Confusion re. correct tire pressure

[KenZ71]

CAT scales are easy

1) Download the app "Weigh My Truck" & set your profile and payment method
2) Have a helper as you pull onto the scales so you have one axle on each section
3) once ready enter the location code into the app, follow prompts, pay $13 and boom you get an emailed sheet showing your weights.

Need another weigh, a redo is about a third the original price.

[LETMGROW]

Originally Posted by Flyer15015

I ran 90 all round in our 19.5's when we had our Jayco Seneca 33ss.
Now with our Pace Arrow 22.5's we run 100 all round.
Never had either weighed.

Your milage may differ.
Mike in Colorado

I'm sorry to have to be the one to tell you you are doing everything wrong. I used to feel the same way as you do. I drove dump trucks and 18 wheelers for a while. Empty, partially loaded or filled to capacity I never had the trucks weighed and adjusted the tire pressures even when hauling long distance cross country. We're talking several thousand pounds in variations here.
At least five of our weekend outings are to a campground 21 miles from home we have been going to since 1976. Now that I have read so many threads over the years about the importance of correct tire pressures and all the science involved I do things altogether differently.
It seems as though each time we go to that campground we are loaded differently. Sometimes it will be just my DW and me while other times we may have Grandchildren along. This means we have additional weight for not only the Grandchildren but the extra food and supplies necessary to sustain the Grandchildren for an entire weekend.
There used to be Cat Scales at a station about twelve miles away from my home. The station closed and the scales were taken away. Now I have to drive roughly 60 miles to find the nearest Cat Scales.
So I know I'm traveling safely now I have to know how many extra passengers I will have onboard. Then I have to place concrete blocks and partial bags of Potting Soil in the positions the passengers will be riding in all calibrated for the weights. Then I have to drive the 60 miles and have all four corners weighed then adjust the tire pressures to compensate for the additional weight. I only hope one or more anticipated passengers doesn't decide not to come.
I follow all the information I have gained about this subject to the letter. I even purchased a new certified by the "Bureau of Weights and Measures" tire pressure gauge to be sure the pressure readings I am taking are truly accurate.
Using the charts I have developed over the years I know exactly what each tire should have for pressure before embarking on my journey.
I don't pay any attention to the tire pressure chart in my coach as I don't run the same brand tires the coach was delivered with. Due to tread designs and construction differences I use the recommendations from the manufacturer of the tires I currently have on the coach.
I know each and everyone responding to these threads follows their own advice right to the letter. That's fine so I thought I'd tell everyone how I do it because my method(s) are slightly different.
Safe Travels

[l1v3fr33ord1]

LETMGROW-

Thanks for bringing the conversation back to earth.

Speaking of that, I never thought to use "partial bags of Potting Soil" to distribute weight precisely, but I can see how that would work. If I took them with me on the seasonal stays, that would allow the Mrs. to mess around in the dirt, same as at home. I might have to buy replacement soil for the trip home, though, to keep the coach balanced.

All the readers of this thread-

All joking aside, there is a spectrum of experience- from "set and forget" to measuring tire temps with a calibrated temperature meter- among the iRV2 community. In this thread alone, we've heard from a former trucker and some RV owners at the one end, and a race car designer/crew/driver on the other. And there are many tire threads that sing the same tune.

Even within the motorhome community there is a spectrum of viewpoints and practices. That said, there are two endpoints to this spectrum:

1) Inflate to the placard
2) Weigh and inflate to the charts

Prior posts have laid out the details of both methods, so I won't repeat them here. I can only emphasize- Pick one and go with it, until and unless it no longer works for you.

And, for safety's sake, don't drive on underinflated tires- at least, not intentionally or for long.

[LETMGROW]

Yup, I'd rather ride on over inflated tires than under inflated tires.

[wolfe10]

Originally Posted by l1v3fr33ord1

LETMGROW-

Even within the motorhome community there is a spectrum of viewpoints and practices. That said, there are two endpoints to this spectrum:

1) Inflate to the placard
2) Weigh and inflate to the charts

Not sure there is/should be much confusion here.


You should HOPE that the PSI on the GVWR plaque is higher than required based on actual wieght. Since that PSI is based on each axle being loaded to its GAWR if this IS the correct PSI based on weight, it indicates that you have no safety reserve/axle is carrying all it was designed to do/ is working at 100% of design capacity.



Is the PSI on the GVWR plaque a good beginning point until you do weight the coach. Absolutely.

[l1v3fr33ord1]

Brett-

An interesting exercise is to run the charts for the placard-listed pressures. For my former coach, here are the results:

Front Axle:
GAWR 7,000 pounds
Chart pressure at 7,000 pounds 79 psi (rounding up)
Placard 92 psi
Chart weight at 92 psi 7,990 pounds
For a difference of 990 pounds, or 495 pounds per tire

Rear Axle:
GAWR 13,500 pounds
Chart pressure at 13,500 pounds 80 psi (rounding up)
Placard 92 psi
Chart weight at 92 psi 15,304 pounds
For a difference of 1,804 pounds, or 451 pounds per tire

I had the RVSEF folks four-corner weigh the coach once, early on. It helped to discover the front-rear and side-side numbers. The weigh crew told me that Michelin, the maker of the tires on my coach, recommended approximately 500 pounds per tire above the chart values. I have not verified that information. But, the 495 front 451 rear values, derived from the placard, appear to match well that recommendation.

Post-weighing I moved some weight back-to-front, and then staying aware of how much the tanks were full, I proceeded to run at the placard values from there on out. No more weighings.

I encourage anyone who's new to this stuff run the numbers through the chart for his tires and coach. It gave me confidence in the placard values, and allowed me to run in "simple mode," without resorting to potting soil. ;-)

I try not to post more than once or twice in a thread, particularly on topics that can raise the room temperature, so I'll move along. Carry on!

[Crasher]

Instead of looking for guidance from other members, why not look to the only known expert on the forum, "Tireman". Anyone, new or old, should read the Sticky:"NEWBIE's WITH THE NEED TO KNOW THEIR RV's & IRV2" at the top of this subject. If you still have questions, come back and ask all of the non-experts for their opinions. Chances are that if everyone were to read the STICKIE first, there would be no need for many to repeat the same responses over and over again and one would have the correct information and answers.

[wolfe10]

Originally Posted by l1v3fr33ord1

Brett-

An interesting exercise is to run the charts for the placard-listed pressures. For my former coach, here are the results:

Front Axle:
GAWR 7,000 pounds
Chart pressure at 7,000 pounds 79 psi (rounding up)
Placard 92 psi
Chart weight at 92 psi 7,990 pounds
For a difference of 990 pounds, or 495 pounds per tire

Rear Axle:
GAWR 13,500 pounds
Chart pressure at 13,500 pounds 80 psi (rounding up)
Placard 92 psi
Chart weight at 92 psi 15,304 pounds
For a difference of 1,804 pounds, or 451 pounds per tire

Mark,


Yes, that IS interesting. It is unusual for a coach maker to recommend PSI more than to support the max axle GVWR.


That raises the question of what are/were you actual weights compared with GAWR. It may be that they knew that the axles would be overloaded. It also could be that they built in the 10% or so safety margin recommended above the minimum to support the weight of the heavier wheel position on each axle. If so, no argument there!

[Lowflyer1]

Originally Posted by propchef

The only accurate way to know the proper inflation is to measure the temperature of the tires after they get hot. Track guys have known this for years.

You are mixing apples to oranges.
For starters, the race car tires are kept under heat blankets and the tires are hot before they even hit the pavement.

[jadatis]

Once you weighed per axle, you can look back the axleweights in my made pressure/axleload list.
In that I give per axle, and build in maximum reserve for load and speed, at wich comfort and gripp is still acceptable.
All for your convenience so you dont need to do pre-calculations.

If you manage to weigh per axle-end, I can make a list for that, in wich you search back the heavyest side on the axle.

Went from size 245/70R19.5
Front in front of cold psi/ Loadindex Single 133/ maxload 4542lbs AT 110 psi.
Drive behind cold psi/loadindex 131/4299lbs AT 110 psi
Max speed given 75mph.

FR axle/cold psi/Rear-Axle
2341 lbs/ 30 psi / 4444 lbs
2481 lbs/ 32 psi / 4709 lbs
2621 lbs/ 34 psi / 4974 lbs
2760 lbs/ 36 psi / 5238 lbs
2899 lbs/ 38 psi / 5502 lbs
3038 lbs/ 40 psi / 5765 lbs
3176 lbs/ 42 psi / 6027 lbs
3313 lbs/ 44 psi / 6288 lbs
3451 lbs/ 46 psi / 6549 lbs
3588 lbs/ 48 psi / 6810 lbs
3725 lbs/ 50 psi / 7069 lbs
3862 lbs/ 52 psi / 7329 lbs
3998 lbs/ 54 psi / 7587 lbs
4134 lbs/ 56 psi / 7846 lbs
4270 lbs/ 58 psi / 8103 lbs
4406 lbs/ 60 psi / 8361 lbs
4541 lbs/ 62 psi / 8618 lbs
4676 lbs/ 64 psi / 8874 lbs
4811 lbs/ 66 psi / 9130 lbs
4946 lbs/ 68 psi / 9386 lbs
5081 lbs/ 70 psi / 9642 lbs
5215 lbs/ 72 psi / 9897 lbs
5349 lbs/ 74 psi / 10151 lbs
5483 lbs/ 76 psi / 10406 lbs
5617 lbs/ 78 psi / 10660 lbs
5751 lbs/ 80 psi / 10913 lbs
5884 lbs/ 82 psi / 11167 lbs
6018 lbs/ 84 psi / 11420 lbs
6151 lbs/ 86 psi / 11672 lbs/ 11500 lbs Rr GAWR?
6284 lbs/ 88 psi / 11925 lbs
6417 lbs/ 90 psi / 12177 lbs
6549 lbs/ 92 psi / 12429 lbs
6682 lbs/ 94 psi / 12680 lbs
6814 lbs/ 96 psi / 12932 lbs
6947 lbs/ 98 psi / 13183 lbs
7079 lbs/ 100 psi / 13434 lbs/ 7000 lbsFr GAWR
7211 lbs/ 102 psi / 13684 lbs
7343 lbs/ 104 psi / 13934 lbs
7475 lbs/ 106 psi / 14184 lbs
7606 lbs/ 108 psi / 14434 lbs
7738 lbs/ 110 psi / 14684 lbs / maxloadpressure
7869 lbs/ 112 psi / 14933 lbs
8000 lbs/ 114 psi / 15182 lbs
8132 lbs/ 116 psi / 15431 lbs
8263 lbs/ 118 psi / 15680 lbs
8394 lbs/ 120 psi / 15929 lbs

[propchef]

Originally Posted by Lowflyer1

You are mixing apples to oranges.
For starters, the race car tires are kept under heat blankets and the tires are hot before they even hit the pavement.

Only F1 tires are kept under blankets and that practice is ending. In more than 30 years of HPDEs and track days I’ve never used racing tires nor used blankets. I use temperature to verify proper inflation. No confusion here.

You missed the point I’m afraid. Checking tire temperatures is a safety issue. Ignore at your own peril.

[eddndee]

I weighed my coach loaded and with the tanks as I usually travel with them. Got the axle weights. I should do something with that info but usually I just have a tire store check the weight and go.

[Ray,IN]

I use the Federal Tire Placard listed air pressure. You will not find any tire mfgr. that recommends using less than that pressure. Even if they publish load/inflation charts they also say to never run less than the Federal Tire Placard recommendation somewhere in their literature on tire inflation.

[LETMGROW]

Originally Posted by eddndee

I weighed my coach loaded and with the tanks as I usually travel with them. Got the axle weights. I should do something with that info but usually I just have a tire store check the weight and go.

How does the tire store check the weight? Do they have scales?