Air pressure threads?

[starleen2]

Ok - I'm At the other end of the spectrum - I have TSC 12 " tires and I run about 50 lbs in them and have no problems and my rigs is about 1000 lbs. They say that they can be inflated to 90 psi - to achieve the rating on the tire - however - I get a little squeamish about inflating to 90 psi - But 50 is a good middle. As noted above there is difference in trailer tires and automotive tires - mostly being in the sidewall.

[Scooter]

If I'm reading your question correctly, you want to know if running a certain tire pressure will do something good or bad for the trailer...Absolutely!

The way your finished, loaded trailer rides is directly effected by what tire pressure you're running. Running a very low air pressure will make the trailer more likely to wiggle and sway behind the tow vehicle. It will seem very bouncy and squishy and wear the tires on the outer edges. If a high PSI is used, the trailer will ride very harsh. Hitting bumps will make the trailer want to jump. The tires will also be over inflated and wear in the middle.

For even wear and a pleasant ride, there is an optimum PSI.

If you know the weight of your trailer loaded and ready, you're half way there. Take your trailer for example: GTW 1000. If balanced correctly, the tongue should have a weight of 100# and each tire should share the rest of the load at 450# each.

Lets say your trailer has 4.80-12 tires rated at a max load of 750# at 60psi. If you take your trailer weight knowing that only 450# is going to be riding on each tire, it's just a simple math formula.

Take your load per tire (450#), multiplied by the max PSI of the tire (60), divide that by the max load of the tire (750), and you get what should be your correct PSI for maximum ride and wear quality.

450x60= 27000/750= 36PSI

So, in this case, your trailer will perform best with a tire pressure right around 36PSI.

This formula can be applied for any tire as long as you know the max weight, PSI, and the actual weight it will be carrying.

Hope this helps.

This formula yields 11 psi for my rig. Youbetcha, I'm willing to try it, but will carefully observe for the first 50-100 miles till I get confident with such low pressures. (I've been running 28 with OK results.)

Admittedly, my 2000lb axle is too stiff for my 850 lb teardrop (90lbs tongue). Tires have 1750 rating at 50 max psi.

[Frog]

I don't think I'd run tires with only 11 PSI. You may have a problem with the tires not staying on the wheel or at least the bead breaking loose enough to lose air, especially if you have to make a quick turn and/or on a rough road. Personally, I'd go more like 25 - 30 psi as a minimum.

I towed a small empty utility trailer from California to Virginia with 4.80 x 8" tires. The trailer weighed 180 lbs empty and the tires were rated at around 600 lbs each. I started out with 60 psi to reduce friction and the darn thing would leave the road on some small bumps. I pulled over and reduced the pressure to about 35 psi and the trailer behaved like it should.

I'd pump them up for a full 1,000 lb load, and accidently put 1,800 lbs in the trailer on an 8 mile run from the stone yard because I grossly miscalculated the weight I was carrying. Those 4 ply tire were on the trailer from 1981 to 2007 when I replaced them with 11,000+ miles on them. They were Goodyear tires and were probably better than the made in China replacements, even upgrading to 6 ply.

[schaney]

I missed this thread before. There is a Tire and Rim Association Standards guide for load / air pressure for any size tire. Just ask for a copy of the page for your tire size at your favorite tire store.

Clarkbre, your formula is close. For the 5.30B-12" tires I normally run, they are rated at a 855 lb load capacity per at 55 lbs. Based on the rate chart I have for them, I run them at 25 lbs, which gives me a 535 lb load capacity per tire. Using your formula I came up with 34 lbs pressure based on the above info.

[kylemorley]

I recall reading once in a book on race car tuning that you set your tire pressure on a race car is by driving a typical lap, then reading the temperature across the tire - if the center is hotter than the sides, you increase it, or vv. The same method should work on a trailer, just by driving down the road a while then checking the heat across the tread. But I have never heard of it being done.

Doing so required a special tire thermometer, but apparently the cheap non-contact thermometers harbor freight and everyone sells will do the job just fine.

[caseydog]

I understand the math (no problem) but it's stated in the HF manual that the tires must be inflated to 60psi.....there is no mention of changing the pressure to reflect the load....there have been instances of individuals on this board who have had tires disintegrate when they run them at less than 60psi......
Philip

The HF manual may say 60psi; however, it says that so when the trailer is fully loaded and the manufacturers GTW is at its maximum you dont have a tire blow out.

Our camping trailers are completely different beasts. For the most part the builder knows close to the final weight, balance, and gear load of the trailer. Adjusting tire pressure, axle location, and tongue length are all part of building and "tuning" the trailer to fit our needs. I guarantee your HF manual doesn't advise moving the axle position and/or altering the frame but it's a very common practice here on this board.

I have a Redtrailers utility trailer (almost identical to HF) and always run a tire pressure of 50psi. It rides like crap when it's empty but when it's got a weighted load it rides very nice.

In the cases where tires have disintegrated, it's easy for someone to blame it on tire pressure...it's the easiest way out. But, in the end, there are always factors that lead to operator error.

I would question everything relating to a tire blowout:
Was the trailer loaded, weighed, and tire pressure calculated?
When was the last time the tire pressure was properly checked?
How many miles were on those tires?
Were the tires rotted or cracked from sitting out in the weather?
What speed was it going when they came unglued? Some trailer tires have a 55mph limit.

"Nope, it was just tire pressure!"...Then why wasn't it addressed before the operator hit the road?

Anyone else want to chip in on this...at the moment I'm not convinced ...especially based on other previous comments...
Philip

You can run 60 pounds if you want. I run softer than what is rated on my TD, because it weighs about 700 pounds.

The thing that causes tires to blowout without any road hazard causing it, is heat. If you run too low for the weight you are carrying, the tires will overheat, and blow out.

This is also true for cars. If you have your SUV loaded with 300 pounds camping gear, and holding up 200 pounds of tongue weight, you should add some air to the rear tires of your SUV.

I am using regular passenger car tires on my TD, and I run 28 pounds of air in them. On my first long trip, I stopped about 30 minutes into the trip, and felt the tires. They were just slightly warm, but not hot. The TD was riding comfortably behind me. So, I'm confident that I am good to go at 28 pounds in my tires.

My tow vehicle manufacturer recommends 36 pounds on my crossover, and 40 pounds in the rear if I am towing or carrying a load in the back.

My suggestion is to do the math, and then test the results. When you find the optimum pressure, stick with it.

CD

[caseydog]

If I'm reading your question correctly, you want to know if running a certain tire pressure will do something good or bad for the trailer...Absolutely!

The way your finished, loaded trailer rides is directly effected by what tire pressure you're running. Running a very low air pressure will make the trailer more likely to wiggle and sway behind the tow vehicle. It will seem very bouncy and squishy and wear the tires on the outer edges. If a high PSI is used, the trailer will ride very harsh. Hitting bumps will make the trailer want to jump. The tires will also be over inflated and wear in the middle.

For even wear and a pleasant ride, there is an optimum PSI.

If you know the weight of your trailer loaded and ready, you're half way there. Take your trailer for example: GTW 1000. If balanced correctly, the tongue should have a weight of 100# and each tire should share the rest of the load at 450# each.

Lets say your trailer has 4.80-12 tires rated at a max load of 750# at 60psi. If you take your trailer weight knowing that only 450# is going to be riding on each tire, it's just a simple math formula.

Take your load per tire (450#), multiplied by the max PSI of the tire (60), divide that by the max load of the tire (750), and you get what should be your correct PSI for maximum ride and wear quality.

450x60= 27000/750= 36PSI

So, in this case, your trailer will perform best with a tire pressure right around 36PSI.

This formula can be applied for any tire as long as you know the max weight, PSI, and the actual weight it will be carrying.

Hope this helps.

This formula yields 11 psi for my rig. Youbetcha, I'm willing to try it, but will carefully observe for the first 50-100 miles till I get confident with such low pressures. (I've been running 28 with OK results.)

Admittedly, my 2000lb axle is too stiff for my 850 lb teardrop (90lbs tongue). Tires have 1750 rating at 50 max psi.

Yikes. You may have issues with holding the bead to the rim at 11 pounds. If you are already getting good results at 28, then stick to that. I would not personally want to go below 20 pounds on any tire.

CD

[Larwyn]

I would keep them inflated kinda tight especially in the summer when the roads are hot. I've seen lots of shreaded small boat trailer tires when the temps hit the 100's. Those little tires make a lot of revolutions and will not stand up to much sidewall flex before overheating and coming apart. If they are running cool, you're doing fine, if not, pump em up.

[Corwin C]

I would be VERY hesitant to try to improve ride by lowering tire pressure. If your ride is too harsh I would look at de-rating the suspension (or throwing in a few extra dutch ovens and the groceries to go with them) and if things are bouncing I would look at possibly adding shocks. I'm aware that this is not an easy or inexpensive fix, but properly correcting issues will pay off in the long run. When playing with the radial and shock forces that a tire experiences at freeway speeds, there is an extreme amount of dynamic, potentially explosive energy involved that I personally hope to never tangle with.

The capacity of a tire is based more upon the volume of air within the tire and the ply structure in the sidewall than the pressure. An extreme example: a racing bicycle tire (very thin, flexible sidewall, very low volume) even though it is only carrying 100 to 150 lbs often requires 90 psi, whereas an ATV tire (also thin flexible sidewall, but high volume) that is carrying well over 200 lbs only requires 4-5 psi. Carrying that example forward, a 15 inch radial tire carrying a 1500 lb trailer may get by very well with 30 psi, but the same weight on a 12 inch radial tire may require 60 psi or more.

Inflation information on the sidewall generally only reflect maximum pressures under maximum loads. A linear formula to attempt to determine the correct pressure will not work in a calculation that requires differential and integral calculus.

My advice: contact the manufacturer of the tire and get their recommendation for tire pressure at the load that you are subjecting the tire to.

Corwin

[Frog]

Corwin: Good if not the best advice about checking with the manufacturer for MINIMUM and for recommended pressure for the load on a particular tire.

[schaney]

Here is a older copy of a page from the Tire and Rim Association Standards for load / air pressure. This is the maximum load standard for given air pressures that any tire of the listed size must meet.

So if you know your loaded weight on the axle, just use the chart to look it up, and this is the lowest you can safely run your air pressure. You'll be safe running your air pressure anywhere from there, to the maximum air pressure rating. Never run lower that the recommended air pressure for a given weight, you're asking for problems.

[Frog]

Schaney:

Could you please send the website for the tire and rim association so we can look up our own tire sizes?

Thanks.

Frog

[danlott]

Here is a link for different tire sizes from Goodyear.

http://www.goodyear.com/rv/pdf/rv_inflation.pdf

Dan

[Frog]

Thanks Dan:

Great info.

People reading this should be aware that putting a load range G tire on a load range E wheel will not automatically increase the carrying capacity of that wheel to the G range level due to wheel strength limits. The wheels and tires and bearings and springs all have to be of equivalent strength.

Frog

[hugh]

I am running 31" light truck tires on my trailer. My TV has 35" tires and if you follow the sidewall directions you would pump them up to around 50 psi. What the jeep forums recommend is pick a pressure and run a large stripe of chalk across the tread, then roll the vehicle in a straight line a few revolutions. If the chalk has worn evenly you nailed it, otherwise air up or down accordingly. So i run about 32 on the TV and pretty much the same on the trailer. I doubt if this would work for trailer tires given there different requirements though.