Finding the Right Tire Pressure: Is 40 psi Good?

Tires are the only thing that stands between your car and the road. Given the vital role tires play in keeping a vehicle controllable and safe, they should always be in excellent condition and correctly inflated. A car’s ideal tire pressure varies depending on load and speed, but is it safe to say that 40 psi (pounds per square inch) is good tire pressure?

40 psi is good tire pressure because it ensures that you don’t run underinflated and is still below the maximum inflation pressure of most tires. You can find a vehicle’s recommended tire pressure on the driver’s door jamb or in the owner’s manual.

This article will discuss tire pressure in more detail and explain the factors surrounding what car manufacturers recommend. It will also cover the advantages and disadvantages of having under and over-inflated tires.

What Is a Good Tire Pressure?

A good tire pressure usually ranges from 32 to 40 psi. The best tire pressure for your vehicle will depend on factors such as your car’s load capacity and weight. Use your car’s owner’s manual to determine the best psi for your tires.

How to Find the Right Tire Pressure

Tires do not have an easy job. Aside from supporting the vehicle’s entire weight, they constantly take a pounding to ensure no other part of the car comes into contact with the road. Keeping a tire’s pressure within its recommended range significantly impacts its performance and longevity.

The recommended tire pressure for each vehicle is never a fixed number; it will vary depending on the type and size of the tires and the vehicle’s anticipated load. Recommended tire pressures usually start at 30 psi and get higher as the vehicle, and its anticipated load gets heavier.

Below is a table that shows what you would typically see on a car’s tire pressure sticker.

Tire SizeLoadPSI (Front)PSI (Rear)
225/55 R16 99Y XL(Up to) 3 passengers and 1 suitcase3530
245/45 R17 99Y XL(Up to) 5 passengers and 3 suitcases3839
225/50 R17 98Y XL(Up to) 3 passengers and 1 suitcase3832
245/40 R18 97Y XL(Up to) 5 passengers and 3 suitcases4144
245/40 R18 97W XL(Up to) 3 passengers and 1 suitcase4438
245/40 R18 97W XL(Up to) 5 passengers and 3 suitcases4849

Based on the table above, we can draw the following conclusions:

  • The tire pressures for a single vehicle range from 30 to 49 psi.
  • The recommended tire pressure increases as the load gets heavier.
  • The recommended tire pressure for the front tires is higher than the rear when there are fewer occupants and luggage.
  • The recommended tire pressure for the rear tires gets higher as more weight is distributed to the back of the vehicle.
  • The recommended tire pressure increases as the wheels get larger and the sidewalls get thinner.

40 psi is a good psi for the majority of tires fitted on cars, SUVs, and light trucks. Most passenger vehicles will have a recommended tire pressure of 32 to 35 psi, but 40 psi is still within the tire’s maximum inflation pressure. 

Please note that inflating your tires to their maximum limits is dangerous. The pressure can rise as the tires get hotter through use. 

How Do Car Manufacturers Determine Tire Pressure?

To understand better how automobile manufacturers come up with the proper tire pressure for each vehicle, let us examine how it’s done and what factors determine it.

Car manufacturers determine tire pressure with the help of tire standardizing organizations and an understanding of factors like the car’s weight and load capacity.

Read on to learn more about how manufacturers find the correct tire pressure for the cars they produce.

Tire Standardizing Organizations Make Tire Pressure Guidelines

Organizations like the Tire and Rim Association (TRA) in the United States, the European Tyre and Rim Technical Organization (ETRTO), and the Japanese Automotive Tire Manufacturers Association (JATMA) all have individual guidelines and methods to determine standard tire dimensions. These organizations also release guidelines related to maximum load-carrying capacity and inflation pressure.

The procedures used by each organization aren’t the same, but the groups do consult with one another. As a result, their recommendations hardly vary. These set standards allow better interchangeability of tire sizes and provide a point of reference for car manufacturers to determine the recommended tire pressures for their vehicles.

Car manufacturers can use the information from tire standardizing organizations to decide which tires to use for their cars based on their weight and load capacity.

Other Factors That Determine Tire Pressure

Even though tire standardizing organizations provide a recommended load capacity and inflation pressure for every tire size, car manufacturers can still have internal negotiations to determine their final recommendations.

Every car manufacturer understands that tire pressure affects a vehicle’s handling, steering feel, fuel efficiency, and ride comfort. For instance, recommending high tire pressures may improve fuel efficiency but compromise ride comfort.

Car manufacturers have to perform numerous tests in collaboration with their tire suppliers to strike a good balance in terms of performance while still conforming to the recommendations set by tire standardizing organizations.

The Effects of Tire Pressure on Tires and Your Vehicle

To further stress the importance of tire pressure, let’s discuss how failure to keep tires correctly inflated can impact the longevity of tires and your vehicle’s performance. Over and under-inflating tires both have negative impacts. 

Over-Inflated Tires Decrease Road Contact

Putting too much air in a tire will cause the middle part of the tire to extend, reducing the amount of rubber that comes into contact with the road. Aside from lowering its contact patch, over-inflating a tire will also make it excessively stiff.

Over-inflation has many adverse effects on a vehicle and the tires themselves.

  • Ride quality: Stiffer tires will translate to a harsher ride. The stiffness puts more strain on the car’s suspension, and directs more of the road’s imperfections to the cabin. 
  • Dependability: Overinflated tires are less dependable in dealing with potholes and road debris since they are more prone to sustaining damage. A forceful encounter may even cause the tires to blow out, which can lead to a loss of control and potential accidents.
  • Traction and handling: A reduced contact patch leads to a smaller footprint and compromised grip, affecting a car’s ability to turn properly. The added stiffness can also impact the suspension’s ability to keep the wheels planted on the ground, affecting overall handling. 
  • Tire wear: Overinflation causes the middle part of a tire to bulge, which concentrates the tire wear in that area. Premature wear in the center of the tire’s tread is a sign of overinflation.
  • Braking performance: Stiffer tires will also compromise braking performance.  According to some tests, the average braking distance is 20% lower in a vehicle with tires inflated to 22 psi compared to tires inflated to 35 psi.

Under-Inflated Tires Are Generally Unstable

Not putting enough air in your tires makes them soft, which causes their sidewalls to flex beyond their intended limit. Under-inflated tires are less stable, causing an irregular contact patch with the road.

Like over-inflated tires, an air pressure shortage also has many adverse effects.

  • Dependability: An under-inflated tire generates more heat which can lead to structural damage. Soft tires will have a compromised ability to absorb shock, leading to the car’s wheels absorbing more impact. This can cause them to deform and shatter.
  • Fuel efficiency: Low tire pressure increases the tire’s heat and rolling resistance, causing the engine to exert more effort. Under-inflation can lower fuel efficiency by as much as 5%.
  • Handling and driving dynamics: Softer tires will compromise steering directness and grip, negatively impacting a car’s ability to turn and the overall level of control the driver has over the vehicle.
  • Tire wear: Under-inflated tires lose their form, creating more contact between the rubber and the road. The added stress on the outer part of the tire tread can increase tire wear by as much as 25%.

Checking Your Tires’ Pressure

Checking your car’s tire pressure takes just a few minutes and can simply be done with a tire pressure gauge. The AstroAI Tire Pressure Gauge features a digital display and comes with batteries and a backlight, making it easy to check your tire pressure, even when it’s dark.

Temperature Affects Tire Pressure

When checking your car’s tire pressure, make sure to account for the temperature of the tires.  The recommended tire pressures indicated by automobile manufacturers are for when the tires are cold.

A 10-degree (Fahrenheit) rise in temperature increases tire pressure by one psi. Tires generally remain cold if driven at moderate speed within a mile (1.6kms). 

If you have to refill your tires with air while the tires are hot, you can account for the heat by filling your tires at four psi above the recommended cold tire pressure.

Consider Purchasing a Portable Air Compressor

To avoid the hassle of having to drive to the next gas station and getting in line to refill your tires with air, you can use a portable air compressor that plugs into your vehicle’s 12-volt socket.

The AstroAI Air Compressor Pump has a programmable inflation feature that automatically turns the compressor off once the tire is inflated to your desired pressure.

Final Thoughts

Maintaining proper tire pressure is essential to tire performance, safety, and longevity.  Automobile and tire manufacturers, alongside tire standardization organizations, go to great lengths to determine the ideal tire pressure for your vehicle to help you get the most of your tires. 

The best tire pressure for your car varies depending on load capacity and speed. It may be challenging to determine your tires’ proper pressure if you install aftermarket wheels. If you have trouble determining the correct tire pressure for your vehicle, 40 psi will ensure that you are not running under or over-inflated. 

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