Question on tire pressure

[58Eastfield]

When I purchased my travel trailer the tires were rated at 50psi on the sidewall. The owners manual also stated 50psi. I recently replaced these tires with new ones. They state on the sidewall that they should be inflated to 70psi max. Do I inflate these tires to 50psi or 70psi?
The tire dealer says to run them at 70psi.

[Airdale]

Originally Posted by 58Eastfield

When I purchased my travel trailer the tires were rated at 50psi on the sidewall. The owners manual also stated 50psi. I recently replaced these tires with new ones. They state on the sidewall that they should be inflated to 70psi max. Do I inflate these tires to 50psi or 70psi?
The tire dealer says to run them at 70psi.

The starting point is the amount of load capacity the original tires provided at 50 PSI.

[jadatis]

The 50 psi is a C-load tire and the 70 psi is a D-load tire probably of European make, because USA system only uses 65 psi for that.
A stiffer tire, like the D-load is in compare to C-load , needs higher pressure for the same load , or other way around has lower loadcapacity for the same pressure.

So expected is that you would need a bit higher pressure then old advice of 50 psi.

But best is to let me calculate a pressure for you , because that 50 psi is mostly determined for GAWR and no reserve .

In my advice I build in a maximum reserve with still acceptable comfort (for tt that your screws wont tremble loose) and gripp.
This can mean that the advice will be 70 psi or even higher, wich is allowed by the tiremakers up to 10 psi , so 80 psi even.

Will give text I used on other fora and topics , with what you need to give me , to make my advice, so I dont have to write it all over again.

Tirepressure advice is all about load on tire and speed ( and sometimes about alighnment - camber angle).

So if you can give details of car and tires , I can calculate an advice pressure with some reserve for things like, pressure-loss in time, unequall loading R/L, incidental extra load, misreadings of pressure scales,and misyudging of weight, etc.

This is from tires next and can be read from sidewall:
Maximum load or loadindex.
Kind of tire to determine the AT-pressure/pressure needed for the maximum load up to maximum speed of tire, or if lower 160km/99m/h/reference-pressure, wich is not the maximum pressure of tire.
Maximum speed of tire, most given as letter ( Q=160km/99m/h,N=140km/86m/h fi)
If you have offroad or tires looking like that , with large profile blocs that cover a part of sidewall, also mention, they are allowed lesser deflection then a normal road tire, then the tire maker used to determine the maximum load (to my conclusion the case for the Bridgestone tires on Ford Explorer in the Ford/Firestone affaire).
If you cant find all of it give sises of tire and Loadkind, then I will google for it.
ST tires are a different story, they are given maximum load on sidewall for speed of 65m/104km/h , though sometimes even N speedrated is given ( 140km/86m/h, a bit confusing, so then also give sises so I can google for others and compare.

From car next and mostly can be found on same plate as the original pressure advices:
GAWR and GVWR ( Gross Axle/Vehicle Weight Rating)
But best would be to determine the real weights in your use on seperate tires or estimate it as acurate as possible, by weighing per wheel(pair) or axle.
Maximum speed , you dont go over for even a minute in your use, eventually different for different situations, for instance when towing or fully loaded.This apart from trafic regulations, if you drive faster then allowed give that speed. Nature punnisches with tire-failure, police only with a penalty.
Give all that and I will calculate and give a picture of one of my filled in spreadsheets in my answer.
If other then original tires, indead as is already answered other advice is needed, a stiffer tire ( fi C-load instead of P-tire) needs a higher pressure for the same load, or the other way around, has lower loadcapacity for the same pressure.

Greatings from a Dutch pigheaded self-declared tire-pressure-specialist.

[58Eastfield]

Thanks. I'll collect all the info and post. Good stuff (From a Scotsman)

[Too Tall]

Set the air to 70 psi first thing in the morning. There rated for higher load. Gives you a margin of safety over the C rated tires.

[okietom]

Trailers are very hard on tires, always run at max pressure.

[Too Tall]

Yes, agree, IMO it's pretty simple actually, just set to the maximum cold pressure that's on the side of the tire. These trailer tires (and axles) are running too close to the maximum allowable weight rating to run anything but the maximum pressure.

The number one cause of blow outs is low tire pressure. #2 is hitting road debri.

[MNtraveler]

I'd be very surprised if the tires state to inflate to the max pressure. Every tire I have ever seen says XX PSI MAX. That is the max as it says. Your proper tire inflation is based on your load - the actual load with gear, water, LP, etc. I also see no reason why a trailer that ran at 50 psi before should run at 70 psi now just because that's the tire max unless you changed class of tires.


Land of 10,000 Lakes
2016 Forester MBS 2401R

[Airdale]

Originally Posted by MNtraveler

I'd be very surprised if the tires state to inflate to the max pressure. Every tire I have ever seen says XX PSI MAX. That is the max as it says. Your proper tire inflation is based on your load - the actual load with gear, water, LP, etc. I also see no reason why a trailer that ran at 50 psi before should run at 70 psi now just because that's the tire max unless you changed class of tires.


Land of 10,000 Lakes
2016 Forester MBS 2401R

For your Original Equipment tires the correct inflation pressure is what is on the tire placard and in your vehicle owner's manual regardless of what the vehicle weighs.

For replacement tires of another size or design or both the correct inflation will be to air them to a PSI that will provide the load capacity the OE tires provided. By doing so you gain nothing with the new tires other than any difference they might have with durability which does not translate to strength.

[OldCoot]

Originally Posted by MNtraveler

I'd be very surprised if the tires state to inflate to the max pressure. Every tire I have ever seen says XX PSI MAX. That is the max as it says. Your proper tire inflation is based on your load - the actual load with gear, water, LP, etc. I also see no reason why a trailer that ran at 50 psi before should run at 70 psi now just because that's the tire max unless you changed class of tires.

Better to know the wt of the trailer loaded and that your tires will carry the load and just inflate to what is listed as Max Cold Pressure on the side of the tire and forget it. Use a TST TPMS and go camping.

[ependydad]

Originally Posted by OldCoot

Better to know the wt of the trailer loaded and that your tires will carry the load and just inflate to what is listed as Max Cold Pressure on the side of the tire and forget it. Use a TST TPMS and go camping.

I wholeheartedly agree.

I will say- if you're running heavy, getting individual wheel weights can be important. Each tire point doesn't carry the same load (even on the same side or on the same axle). It's easy to be unknowingly overloading a tire.

[Airdale]

Originally Posted by ependydad

I wholeheartedly agree.

I will say- if you're running heavy, getting individual wheel weights can be important. Each tire point doesn't carry the same load (even on the same side or on the same axle). It's easy to be unknowingly overloading a tire.

Over 95% of OE tires are already set at maximum sidewall pressures by the vehicle manufacturer. There is no place to go with tire pressure manipulations.

Individual tire loads can be individually overloaded without the vehicle being overloaded.

To counter those conditions with trailer tires already set at maximum sidewall pressures the RMA recommends a trip to the scales where the owner can weigh and then balance the loads across all tire positions, thus, eliminating the overloading condition (s). Overloaded trailers will have to have some weight removed to be properly balanced.


This RMA reference has four very informative chapters. Chapter 4 starts on page 48 and is all about RV tires.

http://www.mcgeecompany.com/wp-conte...ete-manual.pdf

[Too Tall]

That's some good info Airdale, thanks for post the pdf.

Has anyone seen a tire mfg state the temperature at which they call the cold temp?

[pgandw]

Originally Posted by Too Tall

That's some good info Airdale, thanks for post the pdf.

Has anyone seen a tire mfg state the temperature at which they call the cold temp?

Cold temp is ambient temperature. It means the tire has to cool from its rolling temperature for hours - I like to allow 8 hours minimum out of the sun (overnight). Or I add 3lbs to the pressure I put in the tire if I'm doing it while the tires are hot.

It's at best an approximate science. 40 PSI on my tires in Denver turns into 35 PSI on my tires in Lincoln, Nebraska at the same temp.

Likewise, placard pressure in my tires on a 75 degree day will trip the TPMS if the next early AM is down to 10 degrees. Rule of thumb in Colorado upon seeing a TPMS light is to assume you do NOT have a problem unless there is visual/audio evidence the tire is going flat. At first opportunity, fill the tire(s) to normal pressure and continue to observe.

I try to set my camper tires to sidewall max pressure with normal conditions. If temps are going to be significantly lower, or I am going to the lowlands, I will add another 3#. If going to higher altitude or temps are going up, I just let it ride for a slight over pressure.

As somebody else said, you don't need to overthink this. Air to sidewall max pressure, call it good, and go camping.

Fred W
2014 Rockwood A122 A-frame
2008 Hyundai Entourage minivan