Tire Pressure Verification

[CUTiger80]

I am looking for verification from some of you more experienced owners of my interpretation of the data I have collected concerning the appropriate tire pressure in my fiver.
First, my fiver is a 2019 and has the original Sailun S637 ST235/80R16 Load Range G tires. The sticker on the side of the RV says that the tire pressure should be 110 psi, which is what I have been running for the 2 months that we have owned it. The ride is very rough and I have experienced a couple of divots/impressions in the vinyl floor from the slide out rollers. Thus my research into this subject.
On our last trip, I weighed everything at the CAT scales while fully loaded for a 3 week long outing. The weight at the rear axles was 11,640 lbs. That comes out to 2,910 lbs. per tire.
I looked up the tire pressure chart from Sailun and found the information shown below.
Based on my interpretation of this chart and the weights that I got at the CAT scales, it appears that I can be running pressures as low as 85 psi, although my gut tells me to not go below 90 psi.
Am I interpreting this data correctly?

[wiredgeorge]

Wow! Not sure about your tire question but you would appear to be way over your payload hauling that Montana. What is your payload according to your white/yellow payload placard in your door frame? That camper's gross weight is over 16K lbs. Good luck1

[CUTiger80]

Thanks for the quick response.
Per the CAT scales numbers and my calculations, the loaded fiver is 14,580 lbs.
I was getting ready to post something about the towing weights because all of the numbers are totally confusing to me.
The white/yellow placard refers to the Owner's Manual (see below).
There is another placard (see below) that says the GVWR is 10,000 lbs. According to the CAT Scales weights, the truck with fiver attached and all passengers is 11,640 lbs.

[travelin texans]

If you've got original G rated tires then that says that rig is or will be very heavy so my opinion is leave them at 110 psi or whatever the sidewall recommends for max weight. If you lower the pressure you'll probably have irregular tire wear due under inflation or have high temperatures that could cause blowouts.
As George pointed out your truck Is a little lightweight for that rv loaded which is likely the cause of your bumpy ride & not tire pressures. So air up the truck tires to their max load pressures also to help haul it.

[JRTJH]

You post an "interesting on the surface" question about tire pressure and reducing it to obtain a "softer ride"...

Remember that air pressure in the tire is what provides the capacity to carry weight....

If you look at the tire chart, reducing tire pressure lowers the tire's ability to support a heavy load.

You state that the CAT scale axle weight is 11,640 and you divide that by 4 to obtain a "weight of 2910 per wheel". That "false assumption" would mean that each tire supported an equal weight, which is NEVER seen in any fifth wheel. Depending on floorplan, there will ALWAYS be a weight difference at each wheel location. Things like the refrigerator, slide configuration, furniture/equipment location and even the position/fluid levels in each of the holding tanks can dramatically change "individual tire loading".....

By reducing your tire pressure to 85 PSI, you are essentially "removing all excess tire capacity" on the "average wheel weight" which is an incorrect assumption of actual weight carried at each wheel position....

Imagine, the wheel location under the refrigerator, in the slide, with the water tank and a gray galley tank are "over/just forward/aft" of the front axle. That would mean the rear axle on the opposite side may well be carrying only half the weight of the tire on the roadside front axle....

In other words, you might well be carrying 3500 pounds on the left front tire and only 2600 pounds on the right rear tire. Adjusting your tire pressure to 90PSI in each tire would mean you'd have one tire with ZERO safety factor and another with 1000 pounds excess capacity above the actual tire weight.

The "generally accepted rule" is to keep ST tires at the trailer manufacturer's recommended tire pressure or at the tire manufacturer's recommended sidewall pressure....

If you're going to deviate from that "generally accepted rule", then you'd need to first weigh each wheel position individually and use the Sailun chart to obtain a "owner selected tire pressure" that provides sufficient excess capacity to achieve the RVIA recommendation of 10% minimum capacity ABOVE the heaviest tire. Remember that both tires on any axle must carry equal air pressure and with load variability based on tank (liquid) status, all 4 tire positions "ought to carry" the same tire pressure....

In short, without getting "into the weeds" you really need to first determine if the "indentations on the floor" were caused by the rough road/travel conditions because of slide misalignment or from tire pressure..... My guess is the damage you see is from the slide and has nothing to do with the tire pressure.

As George stated, you're dramatically overloaded with your Duramax 2500 and that trailer. You may find that much of your damage is more related to "towing pair incompatibility" rather than from OEM tire pressure recommendations.

[sourdough]

Run the tires at 110psi. More importantly your truck is overloaded. Your placard says you have a 1949 payload and gvw of 10000lbs.

If I understand your numbers your trailer scaled, while hitched, 11640. Unhitched the trailer alone was 14580. That's 2940 on the pin...in the bed...vs a payload of 1949....or approx. 1000lbs overweight with just the trailer hooked up, no folks, no gear - no nothing. Then there's the 10k gvw of the vehicle and the scale of the truck?(or trailer?) 11640 which would indicate the truck is over gvw by 1640lbs. I'm not sure if those numbers are right because it appears the 11640 is used for 2 different weights or I am misinterpreting. Whichever way I suspect you truck is overloaded a lot. A 16600gvw trailer is too much for a srw 1 ton much less a 3/4 ton. I figure it's a rough ride because you're on the bump stops.

[flybouy]

" A 16600gvw trailer is too much for a srw 1 ton much less a 3/4 ton. I figure it's a rough ride because you're on the bump stops."

I think Danny is on point. It's like a man carrying a 150 lb back back that complains about his back hurting.

[CUTiger80]

You guys are really scaring me. I figured that I was marginal on weights, but not "way over payload capacity".
I was going to create another post, and I may still, but following are all of the numbers from the CAT scales, etc. All of these weights are with the truck fully loaded with people, fuel, and stuff and the Montana fully loaded for a 3-week trip.
The total truck weight is 8,600 lbs.
The pin weight of the Montana is 2,940 lbs.
The total axle weight of the Montana is 11,640 lbs.
If you do the math, the total weight of the Montana is 14,580 lbs.
I have measured the height of the truck at the tailgate before and after hooking up and the truck (at the tailgate) drops approximately 3" when the Montana is hitched up and ready to go.
I downloaded the trailering guide from GM for 2019 and the fifth wheel data is confusing to me. I have included it below along with the placard from the door panel of the truck. For the 2500HD 4WD Crew Cab with Duramax, there's not a weight spec provided. It does say that the GCVWR is 25,300 lbs. By my calculations, I'm at 23,180 lbs.
The door placard says that the GVWR is 10,000 lbs. By my calculations, I'm at 11,540 with the fiver hooked up.
I interpret all of this to mean that I'm okay as far as pulling and stopping, but I'm 1,540 lbs over as far as the GVWR for the truck.
Am I interpreting this all correctly or is there something that I am missing?
I was considering adding air bags (which I know will not help the GVWR of the truck) to help with the height of the rear end when the fiver is hitched up. I'm thinking that this could possibly help with the rough ride (at least).
I do appreciate everyone's comments on this.

[wiredgeorge]

OK... to my simple brain. Your payload is 1949. You CAT scale measured pin weight is 2940. This would be 991 lbs overloaded if you have added in the truck's passengers and cargo as you noted.

[CUTiger80]

I think that the available payload is actually 1,400 lbs.
GVWR = 10,000 lbs from the door placard.
Subtract the weight of the fully loaded truck on the CAT scales (8,600 lbs.).
It appears to me that I am 1,540 overloaded, but I like your number better (LOL).

[wiredgeorge]

The payload is what it was coming out of the factory. When you add some fuzzy dice, this takes off approximately 5 oz. from your available payload. Time to think about alternatives and only you can decide what is best. 1. keep going as-is with safety concerns. 2. buy different truck 3. buy different camper.



Since you are paying the bills, where you go with this comes down to your decision. Best of luck!

[sourdough]

Throw away the towing guide and any other brochure; those are to sell you a truck with optimistic numbers you will not see - and they do this to many more folks than yourself. The end all, be all numbers are on the door placard - the brochures/guides/salesman's promises etc. no longer exist - it is now the placard. Those are the numbers for "your" truck not the mythical sales model in the brochure. Don't think about max towing limits either - that is limited by the other numbers first.

The numbers that count? Payload, gawr front/rear, gvwr and gcvwr. That's what you look at and need to stay within the limits of all of them. None of them supercede another, they are all equally important. You've scaled and that is a good thing....but the numbers are very bad.

Payload - 1949. Loaded truck = 8600 vs gvw of 10000 = 1400 payload left. Pin weight 2940 = 1540 over payload.

GVW - 10000. Loaded truck = 8600 + Pin = 2940 = 11540. 1540 over GVW.

GAWR Rear - I did not see any weight per axle so figure it this way. 6200 lb. rear axle - 2940 for pin = 3260. 3260lbs. for the rear end of an 8600 lb. truck. Yes, a tiny portion of the 2940 will xfer forward but not a lot. I suspect you are well over your rear gawr as well.

GM gives you a liberal gcvwr of 25,300. In this case it is meaningless. You are severely overweight in at least the above 3 critical categories. Air bags won't fix this problem nor make you safe.....or stop. You need a bigger truck.

[CUTiger80]

Danny,
Thanks for the response. The front and rear weights from the CAT scales with the fiver hitched are:
Front = 4,880
Rear = 6,660
Where do you find the specs for the front and rear axle weight ratings? I have not seen them anywhere.

[sourdough]

Danny,
Thanks for the response. The front and rear weights from the CAT scales with the fiver hitched are:
Front = 4,880
Rear = 6,660
Where do you find the specs for the front and rear axle weight ratings? I have not seen them anywhere.


Your attachment door placard.2 has them.

[LewisB]

You guys are really scaring me. I figured that I was marginal on weights, but not "way over payload capacity"...I do appreciate everyone's comments on this.[Parial Quote]

I don't think it is our intent to scare you - but it is good that you are scared! If you are ever in an accident on the road, you are going to be "bait" for everything. Just the 3/4 ton badging on your truck under a 39' trailer are enough to give it all away to any highway patrolman who has much experience.

Your truck was never designed to haul a trailer of that size. The tire/loading badge for your truck clearly states "The combined weight of occupants and cargo should never exceed 1,949 lbs.". As pointed out you are severely overloaded on payload, truck GVWR, and probably GRAWR.

Sorry to be frank, but there is no sugar coating for this one...

[CUTiger80]

Danny,
Thanks. I was so focused on the GVWR that I missed that.
So it appears that I am 1,540 lbs. over GVWR and 460 lbs. over on the rear axle.
This has my stomach all tied up in knots since we just purchased the truck about 1 year ago and the fiver about 3 months ago. I just HATE the thought of telling the wife that we either need a bigger truck or a smaller fiver. She loves them both, and we can't afford to do either right now.
The facts are the facts but I felt much better when I was "ignorant".
Are we going to die on our next trip?

[flybouy]

In all seriousness, if you cannot alter the equation then park it until you can. Get a seasonal site and use the camper at that site until you can get an appropriate truck or downsize the trailer.

[sourdough]

Danny,
Thanks. I was so focused on the GVWR that I missed that.
So it appears that I am 1,540 lbs. over GVWR and 460 lbs. over on the rear axle.
This has my stomach all tied up in knots since we just purchased the truck about 1 year ago and the fiver about 3 months ago. I just HATE the thought of telling the wife that we either need a bigger truck or a smaller fiver. She loves them both, and we can't afford to do either right now.
The facts are the facts but I felt much better when I was "ignorant".
Are we going to die on our next trip?


This is a hard pill to swallow, I understand. I am very happy you inquired. Although knowing ties your stomach up, IMO it's far better to know and try to manage the situation than be unaware then do something that comes at a price too dear to pay.

The only answer to your dilemma is doing one of the options you mentioned - bigger truck/smaller trailer. I know it's tough to do but in your case there aren't a lot of options. You are very overweight on payload and gvw. Now some, although wrong, believe there is a cushion you can exploit between the gvw and the gawr. The variance between the gawr and the gvw is there intentionally to provide a cushion for owners because the manufacturer knows human nature and they will overload. Once at the gawr however you are at the limits of the truck....no more cushion. Unfortunately you have exceeded that failsafe as well.

I came to the point of hating towing because I was 200lbs over payload knowingly...not gawr mind you. I had casually mentioned it to DW but she didn't know what I was talking about....she trusts me implicitly and if I took off on a trip with her everything was OK as far as she was concerned because I was doing it. The consequences of some sort of failure became a HUGE distraction to me....on just one round trip to FL. I got to where I couldn't sleep. When I got home I bought a bigger truck.

Will you die? Well, every crystal ball I've had is either so murky or cracked I can't see anything in them. I will say this; in your situation a small event normally avoided by a properly equipped rig could turn into disaster.

I hate saying these things and ruining your day/week etc. but feel you at least need to know where you are. You can mitigate the rough ride, the diesel will pull it; but the truck isn't up for the job. You might get away with it forever or pay a terrible price on the first trip. I've never been a gambler of any kind.

[MarkEHansen]

Well, welcome to the "been there, done that" club :(

Around 8 months after we purchased our new 2019 Yukon Denali, we found it was not up to towing our trailer, and had to trade it in on our current truck. I don't like to think about what I lost on the trade-in deal, but it was somewhere around $20k - Ughhh. However, We are much happier now. We'll recover from the loss of cash.

[CWtheMan]

I am looking for verification from some of you more experienced owners of my interpretation of the data I have collected concerning the appropriate tire pressure in my fiver.
First, my fiver is a 2019 and has the original Sailun S637 ST235/80R16 Load Range G tires. The sticker on the side of the RV says that the tire pressure should be 110 psi, which is what I have been running for the 2 months that we have owned it. The ride is very rough and I have experienced a couple of divots/impressions in the vinyl floor from the slide out rollers. Thus my research into this subject.
On our last trip, I weighed everything at the CAT scales while fully loaded for a 3 week long outing. The weight at the rear axles was 11,640 lbs. That comes out to 2,910 lbs. per tire.
I looked up the tire pressure chart from Sailun and found the information shown below.
Based on my interpretation of this chart and the weights that I got at the CAT scales, it appears that I can be running pressures as low as 85 psi, although my gut tells me to not go below 90 psi.
Am I interpreting this data correctly?

For original Equipment tires there are no options to inflate below what has been recommended by the vehicle manufacturer. To do so is to decrease the load capacity reserves that recommendation provides.

[tech740]

it is nice to see someone receptive and understanding to "bad" news. Most on here are in the been there done that group. The seasonal site idea is great to get use from the RV but not need to move it. You may even find you like using it as a "cabin". Either way stick around and keep us posted.

[NevadaRich]

CuTiger80, I'm just going to make a couple notes....Everyone has given a lot of information to you, only you can decide, but with all that weight, YES you can move it, YES this time you can get where you want to go, but the next time, Some A/hole pulls in front of you thinking you can stop 20k in 10 feet, you will remember what everyone stated, Sorry but you need a 3500 or F350 etc Dully to safely pull that RV, OH YES the RV dealer said as he smiles at you when your driving off the lot!! Good Luck on picking another truck, you will feel better and safer.... By the way I am new here but have been RVing over 20 years and I have a 43ft Toy Hauler

[CUTiger80]

Thanks for everyone's input.
If I had not wanted it, I wouldn't have created the post.
For now, I am going to install a spring kit on the rear, which should help out with the way the truck sits and rides when towing. I know that this is not the permanent fix and does not increase any of the weight specs of the truck.
When it is time to replace the truck in a few years, I will upgrade as many of you have suggested.

[travelin texans]

Fortunately your 2500 diesel is a sought after truck so if you attempted to sell it yourself could possibly come out ok. If you try to trade check the selling price for similar trucks, the dealer is going to try & steal it from you knowing it's probably already resold to someone that's been there looking.
Sorry for the bad news, but as others have mentioned you're not the 1st & sure won't be the last to have fallen into this exact situation.
All the pertinent numbers you need will be on the particular trucks door jamb & the GVWR of a particular rv, pay no attention to salesman, brochures or advertising.

[ND1C]

I got tired of being asked if I could Tow what ever was at the RV Show, My Solution was a DRW 3500HD And a B&W 27K Hitch. Then I told her pick what she wants. Way Overkill for My Half ton tow-able Laredo 245RL 5th wheel (7200Lbs.) But when we Upgrade I should be Ok with most of what ever she wants. Buy the Horse before the carriage. And it never hurts to have some head room and piece of mind.

[MarkEHansen]

That's exactly what we were thinking with our truck. You just can't have too much truck :)

[Jim2366]

After getting the right truck to pull the RV a friend who is a retired pilot gave me some good advice. He flew a private jet for an Orange grower. He told me to always check my tire pressure before each trip. He also told me to stay 65mph or under to reduce the risk of problems. I have been doing both and it makes the trip more enjoyable and relaxing.

Pilots always go through a check list for a good reason so I figure I want to get to my destination too.

[Wingman301]

We had the same situation when we upgraded from a 6,000 lb TT to a 14,000 Cougar and then thought I could tow it with a Ford F-250 SRW. We had tremendous bucking and chucking between the truck and the fifth wheel. I then went to this forum and realized I was over the cargo capacity of our truck. I was sick. I told the wife we either needed to sell our brand new fifth wheel and downsize or we needed a different truck. We traded up to a Ford F-350 Dually and towing the fifth wheel was a pleasure! The difference in the ride and handling was amazing. No bucking or chucking. The truck handled the big fifth wheel beautifully. I was then able to sleep again at night and enjoy our trips. It was tough realizing we needed to make a change, but once we decided and made the change we were both much much happier. Safety first.

[sourdough]

We had the same situation when we upgraded from a 6,000 lb TT to a 14,000 Cougar and then thought I could tow it with a Ford F-250 SRW. We had tremendous bucking and chucking between the truck and the fifth wheel. I then went to this forum and realized I was over the cargo capacity of our truck. I was sick. I told the wife we either needed to sell our brand new fifth wheel and downsize or we needed a different truck. We traded up to a Ford F-350 Dually and towing the fifth wheel was a pleasure! The difference in the ride and handling was amazing. No bucking or chucking. The truck handled the big fifth wheel beautifully. I was then able to sleep again at night and enjoy our trips. It was tough realizing we needed to make a change, but once we decided and made the change we were both much much happier. Safety first.



Great post Wingman. Although I won't buy a dually you have stated exactly what every person I've known has said about upgrading and buying the proper size tow vehicle. Thanks.

[ChuckS]

I’d run the cold inflation psi stamped on the side walls of those tires...regardless of your weight...

I’m surprised at the door sticker on your truck for payload capacity... my 2007 GMC club cab 4x4 short bed 2500 Duramax has a lot more capacity then what your sticker shows..

Mine is 2650 on the sticker on the door... I tow a 2014 34 foot Alpine .... run 110 psi in the tires... have for the last 7 years ..

Stuff rides and travels fine

[Northofu1]

I’d run the cold inflation psi stamped on the side walls of those tires...regardless of your weight...

I’m surprised at the door sticker on your truck for payload capacity... my 2007 GMC club cab 4x4 short bed 2500 Duramax has a lot more capacity then what your sticker shows..

Mine is 2650 on the sticker on the door... I tow a 2014 34 foot Alpine .... run 110 psi in the tires... have for the last 7 years ..

Stuff rides and travels fine

That trailer is heavy for that truck, not debating it can pull that weight, the payload seems off. Mine is 2700 with a gas engine. Double cab, standard box 4x4 sle.

[ChuckS]

That trailer is heavy for that truck, not debating it can pull that weight, the payload seems off. Mine is 2700 with a gas engine. Double cab, standard box 4x4 sle.

Cheers ....