Tire inflation

[garbonz]

Okay. I am mystified why oversize rims and tire would be some sort of advantage. I used to like big tires on my Camaro (actually still do) but they seem to be inconvenient and incorrect on a camper.

Do many people here purposely use load range E equipment on a trailer that is designed for LR D? Is there a safety factor I am not aware of or does it seem safer.

I don't want to miss some detail that is alluding me, especially in this critical area.

I check the clearances and there is only 2 inches between the tires and less than 4 in the wheel wells. That 2 inches would turn to about 5.5 or so with the 15 inchers. Is that important.?

[MillerTime]

Ok, ill try to explain.
Lets say my 11,400gvwr trailer actually weighs 10,500 lb loaded. Deduct 1500 lb for hitch pin weight, that leaves 9000 lb spread between 4 tires that are rated for 2640 lb. That is 2250 lb on each tire- which is operating at about 85% of max load.
In a perfect world those would be fine, but pot holes, curbs, camping pad lips can put more weight on individule tires. Or if one tire blows- very likely a second would blow because of an instant overload situation.
- if you were to put a tire rated for 3050lb (e) , it would operate at about 73% max load, - with a little more safety cushion there. Plus stiffer sidewalls will create less heat under the same load. And I think a ten ply holds up a little better for long hauls- imhop.

[garbonz]

Ahhh, interesting.

I would have thought that the bounce pothole would be included in the design of the tire, but maybe not. Then I see discussions about people here trying to get the cheapest tire they can and whining about the cost of LR E tires and that seems to be on the other end of the spectrum.

No easy answer, I guess; but I got to tell my dealer something. Maybe I will change the wheels for clearance and consider the LR E's when I replace the tires on there if the tire guys will do it on the D rims.

My head hurts, I thought this was such a simple question.

[Herk7769]

In my opinion tires are like computer monitors.

Your eyes will love you for using a high end high definition monitor that costs what the computer costs vs an el cheapo monitor that hurts your eyes. Additionally I almost never replace a monitor unless is is too expensive to repair vs replacement. The monitor I have is on its third computer upgrade.

Tires are the same in my opinion. You have a LOT riding on those tires (sounds like a commercial). Going cheap is not an option for me. I want the best tires money can buy for my application. I have Goodyear Marathons and am perfectly happy with them. I will be putting Marathons on the camper again when they "age out" because the tread still looks brand new after over 8,000 towing miles.

Oh, I did "up range" my tires to "D" when I replaced the Carlisle OEM load range "C" tires. At the GVWR of my camper (where I load normally) I am too close to the max load for C for my comfort. Although the max pressure on the D tires is 65PSI, I run then at 58 PSI for the load. (no broken dishes or glasses from trailer bounce - no shocks).

I am totally on board with Millertime on this one!

[Tblackmon9599]

I want to jump in here because I'm dealing with a similar situation, only the opposite problem. HERK, I used your calculations from an earlier post to see where I stand with my factory tires and I want to make sure I'm calculating this correctly:

Akuret ST225/75R15D 2540 lbs are installed from factory on my Salem 346QBUD. Dry weight on sticker is 10,100 and max load is 1981lbs. Axles are rated at 5080 each. Maximum rated weight loaded is 12,081. Assuming 15% pin weight the tires will be supporting 10,268 or 2,567 each? I'm overloaded with the factory tires unless I have much less cargo on board than the rig is rated for? Is my calculation correct?

I have been contemplating an upgrade to the tires anyway just for safety sake alone but after reading through this post a few times I might really have a safety problem that I really need to be concerned with.....

I asked a local tire dealer to try to find me a better tire with a higher load rating and they are telling me that it doesn't exist in my current tire size. I believe them as I haven't been able to find anything other than a D rated tire in the 15" wheel size either. I have contemplated going to a 16" which means new tires and wheels but have been concerned about the fit on the rig, not the hole pattern as much as the decreased clearance between the tires and trailer . I know it will sit a little higher but frankly, my rig rides a little high in the front because of my TV anyway so the bigger tires might actually help level me out a little.

I guess my questions are #1, am I overloaded on my existing tires and #2, can I upgrade to and E or even G rated tire in the 16" size and still be ok?

[Herk7769]

Originally Posted by Tblackmon9599

Akuret ST225/75R15D 2540 lbs are installed from factory on my Salem 346QBUD. Dry weight on sticker is 10,100 and max load is 1981lbs. Axles are rated at 5080 each. Maximum rated weight loaded is 12,081. Assuming 15% pin weight the tires will be supporting 10,268 or 2,567 each? I'm overloaded with the factory tires unless I have much less cargo on board than the rig is rated for? Is my calculation correct?

I use 15% as a wag for tires because the "safe range" for loading a 5th wheel is 15-25% with 20% optimum. 15% would be "worst possible case" when the maximum possible amount of weight is on the camper's axles.

Without determining your actual pin load there is no way to say. For example if you have a mid kitchen model and a large basement area your pin DRY may be on the order of 18% (1818) leaving 10,100 - 1818 or 8282 on the wheels.

In this case each tire would only have 2071 pounds on each tire. At max load of 12,081 and carrying a balanced load at 18% your pin would be 2175 and the tires would support 9,906 pounds or 2476 pounds per tire (well under their max).

As you approach optimum loading (20%), the numbers just keep getting better.

[Tblackmon9599]

Got it. That makes perfect sense. What are your thoughts on the larger tire size? Smart move if I can realistically do it or just keep with factory rated setup?

Thanks for the quick reply, man you're fast!

[Herk7769]

Originally Posted by Tblackmon9599

Got it. That makes perfect sense. What are your thoughts on the larger tire size? Smart move if I can realistically do it or just keep with factory rated setup?

Thanks for the quick reply, man you're fast!

I would use the tire size called for in the camper's tag.
In your case ST225/75R/15s. http://www.ebay.com/itm/NEW-Tow-Mast...-/320930282988


If you think the tires are spec'ed too close to their limit (as mine were), I would go UP a range to "E" rather than change the wheels. That way you can inflate them 10 PSI over the PSI required by the actual load (up the the tire max - 80 PSI) to give you an extra 10 MPH on the speed rating (to 75 MPH).

Normally ST tires are speed rated at 65 MPH at the required PSI for the actual load. You can not boost the D rated tires because they are already AT their max when inflated to 65 PSI.

WARNING - Boosting the load required tire pressure an additional 10 PSI does not give you additional LOAD CARRYING capacity; just the higher speed rating. For example if your E rated tire is carrying 2540 pounds at 65 PSI; boosting the tire pressure to 75 PSI will allow you to drive at 75 MPH AT 2540 pounds of load. NOT drive 75 MPH at 2720 pounds of load. (see attached load pressure chart)

[garbonz]

I'm gonna weigh the unit in travel trim on Saturday, then make my decision. Right now I'm tend to keep the wheels and change the sticker and run at about 65-70 psi.

[Herk7769]

Originally Posted by garbonz

I'm gonna weigh the unit in travel trim on Saturday, then make my decision. Right now I'm tend to keep the wheels and change the sticker and run at about 65-70 psi.

Just be on the look out for rubs or brush marks in the wheel wells.
If you see any you have a blow out waiting to happen.

[garbonz]

Good point.

[jeeplj8]

I want to offer a counter opinion. It is just that, my opinion.

I tend to believe that one reason trailer tire fail at a higher rate than passenger car tires is the extreme sidewall stress that tight turns put on tandem axle trailers. When you make a very sharp turn (backing into a parking spot at your storage lot for example), take a look at the tires in an extreme turn. The leading tire will be leaning one way, the trailing will be leaning the opposite direction. The amount of flex is determined by the sidewall strength, which is in turn effected by the load on the tires. That flex is saving your axles from bending/breaking.

I have come across this with boat trailers. You get to see the effect of a loaded vs unloaded boat trailer, unloaded it will simply drag the second axle scrubbing the tires and pivoting on the lead axle. loaded it cannot.

Many people in the boat world wanted their boat trailer to match their shiny Esclades and Denalis. They went to taller wheels and lower profile tires, which meant less sidewall flex. And they started having problems with bent axles and broken spindles (torsien axles anyway.)

I prefer to have what seems like a good balance. Your trailer weight as calculated by Herk are smack in the middle of load range D. They do offer load range E tires in the 15 inch size your trailer was supposed to come with.

I am just pointing out that a tire with less sidewall flex puts more pressure on other components. If I were in your shoes I think the ride height would be more important to me, but that is because I hate how high my trailer sits.

[Herk7769]

Originally Posted by jeeplj8

I am just pointing out that a tire with less sidewall flex puts more pressure on other components.

And thus the case for ST tires over LT in trailer applications; they are designed from the ground up with that stress in mind.

[going_postal]

Where is this yellow sticker you speak of. I have a 2003 Sierra 5th wheel 27 RLSS.
This has 15" 6 hole alloy wheels and e-rated Carlise tires. So back to the yellow tag, would this trailer have come with e-rated tires?
Gross weight 12080, dry 8570 lbs

[Herk7769]

There should be a sticker on the side of the camper with the tire size and air pressure required for your camper. Mine has yellow highlights.

[going_postal]

I do not see this sticker on the trailer, not on the outside anyway, will check compartments later when feeling better, just had minor surgery.