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Old 01-31-2018, 07:46 AM   #81
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Originally Posted by GettinAway View Post
....... I wonder how much difference is in the actual construction of the tire. The outside diameter it 1.2" larger on the E's.. Is that just from the additional air pressure? Ha! I think it's possible to overthink this a little.

Yes, I think it is quite possible to overthink this - especially when the difference is diameter is due to a DIFFERENT SIZE and not a different Load Range.
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Old 02-01-2018, 08:05 AM   #82
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Yes, I think it is quite possible to overthink this - especially when the difference is diameter is due to a DIFFERENT SIZE and not a different Load Range.
I see.. 225 vs 205.. R15s. My mistake. I "obviously" don't know a whole lot about tires. What's the difference?
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Old 02-01-2018, 08:52 AM   #83
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The difference is 20mm.

A size 205 tire is 205mm wide. The aspect ratio is .75 so the thickness above the rim is 205mm X 0.75 = 154mm. The thickness is doubled because there are two tire thicknesses, one on each side of the rim.

So the tire thickness is 154mm X 2 = 308mm, which is 12.1 inches. Add the diameter of the rim and the total height is 27.1 inches.

A 225mm tire is likewise 28.3 inches. Show your work.
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Old 02-01-2018, 11:14 AM   #84
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Most passenger car tires are so over the limit as far as carrying a load, no one cares. No one needs to know anything other than the 4 tires that touch the ground are round black and fit.

In a trailer or any vehicle that is going to carry a load especially a greater load needs to know that the parts of the trailer that are going to the "heavy lifting" are actually up for the job. If the parts are not up for the job, some days of towing end up with unexpected results that typically make a negative impact on your bank account.

Know what is needed or be ready to pony up to some one else's career choice. 'Cause you are gonna pay.


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Old 02-02-2018, 10:37 AM   #85
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The difference is 20mm.
I didn't think anyone would be able to pass that one up..

The rest of your information was very informative and helpful.
Thanks
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Old 02-02-2018, 12:56 PM   #86
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Most passenger car tires are so over the limit as far as carrying a load, no one cares. No one needs to know anything other than the 4 tires that touch the ground are round black and fit.

In a trailer or any vehicle that is going to carry a load especially a greater load needs to know that the parts of the trailer that are going to the "heavy lifting" are actually up for the job. If the parts are not up for the job, some days of towing end up with unexpected results that typically make a negative impact on your bank account.

Know what is needed or be ready to pony up to some one else's career choice. 'Cause you are gonna pay.


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I think the above is the crux of the problem.

Unlike passenger cars, trailers are (were?) at best marginally sized for tires. Any slight hiccup and there was a real risk of tire failure.

If you will recall, the Ford/Firestone situation some 17 years back had an element about load carrying capacity. That was what the inflation pressure argument was about. This was been completely addressed by the vehicle manufacturers by 2008.

It is possible that this has also been addressed by some of the trailer manufacturers, but it isn't apparent from where I sit.
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Old 02-02-2018, 01:39 PM   #87
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Originally Posted by CapriRacer View Post

If you will recall, the Ford/Firestone situation some 17 years back had an element about load carrying capacity. That was what the inflation pressure argument was about. This was been completely addressed by the vehicle manufacturers by 2008.

It is possible that this has also been addressed by some of the trailer manufacturers, but it isn't apparent from where I sit.
I think I got my first realization of tire issue from that Firestone event. A good friend of mine had an Explorer with those tires. I did some checking and discovered those tires didn't have a defect per se. If neglected and tire pressure was allowed to drop a few pounds the tires were overloaded. My friend thought they would explode just by driving with them. I had to understand the science of what was actually happening to understand the problem. Those tires didn't have much margin. And tires loose air gradually over time. If the air pressure was always inflated to the spec given, THAT tire problem would not show up.


To often owners want to get in, fire up the engine and go. Since the adverse events to an aircraft are so dire that type of operating sequence is almost never done. Cars, trucks and trailers are complex machines. Especially today. And manufacturers have gone to lengths to reduce the maintenance required. However it seems the one constant over the last century for vehicle owners is not keeping up the maintenance.


That Fram commercial comes to mind.


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Old 02-03-2018, 06:32 AM   #88
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.......... Those tires didn't have much margin. And tires loose air gradually over time. If the air pressure was always inflated to the spec given, THAT tire problem would not show up.......
Ah ..... Mmmmmm ...... Not exactly.

The tire DID have a problem - and it was a combination of things that included the way the plant (Decatur) processed rubber. Tires from other Firestone plants didn't have the same level of failures, and tires from other manufacturers didn't have much of a problem at all!

I go into the detail here:

http://barrystiretech.com/fordfirestone.html

I only highlighted the load carrying capacity issue (inflation pressure) because it is largely being ignored when folks are talking about their trailers.
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Old 02-03-2018, 07:15 AM   #89
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I think I got my first realization of tire issue from that Firestone event. A good friend of mine had an Explorer with those tires. I did some checking and discovered those tires didn't have a defect per se. If neglected and tire pressure was allowed to drop a few pounds the tires were overloaded. My friend thought they would explode just by driving with them. I had to understand the science of what was actually happening to understand the problem. Those tires didn't have much margin. And tires loose air gradually over time. If the air pressure was always inflated to the spec given, THAT tire problem would not show up.


To often owners want to get in, fire up the engine and go. Since the adverse events to an aircraft are so dire that type of operating sequence is almost never done. Cars, trucks and trailers are complex machines. Especially today. And manufacturers have gone to lengths to reduce the maintenance required. However it seems the one constant over the last century for vehicle owners is not keeping up the maintenance.


That Fram commercial comes to mind.


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I wish I had a buck for every car I see running on obviously under inflated tires. I actually walk around my truck before driving it but I’ve seen people leave their driveways and shred a flat tire. Plenty of perfectly good vehicle designs have been condemned due to stupidity. My favorite comment is “how can you drive a rear wheel drive in the snow? It must be horrible”.
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Old 02-03-2018, 07:17 AM   #90
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I only highlighted the load carrying capacity issue (inflation pressure) because it is largely being ignored when folks are talking about their trailers.
So, if your tire load carrying capabilities were double what the load actually was, would you run max tire pressure on a double axle AS? I'm sure you've answered this before, but I just haven't seen it.
Thanks
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Old 02-03-2018, 12:19 PM   #91
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So, if your tire load carrying capabilities were double what the load actually was, would you run max tire pressure on a double axle AS? I'm sure you've answered this before, but I just haven't seen it.
Thanks
This may seem like a roundabout way of answering your question, but here goes:

First, many people make the assumption that the trailer manufacturer did a good job of estimating what stuff people put in their trailers - and I have seen some weighings over the GAWR's (Gross Axle Weight Ratings). I don't know if any were Airstreams or not.

Second, many people look at the load rating of the axle and assume - again - the trailer manufacturer selected appropriately sized axles.

Third, many people weigh their trailer and assume all 4 tires carry the same load. I have been using a 15% variation, but I think the value is closer to 10%. (I just don't have enough data points to be comfortable with the lower value)

And lastly, many people forget that ST tires are speed restricted to 65 mph - and to raise that speed restriction to 85 mph - IMHO, a much more sound value engineering wise - the load carrying capacity of the tire has to be reduced by 20%.

But something that I (and the company I worked for during the Ford/Firestone situation some 17 years back) picked up on was that tires ought to be selected to have a 15% unused (reserve) capacity.

So it depends on where you start.

Roger (Tireman9) has made me aware of ply shear at the belt, and I just don't know what to do about that. Perhaps what I've listed about accounts for it - perhaps not.
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Old 02-03-2018, 06:29 PM   #92
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Originally Posted by CapriRacer View Post
This may seem like a roundabout way of answering your question, but here goes:

First, many people make the assumption that the trailer manufacturer did a good job of estimating what stuff people put in their trailers - and I have seen some weighings over the GAWR's (Gross Axle Weight Ratings). I don't know if any were Airstreams or not.

Second, many people look at the load rating of the axle and assume - again - the trailer manufacturer selected appropriately sized axles.

Third, many people weigh their trailer and assume all 4 tires carry the same load. I have been using a 15% variation, but I think the value is closer to 10%. (I just don't have enough data points to be comfortable with the lower value)

And lastly, many people forget that ST tires are speed restricted to 65 mph - and to raise that speed restriction to 85 mph - IMHO, a much more sound value engineering wise - the load carrying capacity of the tire has to be reduced by 20%.

But something that I (and the company I worked for during the Ford/Firestone situation some 17 years back) picked up on was that tires ought to be selected to have a 15% unused (reserve) capacity.

So it depends on where you start.

Roger (Tireman9) has made me aware of ply shear at the belt, and I just don't know what to do about that. Perhaps what I've listed about accounts for it - perhaps not.
Capri racer, may i address some specifics? I have a fc20 bambi with a gawr of 5k. The gym's are rated at 2540...so like you said, margin is key and my 40lbs assuming i'm at 5000 which i never come close to attaining, translates to 1 or 2 psi. Badzo! This is why i'm looking at the Gye's and nokians.

The gye's are a ST 225/75R15 10 ply 117/E rated tire (2833 lbs) and with a speed rating of N (87 mph). Not that i'll ever approach that I may break the 65mph sound barrier on occasion...66-67 for brief periods.

Are you saying that regardless of the N/87 rating that because it is still a ST tire, speed should never exceed 65?

The Nokians for comparison are a LT235/75R15 load rated 116/E rated as 2760 and a S 112 mph speed rating

Also are you saying the load rating needs to be reduced by 20%...2833 to 2264

Feedback appreciated.

Bob

Ps..i'll have to go back thru my mail, but When asking JC about my brakes, that they indicated the 20 Actually had a 6K axle, but obviously I stay well under the 5K rating.
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Old 02-04-2018, 07:03 AM   #93
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........ Are you saying that regardless of the N/87 rating that because it is still a ST tire, speed should never exceed 65? .......
Sort of.

If you look at your car, the tires on it have at least an S Speed rating (112 mph) even though you are unlikely to exceed oh, say 85 mph. (Note: I am ignoring winter tires for this example). I think that same principle applies here, except that trailers are even more rarely towed at 85 mph.

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........ Also are you saying the load rating needs to be reduced by 20%...2833 to 2264 ......
Again, sort of.

All these things are interrelated and keeping the speed below 65 mph is like reducing the load.
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Old 02-05-2018, 10:02 AM   #94
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Sort of.

If you look at your car, the tires on it have at least an S Speed rating (112 mph) even though you are unlikely to exceed oh, say 85 mph. (Note: I am ignoring winter tires for this example). I think that same principle applies here, except that trailers are even more rarely towed at 85 mph.



Again, sort of.

All these things are interrelated and keeping the speed below 65 mph is like reducing the load.
CapriRacer, thanks for the info and your experience in all your posts. Much appreciated.

bob
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Old 02-06-2018, 06:57 AM   #95
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Originally Posted by CapriRacer View Post
This may seem like a roundabout way of answering your question, but here goes:

First, many people make the assumption that the trailer manufacturer did a good job of estimating what stuff people put in their trailers - and I have seen some weighings over the GAWR's (Gross Axle Weight Ratings). I don't know if any were Airstreams or not.

Second, many people look at the load rating of the axle and assume - again - the trailer manufacturer selected appropriately sized axles.

Third, many people weigh their trailer and assume all 4 tires carry the same load. I have been using a 15% variation, but I think the value is closer to 10%. (I just don't have enough data points to be comfortable with the lower value)

And lastly, many people forget that ST tires are speed restricted to 65 mph - and to raise that speed restriction to 85 mph - IMHO, a much more sound value engineering wise - the load carrying capacity of the tire has to be reduced by 20%.

But something that I (and the company I worked for during the Ford/Firestone situation some 17 years back) picked up on was that tires ought to be selected to have a 15% unused (reserve) capacity.

So it depends on where you start.

Roger (Tireman9) has made me aware of ply shear at the belt, and I just don't know what to do about that. Perhaps what I've listed about accounts for it - perhaps not.
So, if I understand you correctly, even if I go to a tire with 20% more carrying capacity, I should still run at max psi, because the tires im replacing, that came with the trailer from the manufacturer, may not have had enough load capacity to begin with?
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Old 02-06-2018, 08:52 AM   #96
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So, if I understand you correctly, even if I go to a tire with 20% more carrying capacity, I should still run at max psi, because the tires im replacing, that came with the trailer from the manufacturer, may not have had enough load capacity to begin with?
I'm going to be very careful how I state this:

If you go to a tire that has 20% more load carrying capacity - AND - that occurs at something less than the max pressure, then it depends on how much difference there is.

As a side note: I'm a little confused about your question, because, as a general rule, selecting a tire with 20% more capacity means that you are selecting a tire that you are going to run at the max pressure otherwise you won't get the 20%.
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Old 02-06-2018, 10:06 AM   #97
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After reading some of the posts... in my opinion 26 lbs of air in that tire is asking for problems....45 lbs and it has a chance...anyone try it?
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Old 02-07-2018, 06:26 AM   #98
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I'm going to be very careful how I state this:

If you go to a tire that has 20% more load carrying capacity - AND - that occurs at something less than the max pressure, then it depends on how much difference there is.

As a side note: I'm a little confused about your question, because, as a general rule, selecting a tire with 20% more capacity means that you are selecting a tire that you are going to run at the max pressure otherwise you won't get the 20%.
Sorry for the confusion. Yes the 20% would only be gained by running at max pressure. I just hadn't considered that AS would sell me trailer with not enough tire load capacity. I understand you have to be very careful about making any recommendations.
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Old 02-07-2018, 06:56 AM   #99
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Sorry for the confusion. Yes the 20% would only be gained by running at max pressure. I just hadn't considered that AS would sell me trailer with not enough tire load capacity. I understand you have to be very careful about making any recommendations.
Do not get me wrong.

I am NOT saying Airstream sold you a trailer that does not have enough load carrying capacity in the tires they specified. I am saying SOME trailer manufacturers have done so, and I do not know what the situation is with Airstream. The way to tell is to weigh the trailer.

Then there is this grey area - where technically there is enough load carrying capacity in the tires - BUT - there isn't any margin (aka reserve capacity). Designing a trailer so that the specified tires have some reserve capacity is just good engineering. I think 15% is a good number.

Again, I do not know what the situation is with Airstream trailers, and the way to tell is to weigh the trailer.

I am also saying that without knowing what the situation is, it is a good idea to use tires with more load capacity - just in case.

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Old 02-08-2018, 06:31 AM   #100
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Ok thanks. I should have said AS "might" sell me a trailer with undersized tires, not "would" sell me such a trailer. I've come to the conclusion that there is no absolutely correct answer for tire pressures. I do appreciate the time and effort you took to explain it to me though.
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