Tire inflation question

[abi2001]

We just took delivery of our new FR Wildcat 31SAX a week ago. This is our 3rd rig but first 5th wheel.

The tires are ST225 75R15. (I think we should upgrade to 16s, but that's another subject...)

The tire walls indicate they should be inflated to 80 PSI (cold) but the rig itself says the tires should be inflated to 65 PSI.

Why the 15 PSI difference? Honestly it feels like the tires aren't at all balanced, but I'm starting to think they're underinflated (IMHO) and it's causing the rig to feel bouncier.

What gives?

[bob caldwell]

Every time I try to run 80 lbs everything inside moves around a lot....so I stick with 65.......same size tire as you, only have 2 d rated and 2 e rated....( long story)

[abi2001]

Interesting... Thank you for the insight!

[Blackhat6mike]

Sidewall says 80psi, I run 80psi. Just me.

[abi2001]

That's what I figured... But I just don't understand why the rig says something completely different.

[bob caldwell]

Have the tires on yours been changed to a higher load rating....believe C is what they come with....65lb tire

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[abi2001]

Hmmm... Not sure. That's worth looking in to. We haven't changed them but I don't know if the dealership did or something. Thanks for the tip!

[bob caldwell]

Load rating will be on sidewall, along with a load rating for the 80lb tire at 80lbs....compare that to the sticker....

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[bob caldwell]

To dark here now to see what mine say.....

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[abi2001]

We just stopped to look. The specs/sticker on the rig indicate these are indeed the size and load that came with the rig. :/

[abi2001]

So apparently no swap was done and the inflation instructions on the rig do go with these particular tires. Odd.

[Airdale]

Originally Posted by abi2001

We just took delivery of our new FR Wildcat 31SAX a week ago. This is our 3rd rig but first 5th wheel.

The tires are ST225 75R15. (I think we should upgrade to 16s, but that's another subject...)

The tire walls indicate they should be inflated to 80 PSI (cold) but the rig itself says the tires should be inflated to 65 PSI.

Why the 15 PSI difference? Honestly it feels like the tires aren't at all balanced, but I'm starting to think they're underinflated (IMHO) and it's causing the rig to feel bouncier.

What gives?

The FR specs on your trailer indicate that your GAWR axles are 5200#. The ST225/75R15D tire does not provide enough load capacity to be fitted by the vehicle manufacturer (2540#) on those axles. However, the same tire with a LRE capacity at 80 PSI provides 2830# of load capacity which is above the minimum requirement for 5200# GAWR axles but not at 65 PSI which would make it a LRD.

IMO FR has made an error with the placards on your trailer and should be informed about it so they can make it right for you and any others that have a similar problem with that particular model trailer.

Wildcat Fifth Wheels / Travel Trailers by Forest River RV

To determine the axle rating from the specs you subtract the hitch weight from the GVWR and divide by 2.

Bottom line; Use the sidewall pressures of 80 psi because that's correct for LRE tires and what you need for the 5200# GAWR axles.

[GreenImp]

Originally Posted by abi2001

We just took delivery of our new FR Wildcat 31SAX a week ago. This is our 3rd rig but first 5th wheel.

The tires are ST225 75R15. (I think we should upgrade to 16s, but that's another subject...)

The tire walls indicate they should be inflated to 80 PSI (cold) but the rig itself says the tires should be inflated to 65 PSI.

Why the 15 PSI difference? Honestly it feels like the tires aren't at all balanced, but I'm starting to think they're underinflated (IMHO) and it's causing the rig to feel bouncier.

What gives?

You will get MANY different opinions on where your tire PSI should be, but this is FACT...

The PSI indicated on the side of the tire is the MAXIMUM PSI the tire can safely hold (go read it...see where it says "MAX"?). Note the key word here...MAXIMUM...meaning do not exceed this PSI when the tire is cold.

The PSI indicted on your trailers placard indicates the MINIMUM cold PSI needed to safely carry the trailer/load (go read it...see where it says "MINIMUM"?). Note the key word here...MINIMUM...meaning do not ever let your trailers tires run lower than this PSI when cold.

As long as you are between the minimum PSI indicated on the placard and the maximum indicated on the tires sidewall, you will be "within spec". This of course assumes there are no errors on your placard as suggested above, and also that your wheels are the proper wheels for the installed tires.

A lower PSI will allow the tire to take potholes, curbs, etc. better, and give a softer ride. A higher PSI gives increased load carrying capacity, lower rolling resistance/better mileage, and allows the tire to better take the scrubbing when turning sharp.

[Airdale]

Originally Posted by GreenImp

The PSI indicted on your trailers placard indicates the MINIMUM cold PSI needed to safely carry the trailer/load (go read it...see where it says "MINIMUM"?). Note the key word here...MINIMUM...meaning do not ever let your trailers tires run lower than this PSI when cold.

According to the specs for the OPs trailer he has 5200# GAWR axles. FMVSS 571.120 clearly states the vehicle manufacturer MUST set the recommended tire inflation pressures to a value that will fully support the GAWR axles. For the OP, 65 PSI on the tires he has described as being on his trailer would not satisfy the minimum requirement of FMVSS regulation 571.120 which would require a placard recall.

The OP needs to verify his tire placard, certification label. Sometimes the published specs do not match a specific trailer. Many trailers manufactured in his weight class will have GAWR axles set at 5080# to accommodate tires with 2540# of load capacity. In any case, something is wrong with his tire placard, tire fitments or both.

[abi2001]

Greenimp: the placard on our rig reads maximum, not minimum. We do know the difference. Thanks.

Airdale: this is what I read and understand too. I even found some great comparative charts online. I expressed that info and concern to my hubby but he said (claims/thinks) the hitch weight makes up for the extra support and wasn't worried about it, choosing to keep it at 65 because the run between 70-75 when riding. I agree with you completely. Thank you so much!

The tires currently appear to have bulges in the sidewalls, so it looks like they have internal damage from ride underinflated. I'm currently trying to convince hubby to upgrade the wheels and tires to 16-inch.

[ChooChooMan74]

I just checked out the Maxxis load inflation chart (Same specs for ALL tires). Trailer Tire Load/Inflation Chart | Maxxis Tires USA

You have a 12000lb +/- Fifth Wheel. Minus the pin weight, you are putting a load of 2500+ per tire when you are loaded to GVW (someone said the axles are 5500lbs?) Looking at the chart you have:

65PSI - 2540lbs(LRD)|70PSI - 2620lbs|75-PSI - 2720lbs|80PSI - 2830(LRE)

Personally, I would scale it and go with a conservative figure.

[Airdale]

Originally Posted by ChooChooMan74

I just checked out the Maxxis load inflation chart (Same specs for ALL tires). Trailer Tire Load/Inflation Chart | Maxxis Tires USA

You have a 12000lb +/- Fifth Wheel. Minus the pin weight, you are putting a load of 2500+ per tire when you are loaded to GVW (someone said the axles are 5500lbs?) Looking at the chart you have:

65PSI - 2540lbs(LRD)|70PSI - 2620lbs|75-PSI - 2720lbs|80PSI - 2830(LRE)

Personally, I would scale it and go with a conservative figure.

What they really need to do is tell FR what the certification label says and the size of the OE tires/rims so they can fix the problem.

The correct tire inflation pressures for OE tires are always on the certification label/tire placard. It was a good catch by the OP to have found the tires did not match-up with the placard information. FR is not the only manufacturer that sometimes errors on tire placard information. It's quite common to see placard recalls. In this case they may have to recall the trailer to install the proper rims if they are, in fact, rated lower than the tires..

See the trailer specs in post #14.

Note: Trailer manufacturers are required to keep the serial numbers of the Original Equipment tires on file for five years. But the tires described by the OP are an appropriate fit for the axles so the placard information is wrong. If the rims do not have the load capacity & PSI rating for the LRE tires that's another error by some installer. In any event, FR MUST be informed so they can sort it out.

Here is a reference to an older FR recall that I have in my files.

https://dealers.forestriverinc.com/d...alerLetter.PDF

[Airdale]

Originally Posted by abi2001

We just took delivery of our new FR Wildcat 31SAX a week ago. This is our 3rd rig but first 5th wheel.

The tires are ST225 75R15. (I think we should upgrade to 16s, but that's another subject...)

The tire walls indicate they should be inflated to 80 PSI (cold) but the rig itself says the tires should be inflated to 65 PSI.

Why the 15 PSI difference? Honestly it feels like the tires aren't at all balanced, but I'm starting to think they're underinflated (IMHO) and it's causing the rig to feel bouncier.

What gives?

After I finished another post on this thread awhile ago I decided to look on the WWW for any recalls on your specific model. And, sure enough, there has already been one for placard misinformation but not the same as yours. Here is the reference.

https://www.consumeraffairs.com/reca...rs-022616.html

[abi2001]

You're awesome! Thanks a million!

I really appreciate all of the feedback and help from everyone. We're about to embark on a 3-month cross-country trip and I'm trying to make sure we ride safe. This weekend was only a 2-day maiden voyage for our Wildcat...but I'm not having fuzzy feelings about the tires and I haven't since purchasing the rig. This confirmed my concerns.

Thank you all again. Airdale, I can't thank you enough for going the extra mile for me. You've been extremely helpful.

[GreenImp]

Originally Posted by abi2001

Greenimp: the placard on our rig reads maximum, not minimum. We do know the difference. Thanks.

I am not sure, but it seems as though you may have misunderstood my post. I did not mean to imply that you did not know the difference between minimum and maximum. If I did, I apologize.

Tire placards do not say anything about maximum with regard to PSI. They will often refer to maximum load, maximum cargo carrying capacity, or sometimes even maximum speed, but when when it comes to PSI they only state the minimum PSI required to carry the loaded trailer (often referred to as "recommended pressure"). It's pretty much the entire point of the placard...to help ensure the trailers are using enough PSI to safely carry the load and the proper rated tires to hold that pressure in without failing.

On the other hand, the sidewall of the tires do state the maximum load/PSI they are able to safely carry. This does not mean that the tire is required to be set at this "Max" PSI, but only that you are not to exceed it. All major tire manufacturers have published "Load Inflation Tables" that you can use to determine the proper PSI for any given load. The PSI numbers found on these tables are minimums and will match the PSI given on the placard for any particular weight rating...when they get it right that is, which it sounds they may not have achieved with your trailer.

Many people will simply say to inflate to whatever the tire says on the side. Generally speaking this is a safe practice but it is not necessarily the "proper" PSI for the load. There are disadvantages to having the PSI set too high, although not as many or as drastic as when PSI is too low.

Below are links to a few tire manufacturers load inflation tables...
Trailer Tire Load/Inflation Chart | Maxxis Tires USA
http://www.goodyearrvtires.com/pdfs/rv_inflation.pdf
http://www.rvsafety.com/images/pdf/T...lation2014.pdf