Tire pressure when is hot?

mazda
mazda5

#1

When vehicle is driven, what pressure I should inflate the tires to?
One guy at tire shop said +3psi - so 38psi - the guy inflated said it will be bumpy. Mine is 2013 Mazda 5 - Factory says 35psi.

When I was on freeway (38psi) it felt as if I didn’t have the benefit of the tire (it was so hard) - car was not gripping the road. Besides stuff inside the car was giving resonating vibration.

So next day on this trip, I used my finger nails to release the pressure - measured it after driven on freeway and it was 36psi all around!

Should I inflate to 35psi regardless? What do you guys do?

I do not want the car to float on the road (this is what I felt at 38psi) - I like the car to hug the road as far as possible and not to have a vibrations. Same time, I do not want the tires to wear out unevenly - what is the optimum?


#2

Look on the drivers door jamb.

There will be a sticker that has all the information about the tires.

Including inflation pressures.

That’s what you want to go by.

Tester


#3

That is 35psi
What is if I inflate after driving on local freeway for 30mins - still 35psi?


#4

Always let the tires cool down for fifteen minutes before checking the tire pressure after driving the vehicle.

Or, check the tire pressures first thing before driving the vehicle.

Tester


#5

If you add air to a hot tire after driving add 5 PSI, then make the necessary adjustment the next day when the tires are cool. Normal operating pressure is 3 to 5 PSI above the cold pressure.


#6

I might sound a little snarky - I apologize. This is an issue that is asked but is (unnecessarily, in my mind) made much more complicated than it needs to be - by mechanics and non-mechanics alike.
Find a day that you can check them before driving. Saturdays work best for me.
Get the recommended pressure from the door.
Check them and adjust the pressure if needed. I consider within 3 psi close enough; others will want a tighter tolerance - nothing wrong with that.
Repeat the process at some frequency. I find monthly is adequate, although I’ll recheck tires that might have a slow leak after a few days.


#7

The tires should be at the recommended pressure when they’re cold during the coldest part of the day, so you should measure them first thing in the morning. If you park in a garage, then add 1 PSI for each 10 degrees (Fahrenheit) that the garage is warmer than the outside air to compensate for that.

After you drive for a while later in the day, you are likely to be around 38 PSI, but that’s not when you want to set them.


#8

Check tire pressure in morning before driving vehicle on a set schedule . Inflate to door jamb number, what is so hard about that . Even a short drive to an air pump is not going to be a difference .


#9

This depends on at least two things. One is what sort of driving you just did. If it was unimpeded highway driving for a couple of hours or more, the temperature of the tires should max out. This brings the second issue up, what the air temperature is. If it is 90F or 30F after the highway drive, then the eventual stable tire temperature will be different, leading to different tire pressures. I don’t want to mess around with all that, and will check the pressure when the tires are at ambient temperature.


#10

I always set the tires 2-3 PSI above the recommended value, for two reasons.

  1. If I set it at recommended value, and the temperature falls, the result will be an underpressured tire, not a safe condition. Whereas setting it a few PSI high gives me a margin if the temp falls. 2 PSI is a 20ºF margin.

  2. Increased MPG at a slight expense of ride comfort.


#11

The car shouldn’t perceive much difference between 35 and 38 psi. I wonder what was going on there.

Hot tire pressures should be no more than 10% greater than the cold pressure. So a 35 psi cold tire should rise to no more than 38 1/2 psi. If one experiences more than that, there is something wrong and at the very least, slow down. If you experience more than a 15% buildup, you need to take immediate action - more load carrying capacity (more pressure, larger tire!)

Nowadays, vehicle manufacturers properly size the tires on their vehicles (Not so in the past), so with the exception of trailers, this should not be an issue. Why trailers? Because while cars were all changed by the 1990’s and trucks and SUV’s by 2008, trailer manufacturers were slow to pick up on this - and maybe even today, there are some who haven’t.


#12

I really don’t think a person could tell the difference in driving with a 3 lb 's more in the tires if they were not told about it. Suspect an over active imagination.


#13

Factory say 35, You should inflate the tires to 35 psi when they are cold, not hot off the highway, cold. Drive to the nearest place with air, in the cool of the morning, inflate to 35 and you are good to go.

Check every month. They will likely lose a little (1-2 psi) unless you are heading into summer where they may gain 1-2 psi. Let some out to get to 35. Don’t obsess about 34 or 36 psi, that’s close enough if you aren’t near air.


#14

I inflate my tires to the manufacture’s recommended pressure when the tires are at ambient temperature; i.e. cold. I don’t inflate above that at all, b/c the ride feels too bumpy when the tires are overinflated. If you want to optimize, start at 38 psi, then gradually decrease by 1 psi at a time, until arrive at the performance trade-off you like.


#15

It’s amazing the range of opinions and perceptions one finds on the internet.
I recently responded on another forum to someone who claimed a 1 psi change in tire fill pressure made their car go from OK to unbearable.
I pointed out temperature and altitude can easily make a bigger change from the beginning to the end of a drive, or one day to the next.
Of course I got a slightly nasty response.


#16

Some people are more attuned to changes in tires whether it be pressure or the kind of tires. I would guess that different kinds of cars and different kinds tires have different responses, too. I have to agree with @VOLVO_V70 that there’s probably a high degree of imagination in many cases.


#17

One morning in summer in Montana I checked my tires pressures. One side of the car was facing the shaded park we’d camped in. The other side squarely faced the rising sun. The pressure in the sun-warmed tires was noticeably higher than the shaded side. Black tires with intense morning sun playing on them soak up a lot of heat.


#18

Remember the taxi driver awhile ago? he claimed he could notice 1/2 psi and was adjusting tire pressure several times a night.