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Old 12-01-2014, 04:28 PM   #1
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8310SS Rockwood tires.

Noticed on the FR website they spec out "C" rated tires (ST225/75R15C @ 50PSI) anyone know if they are available with "D" rated @ 65PSI??
I'm a little concerned about "C" rated tires at this trailer weight.

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Old 12-01-2014, 04:40 PM   #2
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Originally Posted by billb800si View Post
Noticed on the FR website they spec out "C" rated tires (ST225/75R15C @ 50PSI) anyone know if they are available with "D" rated @ 65PSI??
I'm a little concerned about "C" rated tires at this trailer weight.

Many thanks,
Bill B.
I was considering ordering a Rockwood SUL last Spring and called the factory reps about the tire and axle ratings. I'm not big on having the tires in particular being maxxed out, especially ones of the quality they put on camper. To make a long story short, I think you'll have to foot the bill to upgrade to D rated after you get the camper.
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Old 12-02-2014, 05:16 AM   #3
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Just put a set of Carlisle E's on my 2014 Windjammer TT.
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Old 12-02-2014, 05:44 AM   #4
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I would recommend upgrading to E rated tires.
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Old 12-02-2014, 08:10 AM   #5
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Just put a set of Carlisle E's on my 2014 Windjammer TT.
Did you put them on the same rims that the C tires were on and what pressures do you have those tires at? Also do you find the E tires have less sway than the C tires?
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Old 12-02-2014, 03:09 PM   #6
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Bill, I had the same concern with my 2014 Flagstaff trailer. We are about the same weight and the exact same tires. I called the Forest River tire supplier, Lionshead tire and wheel (574-533-6169). I asked about upgrading to D or E load range tires. They said that 65psi D’s would be fine, but the wheels were not rated for the 80psi E range.

Everything that I have read says that installing E range tires and under inflating them to 65psi will cause more problems than it would solve. Trailer tires are designed to be run at max inflation or you will get heat build up.

As soon as I took delivery of the trailer I replaced all 5 tires with D range Maxxis. I easily sold the original tires on Craig’s List. We took several trips this year, including a three week trip from Connecticut to South Dakota and back, and the tires performed flawlessly. Good luck with whatever you decide.
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Old 12-02-2014, 03:35 PM   #7
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Bill, I had the same concern with my 2014 Flagstaff trailer. We are about the same weight and the exact same tires. I called the Forest River tire supplier, Lionshead tire and wheel (574-533-6169). I asked about upgrading to D or E load range tires. They said that 65psi D’s would be fine, but the wheels were not rated for the 80psi E range.Everything that I have read says that installing E range tires and under inflating them to 65psi will cause more problems than it would solve. Trailer tires are designed to be run at max inflation or you will get heat build up.As soon as I took delivery of the trailer I replaced all 5 tires with D range Maxxis. I easily sold the original tires on Craig’s List. We took several trips this year, including a three week trip from Connecticut to South Dakota and back, and the tires performed flawlessly. Good luck with whatever you decide.
==========================

The last two trailers I had had D rated tires and they never over heated. Always kept them at 65 PSI. At rest stops I would check for over heating and they ran cool. (Marathons etc..)
In your message they hid a Hyperlink and I checked it out. It's from Ebay on trailer tires. I'm posting it here in case anyone is interested:
trailer tires | eBay

Thanks for your thoughts. I'll probably try and get the dealer to make a swap or like you say just go out and buy a set.
Happy trails,
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Old 12-02-2014, 04:20 PM   #8
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Got rid of the Trail Express tires and had Maxxis 8008 E rated installed with steel valve stems and never looked back.
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Old 12-03-2014, 02:32 PM   #9
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....Everything that I have read says that installing E range tires and under inflating them to 65psi will cause more problems than it would solve. Trailer tires are designed to be run at max inflation or you will get heat build up.


Not sure I agree with this statement. It would be helpful if you could direct me to where this info came from.

In reality (check the load range charts) an ST "E" rated tire inflated to 65 psi is a "D" rated tire and it can carry the corresponding load. The "D" range tire is more than adequate to carry the load for current Rockwood/Flagstaff ultralight RV's. Don't forget to subtract the pin weight when you are calculating axle or tire load. Excessive heat in a tire is caused by overloading or underflating and not by airing up to the appropriate load that the tire is actually carrying.

When I had the factory "C" rated tires on I carried the max allowed which was 50 psi. Now that I have ST Maxxis 8008 load range "D" on I carry the max permissible both specified by the tire and the wheel supplier which is 65 psi. I contacted Maxxis prior to buying the "D" rated tires. They said there was no benefit in going to the "E" rated tires as I was limited by the wheel to 65 psi and my actual load on the axle and tires was below the "D" load range anyway.
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Old 12-04-2014, 08:08 AM   #10
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Ron, I also really wanted to put load range E on my trailer for the additional strength of the tire. Here is just one of the places that talked me out of it. I read similar things on various other sites.

Thanks for your input.

Can a Load Range E Trailer Tire be Used in Place of a Load Range D Trailer Tire | etrailer.com
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Old 12-04-2014, 08:19 AM   #11
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If what etrailer says is correct (always inflate to max pressure) why does Goodyear put out a table to show pressure vs load on the marathon?
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Old 12-04-2014, 09:41 AM   #12
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Thanks llberg for the link back to etrailer about the max pressure on ST tires. The author there needs to supply me more info/supporting data to convince me of what he said.

Regardless, you and I are covered as we have "D" rated tires inflated to their max (and the max allowed by the wheels) of 65 psi. Once again, this load range rating of 2,540 lbs per tire surpasses the axle ratings and the actual weight of the RV at each tire.

I am not faulting fellow RVer's who tow a similar rig with "E" rated tires. I believe there was no benefit to me with my known weights and the information passed on to me by both Lions Head wheels and Maxxis technical support.

To me it was a great relief to get the factory spec tires off before a blowout and at the same time upgrade to a known good reviewed "D" rated tire (ST Maxxis 8008). Moving farther up the list to an "E" rated tire would not have improved my comfort zone that much more, if at all. Time will tell if I made the right decisions.
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Old 12-04-2014, 12:19 PM   #13
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Ron, I also really wanted to put load range E on my trailer for the additional strength of the tire. Here is just one of the places that talked me out of it. I read similar things on various other sites.

Thanks for your input.

Can a Load Range E Trailer Tire be Used in Place of a Load Range D Trailer Tire | etrailer.com

Etrailer just wants you to sell you some new rims. A blanket statement saying all ST must be run at max pressure is just silly. You are going to build heat if your load exceeds the pressure rating for that load regardless of whether the tire is a C D or E. Running 65 in an E on a D load is not going to hurt anything, but it will give you a stronger tire.


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Old 12-04-2014, 05:57 PM   #14
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Maxxis also puts out a load pressure chart for there ST tires.
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Old 01-09-2015, 03:05 PM   #15
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If what etrailer says is correct (always inflate to max pressure) why does Goodyear put out a table to show pressure vs load on the marathon?
Load inflation tables work well for normal vehicles like cars, trucks and motorhomes. These have tires "at the corners" of the vehicls so when it turns a corner all tires rotate around centers that "point" to the center of the turn radius.

They also work reasonably well for single axle trailers as the trailer rotates to also point the tires toward the center of the turn.

The problem occurs with multi axle trailers. It is physically impossible for all 4 or 6 tires to point to the center of the turn. The end result is that the tires are dragged around the turn and this puts VERY high internal stress loads on the structure and this can cause internal cracking which can lead to belt separations.
Running the sidewall inflation pressure will lower these stresses but they are still much higher (+20% or more) than normal.

I have covered this in detail on my blog on RVTireSafety.
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Old 01-09-2015, 03:08 PM   #16
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Etrailer just wants you to sell you some new rims. A blanket statement saying all ST must be run at max pressure is just silly. You are going to build heat if your load exceeds the pressure rating for that load regardless of whether the tire is a C D or E. Running 65 in an E on a D load is not going to hurt anything, but it will give you a stronger tire.


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"A blanket statement saying all ST must be run at max pressure is just silly" is based on what Engineering analysis?

My advice is based on Finite Element analysis and well established vehicle and tire dynamic load formula.
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Old 01-09-2015, 09:26 PM   #17
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What does load formula have to do with anything if max pressure is always to be used period?


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Old 01-10-2015, 09:31 AM   #18
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Did you put them on the same rims that the C tires were on and what pressures do you have those tires at? Also do you find the E tires have less sway than the C tires?
Just saw your post, Yes to stock rims,
Just got to Florida 2000+ miles on the same C rims that we put the E Carlise's on before our trip. I ran them at 80#s. The trailer always tows without sway on either C's or E's with our 2500 Sierra GMC Diesel. I just like knowing I have the Carlisle Brand & stronger E tires.
I don't buy the 65# rating issue and feel 80#'s works best for the tire.
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Old 01-10-2015, 10:12 AM   #19
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Originally Posted by lbrjet View Post
A blanket statement saying all ST must be run at max pressure is just silly. You are going to build heat if your load exceeds the pressure rating for that load regardless of whether the tire is a C D or E. Running 65 in an E on a D load is not going to hurt anything, but it will give you a stronger tire.
===============
============================

Under inflating a ST tire will generate a lot of heat. When traveling I always check my tires cold and have maximum PSI (as rated on the tire) in the tires. Then when we stop I check the tires for over heating. Never yet had tires running hot on me. And that includes traveling through Texas- Arizona- Utah- Montana- Wyoming etc...
And it's not advisable to jump two ratings on tires with the same rims. Going up one lever is what the manufacturers allow ( ei, C to a D, D to a E etc..) but not a C to an E rating.

ST = Special Trailer tires are designed to take the lateral stresses placed on trailer tires, Truck tires aren't). If you want to see an exaggeration then when backing tightly into a camping spot get out and take a look at how the tires are angled. Looks like they will pop off the rims they are twisted so badly.
If you would like to understand ST verses LT tires then watch this video:



Happy trails,
Bill B. (Michigan)
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Old 01-10-2015, 10:47 AM   #20
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"A blanket statement saying all ST must be run at max pressure is just silly" is based on what Engineering analysis?

My advice is based on Finite Element analysis and well established vehicle and tire dynamic load formula.
I doubt that you can show us any ST tire manufacturer that will recommend less than full sidewall tire pressures unless the Vehicle manufacturer will also do it. Who controls setting initial recommended tire pressures for OE tires? The vehicle manufacturer.

All tire users look at industry standards for proper servicing of their tires. If not, they should.

Some ST tire manufacturers come right out and tell us that their tires degrade as much as 10% per year. Airing such a tire to the load carried is just like asking for early tire failure. With all safety considerations satisfied you’re right to go up a load range and then use it’s maximum potential.

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