Tire Pressure and temps.

[Wasoki]

This has been our first attempt at being snowbirds, and it has been anything but dull.  On the whole, I'd rather be here in Key Largo than shoveling the 115+" of snow at home.

The question of the day deals with tire pressure and the impact of ambient temperature.  I try to carry 94 to 96 psi.  When I got the unit out of storage, tire pressure in all 6 wheels was down in the 80s. (When I put it away temps were in the 70s and 80s.  When I got it out we were at about 10...)

I aired up before we left. 

On a cool (by southern Florida standards) morning, before moving the RV I checked again and found them all over 105psi.  I bled off so all were back down to 96.

As we consider thinking about maybe some day in the hazy future heading back to the frozen tundra up north (Sense that strong commitment to moving north soon....), am I correct in assuming that I may need to add air each morning as we get to progressively cooler climes? 

Do these swings in pressure sound typical?

 

[donn]

Yes.  But personally I would not have changed the pressure from the 105 number if your heading back north.

 

[SummitJim]

You don't want to go over the maximum pressure on the sidewall when inflating COLD, whatever the ambient temp is. As long as you are not doing that, there's nothing wrong with the higher pressure.  The ride may be firmer, but you have a margin on carrying capacity.  My original tires were load range F with a maximum pressure of 85, which coincided with the recommended pressure for our weight thus no safety margin.  I replaced them with load range G with a maximum rating of 105 psi cold. So now I run them at 90 for an improved margin of safety. Remember that tire pressure rises significantly as you drive, and an under-inflated tire will get hotter and be more prone to fail. I have to confess though, I've never experience the range of temperature variation you will experience when going from Florida to BRRRR.

 

[Jim Godward]

The answer is unfortunately, probably.  You will need to check each morning and adjust as necessary as you go to colder country.  We face this every year going both ways, getting warmer going south and colder coming home.  Usually we can get from MT to southern UT before much change is necessary.  Going north, it depends on local temperatures and may vary each day.

Unfortunately we have not done this for the last 4 years as other issues over rode our ability to go south.   

 

[bobguigley]

A calculation of pressure versus temperature will show that the pressure will rise by one psi for every 11 degree rise in temp.

 

[Gary RV_Wizard]

A calculation of pressure versus temperature will show that the pressure will rise by one psi for every 11 degree rise in temp.

Careful - that's valid only for a certain range of pressures, typically those seen in light truck tires and medium size trailers. The increase or decrease is actually about 1.8 percent per 10 degrees, so a 110 psi tire would see about a 2 psi change.

 

[johnhicks]

  If you need to add air that means you're going north too early. Seriously.