RV Weigh Station that weighs each tire?

[stevenapril]

Originally Posted by jadatis

8050 lbs front gives 94 psi, make it 95psi.

Thanks you! Can you help me to understand why your numbers are much higher than Michelin's numbers? What are they not accounting for?

[Old Scout]

This might be a bit like picking the "fly specs out of the pepper." Hard to find but some public or truck scales have sufficient margins to make separate trips, right and left sides. Dont need to let "perfect become the enemy of the good enough." Within reason, under-pressure is more dangerous than over-pressure. Weighing the rig fully loaded the first time could be "enlightening" but adding back 5 or 10 percent tends to get you back to where you started, perhaps.
Interesting side note--for class-A's with air bags, I was surprised to find out how much weight could be redistributed by modest adjustments to ride height, especially cross-corner. And without changing actually ride height. Of course, this assumes a balanced distribution, sides to side by axle, is a good thing--I tend to think it is.

[jadatis]

Originally Posted by stevenapril

Thanks you! Can you help me to understand why your numbers are much higher than Michelin's numbers? What are they not accounting for?

First is because I give 90% of calculated loadcapacity for the pressure, michelin gives for 100%.
Then you might argue that they build in a reserve when determining maxload, and mayby a little, because their calculated maxload for the speed, is rounded down to the lower loadindex step. But I would not bet on it, that they did more.

I once determined by reactions about bumping, that if in real 85% of the load calculated for the pressure for 99mph, on tire, that then comfort and gripp is still acceptable. Was for LT, so mayby your semi truck tire a lower speed.
So I dont go for minimum, but maximum.

Now if equal weight R/L on the axle, ( wich never is) 90% used, so still acceptable comfort and gripp on both tires on tge axle.
But if one side 85%, and the other 95%, still comfort, and still reserve on the 95%.
This can be seen as a 47.3/52.7 weightdivision on the axle.
And I gave it for 75mph, max of your tire, so it can be higher pressure even.

But you could also do it yourself, making determined axleload 90% of loadcapacity for the pressure, by doing axleload/0.9, or the same is adding 11.11% to the axleload, and then look back in Michelin list. But I did the rocket science to make it easy for you.

Second is, I added the RV list I used and checked.
Mayby you used the same.
For your sise I checked the list to be made with an even more bad formula then for LT used in US.
That is loadcapacity is (pressure/ maxloadpressure) ^0.65 x maxload. Lt in US power ^0.7

Why Michelin, a from origen European brand uses that instead of the in Europe used power of ^0.8 in the formula for all kind if tires, since decades, and since 2006 also in US for P-tires., I think is because of fitting in the TRA system, all brands in US give same list.

I also checked the 315/80R22.5 in their pdf, and it was even calculated with a power ^0.82, a power an American IR J. C. Daws adviced for P-tires if only power equation is used. For trucktires he adviced power ^0.95. The closer to power 1, the lower loadcapacity it gives, so leads to higher pressures. Power 1 is the same as lineair calculation.

I think the 315/80R22.5 is more used by fleetowners, and they dont have to sew them if to many tires blow, they yust dont buy tires from them anymore.

I use power ^ 0.95 in my calculations and a zeropressure loadcapacity of 5% of maxload for a 36 psi tire, and lower % for higher pressure.
Looked it off from a pdf of Mr Daws.

[Mike8253]

Originally Posted by stevenapril

Full fuel, propane and water and loaded for a weekend camping trip. Tires are Michelin 22.5" 255/80R22.5 XRV

The front was 8,050... 4,025 each tire...and the Michelin chart recommended 75 lbs

The rear was 14,080... 7,040 per side ......and the Michelin chart recommended 75 lbs

I went with 80 lbs in all tires. It rides so much better at 80 lbs vs the 100 lbs from the factory.

When my Dad was still with us, he used to tell me that he "would never eat a vegetable that he couldn't spell." With all due respect to the knowledge that jaditis has re: this subject, I can't follow the logic, so I follow what the tire manufacturers publish for inflating their tires. When I have to air up my tires, I just want a quick reference to know what the inflation needs to be for the weight. So I weigh my RV at a CAT Scale, determine the appropriate weight numbers to do the look-up on the manufacturer's chart, add 5% to the appropriate inflation PSI and then round that up to the nearest 5 PSI increment.

In your case, for your rear axle, I think your assessment is good for your weight, although the 5 PSI adder is less than 5%. On your front, the maximum weight for 75 PSI is 4070 lbs., so you are really close with your 4025 weight. For me, I'd use the next higher value of 80 PSI as my base, and add 5% to that, again with the round-up. I think your ride will still be appreciably better than what your started with, but your margins will also be much better as well. For what it's worth...

[jadatis]

Reaction to post #32, above here.
I only gave in post #31 the explanation why my list leads to higher pressure.
Once you understand that, you can forget it, and use my list.

Much simpler then what you do now, with adding first and rounding up etc, yust look 99% acurate determined axleload back in my list, and use the pressure belonging to that..... Ready.

Mind that if you ever weigh per axle-end, I have to make a new list, in wich I give 95% of 1 tire for single load, and 2 tires for dualload. Then search back the heavyest side on axle, and use that pressure, then hope for comfort, the lightest side stays above 85%, but if not, so be it, better a bit discomfort then chance on overheating heavyest side tire('s)

[Mike8253]

Originally Posted by jadatis

Reaction to post #32, above here.
I only gave in post #31 the explanation why my list leads to higher pressure.
Once you understand that, you can forget it, and use my list.

Much simpler then what you do now, with adding first and rounding up etc, yust look 99% acurate determined axleload back in my list, and use the pressure belonging to that..... Ready.

Mind that if you ever weigh per axle-end, I have to make a new list, in wich I give 95% of 1 tire for single load, and 2 tires for dualload. Then search back the heavyest side on axle, and use that pressure, then hope for comfort, the lightest side stays above 85%, but if not, so be it, better a bit discomfort then chance on overheating heavyest side tire('s)

As I said in my post, I do respect your obvious knowledge of the subject. My issue with your results is the seeming presumption of high driving speed and its direct influence on your calculations of required PSI's. I'm sure that there are Class A's being driven at 75 mph or higher out there, but I'd venture to say that a distribution of driving speeds results in the average being in the mid-60's. Not sure what the OP's typical speed is, but I'm around 62-63. For me, your inflation numbers are too high. For that reason I'm satisfied with the tire inflation charts as they are. Also, as I've made physical changes to my MH, and also as I've changed the way we load up depending on length of our trips, I'll re-weigh our MH to make sure I know what my real axle weights are. With that info, my lookup is easy, and I'm confident of my numbers. But I do appreciate your insight and interest.

[macnut]

Originally Posted by Stuart W

As a great starting point, call Newmar Customer service and provide your unit number, they can email you the corner weights that it was at as it left the factory.

Thanks Stuart W ! Newmar Customer Service was able to send mine to me!

[Clemson]

Four corner weighting is just not necessary for 99% of Class A coaches. Go to a CAT scale and weigh each axle and divide by 2. Steer, duals and tag then adjust to COLD tire pressure charts from your tire OEM and enjoy

[TB673]

Originally Posted by Winemaker2

Yes. Also, @ escapees park in mid state FL EZ on/off I75 (I forget the exit)

Sumter Oaks RV Park
4602 CR. 673
Bushnell, Fl.
Exit# 309

Tim

[Isaac-1]

Originally Posted by Clemson

Four corner weighting is just not necessary for 99% of Class A coaches. Go to a CAT scale and weigh each axle and divide by 2. Steer, duals and tag then adjust to COLD tire pressure charts from your tire OEM and enjoy

Possibly not on larger diesel pushers, but on many gas Class A's there can be a considerably side to side weight variation

[tnedator]

Originally Posted by Isaac-1

Possibly not on larger diesel pushers, but on many gas Class A's there can be a considerably side to side weight variation

Years ago I read a recommendation to take .53 of the axle weight, which if my math is right, would be equal to one side being 12.7% heavier than the other. That's the approach I've been using, since I haven't managed to get to a four corner site.

So, at my last weigh in, my front axle was 14,320. .53 of that, is 7,590, so I assume each front wheel is 7,590. Which on the load chart for XRV is 115, so I run 115 to 118. I typically inflate to 118 and as long as they are 115 or higher, leave them alone.

The flip side on my rears/tag, I'm lower than the bottom of the chart, which starts at 75, so I run 85.

I'll be in Florida next month. Might see if I can manage to get by escapees.

[jadatis]

Answer to post #39

In my made list you dont need to do all those calculations in front.
All build in
Your given 47/53% weightdivision.
My build in reserve, giving 90% of the calculated loadcapacity, covers 47.3/52.7 % weightdivision, and then still heavyest side using 95% of loadcapacity.
See my post #31 for explanation.

[shepardmike]

Originally Posted by TB673

Sumter Oaks RV Park
4602 CR. 673
Bushnell, Fl.
Exit# 309

Do you have to make an appointment or just show up? Easy access with TOAD?

[TB673]

It's been a couple years but I called and made an appt.
I beIieve that the weighmaster lives on site.
Just Google "Smartweigh" for the phone number.



Tim