Correct tire pressure

[Centerfielder]

I'm a recent A/S owner and newly educated to the importance of tire pressure.

I have been unsuccessful in determining what the correct psi is for my rig. I have a 2004 25' Safari double axel, with GVWR of 6300 lbs. I have factory installed Goodyear Marathon Radials for Trailers, Model # ST225/75R15. My A/S manual only says to follow the manufacturer's recommendations.

The tires themselves says max inflation is 65 spi. I have been running them at 62 psi with no problems. I believe this is close to the psi set by the factory; however, I didn't check them until 8 months after I got the trailer. By then they had been through a cold New England winter and registered about 57 psi.

More than one Airstreamer I talked to at a recent rally (none with rigs similar to mine) gave a common answer: 50 psi.

Any suggestions? Thanks, Bob

[pjlingl]

Bob:
My trailer (93 Excella 28') has a data plate on the road side up front which specifies unit weight, tire size, and inflation pressure. In my case, I run Marathon 225/75-15 and I inflate them according to the data plate- at 50 psi. There is another reason I use this pressure. I did not know the difference when I changed tires, but I should have had metal valve stems installed. The rubber stems in my tires are not rated at 65 psi as the tires are and have been known to blow out while rolling down the road. A sudden flat is usually not good on an Airstream. Jeff

[Action]

To reach the full load rating for the tires, the tires need to be inflated to max.

Inflating tires to max has some other benefits:
Better fuel economy for tow vehicle.
Longer tire wear.
Cooler operating tire - again longer wear life.
And like stated above, can carry a greater load.

Trailers typically operate at a high percentage of the total tires capacity. So knowing the total load of the trailer is usefull. And then knowing the total capacity of the tires. Having a total load no greater than 90% of the tire capacity saves the tires from being too stressed. They get enough of that in just being on the pavement.

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[WayWard Wind]

We have an 04 25' Safari & I run our tire pressures at 65# cold. I keep close watch on the outside temps, along with the tire pressures & it's really interesting the pressures changes that occur. We will be changing out the rubber tire stems for metal ones, hopefully this next week. I'll be taking the unit right to the tire shop & remove the tires & have them change the stems on site. Quoted me $ 3.00 per tire. Not bad for peace of mind.
Best,

[DEO]

Originally Posted by Action

To reach the full load rating for the tires, the tires need to be inflated to max.

Inflating tires to max has some other benefits:
Better fuel economy for tow vehicle.
Longer tire wear.
Cooler operating tire - again longer wear life.
And like stated above, can carry a greater load.



>>>>>>>>>>>>>>>>>>>>>>>>>Action

When you make this reference do you mean for the trailer only or should I be maxing the tire pressure on my truck also?

[wahoonc]

Originally Posted by DEO

When you make this reference do you mean for the trailer only or should I be maxing the tire pressure on my truck also?

DEO,
I max the tire pressures on my truck when towing, it will give you the maximum tire loading capabilities. If I understand correctly the manufacturer's tire pressures on a vehicle are based on light loads, and are more for comfort than capacity.

Aaron

[Silvertwinkie]

Ditto. I have both our 04 Safari and our car maxed when towing and I set them before I go.

The coach is set to 65psi and the car 44psi. I've gone with this setup over 850 miles so far. With our '04 Bambi, I had the Bambi again at 65psi and the car at 44psi which is what is on the tire. I had well over 1500 miles of towing with the Bambi last year.

I have also taken measurements on the coach and car after about 100 miles in 75 degree outdoor temps. The coach was at 68psi and the car was at 49psi. It's been suggested that this is taken in to consideration when max tire pressure is created.

I was in 80 degree temps in southern Indiana last weekend and although I did have the tires set to max when I left, the warmer outdoor temps had increased the "cold" tire pressure by a few psi on both the car and the coach. I let out some air to get to the max setting.

[Centerfielder]

Thanks for all the good input. I had not realized the location of the data plate. I will check it out today. I have rubber stems, so that's something I will have to address.

Have a nice holiday weekend. Hopefully in your Airstream.

Bob
WBCCI # 24312

[Cracker]

My 30' 2000 Excella uses the same ST 225/75 R15 LR "C" as Centerfielder's Safari - however the capacity of the Excella is 8,300 pounds. The maximum inflation for the load range "C" tire is 50 psi - which gives a capacity of 2,150 pounds. That translates to 4,300 pounds per axle or 8,600 lbs net on the axles. Of course, +/- 830 pounds of that weight should be on the tongue - which means the axles should only be seeing 7,770 pounds or 1,943 pounds per wheel. That only permits about a 200 pound "out of balance" load per tire. The net of all of this is that there isn't much room for error - at least with the 30' trailers. On the other hand, if I run my LT 235/75 R15 LR "D" rear dual truck tires at the maximum 65 psi inflation, I have the same 2,150 pound capacity per tire - and the same net 8,600 pounds for the dual axle. The only problem with that is that, when the truck is unloaded, the weight on the rear axle is only about 3,300 pounds. That's about 1/2 of the tire capacity at an inflation of only 45 psi - the minimum inflation recommended by Goodyear - regardless of load. The loaded weight of the truck rear axle gets a bit more complicated with the load equalizer hitch, plus the cargo, but it will probably not add more than 2,000 pounds to the axle at worst. When all is said and done, I'll probably maintain the duallys at 50 psi - loaded and unloaded - just to soften the ride. At 65 psi on the duals the ride is much more harsh. The front tires on the truck pose a different problem since, with the diesel and 4-wheel drive, the weight on the front is about 4,350 pounds unloaded. The front tires, when inflated to 65 psi, only have a net capacity of 4,670 pounds - which means that I have to be careful to insure that I don't transfer too much weight back forward with the equalizer hitch. Interestingly, the weight of the truck and the trailer should be almost identical when loaded for travel. I have yet to weigh them in this configuration.

[wflorencejr]

Hey, Cracker...Saw the thread on tires, etc. Sounds to me like your should be running at least "D" rated tires on the 30' A/S. That should take care of the trailer. As for the truck, my 2001 Dodge HD Diesel 2500 uses "E" rated Michelins. I find that with the 65Psi for the trailer tires (recommended) and with 65 front and rear for the truck I'm covering the weight issue. My Safari S/O 2004 28' has a GVW of 9100#. Haven't weighed it, but, probably comes in at about 8800# or so with the stuff we carry. (about 15 gallons of water and usually low blackwater and no grey water aboard.) The truck rides way too rough with 75-80 Psi. The trailer rides better than the truck in any case. I don't subscribe to the idea that A/S needs a softer riding tow vehicle after pulling two previous ones up your way, out West and on some pretty bad roads. Hope this helps. Regards,

[jcanavera]

In 2001 some 30' Classics got out of the factory with "C" rated tires, which was a mistake. One of our fourm members blew out 2 of the "C" rated tires on the way up to the International in Vermont. On the way up he found out that he should have had "D"s. The dealer replaced them all at no cost.

I run my tires at max inflation also. I always have, and have never had a tire problem in 20 years of towing. When you reduce tire pressure below maximum inflation pressures stamped on the sidewall, you are lowering the weight carrying capacity of the tire.

Unless you have an inflation chart from the tire manufacturer, any reduction in pressure is a two fold guess on your part. First you are assuming you know the weight of the trailer with your current load. Secondly you also know the capacity of your tires based on your current inflation pressure.

Most tire failures in trailers occur for two reasons. One is the fact that the tires have passed their useful life and should have been replaced. Two the tires were under inflated.

Last word on the topic from me. The load capacity of a tire is also affected by speed. The slower you travel the greater capcity of the tire, since its building up less heat. Along with the chart that shows tire capacity based on air pressure, there is another that reflects speed. Did you ever note in your manual why they say you can tow a tandom axle Airstream with only three tires at a lower speed? Yep because that single tire can carry more weight if you keep the speed down.

Jack

[Action]

Jack - Just a slight correction. It's not underinflated tires that cause a failure it's heat. Heat Kills tires. When the tire is underinflated (or under heavy load, higher speed) it generates heat. Heat causes bad things to happen to tires.

And you are correct on the inflation. Anything less than full is a guess. Trailers tend to run near max load anyway. So max inflation should be the rule with few exceptions. Passenger car and light truck are a different matter. Most of the time they are not running with a full load. (hmm sounds like another story) So using the vehicle manufacture's recommendation usuall will fit for a normal (unloaded) situation. Like your daily driver back and forth to work. Nothing (drivetrain, suspension, or ?) is really working very hard, unless the weather is poor.

So to answer another Q - when towing I max out the tire pressure. Again it's a big load I am towing. Stress = heat.


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[Cracker]

I don't disagree with wflorencejr on the load-rated "D" tires for the 30' however, mine are the original OEM tires and the trailer has only been towed about 750 miles. I'll probably change the tires, based on the 6-year age, long before the tread is gone. When I was purchasing a spare for my trailer last winter I double-checked with Airstream and the recommended load range was "C." To advoid mis-matching the tires I stayed with the "C."

With respect to having a tire inflation chart from the tire manufacturer, that's where all of my data comes from. Goodyear provides a complete inflation chart on the internet - however I've got it saved in an Adobe format and I don't have the website address. The combination of tongue weight and axle weight equal to or less than 8,300 lbs is Airstream's design weight for the 2000 30' Excella. I use a Sherline scale to check my tongue weight and it is presently 745 lbs with the trailer virtually empty of cargo and fluids. As for the truck, the unloaded weights I stated are actual scale weights with a full tank of fuel and my wife and I in the cab. Once I get loaded for travel I will re-weigh all axles and make any final adjustments. For reasons previously stated, adjustments shouldn't be needed in any of my tire pressures unless I'm way off on the cargo load of the truck.

I'm not sure when Airstream went to the 8,900 lb loaded weight on the 30'. Was it in 2001 - as Jack's comment would imply? If so, the load range "C" tires would be even more marginal - although within range if +/- 890 pounds was on the ball. Improper side-to-side loading can sure make a difference, as can being out of level from front to back. I'm trying to find a scale where I can check my side-to-side loading - at least once - just so I'll know if it's close to being equal.

One last comment with respect to maintaining maximum inflation. You can buy a very inexpensive gauge at any auto parts store that will permit you to quickly check tread wear across your tires. This, in the long run, is one of the best ways to determine if the inflation guidelines you're using are working. In addition, I do a 7-tire rotation on my truck every 7,500 miles and, with the help of an on-board air compressor, I religiously maintain my inflation settings. This may sound a bit anal-retentive - but with 12 tires between the trailer and the truck they represent one heck of an investment! I started trailering in 1963 and I've never had a tire failure on the road with my trailer or tow vehicle! That represents a lot of luck - but I'd also like to think that tire care has a lot to do with it!

[Cracker]

I just noted Action's comment about using the manufacturer's recommendation for tire pressure. That probably works real well for regular passenger vehicles but, on my dually, GM lists the correct inflation for the rear tires at the full 65 psi - as though you were loaded to the max. Talk about a rock!!!

[jcanavera]

Originally Posted by Action

Jack - Just a slight correction. It's not underinflated tires that cause a failure it's heat.>>>>>>>>>>>>>>>>>>>>>>

Yep I neglected to explain the physics. Same goes for speed. Higher speeds also cause heat.

Jack

[vajeep]

Hello all,
The Overlander is in rehab till spring, but the 04 2500 Suburban tire pressure:
Solo 50psi all around. Towing 50psi front 80psi rear. Hint always keep your spare at 80psi(easer to let out)
Have a great digital gage from Brookstone that makes checking psi fun.

Hope this hekps.
abe

[davidz71]

As I see it, there is no need to max the tire pressures on the trailer if you are not carrying the max load. If you are not carrying water in the fresh, gray, black tanks and are not fully stocked for a long trip then why do it. I run 58 lbs on my '77 Excella 50 because I am no where maxed out. Of course, you should head to the truck scales to find out just what your loaded trailer weighs and fill your tires accordingly. My 2500hd with E rated Steeltex tires runs 70 lbs. in the rear for towing rather than the 80 for the maximum. I ran 65 lbs. one time and it seemed a little mushy in the rear. Tongue weight is a little over 1,000 lbs.