Correct tire pressure/load?

[wtbuck12]

Not sure if I'm figuring this correctly. I installed a set of Goodyear Endurance LHS 295/75R 22.5 load range H on my MH and am trying to figure pressure. The front axle weight is 10,420 lbs and the rear is 18,260. I figured 105 psi in the front and 95 psi in the rear should be a safe margin. Does that sound correct, if not what would be the correct pressures?

[richard5933]

See page #102 of this Goodyear publication for the load & inflation chart for your size tire:

https://www.goodyeartrucktires.com/pdf/resources/publications/2020_goodyear_commercial_tires_engineering_databook.pdf

Sounds like you may be inflating slightly higher than necessary based on the weights you listed.

[wtbuck12]

57 minutes ago, richard5933 said:

See page #102 of this Goodyear publication for the load & inflation chart for your size tire:

https://www.goodyeartrucktires.com/pdf/resources/publications/2020_goodyear_commercial_tires_engineering_databook.pdf

Sounds like you may be inflating slightly higher than necessary based on the weights you listed.

Thanks for the feedback, I was allowing 5 psi for a safety margin. Is that a bad idea?

[frank.bergamo]

Without weighing each individual corner, a 5 psi bump is a good idea. It allows for one side of the axle to be a little bit heavier and still not be under inflated. Hope this helps.

[wtbuck12]

14 minutes ago, frank.bergamo said:

Without weighing each individual corner, a 5 psi bump is a good idea. It allows for one side of the axle to be a little bit heavier and still not be under inflated. Hope this helps.

Thanks, that's what I was thinking. I would rather be over than under but not excessively. 

[richard5933]

A little over for a buffer is a good thing. Aside from allowing for temperature swings, it helps accommodate for side-to-side imbalance. On the other hand, over inflating tires too much can contribute to poor handling and poor braking.

[wtbuck12]

1 hour ago, richard5933 said:

A little over for a buffer is a good thing. Aside from allowing for temperature swings, it helps accommodate for side-to-side imbalance. On the other hand, over inflating tires too much can contribute to poor handling and poor braking.

Agree, thanks for your input. 

[rayin]

Tireman9  recommends a 10% safety margin. The NTSB says to use what the vehicle mfgr. recommends.Keep in mind running a tire at the  load/inflation minimum is running the tire at 100% capacity.

[wtbuck12]

5 hours ago, rayin said:

Tireman9  recommends a 10% safety margin. The NTSB says to use what the vehicle mfgr. recommends.Keep in mind running a tire at the  load/inflation minimum is running the tire at 100% capacity.

Thanks, guess that means I need to raise the pressure a little more.

[manholt]

I have found that what tireman recommends, is not written in stone!  It all depends on load and temp, nothing is constant and if your at 115 psi + 10% = 126.5 psi, that's 1.5 psi over the max cold tire pressure!  As you drive, your tire psi will increase, how much depends on several factures, but basically it's outside ambient temp, road surface temp, humidity...I use 5% in Summer and 7% in winter!  

My coach, when we are on the road, average weight is 63,500+/- lbs + toad.  I run 365/80/22.5 steer axel at 115 psi, 315/80 on drive at 100 psi and same on tag!  My liquid cap is 200 fuel, 140 fresh water (normally 80%), empty gray & blake (80/60). That is the tires that Spartan use on their K3 chassis!  My CCC is 71,000 lbs!

In 54 years and 18 Class A's, I've had 3 blowouts!  That was before radial tires and all 3 was front right.  

Edited November 2, 2020 by manholt

[wtbuck12]

38 minutes ago, manholt said:

I have found that what tireman recommends, is not written in stone!  It all depends on load and temp, nothing is constant and if your at 115 psi + 10% = 126.5 psi, that's 1.5 psi over the max cold tire pressure!  As you drive, your tire psi will increase, how much depends on several factures, but basically it's outside ambient temp, road surface temp, humidity...I use 5% in Summer and 7% in winter!  

My coach, when we are on the road, average weight is 63,500+/- lbs + toad.  I run 365/80/22.5 steer axel at 115 psi, 315/80 on drive at 100 psi and same on tag!  My liquid cap is 200 fuel, 140 fresh water (normally 80%), empty gray & blake (80/60). That is the tires that Spartan use on their K3 chassis!  My CCC is 71,000 lbs!

In 54 years and 18 Class A's, I've had 3 blowouts!  That was before radial tires and all 3 was front right.  

Thanks for your input. 

[richard5933]

As they used to say in grade school, always show your work. Here's mine:

Using tireman9's formula, I have calculated that the front tire pressure would be 95psi and the rear would be 90psi. How'd I get those numbers?

I took the axle weights and multiplied by 0.53 to get the axle end weights. This provides a 3% buffer to account for side-to-side variance. Then I split that number again to find the calculated wheel weight. I used the calculated wheel weight and the charts from the manufacturer to find the recommended tire pressure. I rounded UP to find this number. Then I added a 10% inflation buffer, which I rounded up since most gauges only show larger marking at increments of 5psi.

Anything higher wouldn't be justified by the numbers and will likely result in harsher ride and poorer handling. Of course, you'll need to tweak these numbers to suit your particular driving likes/dislikes.

Edited November 2, 2020 by richard5933

[wtbuck12]

1 hour ago, richard5933 said:

As they used to say in grade school, always show your work. Here's mine:

Using tireman9's formula, I have calculated that the front tire pressure would be 95psi and the rear would be 90psi. How'd I get those numbers?

I took the axle weights and multiplied by 0.53 to get the axle end weights. This provides a 3% buffer to account for side-to-side variance. Then I split that number again to find the calculated wheel weight. I used the calculated wheel weight and the charts from the manufacturer to find the recommended tire pressure. I rounded UP to find this number. Then I added a 10% inflation buffer, which I rounded up since most gauges only show larger marking at increments of 5psi.

Anything higher wouldn't be justified by the numbers and will likely result in harsher ride and poorer handling. Of course, you'll need to tweak these numbers to suit your particular driving likes/dislikes.

Those are the numbers I came up with originally. Then I to add a little langnape.LOL I will probably end up between the two numbers.  Thanks for you through presentation. 

[frank.bergamo]

Back to my original post, weighing each individual corner will give me the exact weight I need, to determine the proper tire inflation. With the coach fully loaded with water, fuel, supplies, and whatever else you may choose to haul down the road, you can get an accurate weight on each corner to come up with the proper PSI. Hope this helps.

[rayin]

5 hours ago, manholt said:

I have found that what tireman recommends, is not written in stone!  It all depends on load and temp, nothing is constant and if your at 115 psi + 10% = 126.5 psi, that's 1.5 psi over the max cold tire pressure!  As you drive, your tire psi will increase, how much depends on several factures, but basically it's outside ambient temp, road surface temp, humidity...I use 5% in Summer and 7% in winter!  

My coach, when we are on the road, average weight is 63,500+/- lbs + toad.  I run 365/80/22.5 steer axel at 115 psi, 315/80 on drive at 100 psi and same on tag!  My liquid cap is 200 fuel, 140 fresh water (normally 80%), empty gray & blake (80/60). That is the tires that Spartan use on their K3 chassis!  My CCC is 71,000 lbs!

In 54 years and 18 Class A's, I've had 3 blowouts!  That was before radial tires and all 3 was front right.  

Your CCC= cargo carrying capacity is 71,000lb???

[five]

I have weighed my coach, but only axles, unable to get corner weight.  I take the total axle weight, divide by two and select the next weight up from the weight listed in the chart for half the axle.  I use that weight plus 10 PSI as a fudge factor for side to side imbalance.

[jleamont]

While not accurate you can look over the coach floor plan and cargo and get some idea if there is an imbalance on a larger scale. Our coach is a good example of weight imbalance.

Drivers side

• Our slides are on the driver side only (2 slides).
• Kitchen is on the front slide, (=heavy)
• King size bed that lifts 
• Pull out bed/couch
• Spare tire in basement
• Of course, put me in the drivers seat now were leaning 

Passenger side

• couch
• dinette booth
• residential refrigerator
• restroom (sink and toilet)
• Vanity sink in bedroom
• clothes storage (dresser)
• I keep my tools under the dinette on this side to help a little 
• Gallon water storage under dinette (maybe 10 gallons)

 

Edited November 9, 2020 by jleamont

[tireman9]

On 11/2/2020 at 7:04 AM, richard5933 said:

As they used to say in grade school, always show your work. Here's mine:

Using tireman9's formula, I have calculated that the front tire pressure would be 95psi and the rear would be 90psi. How'd I get those numbers?

I took the axle weights and multiplied by 0.53 to get the axle end weights. This provides a 3% buffer to account for side-to-side variance. Then I split that number again to find the calculated wheel weight. I used the calculated wheel weight and the charts from the manufacturer to find the recommended tire pressure. I rounded UP to find this number. Then I added a 10% inflation buffer, which I rounded up since most gauges only show larger marking at increments of 5psi.

Anything higher wouldn't be justified by the numbers and will likely result in harsher ride and poorer handling. Of course, you'll need to tweak these numbers to suit your particular driving likes/dislikes.

I like your approach. Until you get actual individual tire position weights you should be good.