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Old 08-22-2013, 06:33 PM   #29
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I have always inflated trailer tires to at least 50 psi. Seems like less would cause some strange tread wear.
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Old 08-23-2013, 06:10 AM   #30
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Originally Posted by LFC View Post
Then I guess Airstream is wrong ?

Airstream told me that's the reason spare tire carriers aren't standard equipment on double and triple axle trailers.
Allow me to be clear on this - and I hope Tireman9 will chime in as well.

If Airstream is NOT providing a spare tire AND they are advising operation without replacing a tire - even on a triple axle trailer and even at 35 mph, then they are wrong - or at least wrong headed. This is NOT supported by the available data.
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Old 08-23-2013, 06:18 AM   #31
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On edit I went back and looked at the specs for your trailer. It came equipped with 7:00 x 15" rims fitted with 8 ply nylon tubeless tires. I'm hoping CapriRacer can provide us with the load capacity for those tires.
Opps! It looks like I missed this.

A 7.00-15LT comes in different Load Ranges (Ply Ratings) and the load tables indicate max loads for both single and dualled application. I'll only quote the singles since we are talking trailers:

7.00-15 LT Load Range C ( 6 Ply Rating) max load 1820# @ 45 psi (50 is a Radial)

LR D (8 PR) 2150# @ 60 psi (Radial = 65)

LR E (10 PR) 2470 @ 75 psi (Radial = 80)
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Old 08-23-2013, 10:45 AM   #32
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As a tire engineer I am suggesting that tandem axle trailers run the inflation associated with the tire max load. This will help decrease the interply shear forces caused by the axles not "pointing" to the center of the circle whenever you make a turn.
This side force greatly increases the forces between the belts that are trying to tear the tire apart.


There are those of us here who use -- or have used -- equipment trailers behind a pickup to make a living. While the tire spec is "greater" on tridem or tandems for the trailer the principle remains the same: sooner or later one will make a tight turn or set of such turns [usually in backing] or a u-turn and the tires can be torn right off the rims.

Make it easy. Finding the exact right tire/wheel may be a lot of work. But keep the TT tire pressure to sidewall max.

The TV is where one wants to work with vehicle manufacturer charts (and RMA information) to get the best pressure
where individual tire position weights are known.

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Old 08-23-2013, 01:04 PM   #33
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Originally Posted by slowmover View Post
As a tire engineer I am suggesting that tandem axle trailers run the inflation associated with the tire max load. This will help decrease the interply shear forces caused by the axles not "pointing" to the center of the circle whenever you make a turn.
This side force greatly increases the forces between the belts that are trying to tear the tire apart.


There are those of us here who use -- or have used -- equipment trailers behind a pickup to make a living. While the tire spec is "greater" on tridem or tandems for the trailer the principle remains the same: sooner or later one will make a tight turn or set of such turns [usually in backing] or a u-turn and the tires can be torn right off the rims.

Make it easy. Finding the exact right tire/wheel may be a lot of work. But keep the TT tire pressure to sidewall max.

The TV is where one wants to work with vehicle manufacturer charts (and RMA information) to get the best pressure
where individual tire position weights are known.

.
I've seen this happen. I watched an SOB tandem going into a back in site in Colorado and during the pivot he had one tire deflate as he broke the sidewall bead with the wheel. So he straightens out the trailer and puts on the spare. Then he starts his back in and at that same pivot point the sidewall bead on the spare separates from the wheel.

I've done it once and it was my own fault. I was moving in January and was moving my HiLo tandem axle trailer from a rental home into my garage. Typically before moving the trailer for the first time in the spring, I always check and pressure up the tires. This time since I only had to move the trailer 3 miles, I figured I'd forgo checking the tires. As it ended up they weren't where they should be and during the back in pivot in my drive, I broke a sidewall bead with wheel.

While those who follow the philosophy of pressurizing the tires based on their load, I've not seen, (or probably will I ever) see what pressures you need to counteract the forces applied to a sidewall during a pivot. Especially since the force involved varies based on the sharpness of the pivot and the surface the tire is on. That's one of the supporting factors I consider in inflating to max sidewall pressures on my tires. I typically avoid pull through sites due to the fact that in the places we travel to, the pull throughs sites tend to be more exposed and less private. I do a lot of backing.

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Old 08-23-2013, 03:07 PM   #34
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Originally Posted by CapriRacer View Post
Allow me to be clear on this - and I hope Tireman9 will chime in as well.

If Airstream is NOT providing a spare tire AND they are advising operation without replacing a tire - even on a triple axle trailer and even at 35 mph, then they are wrong - or at least wrong headed. This is NOT supported by the available data.
It's not "if"....

Would you like me to take a picture or scan of my airstream owners manual ?
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Old 08-23-2013, 05:19 PM   #35
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Quote:
Originally Posted by CapriRacer View Post
Allow me to be clear on this - and I hope Tireman9 will chime in as well.

If Airstream is NOT providing a spare tire AND they are advising operation without replacing a tire - even on a triple axle trailer and even at 35 mph, then they are wrong - or at least wrong headed. This is NOT supported by the available data.
Airstream does note in their trailer manuals that in emergency circumstances you can tow at reduced speeds. The axle remains high enough once the wheel is removed that you can move the trailer.

At one time I used to have a tire chart that showed the load capacity of fully inflated tires (max inflation) at different speeds. In some cases if you had adhered to the Airstream recommended speed, you could tow safely for a limited distance. (At least based on that chart as you step down the speed the tire load capacity goes up). Last time I saw that chart was probably 10-12 years ago. I tried to find it but cannot.

I'm assuming that Airstream took into account the reserve capacity of the tire plus the additional load capacity based on slower speed. Those of us with the heavy Airstreams don't have that reserve. In my case I wouldn't attempt this due to my Classic weight.

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Old 08-25-2013, 02:07 PM   #36
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Originally Posted by CapriRacer View Post
Opps! It looks like I missed this.

A 7.00-15LT comes in different Load Ranges (Ply Ratings) and the load tables indicate max loads for both single and dualled application. I'll only quote the singles since we are talking trailers:

7.00-15 LT Load Range C ( 6 Ply Rating) max load 1820# @ 45 psi (50 is a Radial)

LR D (8 PR) 2150# @ 60 psi (Radial = 65)

LR E (10 PR) 2470 @ 75 psi (Radial = 80)
I took BlackAce at his word and read the question as 7.0x15 rim but tire size is unidentified.
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Old 08-25-2013, 02:19 PM   #37
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Allow me to be clear on this - and I hope Tireman9 will chime in as well.

If Airstream is NOT providing a spare tire AND they are advising operation without replacing a tire - even on a triple axle trailer and even at 35 mph, then they are wrong - or at least wrong headed. This is NOT supported by the available data.
I too have to wonder who at Airstream cam up with this idea. Now I do understand the idea of no spare as the lawyers will say that if you provide a spare you are expecting the user to change the tire and users may not have the knowledge or equipment to do that safely and be injured. At which point some ambulance chaser will sue Airstream.

I would be really interested to hear Airstream say that they are accepting the responsibility for the tire durability after someone followed this instruction and drove more than one mile.

Lot of "Ifs" Only way this might be OK is IF the other tires are inflated to their sidewall pressure and IF the actual load on the tires is only 66% of the max load on the tire sidewall and IF the suspension and axle design evenly distribute the load uniformly to the other 3 tires.

I would be willing to put some money down that whatever load is on the tires it will never distribute evenly to the remaining three. If that were true then each & every Airstream must have exactly 50/50 axle to axle loading and exactly 50/50 side to side loading at all times.

I would really like to see the individual tire loads on any multi axle Airstream from RVSEF.
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Old 08-25-2013, 04:08 PM   #38
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I went to a RVSEF weigh in with my 2001 27' Safari. Hitched up, three of the 4 wheels were within 10 lbs. The fourth wheel which was the rear curbside axle was carrying 40 lbs more weight. This was with my normal camping load including clothing and food. That particular trailer had a street side bath and shower and a curb side closet, twin beds and no dinette.

Trailer weighed in at 6,500 lbs with no water. Airstream's weight chart showed the trailer to be 6,000 lbs with no liquids. I kept that information somewhere and if I find it I'll give you the weight carried per wheel. We weighed the trailer unhitched and hitched up using 4 individual wheel scales.


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Old 08-25-2013, 10:18 PM   #39
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Thanks everyone for all the insights on this. It all gets real in the morning as we head out on our first full day on the road.

After much thought, we've decided NOT to take along our spare tire. Its maximum cold pressure is only 35 PSI, so I'm not sure how much help it would be even if we tried to use it in place of a failed 65 PSI tire.

I get that limping along with only 3 tires might cause those to also fail, but in that case, we'll plan to replace the whole set, keep the best one as a spare, and then we WILL have a 65 PSI spare for the next time. Hopefully by then we'll have figured out a good way and place to keep it until needed.

Thanks for the warning about shear pressure when backing. We'll be extra careful about that, avoiding sharp turns whenever possible.

Based on our experience watching bike tires pumped to the maximum pop on hot days, we'll start out with the pressure a bit below maximum, as we are expecting hot days initially. We're also aiming for 55 MPH tops on the road, both for mileage and for tire health.

We'll update this once we know how it all turned out...
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Old 08-25-2013, 10:34 PM   #40
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Based on our experience watching bike tires pumped to the maximum pop on hot days, we'll start out with the pressure a bit below maximum, as we are expecting hot days initially.
We'll update this once we know how it all turned out...
Keep in mind that a bicycle tire really can't be compared since the construction is not the same. Your tires on your tow vehicle and trailer are designed to be able to accommodate heat generated on the road and max. cold temperature instructions account for potential pressures increases that occur once rolling.

The only time I truly make adjustments on tire pressures on the road is when we are changing climates. In those cases I may reduce or increase my pressures to get them back to max inflation recommendations. Note however I only do this when the tires are cold. Never when they are warm from running or from direct sun exposure.

For example sitting in my driveway, the morning sun hits the tires on the street side. It's not unusual to see a 2-4 lb difference from side to side of the trailer. So one side in the shade will be sitting at 80 psi, and the sun exposed side could be 84. I will not adjust the pressure to match the curb side since the pressures will even out once we start rolling.

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Old 08-25-2013, 11:40 PM   #41
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Mr. Jim

Are you sure that you are not reading the warning for the MAXIMUM pressure when mounting the tire on a rim? To get the bead placed properly on the rim.
35 lbs sounds low for a trailer tire.
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Old 08-26-2013, 06:33 AM   #42
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Thanks for the warning about shear pressure when backing. We'll be extra careful about that, avoiding sharp turns whenever possible.
That only applies if you load your Airstream with an extra 2 or 3 thousand pounds of concrete.
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