How do you rate your trailer load to tire max load? rig?

Iggy · 07-22-2010, 09:20 PM

UPDATED NUMBERS and CALCULATIONS

I'm trying to see if my C rated tires are able to handle my 5th wheel as well as the load. Tell me if my way of calculating is right or wrong.

My trailer dry weights 7,463 lbs
My max load is 1,674 lbs
My 5th wheel hitch weight is 1,108 lbs
My trailers 4 tires are rated Load Range C with max at 2,150 lbs at 50 psi

If I add my trailer weight plus max load weight minus my hitch weight I come up with 8,029 lbs divided by 4 tires equals 2,007 lbs on each tire.

And the tires at 50psi of 2,150lb has some extra lbs of about 142 lbs each.
So what I plan is buying a better quality load range C tires.

Meaning my wife can add an additional 571 lbs to the trailer before the tires overheat and blow.
Thanks!

Dave_Monica · 07-22-2010, 09:33 PM

That's correct...that would be the maximum load on the tires with the trailer at it's GVWR. The pin weight will be higher than 1108 lbs if the camper is loaded to it's GVWR. You must have some bad keys on your calculator though. 7463 + 1674 - 1108 = 8029 or 2007 lbs per tire.

I'm not sure where you got the tire load info. I'm sure that the tires on your 8285WS is the same as our 8280WS which comes with 225/75R15 'C' rated at max 2150 lbs.

Dave

Iggy · 07-22-2010, 10:22 PM

Quote:

Originally Posted by Dave_Monica

That's correct...that would be the maximum load on the tires with the trailer at it's GVWR. The pin weight will be higher than 1108 lbs if the camper is loaded to it's GVWR. You must have some bad keys on your calculator though. 7463 + 1674 - 1108 = 8029 or 2007 lbs per tire.

I'm not sure where you got the tire load info. I'm sure that the tires on your 8285WS is the same as our 8280WS which comes with 225/75R15 'C' rated at max 2150 lbs.

Dave

Thanks Dave for correcting my numbers. I pickup my 8285WS tomorrow and will get more details. I'm just trying to figure if I should look around for a D rated tire if I was close to max these. I do think they are 225/75/15 but I have the aluminum rims which is another issue because I think they will only hold a max of 60psi and if I go to a D Range time 8 ply or more I think I may need a steel rim thatcan handle the higher psi.
The aluminum rims are rated 15X6JJ and have a max psi rating of 60 psi.
This issue may be a Catch 22 and if I decide to change I may need to also upgrade to steel rims.

Dave_Monica · 07-22-2010, 10:50 PM

Save your money for more trips to Camping World!

Going to D rated tires is a bit of a waste as the camper has only 4000 lb axles which would be the weight limiting factor. It's unfortunate that Forest River doesn't offer a axle upgrade option on their 5er's and the standard axles are so close to the limit.

Dave

Iggy · 07-22-2010, 11:29 PM

Quote:

Originally Posted by Dave_Monica

Save your money for more trips to Camping World!

Going to D rated tires is a bit of a waste as the camper has only 4000 lb axles which would be the weight limiting factor. It's unfortunate that Forest River doesn't offer a axle upgrade option on their 5er's and the standard axles are so close to the limit.
Dave

This is why it is a Ultra Lite trailer.
No extra weight at all.

**Herk7769** · 07-23-2010, 07:41 AM

Quote:

Originally Posted by Dave_Monica

Save your money for more trips to Camping World!

Going to D rated tires is a bit of a waste as the camper has only 4000 lb axles which would be the weight limiting factor. It's unfortunate that Forest River doesn't offer a axle upgrade option on their 5er's and the standard axles are so close to the limit.

Dave

I am aware of the 4000 pound axles, BUT:

1: The Carlisle Load range C OEM tires are THE WORST tires in the industry. (Their D range tires are MUCH better but still score well below every one else's C rated ones.) More blowouts and accelerated tread wear with these Chinese tires Load range Crap tires when you check the forums.

2: Load range D tires have 2 more belts (plys) and some even have a Kevlar ply for limited impact protection.

3: Load range D tires have stiffer sidewalls so even if you run them at the correct cold PSI for your actual weight (50 PSI; not their max rated 65 PSI) they run cooler and last longer.

4: After my Carlisle Class C tire exploded on the DC beltway at rush hour (like all day), I now have 4 new Goodyear Marathon D rated tires on my camper (Made in the good old USA). Remember to replace the stems with the high pressure type for stiffness especially if you use the pressure transmitter caps.

Blow Out - Carlisle Range C pictures from travel photos on webshots

Blow Out - Carlisle Range C pictures from travel photos on webshots

Oh and did I mention that they were made a YEAR before FR installed them on my camper? Their 3 year warranty already was 1/3 used when I picked up the camper and I had the camper a year before the blowout. Thus, while still "under warranty" the credit was not going to be much.
The dealer DID say the ancillary damage to the fender would be covered "if my claim was approved" but the fender trim was just 40 bucks so I just bought the trim piece and repaired the damage myself.

When Goodyear looked at the OTHER tires as they came off, they marked the tires to show where dry rot cracks and bubbles were already weakening the sidewalls and around the rim bead.

Not only THAT, but the dealer just dumped me to contacting the tire manufacturer directly! I do not know if that is industry standard BS or not, but it was without a doubt THE LAST STRAW with that dealer.

LadyWindrider · 07-23-2010, 07:45 AM

Not all Goodyear Marathons are made in the "good ole USA". Check the side wall of your tires and you may find "made in good ole CHINA"

**Herk7769** · 07-23-2010, 08:00 AM

Quote:

Originally Posted by Iggy

Thanks Dave for correcting my numbers. I pickup my 8285WS tomorrow and will get more details. I'm just trying to figure if I should look around for a D rated tire if I was close to max these. I do think they are 225/75/15 but I have the aluminum rims which is another issue because I think they will only hold a max of 60psi and if I go to a D Range time 8 ply or more I think I may need a steel rim that can handle the higher psi.
The aluminum rims are rated 5X6JJ and have a max psi rating of 60 psi.
This issue may be a Catch 22 and if I decide to change I may need to also upgrade to steel rims.

Went over this as well with Goodyear.

50 PSI is within the safe inflation pressure for D range tires. You do not have to inflate to the MAX RATED pressure unless you need the MAX RATED LOAD for the tire.

With Load Range C tires you MUST inflate to the MAX RATED PSI since with even minimum junk we run pretty close to the max rated camper weight.

With Load range D you have a huge safety buffer (weight wise) and 60 PSI would be well within the safe inflation zone.

**Herk7769** · 07-23-2010, 08:01 AM

Quote:

Originally Posted by windrider

Not all Goodyear Marathons are made in the "good ole USA". Check the side wall of your tires and you may find "made in good ole CHINA"

Stamped "Made in USA" on sidewall.

There are some Marathons "made in Canada" but not the ones on the camper.

None are made in China according to the dealer.

Goodyear does have a cheaper trailer tire (not Marathon series) made in China so be careful.

Iggy · 07-23-2010, 09:00 AM

Ok Lou. So you have Goodyear Marathons on your rig at 60 psi. Correct?
Do you have the aluminum rims or the stardard metal rims?
I have been told that the 15X6JJ rims (aluminum) are rated for 60 psi which is fine. If my local American Tire dealer has Goodyear Marathons I plan on seeing if they will put the D rated (8 ply) on them.
See the attached picture of my rims

Iggy · 07-23-2010, 09:03 AM

Here is a Maxxis chart (pdf) and another chart that shows what pressures you can put in a C or a D rated tire and what load it can handle.
225/75/15 tire

**Herk7769** · 07-23-2010, 09:03 AM

I have the stock steel rims. They are stamped 50PSI maximum.

Since I put 50 PSI in the D rated tires everything is on the "Up and Up"

If your rims are stamped 60 PSI I would feel very safe running your D rated tires at 60 PSI.

This is totally safe. My GMC has 4 E rated tires on it, but the tire plate on the door says to run the rear tires at 80 PSI but the front tires must be inflated to 65 PSI for its maximum load and optimum handling.

**Herk7769** · 07-23-2010, 09:11 AM

Quote:

Originally Posted by Iggy

Here is a Maxxis chart (pdf) and another chart that shows what pressures you can put in a C or a D rated tire and what load it can handle.
225/75/15 tire

Thanks Iggy. My point exactly.

The parenthetical letters show the maximum weight at that PSI for that load range.

Oh, and I have 50 PSI in my steel rims. The 60PSI was for your Aluminum rims.

The this attachment shows how you can get more than 65 MPH out of a trailer tire but watch the "caveats" biggie -> "Up to the max for the rim"

Iggy · 07-23-2010, 10:27 AM

When considering a trailer tire, here are a few important things to look at.
TIRE CONSTRUCTION TYPE - Bias Ply vs. Radial
TIRE APPLICATION TYPE - (ST) Special Trailer vs. (LT) Trailer
LT doesn't not mean "light truck" but trailer.
TIRE SIZE - % of section height / section width Refereed to as 'Aspect Ratio'
TIRE LOAD RANGE - Load carrying capacity and air pressure rating

::::NOTES:::

Inflation
Always inflate trailer tires to the maximum inflation indicated on the sidewall.
Check inflation when the tires are cool and have NOT been exposed to the sun.
If the tires are hot to the touch from operation, add three psi to the max inflation.
Underinflation is the number one cause of trailer tire failure.

Load Capacity:
The combined capacity of all of the tires should exceed the loaded trailer weight(GVWR) by 20 percent.

Speed
All "ST" & "LT" tires have a maximum speed rating of 65 mph.

Time
In approximately three years, roughly one-third of the tire's strength is gone. Three to five years is the projected life of a normal trailer tire.
It is suggested that trailer tires be replaced after three to four years of service regardless of tread depth or tire appearance.

Mileage
Trailer tires are not designed to wear out.
The mileage expectation of a trailer tire is 5,000 to 12,000 miles.

These 'Special Trailer' (ST) tires have been constructed for better high speed durability and bruise resistance under heavy loads. Trailer tire construction varies substantially from automotive tires, therefore it is essential to choose the correct tire for your towing application.

In general, trailer tires have the same load range (or ply) from bead to bead and are bias ply construction.
This allows for a stiffer side wall which provides safer towing by helping to reduce trailer sway problems.
The use of (LT) tires offer a wide range of specialized trailer tires for heavy loads on average sized wheels. LT doesn't not mean "light truck".

The use of 'Passenger Car' (P) is not recommended for towing because their construction, they normally do not have the sidewall plys, or weight rating sufficient for trailering,...usually radial or bias belted, allows for more flexible side walls.
Using a "P" tire could lead to increased trailer sway and loss of control.

**Herk7769** · 07-23-2010, 11:36 AM

I am so screwed!

I hope I get more than 5,000 - 12,000 miles on THOSE!
And GMC recommends running them under-inflated by 15 PSI on the Front!
Agree totally about the P tires!

I pondered the imponderable and want to run this by you guys.
Forgive me for

The idea of variable tire pressures, I am told, is to have the full tread of the tire in contact with the road for a given weight on the tire (load). The sidewall construction is a (not the only one) factor (the stiffer the more weight it can carry before flexing) in determining load rating.

When tire pressure is correct for the weight ON IT the full tread is in contact with the ground.

When it is too high for the weight on it, the tire "balloons" and the weight is on the center of the tire tread and wear is in the center of the tire.

When it is too low for the weight on it, the tire contacts the ground on the outer sides of the tread and wear patterns show wear on the outside edges and much less in the center. Also there is much more weight supported by the sidewalls which causes them to flex more as the wheel turns. This builds up heat in the rubber and causes early sidewall failure.

At least that is how I understood it.

LadyWindrider · 07-23-2010, 01:02 PM

Yep, but you left out RPM and centrifugal forces acting upon a tire. The faster you go, the larger the diameter, and the more the tire runs on the center of the tread. Look at it this way, if it was easy, a cave man could do it.

Just chalk up tire pressure to another thread that will never be answered, just like which motor oil is best, which hitch is best, which campground is best......... and the list goes on. Personally, I go by what is on the tire, that is the most current information available, and put there by the tire manufacturer. What is on the door or in the manual may have been true at the time, but if the manufacturer changed the way they make tires, or did something to alter pressure requirements, it will be stamped on the sidewall. The car company will not issue a new manual or a door sticker.

**Herk7769** · 07-23-2010, 03:33 PM

Quote:

Originally Posted by windrider

Yep, but you left out RPM and centrifugal forces acting upon a tire. The faster you go, the larger the diameter, and the more the tire runs on the center of the tread. Look at it this way, if it was easy, a cave man could do it.

Just chalk up tire pressure to another thread that will never be answered, just like which motor oil is best, which hitch is best, which campground is best......... and the list goes on. Personally, I go by what is on the tire, that is the most current information available, and put there by the tire manufacturer. What is on the door or in the manual may have been true at the time, but if the manufacturer changed the way they make tires, or did something to alter pressure requirements, it will be stamped on the sidewall. The car company will not issue a new manual or a door sticker.

Did you read the Goodyear articles on this issue?
Lots of good current data in there.

mjones12 · 07-23-2010, 09:06 PM

Does the Marathon come in D rating on the 14-inch tires? I was under the impression that you had to go to 15-inch for the Marathon D's. I could be wrong. I had a set of Kumho D-rated 14-inchers that I was very pleased with, as were a lot of my friends. They are Korean, but last I heard, they were building a plant over here.

**Herk7769** · 07-23-2010, 09:43 PM

Please check the Goodyear web site. Their full product line is there.

bobsquarepants · 07-23-2010, 11:49 PM

Iggy, I stripped off brand new Duro load range C on my 8281SS and put on Maxxis D's...with high pressure stems, and balanced. Maxxis are a good tire but they do require some lead to smooth them out. I did this because... (a) I don't trust Duro's...(B) there was some question whether or not they were stressed during delivery from the factory as all of them were low, and the rear left had a nail in it. when I picked the trailer from the dealer (c) D's were 8 bucks more than C's so no brainer there.

Just came back from a 800 mile trip to the mountains and had zero problems and piece of mind. I ran mine at 55psi with the aluminum rims.

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