Load Index

The load index is a standardized measurement used globally to ensure that tires are matched correctly to a vehicle's weight requirements – thus acting as a safety threshold that prevents structural failure under stress. It is a numerical code that represents the maximum weight capacity each tire can safely support.

Understanding what the load index on tires means is crucial for vehicle maintenance, as it ensures that you don’t accidentally compromise safety by installing tires with insufficient load capacity.

The load index is an assigned numerical value – ranging from 0 to 279 – that corresponds to the maximum load-carrying capacity of a single tire. It is important to note that the number itself (e.g., 91) is not the weight in kilograms or pounds, but a code that refers to a specific weight in a standardized load index chart.

Exceeding the load capacity of your tires is a leading cause of tire failure. Overloaded tires build up excessive heat, which can lead to structural damage or a sudden blowout, especially at high speeds or in hot climates.

Locating the load index is straightforward once you know where to look on the tire’s sidewall. It is part of the standardized service description that includes both the load capacity and the speed rating.

Reading the sidewall markings: On the sidewall of any modern tire, you will see a string of numbers and letters. For example, in the sequence 205/55R16 91V, “91” is the load index. This is the number you must match or exceed when purchasing replacement tires.

While often used interchangeably, there is a technical distinction. The load index is the numerical code (e.g., 91) printed on the sidewall, whereas the load rating – or load-carrying capacity – refers to the actual weight in pounds or kilograms that the tire is rated to carry. Essentially, the load index is the shorthand symbol, and the load rating is the real-world performance value it represents.

While these terms are always grouped together, they serve different purposes. The load index tells you how much weight the tire can carry, while the speed index (the letter following the number, like "V") indicates the maximum speed the tire can safely maintain under that specific load.

This table provides a quick reference for converting the numerical load index into actual weight capacities (per tire). Use these values to ensure your tires are capable of supporting your vehicle's fully loaded weight.

• Passenger cars (LI 70 to 90): Typical for compact and mid-size sedans, supporting 335 to 600 kg (739 to 1,323 lbs) per tire.
• SUVs & minivans (LI 90 to 105): Standard for family vehicles, supporting 600 to 925 kg (1,323 to 2,039 lbs) per tire.
• Light trucks & heavy SUVs (LI 105 to 120): Necessary for towing and heavy loads, supporting 925 to 1,400 kg (2,039 to 3,086 lbs) per tire.

The weight-carrying capacity of a tire is not static. It depends heavily on the air pressure inside. Without the correct inflation, even a high-index tire cannot perform its job safely.

A tire's load index rating is only valid if the tire is inflated to its maximum cold inflation pressure. For daily driving, you should follow the vehicle manufacturer's recommended PSI, but when hauling heavy loads, you may need to increase the pressure – just be sure never to exceed the maximum limit.

Air carries the weight, not the rubber. If your tires are under-inflated while carrying a heavy load, the sidewalls flex excessively, generating internal heat that can lead to a catastrophic tire failure.

Different types of vehicles require specific tire constructions to handle their unique weight distributions and usage patterns. Choosing the wrong tire category can compromise safety.

• Passenger cars vs. light trucks (P-metric vs. LT-metric): In the US, "P" tires are for passenger cars and "LT" tires are for light trucks. LT tires are designed with more heavy-duty materials to handle higher pressures and heavier loads, making them essential for towing and off-road use.
• XL (extra load) and reinforced tires: Extra load (XL) tires are specifically engineered to carry more weight than a standard tire of the same size. Their design allows for higher inflation pressures, which is common in high-performance vehicles and heavy EVs.

When the time comes to replace your tires, you have some flexibility, but there are strict safety limits you must respect. You should always use caution when deviating from the original equipment (OE) specs.

Upgrading to a higher index: It is perfectly safe – and often beneficial – to install tires with a higher load index than the ones that originally came with your vehicle. This can provide a greater safety margin and better stability when the vehicle is fully loaded.

Why you should never go lower than the OEM specs: You should never install tires with a lower load index than what the vehicle manufacturer specifies. Doing so can result in poor handling, increased tire wear, insurance complications, and a significantly higher risk of blowouts.

The tire load index is a vital safety specification that ensures your tires can handle your vehicle's weight and cargo. Choosing the correct index prevents overheating and catastrophic tire failure while maintaining the structural integrity of your tire's footprint.

Always remember that while you can safely upgrade to a higher load rating, you must never go below the manufacturer's original specifications. By pairing the right load index with proper inflation pressure, you ensure a safer, more efficient, and more reliable driving experience.