Changing Load Range From C to D

[Cracker]

Any comments, pro or con, about changing the load range? ST 225/75 R15 D tires are rated 2,540 lbs at 65 psi and E’s are rated 2,830 lbs at 80 psi. If I continue to run the E’s at 65 psi, to maintain a softer ride, what effect, if any, will that have on the tire? I would love to stay with the load range D but it’s not offered in many of the higher quality tires. I’m looking at the Goodyear Endurance as an alternate, but it is only offered in load range E. Walmart does still have the Goodyear Marathon - but they don’t mount or balance in my area and I want to stay with the local tire shop.

[sourdough]

So I understand....are you going from c to d (title of post), d to e or c to e?

[ctbruce]

1. Stay away from the Marathons. Do a search on here for reasons why.

2. The manufacturer will recommend running at maximum inflation. It's pretty good advice. It'll keep you from overheating the tire.

3. Some do run at lower pressures and will probably kick in here any time. You lose load capacity when you do so keep that in mind.

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[Cracker]

I jumbled up my alphabet in the heading - but in this specific case I’m looking at going from D to E.

[Cracker]

Originally Posted by ctbruce

1. Stay away from the Marathons. Do a search on here for reasons why.

2. The manufacturer will recommend running at maximum inflation. It's pretty good advice. It'll keep you from overheating the tire.

3. Some do run at lower pressures and will probably kick in here any time. You lose load capacity when you do so keep that in mind.

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I’ve had good luck with the Goodyear Marathons over the years, changing the set every 5 years, but I’m well aware of the Marathon horror stories. Your comments, with respect to pressure, is the very thing that concerns me. I do run the tires on my dually at a pressure corresponding to actual scale weights for a given load - but never less than 45 psi - as recommended by Michelin. This provides for a very nice ride, and an excellent wear pattern, but these are truck tires - not ST trailer tires. Because an upgraded ST “E” tire carries a higher maximum rating than the load carried demands, can I adjust the pressure to the recommended pressure for an OEM ST “D” tire and still get the same ride for the trailer - without overheating the E tire or causing other wear problems? Note that the capacity for any given pressure is the same for the D or E rated tire Up to the maximum for the D. The difference in sidewall flex for ST tires versus LT tires is the rub I’m concerned about.

[JRTJH]

Most of us who have switched from LRD to LRE tires run them at 80 PSI. The vast majority of those who do this report that the trailer rides smoother, tracks better and we have less "cargo shifting", open cabinet doors and less bouncing of items in the cabinets.

ST tires typically do not "wear out" from tread wear, rather they "time out" from date of manufacture. That's different in LT tires where they typically "wear out" before the "time out".... So, it makes sense to adjust tire pressure to create even wear on LT tires to lengthen their useful tread life. There's no need to do that for almost all of us who have ST tires on our trailer. The tread will still "look new" when we replace them 5 years from manufacture.

So, in my opinion, you're worrying about something that isn't going to matter when you make the decision to buy new tires. I'd suggest running them at 80 PSI to benefit from the improved stability, tracking and smoothness of ride.

YMMV

[sourdough]

I think the key here is the weight of the trailer. It says you have a 294rls; I have no idea what the gvw is but guessing maybe 8-9k?? If so, upgrade to E and run at 80 psi. I moved from a D to E and could not believe how much better my trailer towed/rode.....plus I got an extra margin of capacity that was lacking with the OEM tires.

This is JMO but I would steer clear of the Marathons - look at the NHTSA website for the complaints. I know you've had good luck, and some folks have had good luck with Trailer Kings etc., but the odds are against you and one day "she'll be coming to collect".

The Goodyear Endurance is new with no track record and only the Marathon history as a guideline so I'm waiting for some historical data. I, and many others, have gone with the Carlisle Radial HD and have had very good luck. Good luck to you on finding the tire you need, but, I would do the upgrade unless you are pulling a light trailer. JMO

[ctbruce]

Originally Posted by Cracker

I’ve had good luck with the Goodyear Marathons over the years, changing the set every 5 years, but I’m well aware of the Marathon horror stories. Your comments, with respect to pressure, is the very thing that concerns me. I do run the tires on my dually at a pressure corresponding to actual scale weights for a given load - but never less than 45 psi - as recommended by Michelin. This provides for a very nice ride, and an excellent wear pattern, but these are truck tires - not ST trailer tires. Because an upgraded ST “E” tire carries a higher maximum rating than the load carried demands, can I adjust the pressure to the recommended pressure for an OEM ST “D” tire and still get the same ride for the trailer - without overheating the E tire or causing other wear problems? Note that the capacity for any given pressure is the same for the D or E rated tire Up to the maximum for the D. The difference in sidewall flex for ST tires versus LT tires is the rub I’m concerned about.

I think John covered this very well. Just wanted to say, for others who may look at this later for help. If you inflate your E tires to D PSI, then your load carrying capacity also drops correspondingly to the D capacity. Just so someone doiesnt think they can run them at the E rate at lower pressures.

I run my E tires at 80psi and do not have a rough ride, but they are ST tires so that really doesn't fit your question. Good luck with your decisions.

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[Cracker]

OK - I think the argument for the E tires, and running them at the full 80 psi, makes good sense to a degree, with the only remaining caveat being the reduced contact area with the road for braking. My guess right now, before weighing the trailer is that it will be on the light side of Sourdough’s guess, or right around 8,000 lbs. We generally travel fairly light. With 800 lbs on the hitch, and the remaining 7,200 lbs equally distributed to the wheels, each tire would be seeing only 1,800 lbs. That’s a comfortable safety margin using E-rated tires at full pressure, but my thinking is that they will be running on the center of the tread area. I agree that it will be extremely unlikely that I’ll ever wear a tire out in 5 years but a substantial reduction in contact area does worry me.

[JRTJH]

Wait until you get the tires on the trailer, air them up to 80 PSI, put chalk on the ground and on the tire tread, pull the trailer forward and look at the contact patch. You'll find, as most of us have found, that there is no problem with "loss of tread contact with the pavement. You're making this much more difficult than it really needs to be. Try the chalk test, then you'll understand what a "bazillion convincing words" on the forum won't tell you. Some things you either have to take someone's word as true or go out and do the chalk test for yourself. Convincing through a forum discussion won't work to get you to understand, so grab your chalk, air compressor and new tires: Convince yourself what so many of us already know and have tried to tell you.....

You simply can't compare ST tires and their footprint to LT tires and their footprint. It's apples and oranges....

[Cracker]

John, the last thing I brought up was the contact area, and at no time have I failed to pay attention to you, or anyone else with reference to the comments that have been made. I’ve simply been trying to reconcile questions that I’ve had. If you have, as you stated, done a chalk test to see how the tread pattern varied, then surely you must have had the same concern in the past that I just now expressed? Having not been privy to your results, why was my question out of order? I ask questions to avoid the necessity of re-inventing the wheel - and I pay close attention to the answers. Where you came up with the idea that I wasn’t understanding, or refused to pay attention to what “everyone” was telling me, is beyond me. I think that you and I got off on the wrong foot, and I trust that we can move forward hereinafter as friends.

[sourdough]

Cracker

I think everyone is trying to address your concerns as best as possible. John has, and does, his very best to give all of us very concise info.

I think you are making a mountain out a mole hill. With the 8k trailer on E rated tires the "rounding"/excessive wear you are worried about is nill. How many miles a year are you going pull the RV? Unless 10k or more why worry? They will disintegrate before that. And, as has been the case so many times, the upgraded tire, stiffer sidewall etc., on an 8k trailer, will make your trailer ride smoother.....not some analogy....real life. JMO

[JRTJH]

A little bit of research on the forum can produce volumes of information about tires, load ratings, differences between ST and LT tires and the list goes on and on. I've typed until I've got "nubs on my fingertips" the same information: over and over again and yet, 3 days later, a week later, the same question and then, when it's answered "at length" again, with clear concise data, out flows another "but what if" to start the process all over again. Yes, it does get frustrating and if I came across "impatient" then it's probably because I've answered that question at least 10 times last year and two or three times this year.... What's wrong with looking back at the section of the forum titled "Tires Tires Tires" and seeing what information is readily available without asking the same thing again?

That said, there is a series of photos in post #69 of the thread located at this link: http://www.keystoneforums.com/forums...230#post272230

The photos will clearly show why management of tire pressure in LT tires with stiffer sidewalls is necessary and why the "softer, more pliable sidewalls" on ST tires don't require such "careful pressure/weight management"

The photos of the ST tire will clearly show why the tread contact patch is not affected by pressure/loading as much as it is with LT tires.... So many people tend to think "a tire is a tire is a tire" NOT SO !!!!!!!!!!!!!!! LT tires and ST tires are two entirely different concepts and they are not managed or used the same. Doing so will cause tire problems rather than make the task easier. Just as you wouldn't jump start a 12 volt car with a 6 volt battery, you shouldn't manage the tire pressure in your ST tires using the concept found in your Ford owner's manual.....

[jsmith948]

Originally Posted by Cracker

OK - I think the argument for the E tires, and running them at the full 80 psi, makes good sense to a degree, with the only remaining caveat being the reduced contact area with the road for braking. My guess right now, before weighing the trailer is that it will be on the light side of Sourdough’s guess, or right around 8,000 lbs. We generally travel fairly light. With 800 lbs on the hitch, and the remaining 7,200 lbs equally distributed to the wheels, each tire would be seeing only 1,800 lbs. That’s a comfortable safety margin using E-rated tires at full pressure, but my thinking is that they will be running on the center of the tread area. I agree that it will be extremely unlikely that I’ll ever wear a tire out in 5 years but a substantial reduction in contact area does worry me.

If you reduce the pressure from the recommended 80 psi, you also reduce the weight carrying capacity. Seems to me, if you are going to run the E rated tires at 65psi, then you may as well just run the D rated tires?

[Cracker]

I just finished an online “Chat” with a Goodyear representative with respect to the GY Endurance tires. She confirmed, in response to my specific inquiries, that running the Endurance tires at 65 to 70 psi, versus 80 psi, was perfectly acceptable, and that it would indeed provide a softer ride for the trailer and greater road contact for braking. That said, I’ll be happy to serve as yet another “test subject” for the Endurance tires, and to pay the higher cost of buying American!

[Cracker]

Originally Posted by jsmith948

If you reduce the pressure from the recommended 80 psi, you also reduce the weight carrying capacity. Seems to me, if you are going to run the E rated tires at 65psi, then you may as well just run the D rated tires?

I would be happy to have “C” rated tires but the choice is very limited - especially for American-made tires.

[CWtheMan]

Originally Posted by Cracker

Any comments, pro or con, about changing the load range? ST 225/75 R15 D tires are rated 2,540 lbs at 65 psi and E’s are rated 2,830 lbs at 80 psi. If I continue to run the E’s at 65 psi, to maintain a softer ride, what effect, if any, will that have on the tire? I would love to stay with the load range D but it’s not offered in many of the higher quality tires. I’m looking at the Goodyear Endurance as an alternate, but it is only offered in load range E. Walmart does still have the Goodyear Marathon - but they don’t mount or balance in my area and I want to stay with the local tire shop.

When you use a replacement tire with a designated tire size that is the same size as the Original Equipment tire (ST225/75R15), it still conforms to the minimum tire size on the trailer’s certification label/tire placard. The only thing that may happen when going from LRD - LRE is you have some reserve load capacity, that can only be used by increasing the tire’s inflation pressure, from the vehicle manufacturer’s recommendation - maybe 65 PSI, to something in-between 65 - 80- PSI.

Some may argue that the LRE is a more robust and durable choice. In fact, it’s the same tire when inflated to 65 PSI. It’s the way the industry works it. It uses the same inflation chart no matter the manufacturer.

Use caution when inflating replacement tires with more than the placard recommended inflation pressures. They may not be certified for the increase in PIS above 65 PSI. If you can't find the PSI limit on the wheel call its MFGR, they are required to provide the info. Insure the OE valve stems are certified for the increased PSI. Wheel load capacity is not a problem because you can only exceed their load capacities by overloading the trailer’s axle loads. You’re not going to do that, Right? HeHeHe!

[ken56]

I replaced the OEM Trailer Kings that came on my Laredo with the Endurance and have been very happy with them. TK's were E rated and the Endurance are E rated and the difference to me was sidewall stability. I run them at the full 80psi for my 10K GVWR Laredo and have never had any cabinet doors open or things shake around so much it was a problem so smoother ride has not been a issue. Seems to me the suspension would play more into that, meaning does your trailer have the Mor-ride or Equi-flex suspension upgrade for the shackles and springs? Huge difference heavier shackles and wet bolts makes.

[ftrupe]

I am changing my Trailer King 225/75/R15 D tires (4 years old) to Carlisle 225/75/R15 E tires, similar to the OP. However. my question is will the rims be ok going from 65 to 80 PSI? My trailer is a 23RB and not heavy, but the E tire is 10 ply as opposed to the D, which is 8 Ply. Also only a $6 difference at Walmart.

[JRTJH]

ftrupe,

It depends entirely on which wheels are installed on your specific travel trailer. Many Keystone "entry level" trailers come standard with white steel wheels. There are some model optional groups that upgrade the white wheels to black or chrome plated steel wheels, then there are some optional groups that upgrade the wheels to aluminum (mag) wheels. So, it's anybody's guess what is actually installed on your trailer. You'll need to remove one of your wheels, look at the back of the wheel and on one of the spokes, you should find the max load capacity. The max load capacity will be stamped into the steel or cast into the aluminum. With that information, you should be able to research any ST tire load chart (I'll link the Carlisle chart below). Locate the specific max load capacity that your wheels have cast on the back, then read left to the tire size and read right to the maximum pressure rating for that wheel. (There may be a pressure rating stamped on the wheel, but typically, only the load rating is stamped and the max pressure is "understood" to be on the same line on the tire chart). That will be the maximum rating for your specific wheels. Every trailer produced has the potential to have wheels that are different than those of other similar models, so it is in your best interest to either verify what is on your trailer or have your tire dealer do it for you.

I'm adding pictures of the typical aluminum casting ratings. You'll notice there are two maximum load capacity cast into the wheel. One is for a 5 lug application the other is for a 6 lug application. The same wheel is cast, then drilled with either 5 or 6 lug holes. With 6 lugs, the wheel can carry more weight, so the cast specs indicate the difference. Usually steel wheels are stamped with the specs in the same location, but some wheels might have the information stamped on the inside of the wheel and you'll need to remove the tire to see the stamp on those wheels.

https://www.carlislebrandtires.com/o...adial-trail-hd

Note: There are some wheels that are rated higher, you can verify that information with the wheel manufacturer either on their website or by calling their customer service. You can find the contact information by going to the wheel manufacturer's website.