Tire pressure

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alrod013

alrod013

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Jul 18, 2010
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On the move!!
Just took delivery of a 2004 Itasca Horizon 40AD.  On our way back to old house to pick up rest of stuff. Kind of confused and concerned about proper tire pressures for this trip. RV is not fully loaded yet, and has not been weighed. Weight will change once we get it all loaded up. We are running on BF Goodrich 275/80/22.5 tires with a max psi rating on the sidewall of 110 at max load. What tire pressure should I use for this trip? Right now, each one has about 100 psi. We are towing a 2004 GMC Canyon. Have asked around at the RV parks we have stayed at so far, and of course have gotten many different answers. Being a newbie, I am rather paranoid about losing a tire!!!
 
I'm having trouble finding an inflation table for Goodrich tires, but since you haven't loaded the RV yet, you're certainly well under the gross axle weight ratings so the 100psi should be fine until you can weigh it and get the correct pressures from an inflation table.

Whether you're towing or not won't change the required inflation pressures.
 
If you max load the axles then you should air up the fronts to 100 psi and the rears to 90 psi per the Goodyear chart for 275/80/22.5 tires. 

On my coach we are running 285/75/22.5 and with our axel weights we use 95 front and 85 rear.
 
I wouldn't use the Goodyear inflation tables for Goodrich tires.
 
There should be a wall sticker to the left of the driver's seat and your tires, GVWR and tire pressures (what the pressures should be if the coach weight was as high as the GVWR) should be listed there. Those pressures would be what you should use until you get the coach weighed in travel mode, then you could reduce the pressures to what the charts call for.

I am running the same size Michelins (owns BFG) and use 100-105#s in the front and 85-90#s in the rear based on my 30k travel weight, but you shouldn't go by that until you have the coach weighed and gotten the BFG pressure tables.
 
Inflation pressures for your size tire can be found in the Goodrich Commercial Tire Reference Chart at

http://www.bfgoodrichtrucktires.com/assets/pdf/BFG_Reference_Chart.pdf


or in the 2011 Goodrich Truck Tire Data Book at
http://www.bfgoodrichtrucktires.com/assets/pdf/BFGTruckDataBook_Jan2011.pdf

Goodrich tables shows weight per axle rather than per tire, and 100 psi in your 275/80's is good for 11,500 lbs on a single axle and 21,040 on a dual. That should be plenty for your coach as long as you have not exceeded the axle maximums.
 
Gary, thanks for finding those Goodrich files.  I now have them stored locally for reference, along with the other tire manufacturer charts.
 
Hi,
Just a random comment. The above recommendations are accurate and good to follow. However, you need to be aware that you'll almost never manage them (w/in +/- 5 PSI because the ambient temperature changes too much. example:
I'm in Ft Myers FL and just adjusted my tires (an annual process usually) to the recommended PSI. Did it about 10:00 AM a few days ago (I shaded the tires that morning). Since I have a TPMS, I connected it to check for leaks (monitors are bad about that). First time I checked, the tires were five PSI high on one side; the sun was out! Later at mid afternoon on the same day, all tires were high by up to 12 PSI; temperature rise plus sun on one side. This morning all were low by up to 8 PSI at 8:00 AM (cool, rainy night).
Why? Because tire pressure changes by about 1 PSI per 2 degrees F. Without moving my MH, I see changes from 70 PSI or lower to as high as 90+ PSI. On the road, you'll see as much as another 15 PSI increase (saw +20 once).
Don't stress out too much, just get them reasonably close!
Ernie
 
Why? Because tire pressure changes by about 1 PSI per 2 degrees F.
Click to expand...

You need to check your data, Ernie. Tire pressures don't change that much with heat. According to Charles Law of Gasses, it's 1.8% of change per 10 degrees F., which for a tire at 100 psi means 1.8 lbs of psi change for every 10 degrees.

I wonder if you may have mis-copied some passenger car data. The rule of thumb for passenger car tires (about 30 psi) is 0.5 psi per 10 degrees, which is 0.1 per 2 degrees. That number is no good for most RV tires, which typically carry much higher pressures.
 
From time to time on this web site I have read comments about this same subject. Everyone is entitled to their opinion.
For over 50 years, as a Cattle Rancher, with two ranches,  with hundreds of tires on Farm/Ranch machinery and equipment, Hundreds of tires on Semi Trucks, hundreds of tires on autos and light trucks, I and my employees have always used the pressure recomendations imprinted on the tire sidewalls all of these years. We have never have any problem doing it this way.
 
Will.
The "recommendation" on the sidewall is the pressure needed for the maximum tire load carrying capacity. It says so right on the sidewall. That's fine if you carry that much actual weight from time to time, but can cause an unnecessarily harsh ride if greater than needed for the actual weight. In extreme cases it can cause steering and handling problems or uneven tire wear.

That said, it is the safest psi to use if you do not have solid justification for a lesser pressure.
 
By going from the 90 psi all around (max on vehicle placard) that the dealer started me with on my Bounder, to the Michelin-recommended 70 psi front, 80 psi rear for my actual weight, I improved the handling considerably, as well as the ride, no longer bouncing like a kangaroo at certain road anomalies and eliminating the squirrelly steering, among other things. I also once had a a shop which insisted that the max on the sidewall (45 psi) on my 4WD Ranger pickup was proper (and set it that way, unbeknownst to me) on a snowy day, instead of the 35 psi I normally used. I didn't get a block away before I had to go back to get the pressure set right (we had quite an argument), since I had trouble in the light snow. Needless to say, I've not been back there.
 
Interesting issue. The tire expert at the Escapees' seminar said to run at the tire manufacturer's chart pressure for the weight on the highest-loaded tire on that axle. The Les Schwab expert in Junction City said to run at the pressure on the coach manufacturer's chart. Escapees guy said that's because of legalities, Les Schwab said that's because of safety and factors other than just weight that can affect tires -- presumably road hazards, handling, etc.
 
The pressure on the manufacturers label is only valid for the OEM tires.  If you change tire size, or even brand, the required pressure may change.  And the manufacturers label assumes each axle at GAWR, not always true.  Always use the chart for the make and model tires on the axle.  And, yes, use the pressure for the most heavily loaded tire on any given axle.
 
I think most tire shops will give you the same answer as Les Schwab, tho some will insist on the sidewall pressure, the worst choice. That is the safe answer and they can give the same answer to all customers. In addition, the tire store didn't weigh your coach and probably doesn't have the load charts anyways. When my coach is serviced or tires replaced, I always tell them what pressures I want and make sure that is what they are inflated to.
 
Gary,
are right; my mistake (and not much excuse, I make/made my living with rubber). I'm using the temperature from the monitors and it apparently is not close. The numbers I cited were at least close to what I actually see. I had the TPMS go crazy (turns on occasionally for a few seconds; otherwise seems normal - I'd assumed a bad ground to the LCD, but who knows) on the trip from Ft. Myers to Destiny Saturday, so maybe the msmt. is screwed up as well.
My Bad! Head hanging!
Ernie
 
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