The acronym RPM is an abbreviation of the phrase “revolutions per minute.” It is the automotive industry’s standardized method of measuring the engine’s revolutions per minute or spins that it makes, also known as engine speed. RPM is a measure of two things: the number of times the engine's crankshaft makes one complete rotation each minute, and simultaneously, the number of times each piston goes up and down in its cylinder.
To see your vehicle’s current RPMs, you will use the tachometer located in the gauge cluster or instrument panel. This is located on the dashboard in front of the driver. Now that you have a basic understanding of what RPM means, the next step is to understand why it is important and how it affects the performance management of your vehicle.
How the Engine Works to Create RPM
When you press the gas pedal, your car engine’s RPMs increase as more power is produced. However, the engine’s maximum power ability doesn’t always happen at the engine’s highest RPM ability. When shopping for new cars, you’ll often see RPMs listed with horsepower. The manufacturer will tell you the vehicle’s peak horsepower ability and at what rounds per minute that horsepower occurs. The combination of these two numbers will tell you how the vehicle’s drivetrain performs.
Understanding peak horsepower and RPMs is important when deciding what type of vehicle you need. High torque power is important for lower speed performance, such as hauling and towing. Torque typically happens at lower RPMs, so these vehicles are tuned for peak power to occur at lower RPMs.
Alternatively, sport and performance cars with turbocharged and supercharged engines will have lower torque ratings and higher horsepower ability. These vehicles are tuned for peak power at higher RPMs for greater engine speed ability. This will make the pavement markers fly by as you increase in gear, the RPMs climb, and the engine produces more power.
Purpose of the Tachometer
When looking at the gauges on the dashboard, you will see a speedometer and a tachometer. In older vehicles, these are physical dials with a printed semi-circle and needle. In newer vehicles, you’ll see digital versions that display the information. For most vehicles, the tachometer displays the engine RPMs in thousand increments. The numbers will range from zero to several thousand. The higher the maximum number, the more power the engine can produce and the more performance-tuned the vehicle is.
To read the tachometer, look at the number it's showing. This signals how many revolutions per minute the engine is spinning. The higher the number, the faster the engine is moving. There is typically an orange zone at the top end of the tachometer and then a red line. The orange area is a warning that you are reaching the engine’s maximum performance ability. However, this red zone is not where you will achieve the engine’s maximum performance power.
The Dangers of Redlining
Red means danger when looking at your tachometer. Pressing the gas pedal and revving the needle past the redline can cause significant damage to your engine. Vehicle manufacturers try to prevent this from happening by installing a rev-limiter that prevents the driver from pushing the engine’s performance past the redline.
When you redline your vehicle, you risk blowing the engine, damaging the transmission, or creating issues with the valvetrain. The engine’s components are moving at a high rate of speed and creating a large amount of excess heat. The increased temperature can cause the engine components to warp or crack.
Tachometers in Manual Transmission Cars
If you drive a manual transmission vehicle, then you will need to pay attention to the RPMs as much as you do the speedometer. The tachometer will aid in signaling when it is time to shift gears. Once you become skilled, you can shift based on the engine’s sound. If you hear a loud whine sound like the engine is overworking, then it is time to shift up. If the engine sounds like it's choking and the vehicle feels like it is bogging down, then you need to shift down.
Watching the tachometer can help you know when to shift before you develop the skills necessary to shift based on sound and feel. You will want to shift before the RPMs climb too high for a smooth transmission up. You will also need to shift down before the RPMs drop too low and the engine begins to stall. The exact RPM you should shift at will depend on the make and model of your vehicle and the speed you are traveling at. Your owner’s manual will give you guidance on this.
Tachometers in Automatic Transmission Cars
Vehicle manufacturers put extensive research into tuning and programming the performance of their automatic transmission vehicles. These modern vehicles will automatically shift gears before the vehicle’s needle reaches the tachometer’s redline. When this shift happens can vary based on how hard you press the gas pedal and the vehicle’s current speed. The goal is to shift at the ideal engine RPM time to blend a smooth ride and efficient performance.
Benefits of Knowing Your RPM
Knowing what RPM stands for is the first step in getting the most out of your vehicle. This is especially true for those who have a manual transmission vehicle. Watch the RPM needle to know the ideal time to shift for the most power.
Instead of generating the most power for a fast engine speed, you can focus on making your vehicle as efficient as possible. Driving at lower RPMs consumes less fuel, making it more efficient. If you consistently drive at higher RPMs, you will see an increase in your fuel economy.
While automatic new cars are tuned to shift at the ideal time, it's still beneficial to know and understand your car engine’s RPMs. Abnormal engine RPMs can be a signal that something's wrong with the functioning of your vehicle. If your RPMs spike and jump while accelerating, it could be an indicator that your spark plugs are bad. Fluctuating RPMs while driving could point to several issues, such as a clogged idle air control valve, leaking engine vacuum, or even major engine problems. Your gears or transmission are slipping if your RPMs increase but your vehicle does not go faster
Finally, there are several moving parts in your combustion engine. The higher the RPMs, the more movement, which creates more heat. Shifting to a higher gear reduces the revolutions and thereby reduces the amount of heat generated. Too much heat in your engine puts excessive wear-and-tear on the components, reducing their useful life.
Understanding your engine’s RPMs will help your vehicle run better and last longer.