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Old 08-27-2014, 06:47 AM   #57
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Perryg114,

First, while eveness of tire wear is somewhat related to inflation pressure, tires are more prone to wear due to mechanical action. In your case, the rear tires are wearing in the center because they are on the driven axle. Steer tires tend to wear in the shoulders. That's why rotating tires is important. It evens out the wear due to the different positions on the vehicle.

Second, not all tires are designed to wear evenly, so it is a bad assumption that even wear indicates proper inflation pressure. More importantly, inflation pressure is directly tied to endurance, and using a low pressure increases the risk of a tire failure. - and since inflation pressure is tied to tire operating temperature - and that is tied to wear rate, a lower inflation pressure tends to wear the tire faster even though it is wearing it more evenly. Put another way, a higher inflation pressure results in more life in a tire, eve if it means uneven wear.

And lastly, you mentioned using passenger car tires on your trailer. I hope you are aware that the load carrying capacity of a passenger car tire needs to be reduced 10% when used on a trailer (as well as a pickup truck or a multi-purpose vehicle.) While there is some commonality in tire size between ST tires and P type tires, their load carrying capacities are quite different and I hope you've taken that into account. I would hate for you to have an overloaded tire failure.
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Old 08-28-2014, 12:24 AM   #58
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Quote:
Originally Posted by CapriRacer View Post

I hope you are aware that the load carrying capacity of a passenger car tire needs to be reduced 10% when used on a trailer
Hi, you have repeated this several times; Could you explain or document this? When I see a load capacity on a tire, to me that means that's the maximum load for that tire at maximum inflation; Whether this tire is on a big rig or a wheel barrow. I don't see this 10% rule stamped on any sidewalls that I have ever seen. If anything, maybe a car tire rating should be increased because there is no steering involved and no 300 horse power engine pushing on them when on a trailer. In other words, right now, I'm not buying this 10% rule.


Also while on the subject, or close to it; Another forum member has stated the car/suv wheels are not rated high enough for use on a trailer. My trailer is rated at 6,300 lbs GVWR and my Lincoln is rated at 7,000 lbs GVWR. If my Lincoln wheels aren't strong enough for a trailer, how can they be strong enough for my heavier vehicle?
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Old 08-28-2014, 04:11 AM   #59
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Re: Request for Airstream Tire Recommendations

It seems like every month or two, we rekindle the fire under the Airstream tire debate, whether it's a new post on an old thread, or a little different variation initiated in a new one.

It seems like there are basically three camps in these discussions:
  • Those who think ST tires are fine.

  • Those who have switched to "P" (passenger) or "XL" (extra load) tires.

  • And, those who have switched to "LT" (light truck) tires.

We have at least two members who are tire engineers ("Tireman9" and "CapriRacer") and several others who have worked in the tire industry, all of whom have years of experience.

I would personally welcome the input from each of you on which Airstream models you own, the tires currently installed on them, and the reasons why you chose those particular brands and models.

Perhaps, each of you could enlighten us once and for all on which tires we should be running to reduce the chances of blowouts and tread separation.

Thanks, in advance, for your input!
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Old 08-28-2014, 04:39 AM   #60
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Quote:
Originally Posted by ROBERTSUNRUS View Post
Hi, you have repeated this several times; Could you explain or document this?........
This is part of the tire standard as published by the various tire standardizing organizations. The most familiar tire standardizing organization is The Tire and Rim Association - the US based group. (TRA for short).

I'd give you a link to a copy of the page in question (It appears in every yearbook), but I'm moving at the moment and can't get to all the things I need to show the exact reference. But here's what Tire Rack has to say about this:

http://www.tirerack.com/tires/tirete....jsp?techid=70


Quote:
Originally Posted by ROBERTSUNRUS View Post
.......... When I see a load capacity on a tire, to me that means that's the maximum load for that tire at maximum inflation; Whether this tire is on a big rig or a wheel barrow......
Unfortunately, that is wrong.

The load carrying capacity of a tire is governed by the laws of Physics and in addition to tire size and inflation pressure, other things impact the load rating - speed, road smoothness, and the kind of suspension the vehicle has.

In the case of P type tires, they are designed for cars, not trucks. They can be used on trucks if appropriate changes are made. (Trailers, too!)

Quote:
Originally Posted by ROBERTSUNRUS View Post
.......... I don't see this 10% rule stamped on any sidewalls that I have ever seen........
There is only so much space on the sidewall of a tire. There is so much stuff that is required and so much safety warnings, that there is hardly enough room for it all.

Besides, there are only a few sizes where this situation exists - but the rule applies to ALL P type tires. Not to mention that this is all taken care of by the vehicle manufacturer when they size the tires for the vehicle (assuming they do a good job of that!)

Quote:
Originally Posted by ROBERTSUNRUS View Post
........... If anything, maybe a car tire rating should be increased because there is no steering involved and no 300 horse power engine pushing on them when on a trailer. In other words, right now, I'm not buying this 10% rule..........
The good news is YOU don't have to be convinced. It is part of the standard (and the laws of Physics) and has been on the books for decades (I remember it when I started in the industry over 40 years ago. It's not a new thing!)

And the only time you encounter this is when you're dealing with the transition between cars, trucks and trailers - a situation that comes up only rarely.

Quote:
Originally Posted by ROBERTSUNRUS View Post
.........Also while on the subject, or close to it; Another forum member has stated the car/suv wheels are not rated high enough for use on a trailer. My trailer is rated at 6,300 lbs GVWR and my Lincoln is rated at 7,000 lbs GVWR. If my Lincoln wheels aren't strong enough for a trailer, how can they be strong enough for my heavier vehicle?
Interesting question. Would you say the same about the wheels on a Ford Escort?

Part of the problem is that passenger car tires are inflated to much lower pressures than ST tires. What affect that has on the durability of a wheel is an area I have been trying to explore. The best information I have been able to gather is that compared to the load, inflation pressure plays a very small role in the fatigue limit of a wheel.

Also, we're talking about a complex situation with lots of variables. Take your Lincoln for example. Assuming for the moment the Lincoln has 16" wheels, then the largest 16" tire that fits on a trailer has a load carrying capacity of over 3500# EACH!! - making for a total of 14,000#!!!

Are you saying your Lincoln wheels can stand up to that? (I don't think you are saying that.)

I suspect that people saying that the 2 are NOT interchangeable are referring to the fact that tires of considerably more load carrying capacity CAN fit on those wheels.
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Old 08-29-2014, 08:08 AM   #61
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An official answer for Bob in post 59 from the US Government:

************************************************** ****

49 CFR 571.110

Tire selection and rims and motor home/recreation vehicle trailer load carrying capacity information for motor vehicles with a GVWR of 4,536 kilograms (10,000 pounds) or less.


S4.2.2.1
Except as provided in S4.2.2.2, the sum of the maximum load ratings of the tires fitted to an axle shall not be less than the GAWR of the axle system as specified on the vehicle's certification label required by 49 CFR part 567. If the certification label shows more than one GAWR for the axle system, the sum shall be not less than the GAWR corresponding to the size designation of the tires fitted to the axle.

S4.2.2.2
When passenger car tires are installed on an MPV, truck, bus, or trailer, each tire's load rating is reduced by dividing it by 1.10 before determining, under S4.2.2.1, the sum of the maximum load ratings of the tires fitted to an axle.

S4.2.2.3
(a) For vehicles, except trailers with no designated seating positions, equipped with passenger car tires, the vehicle normal load on the tire shall be no greater than 94 percent of the derated load rating at the vehicle manufacturer's recommended cold inflation pressure for that tire.
(b) For vehicles, except trailers with no designated seating positions, equipped with LT tires, the vehicle normal load on the tire shall be no greater than 94 percent of the load rating at the vehicle manufacturer's recommended cold inflation pressure for that tire.

************************************************** ***********

This is the official word we all have to abide by to maintain our insurance coverage to avoid being considered reckless and thus no insurance coverage......

I upgraded to the SenDel 16" T03-66655T aluminum wheels which have a wheel rating of 3,580 pounds at 80 psi which is 900 pounds more rating than the Michelin LT225/75R16/E LTX M/S2 tires I installed (2,680 pounds at 80, psi). Their galvanized steel S62-66655TG wheel which I used for a spare is only rated 3,500 pounds. These tires and wheels are now standard on the 2015 Classic and have been optional on the Eddie Bauer models.

When I upgraded our 2013 25 FB International Serenity with a GVW of 7,300 pounds to the Michelin LTX (P) 235/75R15 XL tires with a sidewall rating of 2,183 pounds at 50 psi, we applied the required 10% weight reduction to 1,985 pounds capacity for a total tire load capacity of 7,940 pounds. Since we had a 1,175 pound tongue weight, the four tires were only supporting 6,125 pounds or 1,541 pound each. That was a better than 23% load safety margin.

That margin for the 25FB with passenger tires is far greater then the margin on our 2014 Classic with a GVW of 10,000 pounds with the factory installed GoodYear Marathons rated 2,540 pounds tab 65 psi. Using the literature tongue weight of 733 pounds, the tires are supporting 9,267 pounds or 2,214 pounds on each tire which is a margin of 13%.
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Old 08-29-2014, 12:23 PM   #62
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I'm on vacation in Oregon and don't always have good WiFi. BUT
CapriRacer did a great job covering the points regarding the rules & regulations.
The 10% reduction ( technically 1/1.1 or .90909 but 10% is easier to remember and calculate) is decades old info for those who know where to look.
When anyone makes a decision to change tires of any type or size from original there is a LOT of research that SHOULD be done first. Tires are not just round black things but are much more complex than most realize.

Hope we have answered your questions Bob.
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Old 09-02-2014, 08:18 PM   #63
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Oh yea, I forgot to tell you. Goodyear replaced the Marathon at no charge. No further problems. I do keep the tires inflated though. A good lesson for me.
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