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Old 05-05-2022, 11:45 AM   #1
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Need new tires

Hi,
Want to get better tires for my TT. I'd like a larger diameter to go up\down short steep inclines easier. Haven't had many problems (yet), but watched 2 separate tires blow 45 mins apart on my buddy's 5th in front of us last summer so I figured an upgrade is a good idea.

I don't want go so big that something gets comprised. I'm new enough that I don't understand yet if any increase in size at all could cause issues.

What limitations am I looking at with my TT? Any primary questions I should ask the dealer when they suggest tire xyz from the shelf?

32' Bumper to tongue
2018 GD Imagine 2800BH
5500lbs dry
7000lbs max (2 x 3500 axels)
We probably haven't gone over 6300lbs. We drive dry 9/10 trips and only half full once a year.

Thanks for any help or suggestions.
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Old 05-05-2022, 12:15 PM   #2
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There's a tire size chart online at https://tiresize.com/calculator/
Simply put your size tires in and it will provide the comparison so you can chose what size you want.
Also I would suggest Goodyear Endurance tires for your trailer, if they are available in the size you need. They are much better. Higher speed rating and stiffer sidewall. Specifically designed for RV and boat trailer.
As to the pressure you'll need to know the weight and consult the manufactures guide for that weight and tire.
Good luck!
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Old 05-05-2022, 12:26 PM   #3
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Specs for your GD Imagine 280000BH call for 15-inch D rated tires and 9495 lb GVWR, https://www.rvusa.com/rv-guide/2018-...2800bh-tr33306. 15-inch D-rated tires have 8 ply and can support 2150 lbs max / tire at 65 psig (verify with tire manufacturer). If you want more safety margin suggest a higher load rated tire, say E or G. My tow vehicle, fifth wheel trailer and rv all have G rated tires.
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Old 05-05-2022, 07:40 PM   #4
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A 7495 gvwr trailer (Grand Design 2800 bh specs) with 3500 lb axles doesn't need a E load tire or especially a 16"/17.5" load G tire. Those are for heavy weight trailers with 7k and 8k axles.

Even at full 7495 lb load = 1800-1900 lbs per tire. Now add a good 20 percent reserve capacity = 2200-2300 lbs per tire.
Specs calls for 15" wheels so the ST225/75-15 D load range gives your trailer plenty of reserve capacity.

Best to give us your trailer OEM tire/wheel size/trailers gvwr. Makes for easier estimations/guessing/opinions.

The Endurance from Goodyear would be a good choice as are Providers or Carlisle HD tires. All three have good long term service records.
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Old 05-06-2022, 05:37 AM   #5
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The GY Endurance 225/75-15 will be E load range. That's what you want.
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Old 05-06-2022, 06:24 AM   #6
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I went with the Carlisle radial trail on my 6000# 28' trailer and went up a load range. they track well and still look new a year and 3000 miles later.
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Old 05-06-2022, 07:54 AM   #7
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You really ought to go to a scale while fully loaded to get a real number rather than making a guesstimate.
2 3500 lb axles does not necessarily make 7000 lb max. Manufacturers often add tongue weight for a higher number. Some, like mine, actually have a lower max, probably due to frame limitations. There should be a sticker on your unit giving you tire size, max cargo and gross weight.
From personal experience, Maxxis and Goodyear Endurance have done well.
Going up in size can cause clearance issues.
Increases in load range might mean a change in wheels, depending on what air pressure rating your existing wheels have.
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Old 05-06-2022, 08:33 AM   #8
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This is such a great forum. Thank you for the info.

I need better tires, but the only way I'm getting more height is if I upgrade the axels to get a larger diameter wheel on there. Still not sure if we'll keep this for a decade or get something different in a couple years so I'll figure that out before investing in axels.

I've got 2 different brands of D rated tires installed. I'll get at least E rated and will probably get the GY Endurance or the Carlisle depending on availability.

2 x front TT tires are Westlake Super ST
- ST205/75R15
- Max PST 65 / Weight 2150 / 1870
2x rear TT tires are Gladiator QR25 - TS
- ST204/75R15
- Max PSI 65 / Weight 2150 / 1870


Thanks again for the help !!
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Old 05-06-2022, 10:37 AM   #9
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Sounds like a good plan. Either the Goodyear or the Carlisle HD will be an improvement.
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Old 05-06-2022, 10:52 AM   #10
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Why don't you just use the same sized tire and go up a load range to LRE?

All you have to do is ensure the valve stems and wheels are rated for the LRE 80 PSI rating.
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Old 05-11-2022, 08:13 AM   #11
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I agree. Just go up a load range. Another thing that rvers don't often know is the speed range of the tires. was you buddy exceeding the failed tire speed range? I have seen it.
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Old 05-15-2022, 11:01 PM   #12
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While 225/75R15 would be the next size in the GY Endurance, the 205 is acceptable for a 5.5 inch wide rim, while the 225 requires a 6 inch rim width as a minimum. To go larger than the 205 you need to know your rim width.

With the Endurance the 205/75R15 is only available in the load range D and the 2150 lb rating. If you have the room and the rims, you could go to the 225/75R15 load range E if you really want to.

My Bigfoot has a 7000lb GVWR and came with 225/75R15 tires. I have the GY Endurance on it with the 2830 lb rating, and installed 6 lug rims rated at 3200 lbs, but my limitation is the hubs and axle stubs which are rated at 1750 lbs. so the reality is, there is no weight gain, just some durability gain by running a oversize tire.

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Old 05-16-2022, 06:08 AM   #13
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Quote:
Originally Posted by FastEagle View Post
Why don't you just use the same sized tire and go up a load range to LRE?

All you have to do is ensure the valve stems and wheels are rated for the LRE 80 PSI rating.
One of OP desires is to "increase clearance when going up/down steep inclines".

This requires a larger diameter tire and/or raising/flipping the axles.

If not done from the factory you could "flip" the axles, which means putting the leaf springs on top of instead of under the axle. This would provide a few more inches of clearance. However, it is possible your leaf springs are already ontop of the axle. In that case, it is possible to have taller shackles welded on your trailer.

If you go up a tire size, make sure you have plenty of cleance between the top of the tire and the bottom of the trailer to allow the axle to move up it's full range without hitting. If there isn't enough room you are back to easing the axles by either putting the leaf springs ontop or having taller leaf shackles welded on.
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Old 05-17-2022, 10:45 AM   #14
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Quote:
Originally Posted by jrollf View Post
One of OP desires is to "increase clearance when going up/down steep inclines".

This requires a larger diameter tire and/or raising/flipping the axles.

If not done from the factory you could "flip" the axles, which means putting the leaf springs on top of instead of under the axle. This would provide a few more inches of clearance. However, it is possible your leaf springs are already ontop of the axle. In that case, it is possible to have taller shackles welded on your trailer.

If you go up a tire size, make sure you have plenty of cleance between the top of the tire and the bottom of the trailer to allow the axle to move up it's full range without hitting. If there isn't enough room you are back to easing the axles by either putting the leaf springs ontop or having taller leaf shackles welded on.
No one likes the rules and procedures. However, they are in place to insure vehicle safety for the field, meaning future owners are protected.

The first hurtle comes when changing tire designated sizes from those certified by the trailer builder to something different and larger. A tire designated size may have 3/4 additional load ranges. Those do not require any sort of validation other than assuring wheels and valve stems provide the necessary PSI rating for the increased load range letter, to gain maximum load capacity from the tire.

The very first step for increasing tire designated sizes ("plus sizing") is gaining approval from the vehicle manufacturer. Once it's determined the plus sized tires can be used there are industry procedures to follow that will ensure a new recommended cold inflation pressure for those tires is established and documented for the current user and all other consumers.

Once a consumer physically alters a vehicle, the alterations must be certified. Especially welding onto the frame. The welder needs to be certified and the work must be done according to certification standards and documented, normally on the bill of sale.

No matter what sized axles are used the vehicle GAWRs will remained at vehicle certified capacities. However, when those axles are not installed to vehicle standards, the action is considered a vehicle modification and must be documented and certified.

By typing; 49 CFR part 567 on your computers search engine you can read all about vehicle certifications and modifications. (It's not a long winded document).
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