Guides
Tire pressure in Texas heat
Your correct pressure is on the sticker in the driver's door jamb, not the figure moulded into the tire, which is a maximum. Check pressures cold, before driving. Pressure falls about 1 PSI for every 10 degrees Fahrenheit the temperature drops, which is why the light appears on the first cold morning.
Two numbers, and only one of them is yours
Open the driver's door and look at the pillar. There is a sticker there with the tire size the car was built with and the pressures it wants, usually something in the low thirties, sometimes different front and rear. That is your number. It was set by the people who built the car, for that car, with its weight and its suspension.
The other number, moulded into the sidewall next to the words MAX PRESS, is the maximum the tire can hold. It is a property of the tire and has nothing to do with your car. Inflating to it is the single most common pressure mistake there is: the ride goes hard, the centre of the tread wears out early, and grip in the wet drops.
If the car has been fitted with a different tire size from the one on the placard, the placard pressure may no longer be right and it is worth asking. Otherwise, the placard wins every time.
Why cold matters, and what cold means
The placard figure is a cold pressure. Cold means the car has been sitting for a few hours, or has been driven less than about a mile. It does not mean cold weather.
Driving heats the air inside the tire and the pressure rises with it, typically by a few PSI in normal use and more on a long run in summer. If you check a hot tire and let air out to hit the placard number, you have just underinflated it, and you will find out when it cools.
In practice this means checking in the morning before you go anywhere, or at a gas station close to home rather than at the end of a drive across town. If you can only check hot, add three to four PSI to the target and verify it properly later.
The first cold morning, and the light
Pressure falls about 1 PSI for every 10 degrees Fahrenheit the temperature drops. Central Texas does not have much of a winter, but it does have the day in November when an afternoon in the eighties is followed by a morning in the forties.
That is a forty degree swing, so roughly four PSI, and tires that were a little low already cross the threshold overnight. The warning light comes on, the car is otherwise fine, and nothing has actually gone wrong except that the air got colder.
The right response is to put air in, not to ignore the light. A tire that was borderline in October is genuinely underinflated in January, and it will stay that way until somebody corrects it. The light also goes out on its own once the day warms up, which is exactly how it gets ignored.
What summer does to an underinflated tire
Underinflation is the failure mode that matters here, not overinflation. A tire with too little air flexes more than it was designed to, and flexing generates heat in the sidewall. Add hundred degree asphalt and a sustained seventy on I-35, and the heat has nowhere to go.
That is how a blowout happens on a summer afternoon to somebody who was driving normally. The tire did not hit anything; its structure came apart from heat it had been building all the way from Round Rock.
It is also expensive in the undramatic way. A tire run a few PSI low wears its outer edges away while the middle looks fine, and it costs fuel the entire time. Checking pressure once a month is the cheapest maintenance on the car.
A routine that works here
Nothing elaborate, and it takes five minutes.
- Check once a month, in the morning, before driving anywhere.
- Check again whenever the weather turns sharply, in either direction.
- Use the placard number, and set all four to it unless the placard gives separate front and rear figures.
- Check the spare while you are there. It is the one that will be flat when you need it.
- Keep a proper gauge in the car. The ones on gas station air lines are usually wrong, often by several PSI.
- If one tire keeps needing air and the others do not, that is a leak, not the weather. Get it looked at while it is still repairable.
Questions about this service
What pressure should my tires be?
The figure on the sticker in the driver's door jamb, which is usually in the low thirties and sometimes differs front to rear. Not the number moulded into the tire sidewall: that is the maximum the tire can hold, not what your car wants. Set it cold, before driving.
Why did my TPMS light come on when it got cold?
Because pressure falls about 1 PSI for every 10 degrees Fahrenheit. A forty degree overnight drop takes roughly four PSI out of every tire, which is enough to push a tire that was already slightly low past the warning threshold. Add air rather than waiting for the afternoon to switch the light off.
The light went off by itself. Do I still need to do anything?
Yes. It went off because the day warmed up and the pressure came back over the threshold, not because anything was fixed. The tire is still below where it should be, and it will trip again on the next cold morning. Check all four cold and set them to the placard figure.
Can I check pressures after driving?
You can, but the reading will be high because driving heats the air. If you set a hot tire to the placard number you have underinflated it. Either check before you drive, or add three to four PSI over the target and confirm it cold when you can.
Is more air better in summer?
No. Overinflating hardens the ride, wears out the centre of the tread and reduces the contact patch, which costs grip in the wet. The placard figure already accounts for the heat the tires will see. The dangerous direction in a Texas summer is underinflation, because that is what builds heat in the sidewall.
One tire keeps going down. Is that the heat?
No. Temperature affects all four roughly equally, so one tire losing air on its own is a leak: a nail, a corroded rim seat or a failing valve. Have it found while the puncture is still in repairable condition, rather than after it has been run low for a few weeks.
Tell us where you are.
Call or text (512) 573-0135. Give us the cross street or a dropped pin and we will tell you what it costs before anyone drives.
(512) 573-0135