Tire pressure question

[cwall59]

I just picked up my 40’ Majestic. It is a triple 8k axle with Goodyear G114 tires on it . Max pressure is 125 for these tires . My max weight is 26500 and my dry weight is 21040 . I never plan on being fully loaded . Should I run tires at max pressure? The tires were at 116 when I picked it up . I’m also setting up my TST tire monitors so I would like to only do this once . Any recommendations is appreciated.

[geo-gypsy]

Cwall59 -

I you look on the Goodyear website, you will find an inflation chart that specifies the inflation versus the weight placed on the tire. Actually, inflating to the maximum pressure could very well cause an over-inflation problem and wear. I know Harold is pretty specific about tire inflation on delivery. If you have 116 lb, then I would keep the tires at that pressure. But again, look at the inflation versus weight table on Goodyear's website.

Just my two cents,
Ron

[rffowler55]

My tires maximum pressure is 120, my vehicle weight and chart says I would be safe around 95,. I run at 105 to account for weight changes over time and to minimize sidewall sag. I set my TST low pressure warning at 90 and my high pressure at 135. This range is not a recommendation but is what I have found works well for our situation.

[Podivin]

Weigh your rig at a CAT scale, look up the recommended tire pressures in the tire mfg chart, set inflation appropriately - maybe add a little for extra 'stuff' to be added over time.

[cwall59]

I was given information and it had different values . One paper said 100 -105 psi and another says 105 -110 . To use the Goodyear chart I have would I divide the max weight by 6 ? If so that would be 4416 which would put me in the 115 psi range .

[dadej]

Some where on I think IRV2 site there was conversation on trailer tire pressures. There was a guy from the tire industry commenting. If I remember correctly his stance was keep trailer tire max inflated. Running low on pressure even the chart says it is ok can be bad on sidewall especially on triple axles. If you have a IR gun you will be suprised at how the temp fluctuates. I think he goes by Tireman9

[Burrington]

Originally Posted by cwall59

I was given information and it had different values . One paper said 100 -105 psi and another says 105 -110 . To use the Goodyear chart I have would I divide the max weight by 6 ? If so that would be 4416 which would put me in the 115 psi range .

You have to go by the weight on the tires. The GVWR of the trailer is split between the hitch and tires, so you can't use that. The only way to know for sure how much weight is on the trailer tires is to load your truck and trailer for normal travel with all occupants, tanks, etc and go to the scale. The scale gives you three weights: Front truck axle, rear truck axle, and trailer axle weight. Divide the trailer axle scale weight by 6 to get the average weight on each tire. Then look up the proper inflation on the tire chart. You can add a bit more if you want to account for fluctuating weight in the trailer (full tanks vs empty, etc.). That is what is recommended by the tire manufacturers to give maximum wear and safety.

If you under-inflate the tires for the load, you risk over-heating and blowout, as well as premature wear of the outer treads. If you over-inflate, you wear out the inner treads prematurely.

The same thing should be done for your truck. The truck manufacturer specifies the tire inflation (door sticker) based on the GVWR of the truck at full load. If your truck weighs significantly under the GVWR, you may be able to reduce the inflation from the door sticker value and get a better ride and better wear. For most people, the truck is used close to its GVWR, so the manufacturer's ratings are correct.

[mjdenn]

My 2 cents. The prefered method would be to get per tire weights. Its just not practical now. For now get to a CAT scale and get your trailer weight when loaded with a normal load. Take your trailer weight and divide by 6. Add 10% to the per tire number to account for the kitchen side which will be heavier. If its a new trailer get the wheels aligned.

[cwall59]

Went today and weighed Truck and then truck / 5thwheel. My trucks sticker on the 450 , steer axle is 6000 , drive axle 9900 , gross weight 14000 and cargo capacity 4850 . My Majestic has a GVWR of 26500 , UVW 21040 and CCC 4547 .
The first weigh was truck only, full tank ,the wife and I .
Second was truck and trailer . Trailer had my tools in the front main storage , two full 80# propane and about 60 gallons of water . Haven’t had a chance to put much in it yet . Since we won’t be full timing we won’t go to the max weight. How do these numbers look ? They seem to be good so far . It’s a triple axle , rear kitchen Model.

[Burrington]

Here's what all your numbers mean:

14000 - 9680 = 4320 : Available payload of the truck alone (GVWR-GVW).
5480 + 7960 = 13440 : GVW of the truck with trailer attached (GAW Front+GAW Rear)
14000 - 13440 = 560 : Available payload of the truck with trailer attached (GVWR-GVW)
13440 - 9680 = 3760 : Pin weight of the trailer as loaded (GVW(w/trailer)-GVW(w/o Trailer). Can not exceed hitch weight rating.
9900 - 7960 = 1940 : Available rear axle capacity with trailer (GAWR Rear-GAW Rear)
6000 - 5480 = 520 : Available front axle capacity with trailer (GAWR Front-GAW Rear)
31520 - 9680 = 21840 : GVW of Trailer (GCW-GVW Truck). Must not exceed hitch tow rating, or tow rating of truck.
26500 - 21840 = 4660 : Available cargo capacity of trailer (GVWR Trailer - GVW Trailer)
18080 / 3 = 6026 : GAW Trailer axles (GVW Trailer axles divided by 3 axles)
6026 / 2 = 3013 : Average weight on each trailer tire. Use to check tire rating and set air pressure.
8000 - 6026 = 1974 : Available capacity of trailer axles (GAWR Trailer - GAW Trailer)
1974 x 3 = 5922 : Available cargo capacity on trailer axles
5922 + 560 = 6482 : Available cargo capacity limited by trailer axles and Truck's GVWR
31520 = GCW (Gross combined weight). Check this vs the GCWR of the truck which can not be exceeded.

Bottom Line Limitations: 4660 = Real available trailer Cargo Capacity limited by the trailer's GVWR. BUT! Maximum weight that can be added to the hitch
or in the truck is limited to 560 or you will be over the truck's GVWR. So the thing you will have to be careful of is how much weight you put in the front of the trailer, or in the truck. You only have 560 lbs to play with.

[mjdenn]

Cwall there will be a test on Burrington's post. The rear axle weight caught my eye. The 7960 sounds awfully low to me. Our 18 39 Summit scales a thousand pounds more though we have a 4 slide unit.

But to answer the pressure question. 18,080 /6= 3013 lbs per tire add 10% to allow a reserve and set to 3300. If you are coming to the rally there might be a scale to allow per tire weighting.

[cwall59]

I believe it could be the rear kitchen takes some of the pin weight off of the truck.

[mjdenn]

Its possible but your fresh water is back there also. I was thinking it was the 4th slide.

[cwall59]

Generator is behind the axles and refrigerator is at the back .