Cold tire pressure question?

Since this thread is about tires, I recently bought a very good 12 volt, 30 amp compressor from Northern Tool.
I then added a place to clamp it on each side of the trailer. It will reach 4 tires plus the spare. It has a 30 amp fuse at the battery. Very convenient.

I would recommend a close look at the 38 psi tire. You may have a nail or bad valve stem.

Mix up a strong solution of dish soap. That is 2 parts water
1 part dish soap. Completely cover valve stem then wiggle it.

Nails and screws can be difficult to see. If it were mine I would take the tire to a tire shop have them air it up to about 125 % of sidewall pressure and put it in the water tank.

A TPMS system is tailored for this situation. If it is a nail it may hold air when stationary but loose air when under way. So airing up and checking pressure tomorrow may not show up a nail in a tire.

Last month I had a nail in my Subaru. The TPMS warned me before it was a problem.

Then two weeks later the TPMS alarmed that a tire was low on my truck. A 80 psi tire was down to 65 psi. I decided to drive 15 miles to a tire store without the 5th wheel. I had gone less than 1 mile and pressure dropped to 60. Another mile it was 55.

I decided I would not make it and put on the spare and went back to the trailer campground. Home was only 25 miles away from campground.

The next morning took the tire to the tire shop for repair. The TPMS showed the tire still had 50 psi. Bad valve stem and only lost air while tire was spinning.

Set them at 50. My FR Windjammer came with Nitrogen filled tires too but I've never added Nitrogen. I add the 78% stuff that comes out of my air compressor.

MorMJS wrote:
My dual axle TT has Westlake ST205/75R14 with NitroFill tires on it. It calls for "COLD" tire pressure of 50psi
I brought my TT home out of storage today to get ready for a trip and measured air pressure this afternoon and it read the following:
Street side- 38psi front, 45 rear
Curb side- 47 front, 46 rear
I wont have time to have them nitro filled before we leave this weekend so regular air is gonna have to do, but what pressure should these guys read in mid-day heat?

I have the same tires on my Flagstaff.

The COLD pressure on the tire sidewall is the pressure RATING for the tire. It is the pressure which the manufacturer states is required to provide the maximum load that the tire can bear under normal tire operating conditions.

As a consequence, the tires on your trailer should practicably be filled to this level when the tires are 'cold', i.e. basically before the trailer is towed or when the tire air is at a steady state around ambient (outside) temperature. Any cold pressure below that means that the tire bearing load will be reduced - how much reduced is anyone's guess unless the manufacturer provides tables of pressure vs load. Note that the pressure in the tires will rise with speed and ambient conditions as the day gets hotter or the wheels are in the direct sun. The pressure rating account for this up to the maximum rated speed (65 mph for our tires).

Note also that running tires at pressures below the proper temperature will lead to increased heat build-up and heat is one of the leading causes of tire blowouts.

If I were you I would not move the trailer until the pressures are aired up to 50 psi. As others have suggested, you can get a 12V air pump (you should have one anyway if you are RVing) and do this before you leave. One of the mods that I will be doing soon is to add a 12V socket outide the RV so that I can easily reach each tire with my air pump.

Thanks for the info all.

Get a small air compressor and get them all to a first thing in the morning reading of 50. Forget about nitrogen fill. Air is 78% nitrogen and is at your fingertips.

My TT routinely seems to lose 5psi over winter storage, so three of those pressures look "normal". I would fill them up, but keep an eye on that low tire in case it has some sort of slow leak.

I wouldn't bother with "nitrogen fill", but if you know a shop nearby who will do it for free then go for it!

Don't make a special trip to have the tires filled with nitrogen. Just fill them to the cold pressure which is printed on the tires sidewall.

Depends on the weight of your TT.
The specifications of your ST tires I can search , but if you read it from sidewall. I dont have to.

Could be that your TT tires need even more then 50 psi , and 10 psi extra is allowed by most tire-makers, and even used for 75m instead of 65m/h. But even if you drive below 65m its better to use the advice pressure for 75m/h.

No problem not filling with Nitrogen, all gasses can be mixed, and the advantage is not that big.
Miths about it are that tires stay cooler and pressure rises less for temperature rising in tire. these 2 are sertainly not true.

Even al little liquid water could keep the tires rubber cooler because of the energy that is needed to go from liquid to gas. and disadvantages of oxidation of rimm are nihil.

Cold conditions are defined as early in the morning before the day's ambient temperature, sun's radiant heat or the heat generated while driving have caused the tire pressure to temporarily increase.

Check/adjust tire pressure in morning prior to trip........compressed air will work just fine cause it's 78% Nitrogen and cheap.