The proper inflation pressure of Light Truck (LT) tires, Specialty Trailer Tires (ST) and RV/Bus Tires (motorhomes) is based on the load they are carrying.  The exact proper pressure per the tire manufacturer load/inflation tables can't be known unless the truck/trailer (or motorhome) is weighed wheel-by-wheel to know what load the tires are carrying.

The tires on each axle are then set to the necessary pressure required to carry the heaviest load on whichever end of the axle is heaviest.

Also, tire manufacturers recommend setting the air pressure with a safety cushion of 250 - 500 pounds per wheel position based on the load/inflation tables.

"Having said all of the above, trailer tires are normally an exception. Because trailers “squirm” creating significant lateral loading in the tires, it is recommended that they be run at sidewall pressure, unless trying to resolve a ride quality problem."  - RV Safety & Education Foundation

So, unless you have trailer tires that are rated significantly higher than the load you are carrying, which yours probably are not (I believe you have E load range tires), run the max sidewall pressure of 80 psi on the trailer tires. 

As for the truck, yes center wear indicates over inflation.  Just be aware that "over inflation" refers to the tires having too much inflation for the load they are carrying.  "Gross over inflation" means the tires are inflated over the maximum recommended pressure on the sidewalls.

The placards/labels on the door jamb are a guideline for Light Truck (LT) tires.  But without weighing the truck with the trailer to determine what the actual loads are, you don't know the proper inflation of the tires.  Under inflation (not enough psi for the load) is worse for the tires than over inflation by the same percentage, so until you can get weighed, don't go too low on the truck tire psi. 

At any rate, your tires should be lasting much longer than six months even if over inflated at the max sidewall pressure.

Linda & I have partnered with the RV Safety & Education Foundation (RVSEF) which is the most respected source in the industry when it comes to RV tires.  The Executive Director, Walter Cannon, has been doing this for years and he has access to RV tire engineers and tons of data.

The above information is why RVSEF promotes and offers wheel-by-wheel RV weighing services and why we have partnered with RVSEF to offer the weighing service as well.

For more information including some Frequently Asked Questions and where to get your RV weighed, you can go to our RV Weighing page. 

Congrats on your dedication to being safe.  Attitude is a huge part of RVing safely.   

Jack Mayer wrote:

---

I think it needs to be stressed that the max sidewall pressure should only be run on tires that are fairly heavily loaded relative to their rating. . . . also, some tires - like for example the Goodyear G114's that I run, and Howard runs, are so far over-rated that running max pressure is not required or even desireable.

---

 

Jack’s brief comments are VERY important.  Like Jack and Howard, I run G114’s which are far over rated for my 5’ers weighed loading.  I run them just a bit above the Goodyear specifications for weight vs. inflation ratings which is about the 250 lbs “extra” that Howard commented on.  The results have been outstanding as to mileage,  trailer “comfort” and satisfaction that I have lots of headroom = saftey.

This could become a long dissertation, but upgrading, where possible, the load capability of your tires and then running them per the recommended inflation for the load they are carrying, not just the max sidewall pressure, will give you safety and, in my case, an extreme increase in tire life over the “G” tires that came on the rig.

We just completed a trip to the Canadian Northwest Territories and let’s just say my tires made it even though they started with some 35,000 miles on them.  Others, with new tires running at their maximum (and over) capacity didn’t.  This included some 1,200 miles of rock and gravel dirt roads. (You wouldn’t believe how hard these roads are to travel on.)  Upgrade and follow the manufactures recommended pressures.  They do know what they are talking about.

(Yea Howard, I’ve got stories. This trip made the Alaska Highway trip look like a Sunday drive in the mountains.)

Bill

Thanks, everyone, for your input. Very informative and, yes, we're still learning. 

Guess what?  I get to go buy 2 MORE tires today for the truck today here in Coffeyville, KS.  (Mike is workamping at Amazon).  We spent 3 weeks in British Columbia with our son.  Yes, we went up and down his mountain on gravel roads with the 5th wheel.  (I stayed in the truck with it in 4-wheel drive going up but I rode in their car coming down.  I'm a chicken.  LOL)

We only took a week to get here from BC (we were exhausted and wouldn't recommend such a fast trip but Mike was scheduled to start work).  Everything went beautifully until we were about 140 miles from here.  BANG, WHAM.  Honestly thought we had hit something.  Checked all the tires, looked underneath both the 5th wheel and the truck; everything looked fine.

But, having a bit of experience at this over the last 6 months, we weren't convinced that all was well.  So Mike started up again really s l o w.  Sure enough, within 10 feet you could tell we had a bad tire.  The driver's side front tire was completely in shreds and falling off the rim.  (Now why can't we tell that the first time we stop?  He checked all the tires closely and even kicked them for soundness.) 

It was over 100° that day with no shade in site and miles from an exit.  We had to wait nearly 2 hours for help to arrive.  Put the sunscreen in the front windshield, kept the truck idling so the air conditioning worked, I got in the back seat behind Mike (sun was coming in on my side) and we got our rotating portable fan out of the RV and plugged it into the truck's inverter.  It was still warm but nowhere near what it was outside. 

These 2 tires I'm getting today means that we will have replaced EVERY single tire on the truck and the 5th wheel within the last 6 months.  Should have taken out stock in rubber, me thinks.

Can you tell I'm sick of tires?  LOL

Had not really considered the truck tire!  hmmm   .  . . I run at 95 lbs in my G614's and an axel wieght of 11,600.  I have the 36' Cameo with the full wall slide and have never weighed by tire bbut will if ever near someplace I can.

the truck is a 2011 F350 4X4 DRW with LT 245/75R17 121/118R with a loaded axel weight of 7,620 and run them at 85lbs when towing, figuring the max psi.  Can't seem to find an inflation chart for the truck tires.

Would appreciate any comments on the recommendated psi for the truck and trailer.

Thanks . . . . Scott

ps - Howard, good luck on getting out of the way of Irene!

Fred is correct on the placard and its true for Ford, Chevy or whatever vehicle.  As Walter with the RVSF will attest, the tire pressures on the placard on the driver’s side door or door frame are the tire pressures that should be used for your tow vehicles. (We’re speaking here of pickups / SUV’s, etc., not larger MDT’s and HDT’s which are another conversation that I will leave to Jack and is really not applicable to this thread.) We all get really close to the maximum rated capability of our tow vehicles and this placarded pressure is your best and safest choice.

The placard lists the inflation for the vehicle when loaded to its maximum rated axle capability which it most likely is pretty close to when towing.  It will likely be less than the maximum pressure on the side walls of the tires.  Use the placard pressure as it will be correct 99% of the time for towing.  Reducing tire pressure for “a better ride” in a tow vehicle is not a good idea and will lead to wear and blow outs.  Running maximum side wall pressure ratings will also wear the tires faster and accomplishes nothing unless you are overloading the axles – which is a bad thing.

The tires on a vehicle are rated above the maximum axle weight ratings - or should be. (That’s a good and safe thing.) Therefore, that is why you actually use less air pressure than the maximum pressure listed on the tires themselves assuming you are not over loading the axles and is why the vehicle manufactures recommended pressure is less than the pressure listed on the side wall of the tire.

There maybe a few nuances to all this, but the above will be correct for 99% of the RV’ers who tow with a pickup or SUV and don’t want to get into all the engineering details.

Safe travels

Bill

Good information.  The place card is 75psi front and 60psi rear and that gives a cushion of 700lbs front and 1,800lbs rear.  That all makes sense and then don't have to adjust psi's whenever towing, Thanks . . . .

For the trailer I have been under the impression that the best performance including wear came by inflating so that there is a 250-500 lb load cushion per tire.  Any wisdom?