Expert on Tire Pressure

[Flametheus6]

I'm looking for some upfront expertise on tire pressure. Let's say I check my Tires in the morning at 40 degrees outside temp and they say 65PSI. On the Tire it says cold 80PSI. So I drive to my local tire pressure locale and check the pressure and it says 77 PSI and it is now 51 degrees outside. How much air do I put in the tire? The 15PSI it was short? The 2PSI it is now short? The 72PSI that the sticker on the inside of the vehicle door says it should be? Or is this all a racket by the gods to control air? And BTW I left at 0700 for the locale and no train was going the other direction at twice my speed an hour later so I do not need to know when I will be hit by the train.

Thanks

[Flametheus6]

I'm looking for some upfront expertise on tire pressure. Let's say I check my Tires in the morning at 40 degrees outside temp and they say 65PSI. On the Tire it says cold 80PSI. So I drive to my local tire pressure locale and check the pressure and it says 77 PSI and it is now 51 degrees outside. How much air do I put in the tire? The 15PSI it was short? The 2PSI it is now short? The 72PSI that the sticker on the inside of the vehicle door says it should be? Or is this all a racket by the gods to control air? And BTW I left at 0700 for the locale and no train was going the other direction at twice my speed an hour later so I do not need to know when I will be hit by the train.

Thanks

[CD]

Flametheus6
I don't claim to be an expert, but here is what I would suggest. First go to a scales and weigh each wheel (corner of RV). Get a tire pressure chart (go to Goodyear or some other tire manufacturer and copy one) then put at least as much pressure in tires on an axle as needed for the heaviest corner of that axle. You may not need the same on front and back. Be sure to do this when loaded to travel. In your case your tire pressure may have been low for the weight and generated more heat than it should have. It's better to have a little more than needed than to be under. More than needed gives you a rougher ride but being under causes heat. Maybe someone else can give you an answer about your other questions.
On my duals I run 55lbs. as that will carry more weight than the axle is rated for and gives much better ride.

[Loren]

Flametheus6,
Cliff's advice is right on, tire pressure should be checked cold [as you did], or before you drive over 1 mile. The pressure indicated on the side of the tire is the MAXIMUM pressure that tire is rated for in order to carry the maximum load the tire is rated for.
To answer your question I would just add the amount of air you originally determined it needed. In other words-you measure in the morning and decide you need 15 more pounds, go to the service station and add 15 pounds to whatever the pressure is at that time. Actually I would add an extra 3 or 4 pounds and check it next morning hoping it would be a little high so I could let a little air out to bring it to the correct pressure.
Hope you are not confused more now, I have trouble expressing myself well.
Loren

[Gary RVRoamer]

Loren gives excellent advice - just add the amount you determined you were short before starting out. Up to 5 psi extra is OK, so you can adjust downwards the following morning.

You probably don't need the full 80 psi mentioned on the sidewall - that's is for maximum load. But until you get a chance to weigh the trailer and look up the pressure needed to carry that load, go with the max load pressure. You can't go wrong that way (unless the trailer is overloaded).

[Ray,IN]

I agree with Loren to a point. ST tires should be inflated to sidewall maximum when the tires are cold. This is so important that Carlisle tire says if their ST tires are not inflated to sidewall maximum the warranty is voided. LT tires and P rated tires are not included.

[Loren]

Thanks Ray,
When I wrote the above I didn't notice he was pulling a trailer and could have been talking about ST tires.
Loren

[full-timer]

Does cold really mean cold as temperature? I think it means cold,as not running the tire. To get the right measurement it will be 72* weather temp. I have checked mine at 40* and then again at 75* and there was a 6psi difference.

Joe

[Ray,IN]

You are correct Joe; cold means driven for less than one mile after sitting for at least 4 hours, whatever the ambient temperature happens to be at the time. Tire manufacturers build-in adequate safety margins for differences in climate.