Tire Pressure Ignorance?

[RRman]

Traveling this past weekend I stopped at the First AL Rest Area Welcome Center on 1-20/59 North alongside a 2008 Big Sky pulled by a 3 axle 6 Tire MDT. I noticed all the trailer tires looked similarly low and asked the owner from Canada about his tire pressure, which he said was 80 and monitored via TPMS. Okay... He was still there when I returned from doing my business and just couldn't stand seeing those very visibly low, almost 12" flat footprint tires on the Montana and pestered him again where he indicated 68-72 lbs (or was he referring to a metric measurement?).
I suggested 80lbs was the minimum I run my tires at, and usually over the tire rating of 80PSI for max load at 85PSI due to occasional high speed passing on the Interstates(90 PSI when stored stationary for long) based on MOC and Tire Manufacturer suggestions. His truck tires all looked normal! I did encourage him to check out the MOC online.

Anything wrong with my advice?

I still can't believe how low those tires looked or that it was possibly sold with tires in that condition. Who would run tires that looked low without airing them up some more? Would a grossly overwieght trailer cause such flatness even at proper pressure?

[stiles watson]

68-72 sounds like he is asking for a tire failure situation. I would run 80 psi on E-rated tires and 105 on G-rated tires. Anything less would probably cause the tires to heat up excessively.

[exav8tr]

Sounds like an accident waiting to happen.....

[Illini Trekker]

Put new tires on the TV last week at Sam's , went up one size and went with 265/75/16. Left Sam's and as with all new tire you get a different fell, but this felt like driving on marshmallows. Stopped at the next street to look at the PSI it was 38#! Went back and ask to have them add more air, the gal said why 38psi is what they ALWAY put in truck tires. I then explained that the truck needed 65# in the front and I like 70# in the rear. Them told her she should look at the door panel for future PSI help.

[HughM]

I always check behind someone working on my equipment be it the RV or the TV. You would be surprised at the number of things caught by just checking. The latest was fridge control panel work. After I left Lazy Days I couldn't get the fridge on A/C. I took off the outside panel and found that they had unpluged the fridge and didn't plug it back in.
Never trust someone who says "I'm a professsional and I know what I'm doing" They may know what they are doing...they just don't do it.
Hugh

[richfaa]

The E rated tires say...max load at 80-psi cold.. So I assume that means that If I was running at max load the tires should be at 80PSI. Are you not supposed to pressure your tires according to load???? so 68 to 72 COULD be correct. However the big sky does not have E rated tires. We run ours at 80ps1 and according to our tire pressure monitor we have never seen over 8PSI higher at interstate speed..

[stiles watson]

Both my Big Sky rigs came with E-rated tires. How ever they may have changed the OEM size.

[Art-n-Marge]

Okay,

Being a victim of past tire problems fortunately none of them my fault (remember the Mission tire stories? - I know of other brands, too) the tire pressure is absolutely critical to keep things right. I have learned to be very anal about keeping this straight. I preach it every time I can get a chance.

For any E-rated tire (which is predominant on Montanas) the cold tire pressure is 80# for the tire to support its load rating. For G-rated tires I have heard 105 to 115 but I don't know for sure because I haven't had to worry about it but for the next set of tires I might look into this. There are some things that meet my criteria for exceeding specifications. Tires is one of them.

After driving for a while, the tire pressure may always read higher because heat causes the air to expand and elevates the tire pressure slightly. That's why any tire pressure documentation will state NEVER to bleed the tires if they have been driven on. The tire manufacturers have taken this into account when specifying what the tire pressure should be. Note, if you ever measure less than 80# after driving there is a good chance you are leaking air, unless you are driving in the arctic in January. That's the ONLY thing to think about. Being over 80# is not a problem after you've been driving. That's why you check tires when they are cold (undriven).

Tire pressure is measured with lbs or kg. Nothing else counts and I think the kg numbers would be somewhat less for what the Canadian would have specified so in either case I think he is going to have problems if he is only at 68-72.

Another factor is that you should become aware of the maximum speed rating for the ST tires on your rig. I have only seen 65mph maximum speed for an ST tire but have seen MANY trailering RVers powering down the road sustained speeds higher than 70-75 just because their truck can do it. The trailer tires might not be able to sustain those speeds, therefore they will run hotter, causing the rubber to weaken and adding to premature tire wear or even failure. For them, I praise their deep pockets to keep replacing the rubber on their trailer.

When checking your tires the outside ambient temperature MAY have a bearing on the actual tire pressure depending on the temperate. For example, measuring the cold (not driven) 80# of pressure in summer in Death Valley will not be the same as 80# in Wisconsin in February. When it's hot one might have to add more and in winter it might have to be less. There isn't a big difference but the adjustment allows for driving under these extremes. There is a way to caluculate the temperature adjustment but it requires a conversion table that I found once on the internet, but haven't been able to find it since.

Finally, the age of your tires count whether you use your rig or not. Some considerations for preventing premature wear is to overinflate the tires to minimize the "flat spot" caused by lack of motion. You can also use tire covers to prevent sun wear. But with all that it is recommended to check the date code on the tire and replace them every 5-6 years. You might not know where and how the tires were stored prior to being installed on your rig and keep full attention of what they have gone through up to that point. And don't forget about the spare. Not replacing a spare is worthless if you have not paid attention to it, then when you need it, it becomes a problem, too.

Even driving your rig will be stressful on your trailer tires. Not driving straight necessarily but the stresses caused with extreme turns. How many of us remember to pull our rigs backwards and forwards AFTER impressing ourselves with tightturning our rigs into their near impossible camp sites? The axles of our trailers incur incredibly stress when moved into the final position during a turn and especially if they are left in that position. Have you ever noticed it? The tires are not lined up any longer and you wonder, what's wrong with my axles? It not the axles, it's the tires trying to accomodate a turn. There is no differential in a trailer to make this adjustment automaticially. Moving the trailer back and forth will help the tires to realign and stand back up and relieve the stress. This is why ST tires are better than LT tires since they have stiffer sidewalls to handle this stress.

Well? How's that for considering almost everything. I hope this helps everyone become tire comfy and stop trying to defeat what's been known and development since the first pneumatic tire was invented in the early 1900's. Hey! I heard that. I am NOT that old. I just read a lot of historical technical books.

Art