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Old 02-25-2015, 10:43 AM   #1
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Tire Load Rating

Why do manufacturers put tires on that are not rated for the GVWR? I just looked up what tires are going on my new coachmen 320bhds and they are about 600lbs shy of the GVWR. At discount, the E rated tires are actually $1 less than the D rated so I'm not sure why they don't go ahead and put those on in the first place
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Old 02-25-2015, 12:07 PM   #2
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Originally Posted by dcarver View Post
Why do manufacturers put tires on that are not rated for the GVWR? I just looked up what tires are going on my new coachmen 320bhds and they are about 600lbs shy of the GVWR. At discount, the E rated tires are actually $1 less than the D rated so I'm not sure why they don't go ahead and put those on in the first place
One reason is the axle loading is different than the GVWR rating of the trailer. When the legs are extended and supporting the trailer some of the trailer weight is being supported by these legs. When towing some of the trailer weight is being supported by the king-pin that the truck is supporting so again the entire trailer weight is not supported by the dual axles and tires.

Jim W.
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Old 02-25-2015, 01:04 PM   #3
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Oh well that's actually good to know. Thanks! I was kind of worried lol
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Old 02-25-2015, 01:07 PM   #4
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You need to remember that whether you have a 5er or TT that the tongue or pin weight is not figured in for the axle weight. Load up the trailer to the GVWR and hitch up, the weight thats on the tongue/pin is subtracted from the GVWR.


A 10,000b TT will have a 1000-1500lbs tongue weight. Subtract that from the 10,000lbs and you only have 9000-8500lbs on the tires. 225/75/15 D rated ST tires have a combined load rating of 10160lbs. Minus the tongue weight, the trailer is now under the max tires load.
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Old 02-25-2015, 01:09 PM   #5
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Old 02-25-2015, 04:35 PM   #6
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Why do manufacturers put tires on that are not rated for the GVWR?
Not required. What is required is to have enough weight rating to handle the combined GAWR of the trailer. As you've now realized, hitch weight (tongue or kingpin weight) is not hauled by the trailer tires, but by the tow vehicle's tires.

Example. My old Keystone Sprinter 25RKS 5er has GVWR of 7,900 pounds. But combined axle ratings are only 7,000 pounds. If I load the trailer to 7,000 pounds on the trailer axles, with 15% pin weight I'll have GVW of 8,050 pounds, or overloaded over the GVWR of the trailer. If I don't exceed 7,000 pounds on the trailer axles, then I won't exceed the GVWR of the trailer, and my trailer tires rated for 1,820 max pounds each (7,280 gross) are enough for my trailer.

But I blew out two of those tires on the first long trip, so when I got home I changed out all the ST205R15C trailer tires (and wheels) for ST225/75R15D, which have 2,540 pounds weight capacity, or 10,160 gross. That's plenty for my 7,900 pound trailer, and I never had any more trailer tire problems for the next 12 years towing that trailer about 100,000 miles.

My 2012 Skyline Joey TT had ST205/75R14C trailer tires, rated for 1,760 each or 7,040 pounds gross trailer weight. Since that TT has GVWR of only 5,600 pounds, those small 14" trailer tires are all I really needed. I've towed thousands of miles with those stock trailer tires with no problems. But I prefer to have a little more fudge factor, so recently I replaced all 5 with ST215/75R14C with 1,870 weight capacity, or 7,480 max trailer axle weight. With 5,600 GVWR of my TT, those slightly bigger trailer tires gives me a huge fudge factor.
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Old 02-26-2015, 06:40 AM   #7
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...
But I blew out two of those tires on the first long trip, so when I got home I changed out all the ST205R15C trailer tires (and wheels) for ST225/75R15D, which have 2,540 pounds weight capacity, or 10,160 gross. That's plenty for my 7,900 pound trailer, and I never had any more trailer tire problems for the next 12 years towing that trailer about 100,000 miles.
...
Good to hear as our 8000# trailer has the same size tires.

Think that "fudge" factor is important as trailers can be unevenly loaded side to side, and front versus rear axle. Would rather not cut corners on tire or axle ratings for that reason.
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