# Tire pressure

If I check the tire pressure in the morning before the car is driven and it’s low, I then bring it up to the proper psi, what happens when I drive it in extreme heat such as the central valley in Califronia, will it be over inflated and cause problems?

Checking the tire pressure before the vehicle is driven is the proper procedure. Set the pressure according to the sticker in the door frame. The tire pressure will increase a bit with an increase in temperature, but it WILL NOT make the tire dangerously overinflated.

The pressure increase is not that great.

When a tire is inflated to its correct pressure when cold, the increase in tire pressure as the tire heats up is minimal. The reason why the increase in pressure is minimal is because having the correct pressure from the start of your drive reduces the flexing of the sidewalls of the tire.

As tire sidewalls flex, they build up heat. This heat causes an increase in tire pressure, but it also causes a dangerous weakening of the tire’s carcass in the sidewall area. The weakening of the tire’s sidewall is what frequently leads to blow-outs at high speed.

Some blow-outs are due to punctures, but a huge percentage of them are actually due to underinflated tires. Those who begin their drive with the correct tire pressure are far less prone to blow-outs, and of course, they will also experience better handling and slightly better gas mileage.

Thanks for technical info…I will bring up the tire pressure to its proper psi and then check it after driving for a while just to see how much it does go up.

You might want to check the pressure at home before you drive it and then when you get to the pump check the current pressure and then add the same additional psi as you had when they were cool.

That is if your car calls for 30 psi and in the morning you measured 25 psi if your now warm tyres tested at 33 psi you would add 5 psi (38 total) so when they cool down overnight they will be back at 30.

I believe that the specified tire pressure (whether in the owner’s manual or along the driver’s door frame) is usually the cold pressure. The 1-2 PSI increase when warm is accounted for and normal.

For example, if a particular car’s tires are supposed to be inflated to 30 PSI, then that’s what it should read cold, in the morning, before any driving has been done. It will go up a little bit once driving has commenced, but not so much as to create a problem.

As long as your hot tire pressure, set cold before driving per the label on the door frame, does not exceed the maximum permissible pressure on the tire sidewall, you will be fine. You can take some consolation in that tires with higher pressure will produce heat less at a given ambient temperature than tires with lower pressure.

A good rule of thumb is 1 psi for every 10 degrees of temp for a cold measurement. After driving a bit I find my tires read about 3 psi higher when they have warmed up.

Ed B.

“As long as your hot tire pressure, set cold before driving per the label on the door frame, does not exceed the maximum permissible pressure on the tire sidewall”

``````Not exactly true.  The maximum on the tyre is there only to keep you from using it on a car that would put more weight on the tyre than would be safe.  It does not mean that the number on the tire is safe above the recommended number provided by the manufacturer of the car.
``````

There are three issues involved.

1. Maximum pressure: The tyres have a maximum pressure that they can be safely handle. You want to use. In this case you seem to be suggesting you want to use it at the max listed on the tyre, so as far as the tyres go, that should be fine.

2. Ride comfort: You seem to accept the harsher ride and since you are the only judge of that, then that should also be OK.

3. Safety: This is the one that I can’t offer a yes or no answer. While all the authorities (see below) agree that the pressure listed in the owner’s manual is the recommended proper pressure by all authorities, it must be acknowledged that there likely is some amount of flexibility.

Car manufacturers are concerned with many things. They want people to be happy with their cars and that means they want the car to give good mileage and the want the car to ride comfortably.

I have yet to see anyone who has access to real test track facilities and actual test results on modern cars and tyres, offer objective data to support the idea that pressures higher than that recommended by the manufacturer are as safe as the recommended pressure.

My opinion is that a few psi over the recommended value is not likely to compromise safety by any material amount. I would also suggest that there is a point where higher pressure will reduce safety enough to make a difference.

If mileage is more important than safety, go ahead and keep upping that PSI. Other wise, I would suggest reading the following and going along with the professionals. If it really was safe to go higher, then I don’t think all the authorities are going out of their way to tell us to use what the car manufacturer recommends.

http://www.tiresafety.com/
This is sponsored by a tyre manufacturer Bridgstone - Firestone and instructs the reader to check the owner’s manual for the correct tyre pressure.

Here is another from the Goodyear site.
Keep your tires properly inflated and you could improve gas mileage by more than \$1.50 every time you fill your tank. The recommended tire pressure for your vehicle is located on a sticker inside your driver-side door or noted in your owner’s manual.
You might also try the US Department of transportation.
http://www.nhtsa.gov/cars/problems/E...intenances.htm

They say:
You can find the correct tire pressure for your tow vehicle in the owner?s manual or on the tire information placard.

Here’s what I think @Wha Who? meant:

I’ll use my car as an example. The label on my door frame says to inflate the tires to 32psi cold, and that’s what I do. The tire says 44psi max. So when I drive on the highway on a hot day tire temp & pressure will rise. If it doesn’t go above 44psi I’m OK.

The tire says 44psi max. So when I drive on the highway on a hot day tire temp & pressure will rise. If it doesn’t go above 44psi I’m OK.

Actually if you read the WHOLE line it says something like 44psi MAX@1200lbs (or some such weight). So if your car’s weight is less then 4X the weight listed on the side of the tire then it can go beyond the 44psi.

“So if your car’s weight is less then 4X the weight listed on the side of the tire then it can go beyond the 44psi.”

?? I don’t see how the weight enters into the max pressure it can handle. I think it’s the other way around, the tire can handle up to 1200 lbs. at 44 psi, inferring it can handle less weight at lower pressure.

Lots of good info here, but one fact missing, the lower your tire pressure when cool, the hotter the tire will get when driven. Heat is the enemy of the tire, not pressure.

I’d recommend 35 psi for any vehicle except the rear tires on a PU truck that is unloaded.

Keith

Re-read my post (the second one in this thread), where I did speak about heat build-up resulting from low inflation pressure in tires and how this results in blow-outs.

And, giving a blanket recommendation of 35 psi for passenger cars without taking into account the specific handling characteristics of those cars is foolish. Some cars call for lower pressure in the rear tires (Subarus), and some call for higher pressure in the rear tires (the Corvair comes to mind, but there are others).

The only sure things about tires are that low pressure will inevitably lead to poor tread life, inferior handling, and increased risk of blow-out, and that the specific tire pressure recommendations vary from one make to another as a result of handling differences.

Disturbing the ratio of front/rear inflation can result in some very severe handling problems on some models, and as a result, “blanket” recommendations are inherently unwise.

The load carrying capacity of a tire is a function of the size and the inflation pressure.

BUT be very careful how you read what is printed on the sidewall. If you don’t read what is there EXACTLY you will misunderstand how this relationship works. For example:

1. If the maximum pressure listed on the sidewall of a standard load passenger car tire is 35 psi, then what will be written on the sidewall MAY have the form: Max Load XXXX at YY psi. It might not say it this way, but for these types of tires, this is the most common form.

2. If the maximum pressure listed on the sidewall of a standard load passenger car tire is either 44 psi or 51 psi, then what is written on the sidewall of the tire will be of the form: Max Load XXXX, Max Pressure YY. You may find some 35 or 36 psi tires in this form, too! This indicates there is a disconnect between the max load and the max pressure.

That’s because standard load passenger car tires only come in 35, 36, 44, or 51 psi max pressures and the load carrying capacity, while increasing with inflation pressure, the increase in load peaks at 35 (or 36) psi. Pressures beyond 35 (or 36 psi) DO NOT result in increased load carrying capacity.

If you have a tire that says the maximum pressure is something other than 35, 36, 44 or 51 psi, it is NOT a standard load passenger car tire.