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Old 11-05-2015, 12:47 PM   #101
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Originally Posted by lbrjet View Post
Do all of the math you like. The only thing that matters is if your trailer came with 'C's and they are close to being maxed out, change them out with 'D's. It is really just that simple.


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That certainly helps.
It depends on how little load margin there is with the factory tires, and how safe you want to be.

In my case, maybe I'm a little compulsive, but I want the security of knowing that I'm not overstressing the tires in normal usage.

If I just went from 205/75R14 LRC to 205/75R14 LRD (like Kenda Karrier's), the load rating improves from 1760lbs to 2040lbs. Unfortunately, I'd still be overloading the new tires by 300lbs per tire when taking a curve at the advisory 20mph speed.

By going to the Kumho 855 205R14 (this isn't the same as 205/75R14) the load rating goes up to 2270 lbs. The overload on 20mph curves drops to 70lbs per tire. I'm still not fond of this, in part because the diameter went up a little and front and rear tires are pretty close together, but will live with it.

The underlying problem is that my trailer really deserves bigger wheels and more spacing between the axles. This would mean a change in mindset by the manufacturer.
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Old 11-05-2015, 12:57 PM   #102
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My understanding is that dynamic loads are all accounted for in the static load rating.....
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Old 11-05-2015, 01:35 PM   #103
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Gyrogearloose, my DH and I were discussing moving the new axles' mounts (upgrading to larger for 16" wheels), to allow more space between the tires.

We measured our existing on our 2015 Windjammer 3025 and came up with the following:

2.5" between existing 15" tires
Each tire diameter -- 28"
Both tires plus spacing between -- approx. 59"

Wheelwells -- we have approx. 3" above tires to wheelwell, 3" either left or right from tire edge to wheelwell.

Our axles are rated 4,000#'s each.

Our GVWR is 8930 lbs.
Dry Weight is 7900 lbs.
Cargo to be no more than 971 lbs.

As you can see, our dry weight is only 100 lbs. less than our combined two axle ratings.

We are going to check to see if the Michelin XPS tires (load range E tires we put on our Airstream) comes in a smaller height sidewall so that we can perhaps upgrade axles & wheels to 16" and still fit into existing wheelwells with enough clearance between tires and to sides of wheelwells.

Does anyone see a problem with changing the sidewall height? (We may be overlooking some critical point.)

Thanks

Deb
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Old 11-05-2015, 01:54 PM   #104
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Originally Posted by Rbertalotto View Post
My understanding is that dynamic loads are all accounted for in the static load rating.....
Not so, based on the inquiry made by etrailer.com to their tire suppliers on my behalf. I asked if etrailer could supply tires that are rated to handle the dynamic loads that I've calculated. The answer was that the tires aren't tested for anything close to the overloads that they'll see based on my numbers. Look earlier in this thread for details.....


Also, the overloads in crosswind can be continuous, so I don't think any tire testing for transient overload would be applicable.
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Old 11-05-2015, 02:03 PM   #105
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Originally Posted by Windjam2 View Post
Gyrogearloose, my DH and I were discussing moving the new axles' mounts (upgrading to larger for 16" wheels), to allow more space between the tires.

We measured our existing on our 2015 Windjammer 3025 and came up with the following:

2.5" between existing 15" tires
Each tire diameter -- 28"
Both tires plus spacing between -- approx. 59"

Wheelwells -- we have approx. 3" above tires to wheelwell, 3" either left or right from tire edge to wheelwell.

Our axles are rated 4,000#'s each.

Our GVWR is 8930 lbs.
Dry Weight is 7900 lbs.
Cargo to be no more than 971 lbs.

As you can see, our dry weight is only 100 lbs. less than our combined two axle ratings.

We are going to check to see if the Michelin XPS tires (load range E tires we put on our Airstream) comes in a smaller height sidewall so that we can perhaps upgrade axles & wheels to 16" and still fit into existing wheelwells with enough clearance between tires and to sides of wheelwells.

Does anyone see a problem with changing the sidewall height? (We may be overlooking some critical point.)

Thanks

Deb
Deb,

If you were asking me, I'm good at math, but don't want to pretend to be an expert in the subtleties of trailer axles and what might go wrong. If you're going to have a local RV shop swap out for you, I'd ask them. A good shop should have good advice on this.
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Old 11-05-2015, 02:08 PM   #106
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Gyrogearloose, do you have a theory on how so many trailers over the years have remedied the problem by just going from LRC to a LRD? I am definitely interested if maybe I need to find a LRE for my 12Flagstaff 8528RKWS. I've already gone from a LRC to the GY Marathon LRD's.
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Old 11-05-2015, 02:39 PM   #107
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Gyrogearloose, do you have a theory on how so many trailers over the years have remedied the problem by just going from LRC to a LRD? I am definitely interested if maybe I need to find a LRE for my 12Flagstaff 8528RKWS. I've already gone from a LRC to the GY Marathon LRD's.
No idea.
It wouldn't surprise me if a lot of people have driven many miles without failure after upgrading one notch. In some cases the new tires may be enough to eliminate any overload. In other cases they may reduce any overload to the point that the tires handle it even if they're not guaranteed. In my case, I'd rather not bet my safety on tires handling an overload.

It sounds like you haven't had a failure. If I was in your shoes, I'd try to figure out what the load margin is now with the Marathon LRDs. It might turn out that the upgrade you did is enough, or it might not. This depends the specifics of your trailer, tires, and the load you tend to carry. My intent in providing my math earlier is to help people do this for their own rigs.
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Old 11-05-2015, 06:27 PM   #108
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Originally Posted by lbrjet View Post
Do all of the math you like. The only thing that matters is if your trailer came with 'C's and they are close to being maxed out, change them out with 'D's. It is really just that simple.


2010 F250 5.4L 3.73
2011 Flagstaff 831FKBSS
Equal-i-zer 4pt 12K
Just changing the Load Range isn't going to increase load capacity. You need to increase the inflation.
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Old 11-05-2015, 06:31 PM   #109
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Originally Posted by SuicideSaints View Post
I understand the point of the thread and I understand what you are saying, I am just saying that this is a known problem and the only current solution is either roll the maxxed/cheap tires till they fail, negotiate at the time of sale for better tires or drive straight to your shop of choice and get new ones with a higher load rating.

A caveat though which is my main point.....

By the OPs own admission and math, his current tires (at the time of failure) were rated for 1760 each. The trailer is 7700#s - TW (700#s) divide that by 4 tires = 1750 per tire. This is within spec for static.

Now add in 500# of force for dynamic (turns) and add in 400#s for wind force. So that makes the load on the tire 1750 + 500 + 400 = 2650.

In addition to that 2650 it was stated that you "should" have a 20% margin of safety. 2650 + 20% = 3180 to have all my bases covered. Or even if you do 20% safety on the original 1750 tire that still isn't enough.

So this thread would lead me to believe that I need tires that can hold a minimum of 2650 lbs to 3180 pounds (for a 7k# TT) depending on the dynamics and "recommended" safety margin. That is at the top of the range for D tires almost to E tires.

I just dont buy it.......
I believe the 20% is based on the static loads. That would account for a good portion of the theoretical wind and cornering loading.
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Old 11-05-2015, 07:41 PM   #110
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Originally Posted by Tireman9 View Post
Just changing the Load Range isn't going to increase load capacity. You need to increase the inflation.

Obviously.


2010 F250 5.4L 3.73
2011 Flagstaff 831FKBSS
Equal-i-zer 4pt 12K
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