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Open Roads Forum  >  Do It Yourself Modifications and Upgrades (DIY)

 > ST225/75R15 to LT225/75R16 Conversion

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JBarca

Radnor, Ohio, USA

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Posted: 08/30/12 08:08pm Link  |  Print  |  Notify Moderator

This upgrade may not be for everyone, however for those who have made it to the same point I have, this may help. This thread is about my conversion from ST to LT tires and the challenges of this tire size. I had ST225/75R15 Load range D on my camper. After 3 tire failures for detachment of the steel belts in the treads this summer, I kicked up a notch on my tire research on what to do with replacements. I was anticipating this at the 5 year mark and ended up here at the 3.5 year mark. I came to 2 choices. I wanted to have 18 to 20% reserve load capacity above the highest loaded wheel position. I also had to be able to get the tire into my wheel well and an axle flip was not in the cards. I narrowed this down to:

1. Upgrade the wheels and the tires to ST225/75R15 Load range E. Maxxis would have been the brand if I stayed with ST’s. This size would fit in my wheel well as the OD is the same and I gain more reserve capacity.

2. Upgrade the wheels and the tires to LT225/75R16 Load Range E. These created an OD issue where I would not have enough wheel well clearance.

So here I am earlier this year with a tire failure that I found here in my yard doing annual maintenance on the axles. I have been researching LT tires for my camper for some time. The drawback has been the size, ST225/75R15 Load range D. I have not found any LT tire that fits the same OD and width and has the correct weight ratings in that size. After my 1st failure, my research went into high gear as the problem was now beginning. By the time I converted I was up to 3 failures. The search turned up more and more frequent discussion among at least 1 tire company, 1 TT manufacture and a few tire engineers that tandem axle trailers should have a higher tire load capacity of reserve due to the tandem axle setup. The heat and other factors associated with the side flexing of a tandem axle setup even more aggravates the ST trailer tire problem in the industry.

Sunline, my TT manufacture was good to me. They on purpose at least put tires on the campers, (the newer ones I know of, maybe all of them,) where the tire load ratings can hold the entire GVWR of the camper. Not all brands do this. Since the truck holds up the tongue as long as you do not exceed the GVWR you have some % of reserve built in. How much depends on how your camper is built and how you load it. All tire positions are not loaded equal.

After my tire failure I wanted to know why it failed in case I messed up as I am meticulous to the point of being anal that everything on my TT tires is under the max of everything. So I went to the truck scales and here is what I came up with. Every time you weigh your camper it seems to grow more weight… With full fresh water I have managed to fill mine to just under GVWR. Yet the tires where still not above or at their load ratings but they are not the 18 to 20% more reserve as now thought to be needed for tandem axles.
[image]

In order to get my load ratings up to the 15 to 20% extra reserve capacity on all tire locations I needed to move up to a ST225/75R15 E load range or take the jump to LT tires in 16”. I needed new rims regardless of which way I went. Do I buy 5 new rims and stay with ST’s or buy 5 new rims, go to LT’s and then deal with the tire fender clearance problem? The lack of any US or Canada built ST trailer tire also weighed in this decision.

So after a lot of research and thought I came up with this plan. I bought 1 new Maxxis ST225/75R15 LR D to replace the one failed tire. I was also going to buy a flat deck trailer to transport my tractor and large mower back and forth to another property we have along with other moving needs. That flat deck uses the same ST225/75R15 LR D’s. I made the deal with the local trailer builder that I would bring my own tires and rims and to set the trailer up for 16” tires as they offer that upgrade too. The ST’s they were going to install I did not want. So I bought 5 new rims and 5 new LT225/75R16 LR E tires to first put on the flat deck. The long range plan was to later swap the ST’s from the camper to the flat deck and the LT’s to the camper. For those curious here is the trailer and the tractor.
[image]

Now what made my mind up to go to LT’s?

My ST tires had a lot of stone cuts in the threads. Not a problem of air leaking or at this stage even tire failure, yet they had these very little cuts and the truck that pulls the same camper over the same gravel and campsites has none. I needed more cut resistance and the LT’s I picked offered that.

Quality. My faith in imported ST trailer tires is just not that high. While Maxxis has a higher track record of surviving more, they are not the solve all as they are still ST tires and they too have issues with weather cracking as I have seen on 2 of my sets/campers at year 4.5.

All season tire. We winter camp and not all tires are made for use below or near freezing. This was not a show stopper but a need.

Money, this is always a factor. Trailer tires is not a place to cheap out on. I was going to spend big bucks on new rims and at least Maxxis ST’s in LR E so I’m already spending more than normal. The LT’s I picked where $30 more a tire. So there is a $150 difference between LT and ST. While that is a enough to make one stop and think about it, I’m willing to pay a little more for what I feel is higher quality.

Speed rating and heat. While I only tow at 55 to 60 MPH (and that is all I need or want to) ST’s are maxed at 65 MPH. So I’m running a tire right up at it’s limit for heat generation which is a large part of tire failures. Yes, they are supposed to take it however which is better, running a ST tire rated at 65 MPH at 60 or a LT tire that can go way beyond it as far as being able to handle higher heat?

In this case I picked BF Goodrich LT225/75R16 LR E All season Commercial truck tire. Bought them from Discount tire.
http://www.bfgoodrichtires.com/tire-sele........W/commercial-t-a-all-season/tire-details

[image]

Now the rims. I wanted a quality rim and since I spent enough on the tires I went with steel rims. Sunline also at times used Dexstar’s on them. And after researching they are made here in the US or at least the 16” I bought. Yes, believe it or not… I bought 5 of them from Etrailer and I am pleased with the rims.
See here
[image]

They are painted very well, inside and out.
[image]

And the quality shows right at the stem hole. They on purpose made this flat to allow a metal valve stem to work right on them. See the stamped flat area around the stem hole. I had a heck of a time getting metal stems to seal on the 15” Korea made ones I had on the camper now.
[image]

[image]

[image]

And no need for an external gasket. They seal from the get go like they are supposed to.
[image]

So I mounted all 5, added DynaBeads for balancing and here they are in front of my utility trailer full of work…(mulch)
[image]

So far this was the easy part. I put the LT’s on the flat deck, had the 1 new Maxxis spare, put the unused Denman spare on for the failed one and we headed out on vacation on a 1,600 mile trip. At this point the other 3 Denman’s where OK other than tiny stone cuts in the thread. During the trip I stopped at a gas station after about 800 miles and, holy cow, is that tire a bulge on the thread? Sure is…

If you going to change a tire on a camper, the NYS Thruway rest stop is the place to have do it... I dodged a bullet on these tires letting go a 2nd time. I caught it before it let go. I was lucky, I had extra cribbing with me as I needed it to level up the camper at my mother’s house during the trip. The day was perfect, just hot, and I’m not on the side of the interstate with traffic buzzing by at 65 to 80 mph.
[image]

[image]

We completed our road trip and the time came to sort out the ride height on the camper. This is the harder part of this LT conversion and may be the what stops some from doing this upgrade on this tire size. I’ll post the suspension lift on the next post.

* This post was last edited 12/17/12 08:10pm by JBarca *   View edit history


John & Cindy

2005 Ford F350 Super Duty, 4x4; 6.8L V10 with 4.10
CC, SB, Lariat & FX4 package
21,000 GCWR, 11,000 GVWR
Ford Tow Command
1,700# Reese HP hitch & HP Dual Cam
2 1/2" Towbeast Receiver

2004 Sunline Solaris T310SR
(I wish we were camping!)


JBarca

Radnor, Ohio, USA

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Posted: 08/30/12 08:09pm Link  |  Print  |  Notify Moderator

On my prior setup I had already gone to the Dexter EZ flex and lowered the hangers 1 ¼” along with stiffening up the hangers. Here my research took me to only needing to change the equalizer to a larger unit with more vertical and horizontal distance to lift the camper ½” to replace what I lost going to the BFG LT’s. My first surprise was a 3rd failed ST tire when I took off the tires. The tire would not even roll right the thread bulged so much. Here I dodged a 3rd bullet taking off a failed tire before it blew out. The 4th tire will never see the test of when does it fail. It will not return to service.

I started with the next size up Dexter EZ Flex. It is wider and taller and more weight rating. It gave me the camper lift I needed which was 2 ½” for tire to fender clearance. However I ran into an interference problem in the max travel position of the suspension. See here.

This is the normal level ride height. The shackles are pretty vertical but on a rubber equalizer that is not so much the problem as the rubber changes the actions somewhat.
[image]

Here is the suspension forced to the max travel. I ride up on a ramp to lift the camper and the rear tire off the ground.
[image]

Here is the problem. The spring is touching the EZ Flex casting. This is not a good long term situation.
[image]

To get out of this I need:

1. Longer shackles which in my case will lower the camper again.
2. I need to lower the hangers. I’m already on 6 ¼” hangers and not lowering them anymore.
3. Do an axle flip and end up with 4” of lift on the camper. Do not want this either. I only need ½”.
4. Get the large capacity EquaFlex by Trail Air. This has a different X and Y dimension on the mounting.

I went with option 4. Here it the large capacity Dexter next to the large capacity EquaFlex
[image]

Trail Air sold out to Lippert. And Lippert now markets the EquaFlex under a branch called Mobile Outfitters. http://www.themobileoutfitters.com/

I called them and asked about vertical shackles and their EquaFlex. With the action of their unit they did not have a problem with vertical shackles. You need to watch out you do not end up with an over center condition and get a shackle flop when doing a max suspension travel. While I had a good talk with the one tech person at Mobile Outfitters I could not find any on line dimension sheet for the EquaFlex. He stated you need to just change the shackle length if you have mounting issues.

Not satisfied with this I did have dimensions from visiting a RV dealer and taking them myself off of a Keystone Raptor 5er. This helped and I ordered several different length shackles. The only problem is I upgraded to heavy duty 2.25” long shackles and the many lengths are the standard thin ones. I can only find 3” long heavy duty ones from MorRyde in 3” which is too long. So armed with 3 different length shackles that I would double up and weld to make thicker I started the conversion. In doing the conversion I found if I used the higher up pivot hole I can get the right ride height with my heavy duty shackles. So I tried it. Yes it worked!…well almost.

[image]
I had to make my own wet bolt for the pivot but that was not a problem and I had to make a keeper to not allow it to spin. I have ½” thick hangers so the standard wet bolt is too short. [image]

Here is the back side.
[image]

I had 2 ½” tire clearance and the max angle test past. I have clearance on the fender
[image]

And the max angle works OK too and no shackle flop from over center travel on the rear spring.
[image]

Now I have ¼” clearance where before the EZ Flex hit.
[image]

Believing I had this all set, I checked the WD hitch and headed out on a test ride. Everything worked well. That was until I stopped and rechecked the dimension. Darn…. The rubber compression got me again… This happened on my first EZ Flex as well. When you setup a new rubber equalizer in the static condition even though all the weight is on it, the rubber has not fully compressed to the normal ride height. After riding around a few miles I lost ¼” of tire to fender clearance taking me down to 2 ¼” in place of 2 ½” where I wanted and really needed to be at.

Everything worked, just I’m ¼” short. Me being me I can’t leave it this way as sooner or later I’ll loose a little more over time and then I’m at 2 or 2 1/8” and you can hit when you’re going over some camp ground humps or uneven roads to camp. So jack it up again…a 3rd time.

Now I measured the compressed and settled pivot pin distance on the Equaflex for my weights. Armed with that info I calculated if I move the pivot hole down 1 ¼” to the bottom hole I can gain 5/8” ride height. And it worked. Yes.!!!! Now starting out I have 3” static tire to fender clearance and after riding around for 10 miles I have 2 ¾” and it is staying put. Perfect.

Look at the mounting hole, it is on the bottom hole where I use to mount the older EZ Flex.
[image]

Here is a mock up not yet completed as the nut is off the upper bolt. Good link clearance.
[image]

Max angle test. Good it works and still have the ¼” spring clearance on the front and no shackle flop on the back.
[image]

[image]

Now I have good clearance on max suspension travel
[image]

And here we are at 2 ¾” tire to fender clearance. More than I had on day one from Sunline on the rigid Alko equalizer.
[image]

Now for sure I had to do a WD hitch reset as the whole camper is higher. I now have a 24 13/16” ball height on the camper where before I had 24”. I had to flip the shank up. [image]

So how does it tow? I only have 131 miles on it so far. The rig feels more solid. It was never a problem however I can tell the camper is more solid on the highway at 55 mph. On secondary roads the camper does seem to ride a little stiffer. Not rough but more stiff. Not much and soon I’m sure I will forget the difference. I had to do both a LT tire change and a brand of rubber equalizer that is larger in capacity at the same time. I do not 100% know which is affecting the secondary roads stiffness, the tire or the EquaFlex. However the camper was never this solid at highway speeds even on the original Alko rigid equalizer.

So far I am a happy camper with the LT upgrade. I had to go down to Discount Tire and order 3 more Maxxis ST225/75R15’s LR D’s for the flat deck trailer. Since that trailer does not tow all the time at full load of 9,920#, more like 6,700# with the tractor it and only in 30 mile trips, at a fraction of the annual mileage the camper gets, I feel OK with ST’s on the flat deck but not the camper at these weights and miles towed

Hope all this helps someone in the future.

John

ScottG

Bothell Wa.

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Posted: 08/30/12 08:20pm Link  |  Print  |  Notify Moderator

Great write-up. I think I can even smell the new rubber!


Scott, Grace and Wesly
2003 Dodge 3500 4x4, 6 speed Cummins (lightly bombed),
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tvman44

Southwest Louisiana

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Posted: 08/31/12 07:54am Link  |  Print  |  Notify Moderator

Great move, I did almost the same exact same thing 4 years ago except I used 16" aluminum rims but still BF Goodrich Commercial TA's and already had put EZ Flex a few months before. I will never use ST tires again. These are wearing flat not shifted belts like the chinese******did.


Papa Bob
1* 2008 Brookside by Sunnybrook 32'
1* 2002 F250 Super Duty 7.3L PSD
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LAdams

Northern Illinois

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Posted: 08/31/12 08:56am Link  |  Print  |  Notify Moderator

Excellent write-up as usual John... I sure don't know where you find the time to do all these things... I'm retired and you are way more industrious than I am [emoticon]

Les

JBarca

Radnor, Ohio, USA

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Posted: 09/02/12 09:22am Link  |  Print  |  Notify Moderator

Thanks for the nice comments guys.

Les, in this case I had to find the time.... I must admit, jacking the thing up 3 times was getting to be a bit much. I'm glad I got it by then... What is ideally needed is actual compressed rubber equalizer dimensions for the weight of your camper. I tried to lay all this out in CAD before going to the camper, but the lack of actual compressed dimensions made it complex.

1slomofo

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Posted: 09/03/12 12:46pm Link  |  Print  |  Notify Moderator

great write up. I too am looking to upgrade to 16" wheels. I think im going to go with 235/80/16 instead because it looks like I have plenty of room.

thanks for the time you took!



-2015 32SAG Eclipse Attitude Toyhauler
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kpratte

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Posted: 09/03/12 11:16am Link  |  Print  |  Notify Moderator

Great write-up.. I'm betting a good portion of the extra stiffness is the LT tires.. When I switched from P rated to LT tires on my truck, I noticed a huge difference. Seems now I can feel every crack on the pavement and the tires do have a tendency to skip on washboard roads but cornering is much improved.

- Ken


2018 Toyota Tundra 5.7 CrewMax Platinum, TRD Swaybar, Timbrens
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JBarca

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Posted: 09/03/12 04:02pm Link  |  Print  |  Notify Moderator

kpratte wrote:

Great write-up.. I'm betting a good portion of the extra stiffness is the LT tires..
- Ken


Hi Ken,

Thanks for the good words.

I wrestled with the words to describe the feel. Again I upgraded to a stronger rubber equalizer at the same time. The words, "more solid" seems to fit better than more stiff. I felt the more solid feeling going straight. Even on the ST's and this truck it was very good before. Going from P on your truck to LT is a major difference. I'm sure night and day and stiff for sure applies there.

I do not feel any more or less bumps. And I have both a rubber equalizer and shocks so they may be absorbing the "feel" of stiffness.

What ever words ones uses, so far I'm very pleased with the outcome. We have a 1,000 mile trip coming up this weekend so I'll get more feel to what ever it is. Soon the old feeling will be a distance memory....

Thanks

John

JBarca

Radnor, Ohio, USA

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Posted: 09/03/12 04:06pm Link  |  Print  |  Notify Moderator

1slomofo wrote:

great write up. I too am looking to upgrade to 16" wheels. I think im going to go with 235/80/16 instead because it looks like I have plenty of room.

thanks for the time you took!


Hi Steve,

Thanks for the good words.

Is your toy hauler 11,000# loaded? or is that the GVWR? I saw that in your profile.

What tire size did you have on now?

John

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