Tire pressure

[zzjea]

I have 225/70R19.5 tires (8) on a 36' Dolphin. They were installed new in 03/2011 when I bought it.

The sticker on the inside of the coach says psi should be 65psi.

The printed psi on the tires is 110psi.

They were filled at 90psi and I have been running them at that pressure for almost a year but less than a 1000 miles.

What would the proper psi be for 19,500 lbs GVWR?

[Tha_Rooster]

Just a guess 85 to 90 no way to tell exactly with out weight.

[freebirdbus]

ALL tires have a max PSI and a max load rating molded into the sidewall. Look at your passenger car tires, it is there also. Tires are built to a max load standard, and that rating is at their max COLD pressure. Vehicle manufactures then spec a PSI for that tire's position on the vehicle. Front vs rear PSI based on the weight load on that axle/tire combination. Most vehicle manufactures also spec the change (increase) in PSI if you carry an additional load. I can explain more if you are interested. The most important thing is to have enough air in the tire COLD, check them often, and never let air out of a hot tire, pressure increases with temp, that is normal.

[Monacoach]

What would the proper psi be for 19,500 lbs GVWR?

What you need is your front and rear axle gvw ratings which will also be posted inside your coach. If you post those figures we can easily suggest a psi based on the tire charts. However your manufacturer will have posted in your coach the suggested psi based on the gross weight of your vehicle which is most likely the 65 psi that you mentioned. If you would like to run at a lower psi you would have to weigh all four corners, take the highest weight of each axle and then look at the chart.

[zzjea]

I have ordered a TPMS system from Truck Systems and need to determine best tire pressure to use and program in the system.

Thanks for the feedback.

[zzjea]

5500 front and 4500 rear.

[freebirdbus]

You can run a pressure higher than the one that the vehicle manufacture recommends, but never run a lower pressure! That can lead to a sudden tire failure!

[jzick]

The only way to know what air pressure to run is to load the unit for travel and have it weighed on four corners. You can then go to the tire manufacturer's web site and find the pressure tables. This will tell you what pressures to use. Without weights you are just guessing.

[Mr_D]

Originally Posted by freebirdbus

ALL tires have a max PSI and a max load rating molded into the sidewall. Look at your passenger car tires, it is there also. Tires are built to a max load standard, and that rating is at their max COLD pressure. Vehicle manufactures then spec a PSI for that tire's position on the vehicle. Front vs rear PSI based on the weight load on that axle/tire combination. Most vehicle manufactures also spec the change (increase) in PSI if you carry an additional load. I can explain more if you are interested. The most important thing is to have enough air in the tire COLD, check them often, and never let air out of a hot tire, pressure increases with temp, that is normal.

On truck tires the pressure on the sidewalls is the MINIMUM pressure to support the MAXIMUM carrying capacity of the tire, it is NOT the maximum the tire should ever have like a car tire.

From page 2 of the 06/07 Michelin RV Tire Guide: "If you look at the tire's sidewall, you'll see the maximum load capacity allowed for the size tire and load rating, and the minimum cold air inflation needed to carry the maximum load."

From page 6 of the GoodYear RV Tire and Care Guide
"How much air is enough?
The proper air inflation for your tires depends on how much your fully loaded RV or trailer weighs. Look at the sidewall of your RV tire and you’ll see the maximum load capacity for the tire size and load rating, as well as the minimum cold air inflation, needed to carry that maximum load."

[zzjea]

The tires are:

BFGoodrich
225/70R19.5 ST230™ LRG

Loads per axle
psi kPa lbs. kg.
Single Dual Single Dual

65 450 5510 10400 2500 4720
70 480 5790 10880 2620 4920
75 520 6080 11440 2760 5200
80 550 6390 12000 2900 5440
85 590 6630 12460 3000 5640
90 620 6900 12980 3140 5880
95 660 7280 13660 3300 6200
100 690 7430 13960 3380 6320
105 720 7690 14460 3480 6560
110 760 7940 15000 3600 6800

Max Load & Pressure on Sidewall
110 psi 110 psi 760 kPa 760 kPa
3970 3750 1800 1700

This is a chart from a dealer's website for this tire. I tried to format it to read easier but this forum editor won't keep it when I review it and I assume post it.

It looks like I'm way over the recommended psi of 65 for my weight at 90psi.

1. What pros or cons to keeping it around 90 psi?

2. What pros or cons to setting it >= the 65 psi?

Thanks John

[wa8yxm]

Pressure on sticker is with the unit empty or at best an estimate
Pressure on tire clearly says it is the maximum pressure the tire is rated at when cold

To find the proper pressure go to the tire maker's web site and download the pressure chart for your tire or you can try RV Safety, Merritt Island, Florida they have links to most tire makers inflation pages there, may be easier

[Monacoach]

5500 front and 4500 rear

What are these numbers?

Pressure on sticker is with the unit empty or at best an estimate

I disagree. PSI on sticker is for unit fully loaded ( GVWR) they post the gvwr and stamp the psi right next to it.

[Billieg]

Originally Posted by Mr_D

On truck tires the pressure on the sidewalls is the MINIMUM pressure to support the MAXIMUM carrying capacity of the tire, it is NOT the maximum the tire should ever have like a car tire.

From page 2 of the 06/07 Michelin RV Tire Guide: "If you look at the tire's sidewall, you'll see the maximum load capacity allowed for the size tire and load rating, and the minimum cold air inflation needed to carry the maximum load."

From page 6 of the GoodYear RV Tire and Care Guide
"How much air is enough?
The proper air inflation for your tires depends on how much your fully loaded RV or trailer weighs. Look at the sidewall of your RV tire and you’ll see the maximum load capacity for the tire size and load rating, as well as the minimum cold air inflation, needed to carry that maximum load."

First post to point out the truth, first post to be right on target. The sidewall pressure is the minimum pressure needed to hold the maximum weight. If you have less than the maximum weight on the tires you may lower the pressure. So as some others said, weigh your coach and determine what pressure you need from the manufactures site.

[Crabby Mike]

Originally Posted by Billieg

First post to point out the truth, first post to be right on target. The sidewall pressure is the minimum pressure needed to hold the maximum weight. If you have less than the maximum weight on the tires you may lower the pressure. So as some others said, weigh your coach and determine what pressure you need from the manufactures site.

Right, but ... as a practical matter, since you can't (or certainly shouldn't) add more load beyond the maximum capacity, there is no reason to add more air pressure either. (Unless you like riding on "Fred Flintstone" tires, i.e. "rocks.") Thus, the sidewall pressure shown is effectively the maximum cold pressure you would ever need in that tire.

But yes, the best pressure is that calculated by weighing the coach at each wheel, and setting pressures accordingly using the tire manufacturer's load/pressure tables. And, of course, using the same air pressure for both sides of any given axle.