Fifth Wheel Tire Pressure

Depends on the loads that will be in your use on seperate tires.
This is not total weight minus pinload devided by number of tires on the ground.
Often there is a misbalance between tires on one axle of 48/52% or even more. Then also can be crossed between the axles , but this is not important for the pressure to use.
For that you only have to use pressure for the tire with most weight on it.

Then the tire side, an ST tire is calculated in its maximum load for more deflection allowed because of the lower speed of 65 m/h.
If it was set in the market as LT tire it would have about 15% lesser maximum load , because for higher speed ( LT mostly Q speedrated for 99m/h/160km/h) lesser deflection is allowed because of the more cycles the tire make a second.

Then if you would go from LT maxload for that tire sise and AT-presssure , you can even add a reserve of 18 % , to make the real weight 85% of weight you calculate the pressure for for 99m/h.

This is the upper border at wich still acceptable comfort and gripp, and gives lesser fuel consumption, and comfortable reserve for things like pressure loss in time , misreadings of pressure and weight scales, etc.

But calculating it like this will probably lead to a higher pressure then AT-pressure of yours 80 psi.
Tiremakers allow 10 psi higher, and in a document of Continental/semperit I found 1.4 times At pressure as advice when standing still and then 2 times maximum load allowed on tire.

Tires and valves can stand this higher pressure , rimms dont allow it always , its written on inside of rimms often , max pressure or maxload .

Once read that tires can stand a pressure of 2 to 3 times AT pressure ( yours 80 psi) . This would mean that if you would fill your tires at 1.4 times At pressure at freesing point of water, and temp inside tire rises to even boiling point of water, the pressure would rise to about 2 times AT- pressure , wich they can stand ( your tires 2x 80 psi= 160 psi)

So if you give more details of tires ( maxload ( 117 loadindex so 2830 lbs maxload),maxspeed ( 65m)and loadrange(E-load because of 80 psi) and of 5th wheeler ( number of axles and number of tire on the road and total weight and pinload percentage or weight), I will put it in my Traveltrailer calculator and give an extrasave advice.

reading back I see N speedrated for your tires wich is up to 81 m/h maxspeed , but because of ST it can be that maxload is given still for 65m/h, have to find out by comparing with other tires of same sises and loadrange.

Tire data so I already have, but only need 5th wheeler data.

Some interesting info from Carlisle web site.

–Maintain air pressure at the maximum PSI recommended on the tire sidewall. As opposed to a load chart most tire companies refer to as I noted above.

And;

–3 to 5 years is the average life expectancy of a trailer tire, regardless of mileage.
– It is estimated that in approximately three years, roughly one-third of a tire's strength is gone.
– After three years, depending upon storage and conditions of usage, consider replacing trailer tires even if they have tread depth remaining.
–After five years, trailer tires should be replaced in all cases

Seems like pretty low numbers.

Keep it simple and safe...run them @ 80psi

You need to watch the tire rating vs actual weight in the tire. If they are close by all means go with the max pressure. Otherwise you could go less, but sidewall flex is a killer to most tires.

I've always inflated my ST trailer tires to max pressure to help lessen the amount of flex of the sidewalls. The ones I've examined are so flimsy in the sidewall area that I feel they need all the help they can get. :)

Many tire company's web sites will have a table of inflation pressure vs load on the tire. The pressure on the sidewall is the max pressure for the max load. But the tables recommend lower pressures for less than maximum loads.

A tire that is over inflated for the load on it can cause the tire to wear faster in the center. Inversly, a tire under inflated for the load on it can cause the tire to wear faster on the edges. A correctly inflated tire will wear more evenly providing longer life and better traction.

Keystone doesn't provide Load Range E tires so the air pressure is a lot less. So far most people seem to indicate inputs indicate either 75-80 PSI as best...I have talked to some people that only run 65 PSI...but not sure why they run less. Rig weighs around 11K lbs..fully loaded with everything.

ST tires should always run the pressure stated on the sidewall or more.

What does Keystone say? I know Northwoods says with typical loading they recommend 80 psi (cold)

80 is the max. I run 75 in my tires.