increase fuel consumption by about 10%, while lower values save fuel but result in weaker low-speed performance. Regularly checking your vehicle's manual or VIN code to confirm your ratio is crucial to avoid unexpected issues like uneven tire wear, which can lead to higher repair costs. Additionally, sticking to the factory setting is the safest option; modifying tire size requires adjusting the gear ratio to ensure compatibility and prolong the lifespan of the drivetrain. Overall, choosing the right ratio ensures smoother and more efficient driving.
