xcntrk

Quick question for those more experienced than I. My tandem axle car hauler trailer has load-D rated tires on it with a max cold inflation of 65psi supporting a max of 2150# each. The trailer with loaded vehicle tips in right at about 6500#, or 1625# of weight per tire. With those numbers in mind, the D-rated tires have more than enough weight carrying capabilities for my load, but what should the tire pressures be?

Some say to simply inflate to the max cold tire pressure and roll. I get that logic but where it begins to break down is in southern regions (hot) where the temperature can span 40 degrees between cold inflation and rolling down the hot highway in the afternoon. This can cause the cold tire pressure to increase significantly as the tire heats up and potentially exceed the maximums for the tire (or wheels).

Then I found this tip over on trailer life which says:
"The pressure marked on the tire sidewalls is the pressure required when the maximum weight (also marked there) is being carried by the tires. It’s doubtful that your trailer weighs that much. Therefore, you should weigh the trailer axles on a truck scale (when fully loaded for a trip) and determine the weight on individual wheels and tires. Then look up the manufacturer’s recommended tire pressure, using a load-inflation chart (available on tire manufacturer’s websites and at tire shops). Set the correct pressures before driving off in the morning and then leave them alone all day."

Using that logic, the tire mfg load/inflation sheet says my D-rated tires only need 40psi of pressure to handle the 1625# (6500/4) load placed on them. But logic says, that would be ill-advised to run a tire capable of 65psi at only 40psi as I would imagine it might actually get even hotter with the deflated tread and contact pattern/friction.

So there's got to be some happy middle of the road ideal pressure. What pressures would you run in this situation?

Boxerglocker

This is what I would use....

frieed

The load/inflation sheet is showing that at a 1650# load @40psi the tire will have the same amount of sidewall flex and contact patch as that tire with a full load at max pressure. Put 40psi in it and roll on (adjust for temp if you wish)

03Scott

iTrader: (1)

If it says max cold pressure is x amount then max it out. Here we can get temps from 10 degrees to 100 so you just have to adjust though out the year but with them warming up you shouldn't have a problem. I was watching fishers atv or a show like that and tire direct was on it and they said for trails to max it out cause that's what they are designed for.

smokeywren

The Trailer Life recommendation is simplistic. Follow it only if your trailer tires are car tires (P-series) or light truck (LT) series. But you should never run P-series tires on a trailer, and run LT tires on a trailer only if you can find commercial truck tires of the right size rated for all position or trailer use. Most trailer manufacturers install ST (special trailer) tires on new trailers. For ST tires, you should run the tires at the max PSI shown on the sidewall of the tire, especially on an RV trailer that's usually loaded to the gills.

On cars and pickups, you don't want to overinflate your tires because of the harsh ride, and it wears out the center of the tread. But on trailers, you don't care about the ride, and trailer tires almost always are replaced before the tread gets worn out.

There are very few LT tires rated for all position service (which includes trailer service). I know of only two - the Michelin XPS and a similar Goodyear 16" all-steel commercial truck tire.

If your trailer has LT tires, then find the load/inflation table for that exact type and size tires, and use it, adding about 10 PSI to the PSI in the table. Tire manufacturers are now reluctant to make the load/inflation tables easily available to the public, so you must hunt for one. They are developed and published by the Tire and Rim Assn (TRA) in the USA and Canada, but you must be a member of TRA to get a copy of the load/inflation tables. Tire manufacturers used to publish those tables for the size tires they sold, but the lawyers have made it difficult to continue doing that, so load/inflation tables for tire sizes used on utility and RV trailers are hard to find. Brand of tire doesn't matter, only type and size of tire, so if you can find a load/inflation table published by TRA or any manufacturer, you can use it. One source still available today is Toyo. Definitely use the Yoyo tables for the tires on your cars or pickups, but use them only for LT tires on trailers.
http://toyotires.com/tires-101/load-...flation-tables

Notice there is no load/inflation table for ST tires in that PDF. That's because ST tires should usually be run at max inflation of the sidewall.

The fly in the ointment of the above sermon is that Maxxis publishes a load/inflation table for ST tires. But that's the only exception I know about.
http://www.maxxistires.com/Repositor.../m8008load.pdf

PHX 150

I don't understand why you're wanting to reduce the load rating of the tire, and thereby the safety factor.
The difference in the PSI of a hot tire and a cold one is no where near the 40 PSI you mentioned, and the additional heat is accounted for by the tire manufacturer in their load calculations.
I'd go with the tire manufacturers recommendations.
Put 65 in cold, and enjoy the extra load rating.

DrewTK

By going with a lower pressure, you are decreasing the load rating for the tire. Go with 65 PSI cold. You also haven't considered what happens during a blowout, which we all know happens frequently with trailer tires. If you lose a tire, then the other tire on that side is having to carry the load of BOTH tires. If you 'underinflate' at 40 psi, that tire may blow also because it's overloaded.

brulaz

Trailer manufacturers, at least travel and 5th wheel trailers, post a yellow sticker on the trailer that tells you the tire pressure to use.

And they always say use the max pressure for the ST trailer tires.

Some ST tire manufacturers, like Carlisle, make that a warranty condition.

Goodyear recommends using max pressures but notes that you can reduce it some unspecified amount if max pressure makes the ride too stiff.

And Maxxis says nothing that I can find, but publishes their tire loading table.


I don't know why this is. Certainly with LT tires you adjust the pressure according to the load. ST tires are generally considered a cheaper tire, so maybe that has something to do with it. I've also heard that the scuffing associated double axles on sharp turns puts more stress on the tire sidewalls and bead, making max pressure preferable.

So I use Trailer Manufacturer's specification of Max Pressure (65psi) with my ST Goodyear Marathon D load rated tire's that came with the trailer.

But if I upgraded the tires to the same size but E load rated, I might still use 65psi rather than the new tire's max possible pressure (80psi).

SkiSmuggs

I upgraded my LR D china bombs to Maxxis LR E and run them at 70 lbs, just over the LR D max. I still have more load capacity than the LR D tires, but my tire pump lasts longer.

tomb1269

1st tire pressure only increase 1psi per 10 degrees, with that said I am careful not to take a trailer from storage (month or more with out use) and inflate the tire to max pressure if it means putting more than 15psi in. Particualrly in late spring if its the 1st time out for the year. I have had a trend seperation happen do to that very thing. I checked the tires, they were low, one as much as 15 psi down so I air'd the tire up to the 70 psi indicated and had the tread seperate not 30 miles down the highway. I will agree that tread seperation was most likely enevtiable however the trailer was only 1 1/2 years old from date of purchase (2 model years old).