Tire Pressure Question

[mikemc53]

2022 Gulfstream Conquest 6280 on a Ford E350 chassis. The tire pressure recommended on the driver door tag says 75 psi front and 65 psi rear (drw). Last year I had a young tire tech tell me that they should all be at 80 psi, which I thought might be a bit high.

I run about 80-85% weight capacity and I was wondering if the door tag is accurate. The reason I ask is that the door tags are likely put on before the vehicle is modified to become a motorhome. Would that change the recommended tire pressure?

Thanks in advance.

[Old-Biscuit]

Door tag references the MH weight and recommended tire pressures

Until you actually weigh your MH use the door tag psi

[BarryG20]

The only real way to know what the proper psi to use is to weigh the vehicle as you normally travel (4 corner weight would be best) then look up the load inflation table for that tire. If you want to go higher than it states due to safety margin, handling characteristics, uneven axle load etc fine but at least you have the tire manufacturers recommendation as a starting point

[THenne1713]

Weighing at a CAT SCALE at PILOT/ LOVES, FJ, WILL ANSWER, but young tech = wrong, but yes, 80 FOR SPARE TIRE, easier to deflate roadside, or later at COLD CHECK than adding air roadside after tire change.

[jadatis]

Once you determined the axleloads, better axle-end loads, 99% acurate, wich only can be done by weighing fully loaded as you go on tripp, I can determine a pressure with maximum reserve, but still acceptable comfort and grip.

So thats the most important thing, but in front I can make a costom made pressure/axleloadcapacity list, with that maximum reserve, so you dont need to do pre calculations, like deviding by 2 or 4, and add reserve yourselfes. And my list is safer then the official list, because made with a formula closer to the ever to be constucted ideal formula to laws of nature.

Need from tires next, most can be read from sidewall.
1. Maximum load or loadindex single and dual.
2. Loadrange to determine the maxloadpressure.
Yours 80 psi so E-load, I think.
3. Speedcode.
Sizes would be nice too.

And if you give GAWR and GVWR , we can yudge if for those pressure can be lower, so if vehiclemaker putted some reserve in tires, probably not, and then the 80 psi is needed as long as you did not weigh.

I did this kind of post in other topics, and toke care that they stayed below 50 reactions.

[sibe]

Originally Posted by BarryG20

The only real way to know what the proper psi to use is to weigh the vehicle as you normally travel (4 corner weight would be best) then look up the load inflation table for that tire. If you want to go higher than it states due to safety margin, handling characteristics, uneven axle load etc fine but at least you have the tire manufacturers recommendation as a starting point

Good advice as many other answers.. Many door stickers by coach builder or even OEM, is based upon the tire that was chosen at that time..

One tire size or tire carcass (115R or 120R etc etc ) plus the manufactures spec will put you in a weight rating.. BUT pressure that manufacture can vary by weight/load per their final design..

SO weighing and getting a 4 corner load is ideal of your RV or atleast frt and rear.. Then adjust the pressure per the actual ratings , use the door tags as a reference.. If the RV is just a couple years old then the tires and spec should be pretty good,, if the RV is 15 years old lean more toward the tires you have as the lead factor and the RV loads..

IMO

[Winemaker2]

If you don't/ can't get 4 corner wts done don't assume balanced loads on axle ends. I'd figure at least a 10% imbalance end to end / side to side and use the higher load to calculate pressures.

[Mudfrog]

Originally Posted by mikemc53

2022 Gulfstream Conquest 6280 on a Ford E350 chassis. The tire pressure recommended on the driver door tag says 75 psi front and 65 psi rear (drw). Last year I had a young tire tech tell me that they should all be at 80 psi, which I thought might be a bit high.

I run about 80-85% weight capacity and I was wondering if the door tag is accurate. The reason I ask is that the door tags are likely put on before the vehicle is modified to become a motorhome. Would that change the recommended tire pressure?

Thanks in advance.

The bolded offers up an interesting question. I tried an internet search but wasn't able to come up with an answer. My gut feeling is that, similar to a class A manufacturer, the door sticker is placed by the motorhome manufacturer after completion with all factory options installed. Again, this is a guess.

As far as the young tire guy, I have the feeling he offered up his recommendation based on what he read on the tire's sidewall and is most likely incorrect. Wouldn't hurt the tire much, maybe a slight increase in center tire wear, but you'd probably have a firmer/harsher ride than you might like.

You stated you run around 80 to 85% of the gvwr so it kinda sounds like you've had your rig weighed. If you're guessing though, then you could be way off with your numbers. Weighing the rig loaded and utilizing the proper tire pressure chart will give you the correct pressures to use. I would say to use the pressures listed on the door sticker if you haven't had the rig weighed.

[Ron Dittmer]

I practice the same as most replies.

Weigh your rig on a CAT Scale, located at most truck stops. Weigh the front axle first, then both axles together. Do so during a trip with everyone in their typical seating positions, your gas tank filled and fresh water tank filled, to represent your worse case scenario.

Adjust your tire pressure per the actual load as stated by the tire manufacture. I add an extra 5 PSI for extra margin.

Here is one example of a tire manufacture's weight chart. I have these tires on my 2007 E350-V10 motorhome.

[jadatis]

At post #9.

The cross climate 225/75R16 is also sold in Europe, but then in 118/116R, then maxload single 1320kg/2910lbs AT 5.25bar/76psi.

The LT 1215kg/ 2680lbs AT 80psi/5.5bar.
Loadindex 115/112.

To my opinion they are the same fabricat but different print to fit into the TRA system.

Second is that the list here given is first calculated with use of official in US formula for LT tires, wich leads to higher loadcapacity's for the pressure.

I have an old list of Michelin of this sise aggillis 81, but for Crossclimate they will use the same.
In that calculated with the European officiall used formula for all kind of tyres, and leads to lower loadcapacity's for the pressure.

Luckyly this compensates the differences in the lower pressures.

But still strange, and I thinks its all to fitt into the system of the country they sell the tire too.

But not verry sound to laws of nature.

So if topicstarter has this size, and I want to make an extra safe pressure/axleloadcapacity list for him, I must give both LT-tire and C(for comercial) - tyre., can give 2 in my list, and here only singleload, axle.

Continental has this sise also in 121/120R
Then 1450kg/3180lbs AT 5.75bar/83 or 84psi

This all to show that you should not have a religius trust in the tire-(and vehicle-) makers information.
Even 2 trusted tire-organisations have contradicting information.

[Ron Dittmer]

I should have included this in my last reply.

I have also heard that following the tire chart alone is not the only consideration. The flexing of front tire sidewalls (especially in tight turns) is another consideration, something that cannot be reflected in such a chart.

In my particular case with my own rig, the weight on the front axle is a consistent 3260 during our trips. That is 1630 per tire. If I follow the tire manufacture chart, I should put 40 psi in the front tires. That works fine for vertical loading, but it does not consider an 11,500 pound rig pushing hard on the outer front tire during a tight turn while braking hard. The horizontal forces on that tire will flex the sidewalls beyond safe limits.

I ran with 50 psi in my front tires during our last trip. The RV tire pressure chart states 65 psi. Next trip, I am thinking of increasing the front tires to 55 psi. I am trying to find a good compromise between horizontal force safety, and ride-comfort. It was very nice-riding with 50 psi, and the rig handled decently. I am certainly cheating. One thing for sure, having the full 65 psi in my front tires makes for a rougher ride.

For motorhomes, you can't go wrong following the tire pressure chart sticker supplied by the RV manufacture. In my case, those numbers match Ford's tire pressure specifications which reflects the chassis Gross Axle Weight Rating.

[jadatis]

Made the different lists using 100% of loadcapacity, yyst as the officiall list is made.
Yust for information, to show the differences.
Used my own determined even tighter formula that leads to lower loadcapacity's for the pressure then the european formula.
In front of the cold psi, for the 118/2910 lbs, AT 77 psi, behind my calc for the 115/2680 lbs AT 80.
Behind that the loadcapacity's as given in the list.
See that 45 and 40 psi gives in front lower loadcapacity then the official US list at the last colom.

Then about the AT 90psi given at the bottom.
Thats yust the maximum allowed cold pressure and not the maxloadpressure.
So they allow you to use 90 psi cold, but dont support the higher loadcapacity for it.
Continental groop often gives on C(omercial)-tyres and the maxloadpressure right behind the loadindex and speedcode, and a " maximum inflation pressure" of 10 psi higher, wich is also cold pressure.
Many think you are not allowed to fill cold higher then the here 80psi maxloadpressure.

So this last part is not an error, yust " nice to know" information.

Here the list

118At77/ cold psi/ 115at80/officiall list
1411 lbs/ 35 psi / 1254 lbs /
1593 lbs/ 40 psi / 1416 lbs / 1650
1774 lbs/ 45 psi / 1576 lbs / 1790
1953 lbs/ 50 psi / 1736 lbs / 1940
2132 lbs/ 55 psi / 1895 lbs / 2060
2310 lbs/ 60 psi / 2053 lbs / 2190
2487 lbs/ 65 psi / 2211 lbs / 2335
2663 lbs/ 70 psi / 2367 lbs / 2440
2839 lbs/ 75 psi / 2524 lbs / 2560
3015 lbs/ 80 psi / 2680 lbs / 2680

[sibe]

I was going to post some charts on tires for various suppliers to only ass confusion, Michelin has 3 possible RV tires in the same tire size and 16 rim range ,, loads vary on each and pressure ,, Most 16 load E have that 80psi max as a norm but some carry 200-400 lbs or more each..

Do your research..
Know your vehicle load..

The older C with 16 rims.. VS 17 and up to occasional 19.5... Side wall flex aka sway will vary and so may overall ride..
IMO the 16" is a tad more critical when you are the max aka normal C class load..
I am one on that few pounds extra in PSI.. In my case 70 rear and 60 frt by scale and chart,, I aired my up this week for a trip this friday.. 65 frt , 74-76 rear.. I am pulling a 7x14 trailer with about 300-400 tongue added...

Towing always changes the game,,,

[jadatis]

At post #11.

Then I made you a list with maximum reserve, and for axleload given, all for your conveniënce.
Use the last colom to look your axleload back in, thats for the LT, the colom in front of psi is the C-tyre, but you could compare, because to my opinion same construction.

Draw your own plan, but dont devide by 2 and dont add reserve, all done for you.

Then you see that 55psi front could give low comfort, and 50psi is with max reserve and still acceptable comfort.

Li 118 at 77psi/ cold psi/ LI 115 at 80 psi
2211 lbs/ 30 psi / 1965 lbs
2343 lbs/ 32 psi / 2083 lbs
2475 lbs/ 34 psi / 2200 lbs
2606 lbs/ 36 psi / 2316 lbs
2737 lbs/ 38 psi / 2433 lbs
2868 lbs/ 40 psi / 2549 lbs
2998 lbs/ 42 psi / 2665 lbs
3128 lbs/ 44 psi / 2780 lbs
3258 lbs/ 46 psi / 2895 lbs
3387 lbs/ 48 psi / 3011 lbs
3516 lbs/ 50 psi / 3125 lbs
3645 lbs/ 52 psi / 3240 lbs
3774 lbs/ 54 psi / 3354 lbs
3902 lbs/ 56 psi / 3468 lbs
4030 lbs/ 58 psi / 3582 lbs
4158 lbs/ 60 psi / 3696 lbs
4286 lbs/ 62 psi / 3809 lbs
4413 lbs/ 64 psi / 3923 lbs
4541 lbs/ 66 psi / 4036 lbs
4668 lbs/ 68 psi / 4149 lbs
4795 lbs/ 70 psi / 4262 lbs
4921 lbs/ 72 psi / 4374 lbs
5048 lbs/ 74 psi / 4487 lbs
5174 lbs/ 76 psi / 4599 lbs
5301 lbs/ 78 psi / 4711 lbs
5427 lbs/ 80 psi / 4824 lbs maxloadpress LT
5553 lbs/ 82 psi / 4935 lbs
5678 lbs/ 84 psi / 5047 lbs
5804 lbs/ 86 psi / 5159 lbs
5929 lbs/ 88 psi / 5270 lbs
6055 lbs/ 90 psi / 5382 lbs