Right next to your tire's speed rating letter is a two or three digit number (like 91, 105, or 120). This is the Load Index. It correlates directly to the exact amount of weight, in pounds or kilograms, that a single tire can safely support when inflated to maximum pressure.
The Hidden Danger of Stretched Tires and Upsizing
When upgrading to massive wheels with rubber-band thin low-profile tires, many amateur mechanics inadvertently buy tires with a significantly lower Load Index than their factory specification.
This is exceptionally dangerous on heavy vehicles like SUVs, EVs, or pickup trucks. Electric vehicles, for example, carry thousands of pounds of battery mass below the floor. If you install an aesthetically pleasing aftermarket tire with a Load Index of 85 (1,135 lbs per tire) on a heavy EV that demands a Load Index of 102 (1,874 lbs per tire), the tire's internal structure will be perpetually crushed under the vehicle's resting weight. Hitting a bump at high speed forces the weight limit far past the tire's breaking point, severing the internal bead cords instantly.
Light Truck (LT) vs. Standard (P)
If you drive a truck and tow trailers, ensure you are buying "LT" (Light Truck) graded tires rather than standard "P" (Passenger) tires. LT tires feature 10-ply rigid sidewall construction specifically designed to resist squirming under massive towing tongue weights.