Tire Pressure

[Bluetick1955]

Just replaced china bombs with Goodyear Endurance ST205/75/15.


My trailer shows pressure 50psig and old tires showed 50 psig


Goodyear tires show ma 65 psig. Which pressure should I run?

[fonzie]

I would run them at 65 psi or if you know actual weight of trailer at axles, you could use this chart.
https://www.goodyearrvtires.com/pdfs/rv_inflation.pdf

[Bluetick1955]

Originally Posted by fonzie

I would run them at 65 psi or if you know actual weight of trailer at axles, you could use this chart.
https://www.goodyearrvtires.com/pdfs/rv_inflation.pdf

My GVW is 7700 lbs. Prob not too far off. I assume total divided by 4?

[eye95]

Originally Posted by Bluetick1955

My GVW is 7700 lbs. Prob not too far off. I assume total divided by 4?

Dividing by 4 would give you the approximate load on each of the 4 tires. Weighing would be more precise and would take into account the weight carried by the hitch.

Once you have a good number for the weight on each tire, look up the recommended psi in the charts the other poster linked.

Both too much pressure for the load and too little pressure for the load are bad. The people who designed the tables know how much pressure for a given load will produce a proper footprint for the tire.

[babock]

With 50PSI, your tires are rated for 2150# each. At 65PSI 2540# each


Even at 50 PSI, you have more than 10% margin when you take into account how much weight is on the tongue.

[The Evil Twin]

I know what some will say....and disagreeing is fine. But.....
That chart is NOT a recommended inflation table. It is a max load table. I would not set my tire pressure by that table. You can, and might get away with it. According to the chart I would be running 42ish psi unloaded, 50 for camping and 100 for loaded with toys. No way. Too much sidewall flex and heat building up at 42. I'll set them to the sticker pressure on the rig.

[babock]

Originally Posted by The Evil Twin

I'll set them to the sticker pressure on the rig.

I agree...I wouldn't go below the sticker pressure on the rig....I also wouldn't put it at max pressure on the tire either.

[eye95]

Originally Posted by The Evil Twin

I know what some will say....and disagreeing is fine. But.....
That chart is NOT a recommended inflation table. It is a max load table. I would not set my tire pressure by that table. You can, and might get away with it. According to the chart I would be running 42ish psi unloaded, 50 for camping and 100 for loaded with toys. No way. Too much sidewall flex and heat building up at 42. I'll set them to the sticker pressure on the rig.

Thanks for the qualification. I thought the poster was citing a recommended inflation table. I strongly advocate use of those tables as opposed to inflation to max psi.

[babock]

Originally Posted by eye95

Thanks for the qualification. I thought the poster was citing a recommended inflation table. I strongly advocate use of those tables as opposed to inflation to max psi.

The table is called a load/inflation table. That's exactly what Goodyear calls it.

[The Evil Twin]

Originally Posted by babock

The table is called a load/inflation table. That's exactly what Goodyear calls it.

It says “tire load limits” on the doc. It is not sounding like that is the recommended pressure for the weight. I am not inclined to run them at the limit. Aside from that- The higher the pressure, the cooler a tire is going to run. I can’t imagine what temps my tires would get to if I put a 10k TH on 40 psi tires. My sticker is the same as the tire anyway though.

[Airdale]

Originally Posted by Bluetick1955

Just replaced china bombs with Goodyear Endurance ST205/75/15.


My trailer shows pressure 50psig and old tires showed 50 psig


Goodyear tires show ma 65 psig. Which pressure should I run?

From the information above I'm going to presume your new tires are the same designated size as the OE tires. That you went from a load range "C" to a "D".

At 50 PSI both load ranges provide identical load capacities. You have the option to increase your new tires load capacity by increasing their PSI anywhere from 50 - 65 PSI. Tire load inflation charts are designed to assist by providing load information in 5 psi increments. Those increases are not recommendations, just facts of what increases in PSI will provide in added load capacity.

[Mike134]

remember it's the air pressure that carries the load. Higher PSI = greater reserve load= less heat generated. Downside if to high a pressure the middle of the tread wears faster than the sides. I upgraded like you from a C rated 50 psi tire to the Goodyear D 65 psi. I run at 63PSI during the hot summer months and 60 in cooler weather. Tread is wearing uniformly so far.

[eye95]

psi is pounds / square inches. If you divide the actual load on the tire by the psi, that is pounds / (pounds / square inches), which yields square inches. This will be directly related to the square inches of tire on the ground, aka “footprint”.

You want the correct footprint. Increasing psi reduces footprint. Decreasing psi increases footprint. Too much footprint (too little pressure), and tires wear unevenly from the outside of the tread. Too little footprint (too much pressure), and the tires wear unevenly from the middle of the tread. The correct pressure will result in more even wear between the tread edges and tread center.

Furthermore, the correct footprint will allow the tire tread to maintain traction and channel water as the engineers designed it to do.

It is possible to be under (or at) the max rated psi for the tire and still be overpressured for how the tire was designed.

[Airdale]

Originally Posted by eye95

psi is pounds / square inches. If you divide the actual load on the tire by the psi, that is pounds / (pounds / square inches), which yields square inches. This will be directly related to the square inches of tire on the ground, aka “footprint”.

You want the correct footprint. Increasing psi reduces footprint. Decreasing psi increases footprint. Too much footprint (too little pressure), and tires wear unevenly from the outside of the tread. Too little footprint (too much pressure), and the tires wear unevenly from the middle of the tread. The correct pressure will result in more even wear between the tread edges and tread center.

Furthermore, the correct footprint will allow the tire tread to maintain traction and channel water as the engineers designed it to do.

It is possible to be under (or at) the max rated psi for the tire and still be overpressured for how the tire was designed.

PSI is created by the tire’s inner liner and wheel inner area that the injected air is forced upon.

Servicing of automotive tires is very different than servicing RV trailer tires because they are mileage tires and are required to have load capacity reserves. They are designed to withstand forces from steering and traction. Passenger tires have quality grading.

Trailer tires are not required to have load capacity reserves. They are designed to carry heavy loads and withstand severe sidewall forces. They have much shallower treads than automotive tires for cooling. They are age-out tires. They are designed to operate at full sidewall pressures at all times. The larger their footprint on the pavement the more susceptible they are to damage caused by shear forces ("Interply Shear").

The minimum inflation pressure for RV trailer tires is displayed in the vehicle owner’s manual, tire & load placard and the vehicle certification label. The minimum inflation pressure for replacement tires is derived from the minimum the OE tires provided. Options are whatever is left, if any, all the way to sidewall max.

[flyflotrtim]

I would run at full sidewall pressure less 5 psi. set at cold temperature. I don't trust the gauges to be exact and therefore reduce max pressure by 5. I'm not aware of any advantages gained by reducing trailer air pressure other than softer ride which is not a concern for me.

[eye95]

If it were not proper to inflate tires based on the load they will be holding up, then industry engineers who designed the tires would not produce inflation tables.

They do produce these inflation tables. Even for trailer tires. The engineers who design the tires tell you to inflate based on the actual load to be carried.

Moving on.

[Airdale]

Originally Posted by eye95

If it were not proper to inflate tires based on the load they will be holding up, then industry engineers who designed the tires would not produce inflation tables.

They do produce these inflation tables. Even for trailer tires. The engineers who design the tires tell you to inflate based on the actual load to be carried.

Moving on.

Parodically your argument comes-up in relation to general automotive and RV tires.

The automotive industry mandates load capacity reserves for all general automotive products. You cannot have load capacity reserves and inflate to the load carried at the same time.

The only industry that mandates tire inflation for the load carried is the commercial trucking industry.

No one will officially recommend anything other than what has been recommended by the vehicle manufacturer as the correct tire inflation pressures for vehicles built under the guidance of FMVSS.

The only authority for setting recommended OE tire inflation pressures for vehicles built under the guidance of FMVSS are vehicle manufacturers.

For many years tire inflation charts have been standardized and approved by the Tire and Rim Association in the USA. Their primary purpose is for setting recommended cold inflation pressures for OEM tires and plus sized replacements.

[SailorSam20500]

Roger Marble the tire guy published an article on the RVTravel.com yesterday answering this specific question. For towable trailers, especially multi-axle trailers, the suggestion is to run at the max cold inflation number imprinted on the tire. I'll follow Rogers recommendation - I recently replace my tires and went from LR-D to LR-E, so I'm now running at 80 PSI up from 65 PSI.

[babock]

Originally Posted by SailorSam20500

Roger Marble the tire guy published an article on the RVTravel.com yesterday answering this specific question. For towable trailers, especially multi-axle trailers, the suggestion is to run at the max cold inflation number imprinted on the tire. I'll follow Rogers recommendation - I recently replace my tires and went from LR-D to LR-E, so I'm now running at 80 PSI up from 65 PSI.

So I went from load range C to load range E on my 24' boat trailer because you couldn't find C in that size. No chance in hell I would air these up to 80PSI.

And his website confirms this.

https://www.rvtiresafety.net/search/label/Inflation

[SailorSam20500]

Originally Posted by babock

So I went from load range C to load range E on my 24' boat trailer because you couldn't find C in that size. No chance in hell I would air these up to 80PSI.

And his website confirms this.

https://www.rvtiresafety.net/search/label/Inflation

Is your boat trailer multi-axle? If not, I agree, much less reason to go to max CIP.
Here's the article:
https://www.rvtravel.com/rv-tire-saf...terms-rvt-963/


From the article:
"
So what should an RV motorhome owner do?
1. Learn your actual loads on your tires by getting on a scale for each tire position.
2. If you can’t get individual axle end loads assume the heavy end has 53% of the axle load.
3. Use the tire Load & Inflation tables to learn the minimum cold inflation needed to support your actual (or 53%) load.
4. Consider applying a +15% to the load figure to give yourself a reasonable reserve load and consider that your minimum cold inflation. You could also consider adding 10% to the load table pressure if that is easier for you to calculate.
5. Consider adding 5% to the inflation in #4 and use that as your “set pressure.” This gives you a cushion for day-to-day temperature variation which can change inflation pressure 2% to 5%.
So what should an RV trailer owner do?
Do 1, 2 and 3 above.
4. If you want to try and lower the interply shear, I recommend you increase the inflation to the number on the tire sidewall and use that for your set pressure. If you have increased the tire load range from, say, a LR-D to LR-E, you can use as an inflation number the 65 PSI for LR-D and the 80 PSI for LR-E tires, and use that as your set pressure.
5. Try and learn the wheel max pressure rating and do not exceed that number."


And:
"Actually, this clarification confused me. Specifically #4 for a trailer. If you change tires and go up a load level as noted LR-D to LR-E are you suggesting that we should use the CIP of the LR-E assuming the wheels are rated for the higher air pressure? A clearer recommendation would be to always use the CIP for the max load when installed on a multi-axle trailer if this is the case.

Reply
Roger Marble
2 days ago

Yes use the higher CIP if wheel is rated for it. It’s not a good idea to make hard, absolute suggestions on changing parts and ratings as we do not know all the related facts."