Age old question tire pressure?

[Lakeman1]

Originally Posted by bentjm

Every placard I have ever seen just mirrors the maximum pressures listed for the tires that came originally on the coach.

The manufacturers of commercial tires publish weight/pressure tables for a reason.

The max pressure in the sidewalls of my Toyo m144 295/80 22.5 tires is 120 psi. Based on the weights via Cat Scales of my coach, I run 83 in the drive tires and 98 in the steers.

Running 120 psi in all six would result in a horrible ride and weird tread wear patterns.

The PSI listed on the sidewall is the max for that tire at it's max load. My place Card is for my coach loaded to it's max load (gross vehicle weight). At the scales I am at 22,500 with 9,000 front and 13,500 rear. I run 95 front and 85 rear.

[bentjm]

Originally Posted by Lakeman1

The PSI listed on the sidewall is the max for that tire at it's max load. My place Card is for my coach loaded to it's max load (gross vehicle weight). At the scales I am at 22,500 with 9,000 front and 13,500 rear. I run 95 front and 85 rear.

Apparently, in the early to mid 2000s, Newmar did not bother doing that. My placard says 120 psi for all tires. 120 psi is way high even at max weight - especially at the rear.

[Alan_Hepburn]

Originally Posted by Lakeman1

The PSI listed on the sidewall is the max for that tire at it's max load.

Actually, the sidewall pressure states it is the MINIMUM pressure required to carry the MAXIMUM weight...

[Tireman9]

I see that no one has objected to my advice.

[Crasher]

Originally Posted by Tireman9

I see that no one has objected to my advice.

No reason to object, as your suggestions are always right on money. One question I have had is the added 10% "for safety". Is the tire any safer above the recommended psi to carry the load, or it is a "convenience factor" to avoid having to "chase" the pressures due to ambient changes?

[bentjm]

Originally Posted by Tireman9

I see that no one has objected to my advice.

I collected some data today:

New Toyo m144 295/80 22.5 tires.

As posted earlier, 125 psi max on the sidewall (I posted 120 psi - that is what I get for reading them in the dark). Based on my weights from Cat Scales when I was running heavy - full fuel, full fresh water, and all the other crap in the basement - with a 5% safety margin I run 98 psi cold in the front and 83 psi cold in the rears based on Toyo's charts.

After running 120 miles today in mid-60s, sunny weather, I pulled off and checked pressures and temps.

Fronts were at 120 degrees and 115 psi. Outside rears were at 100 degrees and 95 psi. Inside rears were at 115 degrees and 99 psi.

What does all that mean? I really don't know.

[Crasher]

It means your tires are operating normally and as designed. All tires on any vehicle will heat up from rolling resistance. A 12-15% increase is normal for a loaded 22.5" tire.

[jadatis]

Originally Posted by bentjm

I collected some data today:

New Toyo m144 295/80 22.5 tires.

As posted earlier, 125 psi max on the sidewall (I posted 120 psi - that is what I get for reading them in the dark). Based on my weights from Cat Scales when I was running heavy - full fuel, full fresh water, and all the other crap in the basement - with a 5% safety margin I run 98 psi cold in the front and 83 psi cold in the rears based on Toyo's charts.

After running 120 miles today in mid-60s, sunny weather, I pulled off and checked pressures and temps.

Fronts were at 120 degrees and 115 psi. Outside rears were at 100 degrees and 95 psi. Inside rears were at 115 degrees and 99 psi.

What does all that mean? I really don't know.

Front 98psi filled at an average ambiënt temp of 65 degrF, and rising to 115 psi gives 144 degrF in tire, and not120 degrF.
So, or you have External tmps sensors or you used a heatgun, wich measures the outside of tire.
Then try to aim at the rimm. Wich transports the heat of inside tire air ( or whatever gascompound) better to outside, so probably closer.

This 144 degrF is when driving in the mids 60 ( degrF? ) , and no external factors, to my conclusions , on the hot side.

Can get lower if you use higher pressure.

How did you determine the goal-pressures?

To complete my post
Rear 83psi at 65 degr filled.
95 psi / 129 degrF. Measured 100 degrF
99psi/ 151 degrF measured 115 degrF.

So give me the weights, and I will calculate an advice pressure for you. Think it will be higher.

[intercept]

Your temps and pressures are right on the money. I have monitors on all the tires including the toad. I see exactly the % increases you see.

There is one interesting note: You will find the rear insides especially the right side will be higher in temps and pressure after running crowned roads. The crown takes off some of the loaded contact on the crown. some country roads can vary 5 to 8 psi and degrees. Just an PIA thought

The toad right front is always hotter and higher by 5 to 10% than the MH tires of which the dealer says is due to the uneven drag imposed by the FWD of the car differential.

[bentjm]

Originally Posted by jadatis

Front 98psi filled at an average ambiënt temp of 65 degrF, and rising to 115 psi gives 144 degrF in tire, and not120 degrF.
So, or you have External tmps sensors or you used a heatgun, wich measures the outside of tire.
Then try to aim at the rimm. Wich transports the heat of inside tire air ( or whatever gascompound) better to outside, so probably closer.

This 144 degrF is when driving in the mids 60 ( degrF? ) , and no external factors, to my conclusions , on the hot side.

Can get lower if you use higher pressure.

How did you determine the goal-pressures?

To complete my post
Rear 83psi at 65 degr filled.
95 psi / 129 degrF. Measured 100 degrF
99psi/ 151 degrF measured 115 degrF.

So give me the weights, and I will calculate an advice pressure for you. Think it will be higher.

I used a laser thermometer..

The pressures came from Toyo's chart.

The tires were checked and filled at 50 degrees.

My coach weighed at 13,040 front and 19,960 rear on the Cat scales.

[Crasher]

Originally Posted by bentjm

I used a laser thermometer..

The pressures came from Toyo's chart.

The tires were checked and filled at 50 degrees.

My coach weighed at 13,040 front and 19,960 rear on the Cat scales.

I generally set my pressures at the load inflation recommended amounts plus 5-8 psi more, at "65 degrees". That gives me a safe pressure down to 30-35 degrees (tires lose 2% per 10 degrees) and up to 100 degrees. Once set to those pressures, I may have to adjust pressures once a year.

[jadatis]

Originally Posted by bentjm

I used a laser thermometer..

The pressures came from Toyo's chart.

The tires were checked and filled at 50 degrees.

My coach weighed at 13,040 front and 19,960 rear on the Cat scales.

Then recalc.
Fr 98 psi at 50 degrF / 115psi at 127 degrF.
Rear out 83psi at 50 degrF / 95psi at 113 degrF
Rear inner 83psi etc / 99 psi at 133psi.

I once estimated temp in tire when outside temp 68 degr F , to be allowed 140 degrF, but colder always better.
So these temps are within the limmits.

Filled in in my made pressure calculator your weights and Load-index 144/140 at 120 psi
But correct me if wrong

Gave high front so first I Will google your tire to see if loadindex is higher. That answer in nex post.

Could still edit:
Toyo list gave LI 152/148 for 295/80R 22.5 at 120 psi
Then gave Front 110 psi, and rear 94 psi.
So about 10 psi higher. And this is for 75 or 81 mph, is L or M speedrated.
So comfort and gripp still acceptable with these pressures, to my conclusions in time .

Calculated with my determined extra safe formula, wich gives higher pressure then the official lists, and 10% reserve added to your given loads.

The outer rear need also the 94psi ( make it 95psi) , if you would keep them lower, they dont lift up the inner tires, so more weight shifts to the inner tires. But OK all tires on the axles must have same pressure.
But you might think, outer are not that hot, so dont need the higher pressure

[Tireman9]

Originally Posted by bentjm

I collected some data today:

New Toyo m144 295/80 22.5 tires.

As posted earlier, 125 psi max on the sidewall (I posted 120 psi - that is what I get for reading them in the dark). Based on my weights from Cat Scales when I was running heavy - full fuel, full fresh water, and all the other crap in the basement - with a 5% safety margin I run 98 psi cold in the front and 83 psi cold in the rears based on Toyo's charts.

After running 120 miles today in mid-60s, sunny weather, I pulled off and checked pressures and temps.

Fronts were at 120 degrees and 115 psi. Outside rears were at 100 degrees and 95 psi. Inside rears were at 115 degrees and 99 psi.

What does all that mean? I really don't know.

What it means is that things are normal.

[Tireman9]

Originally Posted by Crasher

No reason to object, as your suggestions are always right on money. One question I have had is the added 10% "for safety". Is the tire any safer above the recommended psi to carry the load, or it is a "convenience factor" to avoid having to "chase" the pressures due to ambient changes?

More of a convenience factor