“You’re going to be tuning the pressures to fit that envelope of air that those tires allow,” Robinson said. Tire engineers from companies such as Michelin will work alongside automakers’ engineers using the TRA and ETRTO guidelines. Sarah Robinson, a driving-safety expert at Michelin, said the manufacturer’s recommended tire-pressure level dates back to the beginning of a vehicle’s development process.

Here’s an example: On the tires on a Lexus LC500 we have at the C/D offices just now (pictured above), you can read a maximum pressure of 51 psi, but the automaker recommends 33 psi (shown on the sticker below) for both front and rear tires. Some cars and trucks wind up with different recommended pressure levels for front and rear tires, even on all-wheel-drive vehicles. Vehicle manufacturers come up with ideal tire pressures based on factors such as how much load a car or truck puts on its left front wheel during a right turn at 60 mph, for example. But cars and trucks all have varying weights and sizes, and they handle and perform uniquely, Toth noted. “There’s a load/inflation table for every size of tire in the universe,” said Bob Toth, director of industry relations at Goodyear.

Tiremakers start with a set of standards, set by the Tire and Rim Association (TRA) in the United States and the European Tyre and Rim Technical Organisation (ETRTO) across the pond, and use their guidelines in developing tire sizes’ maximum psi and maximum load levels.

Proper tire psi