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Cold tire pressure refers to the tire pressure value measured when the vehicle has been parked in a stationary state for at least three hours or driven no more than 2 kilometers. At this time, the tire temperature is consistent with the ambient temperature, which can accurately reflect the actual pressure state of the tire. Since friction between the tire and the ground during driving generates heat that causes tire pressure to rise, the data measured in a hot tire state needs to be subtracted by approximately 0.2 bar to be regarded as cold tire pressure. The standard cold tire pressure values for different vehicle models usually range from 2.1 to 2.7 bar, and the specific values can be found in the vehicle manual or body labels (such as the B-pillar or fuel tank cap). Maintaining the correct cold tire pressure is crucial: excessively high tire pressure will intensify tire noise, affect braking performance, and cause abnormal wear, while excessively low tire pressure will increase fuel consumption, accelerate tire deformation, and even lead to the risk of tire blowouts. It is recommended to check the cold tire pressure at least once a month, and be sure to confirm that the tire pressure meets the standard before long-distance driving. The pressure can be appropriately increased by 0.1 to 0.2 bar when the vehicle is fully loaded. In addition, regular tire rotation (every 10,000 kilometers or when the tread depth difference reaches 1.5 millimeters) helps to extend tire life.

The PSI (pounds per square inch) of a tire is a key indicator for measuring tire pressure, which directly affects driving performance and safety. When the tire pressure is higher than the recommended value (usually 22-32 PSI for family cars; refer to the vehicle manual or the label on the door frame for specific values), the contact area between the tire and the ground decreases, leading to increased central wear, reduced grip, longer braking distances, and decreased driving comfort. Conversely, insufficient tire pressure increases rolling resistance, raises fuel consumption, causes excessive sidewall wear and even the risk of tire blowouts, and makes steering response sluggish. Proper tire pressure optimizes fuel efficiency, extends tire life, and ensures handling stability. It is recommended to check tire pressure at least once a month, and it is even more necessary to confirm it before long trips. The measurement should be carried out when the tires are cold to avoid errors. Different vehicle models have different tire pressure requirements due to differences in load and design, and appropriate adjustments are also needed when seasons change. Maintaining the manufacturer's recommended value is the core of balancing safety and performance.

The 4 PSI rule refers to the recommended inflation pressure range for tire pressure adjustment. It is typically based on the tire pressure value recommended by the vehicle manufacturer and allows a fluctuation of ±4 PSI (approximately 0.28 bar) to accommodate different driving conditions or load requirements. For example, if the standard tire pressure is 32 PSI, the acceptable range would be between 28 and 36 PSI. However, attention must be paid to the MAX PSI (maximum pressure limit) indicated on the tire sidewall to avoid overpressure risks that may lead to tire blowouts. As an imperial unit of pressure, 1 PSI is approximately equal to 0.0689 bar or 6.895 kPa. In the Malaysian market, tires are commonly labeled with both PSI and bar units. For instance, passenger car tire pressure is usually recommended at 30-35 PSI (2.1-2.4 bar), while SUVs may require 35-40 PSI (2.4-2.8 bar). Regular tire pressure checks are essential, particularly before long-distance trips. Insufficient tire pressure increases fuel consumption and accelerates tire wear, whereas excessive pressure reduces traction. It is advisable to use a digital tire pressure gauge for monthly inspections and consult the manufacturer's recommended values found on the door jamb or fuel filler cap. Note that applicable pressures may vary significantly across different vehicle models or tire types (e.g., high-performance tires vs. off-road tires). When replacing tires, strict adherence to the pressure requirements corresponding to the new tires' load index and speed rating is imperative.

Low tire pressure can have multiple negative impacts. Firstly, it significantly increases fuel consumption. As the contact area between the tire and the ground expands, rolling resistance rises, requiring the engine to consume more fuel to maintain driving. In terms of handling, the steering wheel becomes heavy and may pull to one side, affecting driving safety. More seriously, low tire pressure causes abnormal tire heating, accelerating cord breakage and rubber aging, leading to increased shoulder wear and shortening the tire's service life by approximately 30%-40%. When driving at high speeds, the tire may experience wavy wear due to structural deformation, further increasing the risk of a blowout, which is one of the most dangerous safety hazards during high-speed driving. Additionally, insufficient tire pressure reduces braking efficiency, prolonging the braking distance during emergency braking. It is recommended to check tire pressure at least once a month. Standard tires should be maintained at 240-250 kPa, while reinforced tires should be at 280-390 kPa. In summer, the pressure can be slightly reduced to 2.4 bar to account for thermal expansion. If the tire pressure is found to be below 170 kPa, it is considered a dangerous state and requires immediate attention. Common causes include natural leakage, temperature changes, or poor wheel hub sealing, and professional repair services should be sought promptly. Maintaining correct tire pressure not only ensures driving safety but also saves about 3%-5% in fuel costs and extends the tire's service life.

A tire pressure of 40 PSI may be on the high side for most family sedans, but this needs to be judged based on the specific vehicle model and the manufacturer's recommendations. The standard tire pressure range for most vehicles is usually between 30-35 PSI; for example, the recommended value for the Honda Accord is 32-35 PSI, and 40 PSI may exceed this range, which could lead to excessive wear on the central area of the tire, reduced grip, and decreased comfort. However, high-performance models or vehicles with special configurations may allow for higher tire pressures—some sports sedans, for instance, recommend maintaining a pressure between 40-45 PSI. Tire pressure needs to be adjusted according to the climate: it will naturally rise in high-temperature environments and may drop in low temperatures. It is recommended to check the cold tire pressure (after parking for more than 3 hours) monthly and refer to the official data on the door jamb label or the user manual. Maintaining excessively high tire pressure for a long time may shorten the tire's lifespan and affect handling stability, but short-distance driving usually does not immediately cause safety issues. If the pressure shows 40 PSI after inflation, you can compare it with the recommended value in the manual and release some air to a reasonable range if necessary. Regular tire pressure maintenance not only improves fuel efficiency (fuel consumption increases by about 3% for every 5 PSI the tire pressure is low) but also avoids the risk of tire blowouts. It is recommended to use a digital tire pressure gauge or have it checked at a professional service point to ensure accuracy.