Tire pressures. How can this be?

[aviator41]

So, I'm digging through all the technical information on our RV and finally made it to the tire info.

Our RV has Towmaxx ST tires on it. Yes.. I know... Towmaxx means "replace immediately" in some circles.

Anyway.. here's where I'm confused. the tires are ST235/80R16-E's

According to the Towmaxx website, these tires are rated at 3520lbs @ 80psi when mounted single. Okay, cool. There are four tires on my particular RV, which means it has a total load capacity of 3520 X 4 = 14080lbs. But wait, the GVWR on this RV is 15,500lbs!

So, the tires being the lower number, does this mean that I can carry no MORE than 14080lbs hitched or do I need to account for hitch weight as well? This is 2580lbs. subtract that from the GVWR and you have 12,920lbs which would put me under the max rating for the tires.

This is where I need some help. am I calculating this right?

GVRW - hitch = sprung weight
Sprung weight / number of tires = Max weight per tire

I'm hoping this is right. I'm trying to figure required tire pressures (in case anyone is wondering why I'm doing this)

Now I know - I KNOW - I need to go get weights done. I get it. I just don't happen to have a Cat scale at my desk and wouldn't you know it, I left my RV at home when I came to work this morning. So I'm using published, generic weights here - keep that in mind. However, if I'm doing the math right, then I can plug in my scale weights in when I get them this weekend.

[tinner12002]

jwakeman wrote:
what about the ST speed rating of 65mph? Also I see dozens of transporter on I80 all doing 65MPH or less what do they know we do not know?

They know they don't want to have a blowout and destroy the new RV with the cheap RV tires that come on them from the factory.

[tinner12002]

Best thing to do is find a drive on scale and weigh your total rig then drive truck only off of scale to just weigh your RV and that will give you a total rig weight and your 5th wheel weight, then as NC Hauler said, check your truck weight before hooking up your 5ver.

[fj12ryder]

aviator41 wrote:
I personally am a Maxxis fan. Been for a very long time. I've run their trailer tires on utility trailers, the MT tires on 4 different trucks and even their ATV tires back when I was young, foolish, and racing a suped up Honda 400EX.

By far the best tire I've ever had the pleasure of buying. I've heard lots of good things about the Sailun tire, but Maxxis is where my money will go as I have confidence in their products.

I would have certainly paid a reasonable amount to upgrade the axles and tires on our newly purchased RV, had we been given the option! No question about it.

IMO ST tires in general are fine for lightweight trailers, not heavy long fifth wheels.

[fj12ryder]

bbaker2001 wrote:
so if part of the weight is pin weight, when unhitched, what happens to the weight.
also is it ok to set down stablizers when unhitched to take some weight off tires and frame

When you unhitch, the front legs take the burden. You can put down the rear stabilizers, but you're not going to take much weight off the tires because the stabilizers aren't designed to lift the trailer, just make it a bit more solid by adding a stabilizing force.

[aviator41]

I personally am a Maxxis fan. Been for a very long time. I've run their trailer tires on utility trailers, the MT tires on 4 different trucks and even their ATV tires back when I was young, foolish, and racing a suped up Honda 400EX.

By far the best tire I've ever had the pleasure of buying. I've heard lots of good things about the Sailun tire, but Maxxis is where my money will go as I have confidence in their products.

I would have certainly paid a reasonable amount to upgrade the axles and tires on our newly purchased RV, had we been given the option! No question about it.

[bbaker2001]

so if part of the weight is pin weight, when unhitched, what happens to the weight.
also is it ok to set down stablizers when unhitched to take some weight off tires and frame

[Me_Again]

Towmax AKA Blowmax!Seldom make 4K or 2 years. Put some Sailun S637 on it and don't look back!

Chris

[B_O__Plenty]

For what it's worth....The day will come when you WILL be sorry you didn't replace those Tow Max tires with something decent..

B.O.

[jwakeman]

what about the ST speed rating of 65mph? Also I see dozens of transporter on I80 all doing 65MPH or less what do they know we do not know?

[Rvpapa]

Posted: 07/20/16 01:46pm Link | Quote | Print | Notify Moderator

So, I'm digging through all the technical information on our RV and finally made it to the tire info.

Our RV has Towmaxx ST tires on it. Yes.. I know... Towmaxx means "replace immediately" in some circles.

Anyway.. here's where I'm confused. the tires are ST235/80R16-E's

According to the Towmaxx website, these tires are rated at 3520lbs @ 80psi when mounted single. Okay, cool. There are four tires on my particular RV, which means it has a total load capacity of 3520 X 4 = 14080lbs. But wait, the GVWR on this RV is 15,500lbs!

So, the tires being the lower number, does this mean that I can carry no MORE than 14080lbs hitched or do I need to account for hitch weight as well? This is 2580lbs. subtract that from the GVWR and you have 12,920lbs which would put me under the max rating for the tires.

This is where I need some help. am I calculating this right?

GVRW - hitch = sprung weight
Sprung weight / number of tires = Max weight per tire

I'm hoping this is right. I'm trying to figure required tire pressures (in case anyone is wondering why I'm doing this

Now I know - I KNOW - I need to go get weights done. I get it. I just don't happen to have a Cat scale at my desk and wouldn't you know it, I left my RV at home when I came to work this morning. So I'm using published, generic weights here - keep that in mind. However, if I'm doing the math right, then I can plug in my scale weights in when I get them this weekend.

Don't do it. Inflate to max sidewall pressure.
Art.

[Sport45]

Another difference between 5th wheel RV's and GN utility trailers is the GN trailer is often loaded from the rear with heavy equipment. During the loading process the hitch may see none of the trailers weight and the truck actually may be holding the trailer down. During these times the tires have to take the combined weight of the trailer and load.

[laknox]

aviator41 wrote:
Okay. I think I have a handle on it. I was originally not sure of how the pin weight would affect the overall weight of the trailer as distributed over the axles. This clears it up for me.

Thanks guys, I really appreciate the help. I'm trying to avoid blow-outs and I know that having the tire pressures correct is important to that. I'll run everything over a scale this weekend as we head out to get exact numbers.

This is where you see the biggest difference between a FW RV and a GN utility trailer. Almost every time you look at a commercial utility GN, the axles and tires will carry the full GVW, and do =not= account for the pin weight. It also shows you how much profit the mfrs are willing to give up by not offering simple options like upgraded axles/tires, disc brakes and independent suspension from the factory. How many of us would, if ordering new, want the next higher rated axle/tire combo if it were even slightly above "street price" for a conversion? I'd love to know how many Jayco Eagle HTs are being made with the 16"/Maxxis option which is, IMO, overkill for a 10k FW, but the =confidence= you have in not worrying about your tires for a while, has got to count!

Lyle

[time2roll]

When time for replacement I recommend tires that cover the full GVWR.
Pin weight should be the safety margin.
JMHO

BTW tire pressure should be sidewall max when cold.
Cold is before you roll and before the sun hits it.
No scale weight or anything else needed to calculate.

[Old-Biscuit]

There is pin weight and there is axle weight and there is TOTAL weight

Axle weight is what tires have to carry

Pin weight is what tow vehicle has to carry (or landing gear when no hooked up)

Total weight is pin wet plus axle weight.