Tire upgrade air preasure ?

KD4UPL wrote:
You need to look up the load inflation table for your tires, weigh your truck, and inflate accordingly. Using too much pressure will result in a harsher ride and wear out the middle of the tire. Using too little pressure will create extra heat in the tire and wear out the edges.
Just going by a sticker or the sidewall works okay on cars that always weigh about the same or trucks that stay fully loaded all the time. If you some times drive empty, sometimes loaded, sometimes towing heavy, etc pressure would be adjusted ideally.

Goodyear Marathon and Endurance are ST trailer tires.

Your old and new tires are both ST ( Special Trailer) tires.
those are calculated in their maximum load for speed of 65m/104km/h.
Can even be that they give N speedrated on sidewall, wich is max speed 140km/87m/h. But St system calculates still for 65m/h.
This gives more deflection then when maximum load would be calculated for an LT tire wich is calculated for 160km/99m/h.
Better is to calculate the ST tires as if they where LT tires, so calculate maximum load for 160km/99m/h.
I found out the system for that , wich tiremakers also use, and rule of tumb is for every 10km/6.5m/h 1 Loadindex step different.
Higher speed > lower loadindex. Lower speed > higher loadindex
Then calculate the pressure for the axleload +10% (to cover unequall loading R/L per axle). And this would give for your old ST tires already a higher pressure then 65 psi. So doing that for the new St tire with 80 psi and higher maximum load, it could end in mayby even that 80 psi.

What do I need to calculate that needed pressure for you with my made extra save calculator.

Tire data ( can be read from sidewall) search for next.

Maximum load or Loadindex.

Loadrange or pressure behind AT , wich is the referencepressure in the official formula , I once got hold of and went running with.
for your tires this is old 65 psi and new 80 psi.

Speedcode, letter J is 100km/62m/h N = 140km/87m/h or that ST is exeption to universal system , Europa works with "for trailer use only "tyres, and those are N speedrated and maxload is also calculated for that speed. American tires dont always give a speedcode .

From vehicle,

best seperate axle-end loads weighed, second best axles weighed, but as long as you did not weigh, we will have to do with the Gross axle weight ratings ( gawr) but also give G Vehicle WR ( GVWR). For a trailer if 2 axles mostly the same GAWR .

maximum speed you use and wont go over for even a minute.

About that system of lowering maxload or highening up, I made a topic a while ago on this forum.
How to compare tires for aftermarked replacement

So end conclusion , your idea of going in the middel would be good because you are going to a stiffer tire ( to hold the higher pressure in) wich has lesser surface on the ground at the same deflection, but because calculated in both cases for 65m/h you can use higher pressure with still acceptable comfort and gripp, and you micht end up needing the full 80 psi.

ScottG wrote:
Even if the metalwheel said 65 max, I'd probably go to 80. It just isn't that big of a difference.

Does make a BIG difference
65 to 80 is a 23% increase

Rims not rated for that will make a big difference.

Lwiddis wrote:
"I decided to split the difference at around 72-73 lbs but.."

Spilt the difference based on? Sorry, Baber, I don't believe you know more than the tire manufacturer. In fact bunches less like me.

Give it a rest buddy... you should go pester your wife or someone else.

The Goodyear endurance tires do have a load inflation table unlike many trailer tires.
http://www.rvtiresafety.net/search/label/Goodyear%20Endurance

In my case using the trailer manufacturers spec of 65psi on my new 235/80/16 lre endurance tires still gives me almost an additional 400lbs per tire of load capacity instead of the max rating of 3420 at 80psi(though according to the table I could go as low as 45psi based on my weight). I did upgrade my tires from 225/75/15 lrd. I personally prefer not to run any higher pressure than needed including a safety margin just to keep the trailer from bouncing around any rougher than it needs to. Same with my TV I run the pressure required for the load. With that being said at this point in time I am not sure I am comfortable running 45 psi on the trailer with these tires though as I get some more miles on them and see how it handles and tire wear I may lower it from the 65 psi down to 60 or perhaps even 55.

I run mine at 75 (went from "D" to "E"). the tires are wearing perfectly even and have no abnormal wear. the trailer will handle better also at the higher pressure.

babar445 wrote:
what others have done or recommend when upgrading to a larger capacity tire.

When we went to load range E (up from load range d) and filled tires to 80 psi, we had a problem with stuff bouncing around in trailer. And a rear kitchen doesn't help. Looked up inflation chart for tires and then got weighed. Now we fill up to what manufacture spec's say plus 15 percent more. Was nervous first couple of times. Works for me but others might not like.

Even if the metalwheel said 65 max, I'd probably go to 80. It just isn't that big of a difference.

Run them at 80 unless the wheel calls for less.

The advantage of the 80 psi E tire you bought over the OEM 65 psi D tire comes only at those higher pressures. Derating the new E to a D doesn't make cents/sense for tires in a trailer position. The E tire advantage is lost.


Goodyear Tire and Rubber .... weighing RVs
Special Considerations

Unless trying to resolve poor ride quality problems with an RV trailer, it is recommended that trailer tires be inflated to the pressure indicated on the sidewall of the tire. Trailer tires experience significant lateral (side-to-side) loads due to vehicle sway from uneven roads or passing vehicles. Using the inflation pressure engraved on the sidewall will provide optimum load carrying capacity and minimize heat build-up.*