Tire pressure

[ga traveler]

Originally Posted by 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

#1 the higher pressure you use the less rolling resistance. Slightly more miles per gallon. ( i do mean slightly) Also a little less heat in the tire. A tire will flex in the sidewall every time it goes around. The more pressure the less flex. #2 at 65 psi you will get a softer ride. There is a big misunderstanding about the tag at the drivers seat. Some people think it is a generic tag for all motorhomes. If you look on the tag you will see the vin for your motorhome. That tag is for your motorhome and only your motorhome. You will also see that it says the press is for the max weight front and rear. That means you can run that pressure at max. weight of your motorhome.

[Mr_D]

Originally Posted by ga traveler

#1 the higher pressure you use the less rolling resistance. Slightly more miles per gallon. ( i do mean slightly) Also a little less heat in the tire. A tire will flex in the sidewall every time it goes around. The more pressure the less flex. #2 at 65 psi you will get a softer ride. There is a big misunderstanding about the tag at the drivers seat. Some people think it is a generic tag for all motorhomes. If you look on the tag you will see the vin for your motorhome. That tag is for your motorhome and only your motorhome. You will also see that it says the press is for the max weight front and rear. That means you can run that pressure at max. weight of your motorhome.

The only time the weight sticker should be followed is if you've weighed the rig and are at the max GAWR, OR you haven't bothered to weigh the rig yet.

According to the tire manufacturers a tire3 run at a higher pressure than required by their charts will wear out sooner (not a problem for most RV owners), has less contact patch so less traction/braking force and be MORE susceptible to impact damage from curbs, potholes, etc.

[W4MBG]

the tire pressure molded into the sidewall of the tire is the MAXIMUM pressure the tire is rated to hold when carrying the tire's MAXIMUM rated weight. yes, the charts show the MINIMUM pressure for the listed weights, but you may not go higher than the sidewall pressure. otherwise, people would hook up nitrogen bottles and stuff 1800 psi into their tires to get better fuel mileage. hmmmmm, there's an idea... not.

[PHESPE]

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.

" ......Tires are built to a max load standard, and that rating is at their max COLD pressure.... "

Except the pressure IS NOT the "max COLD pressure." It is the pressure for the MAXIMUM Load.

Look at the side walls of your tires to see where the word "maximum" is used.

It's not in front of the Pressure marking

PHESPE

[Mr_D]

Originally Posted by W4MBG

the tire pressure molded into the sidewall of the tire is the MAXIMUM pressure the tire is rated to hold when carrying the tire's MAXIMUM rated weight. yes, the charts show the MINIMUM pressure for the listed weights, but you may not go higher than the sidewall pressure. otherwise, people would hook up nitrogen bottles and stuff 1800 psi into their tires to get better fuel mileage. hmmmmm, there's an idea... not.

Wrong

As I posted in post #9 !

On truck/MH tires it is the MINIMUM pressure required to support the MAXIMUM rating of the tire.

On car tires it is the maximum cold pressure the tire should have.

[deanjeep]

Your wheels are also rated for a maximum pressure. On mine it is 120psi. The tire is rated for higher than that but you should not exceed the max allowed by your wheel.

[Mr_D]

Originally Posted by deanjeep

Your wheels are also rated for a maximum pressure. On mine it is 120psi. The tire is rated for higher than that but you should not exceed the max allowed by your wheel.

Also true. Our 275/70's were rated for 131 psi, wheels for only 120.

According to the tire's weight chart we needed 125 psi, but the wheels were only rated for 120. Michelin gave us a letter that stated we could use the 125 psi rating with 120 psi in the tires. We ran them that way for over 30,000 miles with no trouble.

[deanjeep]

Generally speaking, most tires that you have on your coach are going to be rated to carry more weight than your coach actually weighs. They are also likely rated to carry more weight than your axles are rated for. Do yourself a favor and get your coach weighed and then go off of the tire manufactures inflation table. Most of this talk of max air pressure is irrelevant because Max pressure is likely too much pressure in coach applications. Correct inflation is what you want.

[wa8yxm]

Originally Posted by Monacoach

What are these numbers?


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

Question: How can the factory know how heavy YOU are going to load your trailer or motor home?

Answer: Call the Physic Hotline perhaps?

Thus, it is either Empty, or a GUESS, (They Guess the loaded weight). which, save for the explanation of Guess, is what I said and you are arguing with.

Oh, they could go with "Loaded to the max" but that.. is still a GUESS.

The only way to know for sure the proper pressure is to scale the rig.

[jabfado]

Leave them at 90 PSI and go enjoy yourself.

[Monacoach]

Quote:
Originally Posted by Monacoach
What are these numbers?


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










Question: How can the factory know how heavy YOU are going to load your trailer or motor home?

Answer: Call the Physic Hotline perhaps?

Thus, it is either Empty, or a GUESS, (They Guess the loaded weight). which, save for the explanation of Guess, is what I said and you are arguing with.

Oh, they could go with "Loaded to the max" but that.. is still a GUESS.

The only way to know for sure the proper pressure is to scale the

What the manufacturer is doing is posting the gvwr of your motorhome and then looking at the tire chart and posting the recommended psi based on the gvwr. There is no guessing. And you are right the best thing is to weigh your coach and then look at the chart. I weighed our coach today and the result was 4000 lbs below gvwr.

[Wayne M]

The tire will state: "xxxx lbs @ 110 psi" that is the maximum load that the tire can withstand at maximum weight. There will be one for dual mode also. AS Monacoach pointed out, the placard is based on the maximum GVWR. If you weigh less, the psi will be less.

If weight is unknown it will not hurt the tire to run it at the maximum pressure as indicated on the tire sidewall. Just be sure to check it daily and adjust for altitude and temperature changes if you are running at the max sidewall pressure.

Happy trails.

p.s., look at Roger Marble's posts and his blog for good sound information.

[Monacoach]

Our coach fully loaded to gvwr requires 100 psi in the front and 85 in the rear.. the tires are marked 120 psi..... it would be insane to inflate these tires to 120..... I run the fronts at 90 and the rears at 85..... and thats with a 5 lb buffer.... sorry if I sound like a no it all but I would never set tires at the sidewall stamped max..

[zzjea]

We are camping now north of Houston at Double Lake National Recreational Campground. There is a truck stop on our way home and I will weigh there as I saw they had a scale.

Thanks for the info.

Our rig runs fine with 90psi but I want to be close to recommendations whatever they are.

John