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Old 03-18-2019, 12:10 PM   #1
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Upgrading wheel size from 14 to 15 to allow for higher rated tires?

Hello -

I spoke with my local tire place about replacing my "china bombs" with a better tire like Good Year Endurance on my 2018 Freedom Express Ultra lite.

My trailer has a 7,600 GVWR (with two 3,500 lbs axels which I don't fully understand yet). However, they advised me that with my current tire size (205/75/14) I could only get load range "D" tires which would have a weight rating of 2,025 lbs each. He advised me that with my 7,600 GVWR i'd be cutting it really close. According to the CAT scales my trailer currently weights 6,900 lbs with gear inside.

It seems like i'm cutting everything really close - has anyone upgraded their wheel size to 15s to allow for a E rated tire for more cushion room? Is this advised at all?
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Old 03-18-2019, 01:52 PM   #2
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Hmm, good question. Interested in what the smart ones say.
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Old 03-18-2019, 02:17 PM   #3
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Originally Posted by magnetic157 View Post
Hello -

I spoke with my local tire place about replacing my "china bombs" with a better tire like Good Year Endurance on my 2018 Freedom Express Ultra lite.

My trailer has a 7,600 GVWR (with two 3,500 lbs axels which I don't fully understand yet). However, they advised me that with my current tire size (205/75/14) I could only get load range "D" tires which would have a weight rating of 2,025 lbs each. He advised me that with my 7,600 GVWR i'd be cutting it really close. According to the CAT scales my trailer currently weights 6,900 lbs with gear inside.

It seems like i'm cutting everything really close - has anyone upgraded their wheel size to 15s to allow for a E rated tire for more cushion room? Is this advised at all?

You get the 7600 GVWR with only 7K worth of axles by assuming a portion of that weight will ride on the truck (tongue weight). Means you basically have zero cushion in your rating. I avoid rigs like this. I replaced the same size tire you have with 225/75-15 LRE. Only thing you have to make sure of is that there is ample clearance between the tires when you increase diameter. Also be aware that your camper will sit slightly higher- we had to go from a single to a double step at the entry door.
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Old 03-18-2019, 02:36 PM   #4
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Without replacing your axles (which will come with a new set of problems), buying capacity beyond 1 load range is a waste of money.

Carlisle ST 205/75/14 load range D tires at 65 PSI can support 2040 pounds each (Chart attached). That is 4,080 pounds and well in excess of the maximum your axles can support.

I looked into axle replacement with my previous camper and, after talking with the design engineers, discovered that the camper's walls are the next fail point at gross weights above the axle load limits. Wall cracking at the corners of wall penetrations (windows, slide outs, and doors) farthest from the axles are the fail points due to frame flexing over the hard axles.
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Old 03-18-2019, 02:44 PM   #5
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My opinion, I don't see you gaining anything in doing this. You have axles that are rated for combined 7000lbs and D tires rated to 8100lbs.

I'm on my 4th year with a trailer that has very similar ratings as yours, and still have the original "china bombs" that came on it.

I think the most important thing you can do is always pay attention to tire pressure.
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Old 03-18-2019, 02:49 PM   #6
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Originally Posted by Herk7769 View Post
Without replacing your axles (which will come with a new set of problems), buying capacity beyond 1 load range is a waste of money.

Carlisle ST 205/75/14 load range D tires at 65 PSI can support 2040 pounds each (Chart attached). That is 4,080 pounds and well in excess of the maximum your axles can support.
x2.

We looked into replacing the axels on our trailer and it would have been a waste of money.

If your GWVR is 7,600 and your loaded weight is only 6,900 lbs., you're doing great and well within tolerance. Just make certain that weight is evenly distributed throughout the trailer.

As someone else said, they've had original equipment tires on their trailer with no problems. You need to pay attention to the speed rating on any tire. Exceeding that is not recommended.
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Old 03-18-2019, 03:01 PM   #7
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As to loads, your axles will only "see" the loaded weight, minus the tongue weight.

At 10% trailer loading, for a 7,000 pound loaded camper, you should have a tongue weight of 700 pounds. Thus your axles will see 6300 pounds (or 1575 pounds per tire).

At your GVWR of 7700 pounds and a 10% loading ratio, your tongue weight should be 770 pounds and 6,930 pounds (or 1733 pounds per tire) on your axles. Your OEM tires (load range C are rated to hold up 1870 pounds with a safety rating of about 150 pounds per tire.

Should you "load tongue light" (a very dangerous way to load since you will have sway problems) say 8% (9% is the absolute minimum for tail heavy), at GVWR your tongue weight will be 616 pounds and the axles will see 7,084 pounds. This will slightly overload your 3500 pound axles, but the OEM C range tires would still be OK at 1,771 pounds per tire, with a safety pad of 100 pounds.

I would still put Load range D tires on just for increased road hazard performance.
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Old 03-18-2019, 03:21 PM   #8
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I would still put Load range D tires on just for increased road hazard performance.

And this is a VERY important part that most people ignore. From living and working on farms/ranches, I can testify that there is a significant increase in puncture resistance as you go up in load ranges.
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Old 03-19-2019, 08:54 AM   #9
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Thanks for the explanation everyone - looks like i'll keep my 14" wheels and add the Good Year Endurance D tires.

How about the spare? Should I replace that tire as well with an endurance tire too or is that fine having the OEM tire since it's only a temporary spare?
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Old 03-19-2019, 09:24 AM   #10
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Seems they build many units that are maxed out on axle and tire weight limits . the stupid argument of the TW tanking weight off the axles is great as long as you're sitting still once rolling down the road the axles and tire will at times carry the full load and then some . so your thought of going to a higher load rated is justified , since the D load will give you beyond what you have you'll do better and getting rid of the china bombs is a big help . if you have room for 15" rims and tires going to a e load would be fine as you don't have to run at max cold for lighter loads . MY unit has 4400 lbs axles with a TT weight loaded of around 9300 max is 9800 . no issues as of yet with over 26,000 towing miles but it is on the back of my mind . i went with Eload tires also up from D and wisd i had 16" rim
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