Tire inflation.

^^ Sorry, I mistyped in my earlier post quoted above... I meant ST tires on trailers, not LT.  It does make sense that LT tires (as they are designed for trucks and have softer sidewalls) may be inflated appropriately based on weight.

My "max inflation" recommendation for trailers (on ST tires) is based guidelines such as this one at etrailer.com and the many people here who have commented on the topic, that are smarter than I am. 

Hi. I thought I would resurrect this topic, since the facts probably haven't changed much.
Just to recap, if I follow the pressure on the sticker, I am not underinflating so long as I am not over the weight limit. If I am under the weight limit,  I could just go with the sticker. But if I am under the maximum, I could and probably should  go with a lesser inflation as shown in the tables on the tire makers website. OK so far?
I am getting my new to me RV out for its first trip. My tires are Courser/Mastercraft. Their website has no such tables that I could find. They are not OEM (hope not, it's a '94). The sticker says 48 psi front and back (double). I have 750R16 and the tires say load range D.
As it sits this morning, pressure is over 50psi. Obviously, I should lower it to 48. Could I safely go lower if I am a few hundred pounds under the max weight?

Nearly all tire manufacturers follow the standard of the Tire & Rubber Manufacturers group, so you can safely use another company's inflation table for all but specialty types of tires.

Don't over think this - just avoid ever being too low.  Don't try to adjust for a few hundred lbs difference in gross vehicle weight and don't try to keep up with day-to-day temperature variation. Set the pressure high enough so that it's still OK if a slightly cooler day comes along.  Tire pressure changes about 2% for every 10 degrees up/down, so a  10 degree change doesn't effect it very much.    As seasons change and typical temperatures are noticeably higher or lower, you may want to adjust the psi up or down, but changing pressures daily is a lot of effort with no reward.

Is the 7.50R16 the OEM size? If so, and the OEM was a radial, the OEM recommended pressure is probably valid. If a different size or type, the OEM recommended pressure is meaningless and should be ignored.

7.50R16 is a pretty rare size, so finding inflation info on it (or replacement tires) is difficult. A 235/85R16 is a close equivalent, though.  Search the internet for 'tire data book', which is what the tire industry calls the collection of tire specs that includes inflation tables.  You can probably find one that has a 7.50R16 in it. I know Hankook and Double Coin make that size.

Glad you did, Dennis.

I have read through the entire thread and learned a LOT.  God's timing as well since I am checking air pressure in my tires in the morning and now know to go by the placard and not the sidewall until I can get the coach weighed and adjust accordingly (this will be our first camping trip in it).

Mine too, Fender. Much to learn, but we also have to get out there and learn by doing!

DennisinMaine said:

Could I safely go lower if I am a few hundred pounds under the max weight?

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On a motorhome, yes. Follow the tire manufacturer's inflation table guidelines based on your RV's weight, as Gary mentioned.

On a trailer, no. Or at least not recommended. Some folks have done it (slightly underinflated trailer tires) and been fine, but general consensus is that they should be kept at/near max inflation regardless of trailer weight.

That's what I've learned from the folks here that are smarter than I am, as I mentioned above last year.

DennisinMaine said:

Mine too, Fender. Much to learn, but we also have to get out there and learn by doing!

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True dat.  Like those danged lug nut covers that kicked my arse.  :-\

Can someone recommend a decent air compressor for servicing RV tires? These tires are much bigger than anything else I have, and my little HF pancake machine only goes to 100 psi, taking lots of compressor time to get RV tires up to pressure. I prefer not to spend half a day fiddling with an undersized compressor.

And is there any science behind the recommendation to park tires on wood, or at least, not "on the ground". Does that mean not on dirt?  Concrete?  What does the wood accomplish?  Or is this just some old wives' tale?

Just went through the compressor purchase. My tires need about 90 psi. I bought a Briggs and Stratton 125 psi  . 6 cfm @ 90 psi from Home Depot for under $60. It works great but is a little bigger than the pancake style as it is a cylinder type. The rating is borderline for using air tools ( like an air ratchet to change a tire) but I plan to get an air ratchet to see if I can change a tire with the current compressor. Have not got to that yet but I believe it will probably work with maybe some catch up time during lug removal. It has been great for maintaining tire pressure so far. My only complaint is the quality of the hose and air chuck. They are cheap and will need to be upgraded at some point but work fine for now

The wood blocking helps to provide a nice surface for the tires to rest on. It will also provide a barrier from elements that may be beneath the wood or come flowing by. Some manufactures suggest using a rubber material to help cushion the tires. The most important thing is to block out UV rays and to keep them properly inflated. It has also been determined that it is not good for the tires to be sitting for extended periods of time.

beaverfever said:

remember the air pressure is cold tires not after a trip down the freeway.

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Yes, but I always thought that was one more problem. To get to the weigh station or when stopping for fuel I have to drive the RV and that heats up the tires, so they are not "cold" anymore. They also tell you to not add air to hot tires, but I don't know how to avoid that if you are traveling and check your tires when you stop.

I have assumed that if I check the tire pressure before we leave in the morning and get the "cold" pressure, then check them when traveling and get the "hot" pressure, then I can use the difference to properly air the tires during a trip. That is, add the "hot" - "cold" difference to the suggested tire pressure, but I don't know if that is good or bad.

Doesn't have to be that complicated. Check them when they haven't been driven on and adjust as needed. If you check them after you've been driving awhile they'll be approximately 10 psi higher. Best thing, get a TPMS system and you'll see your tire/temp pressures continuously and you'll learn how yours increase/decrease with temperature

You can use your tire gauge to check the psi when "cold".  If lower than desired, write down the differential for each tire and add that much psi when you get to an air station.  Recheck the tire pressure now that it is "hot" and add the difference you recorded when cold to the hot pressure reading. That becomes your hot pressure target.

Example:
1.  Front tire target pressure is 80 psi.
2.  Left front tire measures 75 psi when cold (before departure). Write a note to self that LF tire needs an additional 5 psi
3.  Drive to a place that has an air compressor
4.  Measure the LF tire pressure again; let's say it is now 78 psi because it has warmed up some.
5.  Add the 5 psi you noted previously to the 78 psi of the warm tire, a total of 83 psi.
6.  Inflate the LF tire to 83 psi

An interesting bit of information: In the morning, If you re parked in the sun, you can find a 5 degree or more difference between the tires on the sun side and those on the shady side.
So it seems wise to not sweat those kinds of dfferences until after you run enough to heat tires up to "operating temperture."

tires been my headache on my motorhome for past 6 months once I found the motorhome came out of the factory over the GVWR.  I got tires on now that will take the additional loads and my eyes are glued to my TPMS display as I watch the temps and pressures go up while on the road.  I can easily see 96-99psi on my rear tires that I cold filled to 83psi (max pressure) for max load carrying limit I need,  but always is freaky seeing 99psi.  My commercial truck tire guy says no problem as the tire is designed with those pressures in mind when driving. He says always concentrate on the cold temp psi.  But still freaky.

decaturbob said:

tires been my headache on my motorhome for past 6 months once I found the motorhome came out of the factory over the GVWR.  I got tires on now that will take the additional loads and my eyes are glued to my TPMS display as I watch the temps and pressures go up while on the road.  I can easily see 96-99psi on my rear tires that I cold filled to 83psi (max pressure) for max load carrying limit I need,  but always is freaky seeing 99psi.  My commercial truck tire guy says no problem as the tire is designed with those pressures in mind when driving. He says always concentrate on the cold temp psi.  But still freaky.

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How do you mean, over GVWR? It would be not be legal for the sale of a unit to be over GVWR at the time of first sale.

FastEagle said:

How do you mean, over GVWR? It would be not be legal for the sale of a unit to be over GVWR at the time of first sale.

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little or no enforcement of such things, especially 10 years ago.  Fleetwood laughed at me when I called to inquire on this issue as nothing been added to the vehicle that account for the weight I got on the CATscale.

I will add some thoughts in here, which is probably worth what you are paying for it.  I have read the entire thread. I have also towed boats and travel trailers, one severally overloaded in the dead of summer since the early 80s on a regular basis. My unofficial tire gauge has always been watching how a tire wears, toes or centerline, after sticking to the recommended cold temp pressure printed on  the tire.

To date I have never had but one blow out, and that was due to age. The tread was fine. Not withstanding watching for any stress cracks on older units, check the manufacturer date on every tire if you are not sure how old your tires are on any older units, whether its a used unit that you have purchased, or one that you have owned since new.

Many people do not consider that the age of a trailer type tire, which has more of a bearing on what happens on the road than minimum tire pressure will when mainly towing in the summer time and warm roads.  I have used the practice of updating to new tires as a form of paying a new yearly renewal insurance policy every few years even if the tread is fine if I have a trailer that I have owned for multiple years. The price for a tandem axle update is nothing when considering being stuck on some of the remote areas that I personally boat and camp on myself. This truly applies on single axle trailers.

decaturbob said:

little or no enforcement of such things, especially 10 years ago.  Fleetwood laughed at me when I called to inquire on this issue as nothing been added to the vehicle that account for the weight I got on the CATscale.

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It's always been unlawful for vehicles to be over GVWR when first sold. You'll just have to explain what you consider over GVWR.