Tire pressure measuring and inflating.

[Kirk]

Thanks for all the recommendations.

As you can see, opinions vary and some members will try to argue over most anything. If you do get a compressor, be sure to check what the pressure is when it starts to operate for one that has a tank. (I prefer those with a tank as it expands things it can be used for.) If you get a tire inflator, then it is the max pressure that is critical but the cheaper ones take a very long time to fill a large motorhome tire and they usually fail pretty quickly with that heavy use. I would probably go with something like this DeWalt from Amazon or something similar. Because it can be some distance to an air source and very inconvenient, I have always used some type of portable compressor.

 

[NMDriver]

Chalk a line across the tire, drive a few miles. Check the line. If the center is missing, let out air, if the ends are missing, add air. Plus it will show alignment issues if only one side is erased by the road.

 

[Professor David]

I would probably go with something like this DeWalt from Amazon

I have this one and it works very well for class A tires. Very easy to use as Kirk writes. However, depends on the battery brand set up you currently have...I use DeWalt cordless tools....you may use a different brand I also have a bit larger compressor onboard now since I'll need to winterize when we make it back to snow country at the end of Feb.
AZ sunset last night.

 

[Gary RV_Wizard]

The tires are rated for a max of 110 PSI.

That's incorrect. Your tire is rated to carry its maximum load at that pressure, but it is NOT the maximum inflation allowed.

Once at the service center do I add 5 lbs to the 110 up to 115 and go over the max PSI rating of 110 for the tire?

Yes. You will NOT be exceeding any maximum. Note that if you had started out at 110 psi and then driven a ways, the psi would still have increased some amount and be above 110. That is normal operation that the tire engineers planned for. You would NOT let air out if you found the tire at 115 psi after driving a bit.

 

[Onyrlef]

The tire's max inflation is on the tire sidewall, not what someone on a forum thinks it might be.
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[Gary RV_Wizard]

The standard sidewall data for the larger truck tires used on most Class A coaches, e.g. 19.5" or 22.5" diameters, varies slightly from passenger car tires. The load and pressure information stipulates the Max Load the tire is rated to handle and the inflation pressure required to support that load.

 

[Onyrlef]

The max load and the max pressure to support that load on the sidewall is a clue as to the maximum amount of air you should ever be pumping into that tire. Notwithstanding having magical insight otherwise.

 

[Gary RV_Wizard]

The max load and the max pressure to support that load on the sidewall is a clue as to the maximum amount of air you should ever be pumping into that tire. Notwithstanding having magical insight otherwise.

Except for a few special situations which are usually cited in the tire makers guide, I agree it's the max you should ever want. And with the caveat that it's the max COLD pressure, not the max operating pressure.

 

[Onyrlef]

Except for a few special situations which are usually cited in the tire makers guide, I agree it's the max you should ever want. And with the caveat that it's the max COLD pressure, not the max operating pressure.

The max operating pressure….really? So what is that exactly and where is that listed so the op can reference it? Or on the other hand would it be practical to abide by what’s on the sidewall and leave the caveat to argument for arguments sake, but not of any other value.

 

[Laura & Charles]

I go by the manufacturer’s inflation chart. I’ve found the sidewall max pressure is way too high and causes really skittish handling.
Here’s Michelin’s table (but they’re all nearly identical).

https://www.rvtirepressure.com/assets/images/extrapages/Michelin_Rv_Load_Inflation.pdf

 

[Onyrlef]

I go by the manufacturer’s inflation chart. I’ve found the sidewall max pressure is way too high and causes really skittish handling.
Here’s Michelin’s table (but they’re all nearly identical).

https://www.rvtirepressure.com/assets/images/extrapages/Michelin_Rv_Load_Inflation.pdf

I also use the Michelin table, the max pressure on the sidewall is not the pressure the tire should be inflated to when cold only the maximum psi to which the tire should ever be inflated when cold. My 6 new 19.5" Michelin XZE's for example were inflated to 120lbs. all around by the installer. The reason being it was the max psi cold for which the tires were rated and perfectly safe and it covered all the bases. It's the vehicle operator's responsibilty thereafter to determine which tire pressure, under 120 is appropriate. I only went out the next morning and adjusted the psi in accordance with my scale wt. and the Michelin Table.

 

[Laura & Charles]

Agreed, installers and dealerships often inflate to the sidewall pressure as it is safe* and it’s a CYA thing.
*safe for the tire to not blow out or overheat. But the way our first coach handled with the front tires maxed out was anything but safe…quite the white knuckle experience until I learned and got her weighed.

Manufacturers have no idea what vehicle their tires are going to be installed on or what weight they’ll be carrying. Installers and dealerships have no idea how much stuff a customer is going to cram in. It HAS to be the end users’ responsibility to determine the proper psi and inflate to that.

 

[Onyrlef]

Agreed, installers and dealerships often inflate to the sidewall pressure as it is safe* and it’s a CYA thing.
*safe for the tire to not blow out or overheat. But the way our first coach handled with the front tires maxed out was anything but safe…quite the white knuckle experience until I learned and got her weighed.

Manufacturers have no idea what vehicle their tires are going to be installed on or what weight they’ll be carrying. Installers and dealerships have no idea how much stuff a customer is going to cram in. It HAS to be the end users’ responsibility to determine the proper psi and inflate to that.

I keep my front tires at the psi Michelin prescribes for the front axle weight, which is the minimum allowable. I don't subscribe to the self appointed internet tire engineers who parse out minimum with proper and lend interpretation to Michelin's intent. The proper psi is whatever produces the best handling and which is at or above the minimum on the table and at or below the maximum allowable on the tire sidewall.

 

[Larry N.]

But the way our first coach handled with the front tires maxed out was anything but safe…quite the white knuckle experience until I learned and got her weighed.

I had the same experience with my first class A, a Bounder. When I got the coach it was squirrely in steering, and there were a couple of bumps I hit on the road (not damaged road, just a poorly done joint under an overpass) that almost threw me out of control. It was also a handful when passing trucks and in crosswinds.

So after I discovered using manufacturer tables and weighing the coach, I dropped the front pressure by 10 psi, and a bit more in the rear, and the coach then handled pretty decently and the ride was even better. So I'm a believer. Also, on a DP I bought new (the Ventana) the tires were overinflated when I got the coach resulting in squirrely handling when on a highway with mild ruts (from traffic), and using the tables cured that problem, too.

So the tire makers certainly know what they are talking about, vs dealers and such who think the sidewall stamp is the only thing to use.

BTW, a number of years back I had a Ford Ranger 4WD pickup that I kept at 35 psi (also Ford's recommendation in the manual). A Grease Monkey I'd used for years inflated my tires to the max sidewall pressure (don't recall the figure), though I'd specified 35 psi all around. There was light snow at the time and, as you'd expect, it handled the snow just fine when I drove to the shop. But when I left after the service, it was squirrely, even in 4WD, so after a couple of blocks I went back to the shop. It was a chore to get them to set them back to 35 psi, with the manager insisting the sidewall stamp was the ONLY correct pressure. Once we got the change made, it handled normally again.

So correct pressure makes all the difference in any vehicle.

 

[Mountain high]

When I purchased my 35 inch Load Range E replacement tires for my 3/4 ton Ram 4x4 Power Wagon pickup the Discount Tire store put 80 PSI in all of them. I informed the manager who stated that all Ram 3/4 ton truck Load Range E tires are inflated to 80 PSI. I showed him the sidewall which clearly states Maximum Cold PSI of 65. He then stated that my 3/4 ton truck was designed for 80 PSI tires and so I had just purchased the wrong tires. I was going to be unsafe with less weight capacity tires. They'll have to remove them.

So I showed him the door pillar label which states for the factory installed OEM 33 inch tires it's 60 PSI front and 65 PSI rear. He then looked at the removed worn out OEM factory tires which were Load Range D tires with a maximum Cold PSI of 65 PSI with the same Load Capacity maximum weight rating as the new tires they had just installed. He finally agreed to release air in all the new tires down to 65 PSI, but not 60 PSI in front. I drove across the street and let some air out of the fronts since they couldn't let me do so on the property.

 

[Onyrlef]

When I purchased my 35 inch Load Range E replacement tires for my 3/4 ton Ram 4x4 Power Wagon pickup the Discount Tire store put 80 PSI in all of them. I informed the manager who stated that all Ram 3/4 ton truck Load Range E tires are inflated to 80 PSI. I showed him the sidewall which clearly states Maximum Cold PSI of 65. He then stated that my 3/4 ton truck was designed for 80 PSI tires and so I had just purchased the wrong tires. I was going to be unsafe with less weight capacity tires. They'll have to remove them.

So I showed him the door pillar label which states for the factory installed OEM 33 inch tires it's 60 PSI front and 65 PSI rear. He then looked at the removed worn out OEM factory tires which were Load Range D tires with a maximum Cold PSI of 65 PSI with the same Load Capacity maximum weight rating as the new tires they had just installed. He finally agreed to release air in all the new tires down to 65 PSI, but not 60 PSI in front. I drove across the street and let some air out of the fronts since they couldn't let me do so on the property.

My truck tires likewise list a max load xxx and a psi of 80 lbs on the sidewall for a single, but that’s not even close to the psi at which I run them. It’s only the psi required to support the max allowable wt. for which the tire is rated and is therefore the max psi. allowable for that tire.

 

[Gary RV_Wizard]

The max operating pressure….really? So what is that exactly and where is that listed so the op can reference it? Or on the other hand would it be practical to abide by what’s on the sidewall and leave the caveat to argument for arguments sake, but not of any other value.

That's was & is my point - the tire makers don't specify a max operating pressure and there is no reason to treat the numbers on the sidewall as being one. I don't think we are at odds on this.

 

[jadatis]

I also answered at the winebago topic, on your basic question.
There I assumed you determined your 105 psi cold with reserve.
In this topic about if 105 psi is wise., but you know best how you determined the 105 psi.

The 10 to 15% higher pressure as suggested, would mean, if 105 psi is lowest with no reserve, an advice of 115.5 psi to 121 psi cold pressure, wich is over the " maxcold" of 110 psi of your tires.

But then even I would fill that 115 psi. 110 is not the maximum allowed cold pressure, its the reference-pressure, as tiremakers call it.

In Europe, where I live, Continental groop tires often give both on sidewal, " maximum inflation pressure" ( = maxcold) 10 psi higher then reference-pressure.

And P-tires and european eqivalent, give only maxcold on sidewall of between 44 psi and 51 psi, and an ocacional XL/reinforced/extraload even 60 psi.
Reference pressure is always 35 or 36 psi for standard load, and XL 41 or 42 psi.

And teststandard of tires is that a new undamaged tire must stand a pressure of 2 to 3 times the reference-pressure.

This would mean for your 110 psi reference pressure tire, that it must stand a warm pressure of 220 psi even.
This would cover a 40% higher filled pressure cold at freesing point of 32 degr F, so 154 psi, and when incidentially tire inside temp goes to boiling point so 212 degr F, pressure goes to 220 psi, so yust within the limit of 2x reference.
Extreme example, but shows that even 10 to 20 psi higher filled cold would be safe ( if tire is not already damaged by using to low pressure for load and speed, only once) .

 

[Tulecreeper]

My guess is, your manual reads the way it does BECAUSE of the TPMS and the fact it would sound warnings if you lowered the pressure to what it should be when unloaded. Its a catch 22 for the manual writers. Either put the correct info in the manual telling you to adjust the pressure depending on loading, and then have customers complaining that they cannot because of the TPMS warnings, or tell you to leave the pressure high, so the TPMS will not sound warnings, but have the truck ride like a lumber wagon most of the time.

My pressure placard calls for the front pressure to be 54 psi, which is about correct for the max weight on the front end for the tires I have. I'm sure your front end is quite a bit lighter, and am surprised that such a high pressure is called for.

Charles

The actual Base Weight on my front is 3400, and 2600 on the rear. I have Firestone Transforce HT 245/70R17E as my OEM tires. Going by the Firestone Inflation Chart for that size tire, I should actually be running 65 in the rear and 80 in the front. But because these are the "E" rated tires, the chart shows that those parameters change to 80 for both front and back.

 

[CharlesinGA]

The actual Base Weight on my front is 3400, and 2600 on the rear. I have Firestone Transforce HT 245/70R17E as my OEM tires. Going by the Firestone Inflation Chart for that size tire, I should actually be running 65 in the rear and 80 in the front. But because these are the "E" rated tires, the chart shows that those parameters change to 80 for both front and back.

You are the second person I've encountered that read these charts the same, incorrect way. The other was a fellow on the Bigfoot Owners Club Forum, who insisted the same thing, because it was a load range E trailer tire then the only pressure you could use was the one with the (E) in the box.

That base weight is AXLE weight. You tires each support HALF of that weight, so a 3400lb base axle weight is 1700 PER TIRE which would be 35+ psi.

How it works is you scale the axle, and then take half of that (for one tire), and read across the chart for your ½axle/1tire weight, as determined by the scale and use the tire pressure at the top of that column (nearest higher or extrapolate). The letters (C), (D), (E) are used to denote the HIGHEST pressure (and weight) allowed for that load range tire. If your truck's rear axle, for instance, on a CAT scale, reads 4800 lbs, you would take the weight on ONE tire, 2400 lbs, and inflate that tire to 60 psi. If by chance, you had Load Range C tires instead, you would be limited to 2205 lbs and 50 psi, as that is the max for that tire, but on any Load Range tire, there is nothing keeping you from lowering the pressure at lower weights (except for your TPMS systems warning system).

The way you are reading it, there would only be three columns, 50 psi, 65 psi and 80 psi and the rest would not even exist.

These are standard charts used all across the tire industry. ANY brand of tire of that specific size and load range, is designed to carry the same weights at the same pressures, no matter the brand.

My truck, the last time I scaled it was 4060 on the front axle, thus 2030 lbs PER TIRE and I have the same size tire you have, So I should be running 45+ per tire. Dodge has 55 psi on my door placard which is based on the Gross Axle Weight Rating FRONT of 4630 which is 2315 per tire which is exactly 55 psi on the chart. My GAWR REAR is 6000, or 3000 per tire which is 80 psi. I keep the front at about 52 psi and the rear usually stays at 70 psi.

Charles