Tire Pressure & Altitude

[akadeadeye]

Going from 1,100 ft. to 8,000-9,500 feet and temps from 90's to 40's lowered my tire pressures 5 to 8 psi. Should I adjust to the pressures I usually carry?

 

Don
 

[rayin]

The trick is to inflate to 10% over your minimum air pressure as listed in the load/inflation chart. This eliminates the situation you have now, according to Tireman9. As long as your tire pressures are above minimum, no worries.

Personally, I use the tire pressures listed on the Federal Tire Placard inside the vehicle, and never have to be concerned about altitude or temperature.

 

[wolfe10]

Don,

The VAST majority of the drop in PSI was because of temperature.  Altitude has very little effect. 

 

And, yes, if you will be operating the coach in cold conditions, you will need to inflate the tires to the correct PSI for your load.

Going from Texas summer heat to winter driving, I always have to add air.

[wayne77590]

As you go higher or lower in altitude the pressure will increase or decrease 0.48 psi and the PSI will Increase/decrease 2.0 psi for every 10 degrees of temperature change.

Let's assume your max tire pressure is 110 psi and your minimum load weight pressure is 90 psi. A fudge factor of 10 psi would make the minimum load weight 100 psi.  If you go from sea level to 10,000 feet altitude you would raise 4.8 psi and with the 90 to 40 degree change in temperature you would drop 10 psi for an overall psi change of 5.2 psi.

With the fudge factor of 10 psi you would still be within your minimum required load pressure.  You can do the math for the inverse situation.  I always set my tire pressure between the max the tire allows and the minimum required for the load.  If you do not have the four corner weights then run max tire pressure allowed and be safe, only adjusting as needed when you get to your destination. There are other scenarios, I'll bet, and the closer the minimum and maximum tire pressures are, the less of a fudge factor is available.

Tireman9, Roger, please correct me if  this is not correct and I'll ask for the post to be removed.

[jleamont]

26 minutes ago, wayne77590 said:

I'll ask for the post to be removed.

No need for that, you can always go back and correct it by using "edit". 

[wayne77590]

Edit is only good for so long then it goes away.  I'll just pester Brett if it is wrong. Might even blame him for....well, we'll see,

[kaypsmith]

23 minutes ago, wayne77590 said:

Edit is only good for so long then it goes away

HUH? I've used edit for years and never seen it go away, unless it contained something that Brett didn't like.

[wayne77590]

Guess I never really paid attention to it. Must be because I'm right all the time.👹

[akadeadeye]

On 9/18/2019 at 8:39 AM, wolfe10 said:

Don,

The VAST majority of the drop in PSI was because of temperature.  Altitude has very little effect. 

 

And, yes, if you will be operating the coach in cold conditions, you will need to inflate the tires to the correct PSI for your load.

Going from Texas summer heat to winter driving, I always have to add air.

Thanks Brett.

And, thanks to the other replies.

 

Don

[rayin]

On 9/18/2019 at 12:31 PM, wayne77590 said:

Guess I never really paid attention to it. Must be because I'm right all the time.👹

What is the other half's opinion? I know what mine would say about me.

[wayne77590]

I'm always right. If you don't believe me just ask me.

Up in altitude pressure increases by 0.48 psi for every 1000 feet of altitude change. Down in altitude, the reverse,

Up in altitude pressure decreases by 2% for every 10 degrees of temperature change. Down in altitude it increases.

The math is fairly simple.

[manholt]

For us, yes!  Average kid today...where's my computer?  What's a slide rule?

[tireman9]

On 9/18/2019 at 11:17 AM, wayne77590 said:

As you go higher or lower in altitude the pressure will increase or decrease 0.48 psi and the PSI will Increase/decrease 2.0 psi for every 10 degrees of temperature change.

Let's assume your max tire pressure is 110 psi and your minimum load weight pressure is 90 psi. A fudge factor of 10 psi would make the minimum load weight 100 psi.  If you go from sea level to 10,000 feet altitude you would raise 4.8 psi and with the 90 to 40 degree change in temperature you would drop 10 psi for an overall psi change of 5.2 psi.

With the fudge factor of 10 psi you would still be within your minimum required load pressure.  You can do the math for the inverse situation.  I always set my tire pressure between the max the tire allows and the minimum required for the load.  If you do not have the four corner weights then run max tire pressure allowed and be safe, only adjusting as needed when you get to your destination. There are other scenarios, I'll bet, and the closer the minimum and maximum tire pressures are, the less of a fudge factor is available.

Tireman9, Roger, please correct me if  this is not correct and I'll ask for the post to be removed.

Sounds good to me.