Florida Heat and Tires: Pressure, Aging and Blowouts

Heat is part of every drive here

In most of the country, summer is a season for tires. In South Florida it's most of the year. The car sits in a sunny lot in Sunrise, then runs the Sawgrass at highway speed, then sits again, day after day.

Heat alone rarely ruins a tire. What does the damage is heat on top of the things that already make a tire run hot: low pressure, a heavy load and sustained speed. This guide covers where that heat comes from, what NHTSA's research says about tires aging in the Sun Belt, and a routine that fits a Florida summer.

Where damaging heat actually comes from

A tire makes its own heat. Every time it rolls, the sidewall and tread flex where they meet the road, and flexing warms the rubber. The outside air sets the starting point; the way the tire is used decides how hot it gets from there.

NHTSA's consumer brochure Tire Safety: Everything Rides On It names the three conditions to watch: excessive speed, underinflation or excessive loading, either separately or in combination, can cause heat build-up and possible tire failure.

Of the three, pressure is the one that goes wrong quietly. NHTSA's summer driving guidance is direct about it: underinflation is the leading cause of tire failure. A low tire flexes more with every turn of the wheel, and a hot day doesn't give it any margin.

Pressure: heat raises the reading, not the need

Warm air in a tire pushes harder than cool air. USTMA's tire care guidance says inflation pressure goes up in warm weather and down in cold weather by one to two pounds for every 10 degrees of temperature change.

That's why a gauge reading taken after a drive, or in the afternoon sun, can look healthy on a tire that's actually low. Two rules from NHTSA keep it straight:

• Check cold. NHTSA defines cold as parked for at least three hours, so first thing in the morning is the easy time.
• Use the door placard, not the sidewall. The number molded on the tire is the maximum it can hold, not the pressure your vehicle calls for.

And one rule for hot days: don't let air out of warm tires. NHTSA's guidance is that pressure rises as tires heat up, so bleeding them down to the placard number leaves them low once they cool. Recheck when they're cold instead.

The numbers behind all of this, including what a cool front does to a tire set on a hot afternoon, are in our guide to tire pressure and temperature.

Load: the number on your door

Summer is road-trip, beach-gear and moving-day season, and every extra pound is carried by four contact patches.

Your Tire and Loading Information placard, on the driver's door edge or door post, lists the vehicle's capacity in plain words. Under the federal placard rule, it reads: "The combined weight of occupants and cargo should never exceed" a stated number of pounds. That line includes people, luggage and anything on a roof rack or hitch.

A loaded car on underinflated tires at highway speed is all three of NHTSA's heat conditions at once. If the trip is long and the car is full, set the pressure cold before you leave.

Aging: what NHTSA found about the Sun Belt

Heat doesn't only matter on the day you drive. It also affects how fast the rubber ages.

NHTSA's tire aging research describes the process as the combined effect of heat and oxygen on the rubber compound over time. Its TireWise guidance lists exposure to sunlight and a warmer climate, along with infrequent use, poor storage and poor maintenance, among the things that contribute to tire aging. And its research found that tire aging is a greater concern in the more southern parts of the Sun Belt states.

South Florida is about as far south in the Sun Belt as the mainland goes. That doesn't give a tire a Florida expiration date. It means age deserves attention alongside tread depth. NHTSA notes that some vehicle and tire makers recommend replacing tires that are 6 to 10 years old regardless of treadwear, and Bridgestone and Michelin both recommend a professional inspection at least once a year from five years on. Our guide to how old is too old for tires lays out the manufacturer guidance side by side.

The temperature grade on your sidewall

Most passenger tires sold in the US carry three UTQG grades on the sidewall (deep-tread winter tires, temporary spares and a few other types are exempt). The last one, temperature, is graded A, B or C. NHTSA's consumer guide describes it as the tire's ability to dissipate the heat generated by driving, with A the highest.

Two things to know before leaning on it:

• The grade comes from a laboratory test at set speeds, not from Florida roads.
• NHTSA notes that the grade applies to a tire that is properly inflated and not overloaded. Low pressure or a heavy load takes away the conditions the grade assumes.

Type a UTQG code from your sidewall to see what each part means:

For the full breakdown of treadwear, traction and temperature, see our UTQG ratings guide.

Where you park matters too

Sunlight is on NHTSA's list of aging factors, and a Florida car can spend more hours parked in the sun than driving. You can't always choose, but when you can:

• Take the covered or shaded space at home and at work.
• If the car will sit for weeks, park it out of direct sun and set the pressure to the placard before you leave. (Snowbirds, our post on a car that sat all summer covers the return trip.)
• Look at the sidewalls of a car that lives outdoors. Cracking in the sidewall or between the tread blocks is a reason to have the tires inspected.

A South Florida summer routine

Extreme Tires in Sunrise measures tread depth at every corner during a tire rotation and sets pressures to the placard, at the shop or by mobile van in the local install area. For a quick self-check first, run your readings through Do I Need Tires Yet?.