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Old 01-03-2016, 07:36 PM   #1
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Unhappy Another tire inflation question

I知 starting this thread on the Tiffin forum because I知 looking for Allegro specific information.
I知 trying to figure out proper inflation for my 2016 32-SA. I have Michelin XRV tires like all the rest 235/80R22.5-G (110 psi MAX). So, according to my weight certificate and the Michelin inflation table my steer axle should be at 90psi for 4125 pounds per axle end. But my drive (rear) axle is at 6535 pounds per axle end and the table says I should be at 75 psi. The sticker inside the door frame says 100 psi front and rear. What the heck should I go by.? What do you guy痴 do?
Just to add, The last motorhome I had I inflated to -5 psi from MAX inflation (printed on sidewall of tire) and it made it drive and handle much better. Should I let 殿ll that air out of my tires. Should I be at MAX on all or any? Clear as mud..! any help is greatly appreciated.
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Old 01-04-2016, 05:16 AM   #2
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I keep my 2012 32CA at 95 front and back. I have had them at 110 and the ride is too rough for me. I got it with 6,400 miles and had the front end aligned at a big truck repair shop and they put 110 in them and I drove it some and then lowered them to 95. I have 15,200 on it now. The longest trip I've been on was a 1,250 mile round trip from GA to Ohio and back, drove fine on mostly interstate hwys. Dave
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Old 01-04-2016, 05:29 AM   #3
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This question always prompts many varied OPINIONS. If not, you will find many if you search on tire inflation. I am one who believes the two main components of an answer depend upon the weight of each axle and the inflation tables from Michelin. Many gas stations have the CAT sign and for $10 or so you weigh your coach when loaded for the road. Look up the proper inflation on the tables and add an additional margin you are comfortable with.

For my road-ready 2015 32ca Allegro, the scale said: 7540 lbs. front, 13000 lbs rear. The tables said: 78 lbs. front, 73 lbs. rear. I carry 88 lbs front, 83 lbs rear in mine.
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Old 01-04-2016, 05:59 AM   #4
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It doesn't matter what vehicle the Michelin XRV tires are on for the PSI to use.
It doesn't matter if the tire is on a Tiffin, Winnebago, Fleetwood or any other make of RV.

Only way to know what PSI to use. Is the have all 4 corners weighted with full fuel tank and inside/outside loaded ready to travel.

Then use the inflation tables from Michelin. Add required PSI for the heaviest side of each axle to each tire on that axle plus add 5 PSI.

But do watch those Michelin's for sidewall cracking.
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Old 01-04-2016, 07:14 AM   #5
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Individual wheel weights are hard to get but axle weights are available at just about any truck stop. Look for the CAT scales (big yellow and black signs with a stylized cat face on them).

So, load your MH as it will be when you travel and drive it to the nearest CAT scale and get the front and rear axle weight. That is one trip to the scale and your axles on the 1st and 2nd weighing pads. Pay the person your $10 bucks (could be $12 now) and get your weight certificate.

With your Michelin RV weight tables in hand and your calculator, you are going to do some math.

Front axle weight + 5% of that weight / 2 = your front wheel weight. Look that number up in the table for tire inflation pressure. Add an extra 5 psi to it as a safety factor.

Rear axle weight + 5% of that weight / 2= your rear wheel pairs weight. Look that number up in the dual wheel section of the chart and add 5 psi to that.

You now have your front and rear tire inflation numbers, your side to side difference has been estimated (that's the 5%) and you are ready to go. When you can, get individual wheel weights and fine tune the numbers.

Yes, your front and rear wheels can be inflated differently. No, what someone else uses for tire pressures is not OK to use on your rig.

Post your weight certificate and I'll walk you through the steps on how to calculate it correctly.
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Old 01-05-2016, 10:55 AM   #6
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Thanks to all. Good formula luvlabs. Got it. Cheers.
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Old 01-05-2016, 12:55 PM   #7
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Rambling around in research information.

This is an excerpt from FMCSA.

No motor vehicle shall be operated on a tire which has a cold inflation pressure less than that specified for the load being carried.


This is an excerpt from SAFECAR (NHTSA).

Remember, the correct pressure for your tire is what the vehicle manufacturer has listed, NOT what is listed on the tire itself.


About tire industry standards.

Industry standards generally form the basis for demonstrating product safety and quality before courts, regulators, retailers, consumers and others.
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Old 01-06-2016, 03:48 AM   #8
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Quote:
Remember, the correct pressure for your tire is what the vehicle manufacturer has listed, NOT what is listed on the tire itself.
How does the vehicle manufacturer know that I changed all 6 tires from a 235/80/22.5 H tire to a 275/70/22.5 G tire?
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Old 01-06-2016, 04:31 AM   #9
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Quote:
Originally Posted by Triker56 View Post
How does the vehicle manufacturer know that I changed all 6 tires from a 235/80/22.5 H tire to a 275/70/22.5 G tire?

I think you have the load ranges on those two tires reversed.

The manufacturer's data plate lists the minimum pressure required for the OEM tire to safely carry the full GAWR for each axle. If your MH is not loaded to the maximum weight, you may be able to reduce tire pressure. It's important to note that there is a minimum tire pressure for duals to prevent the tires from rubbing against each other, and you cannot safely go below that number even if the load is light enough to allow it on a single tire.



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Old 01-07-2016, 10:48 AM   #10
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Quote:
Originally Posted by Triker56 View Post
How does the vehicle manufacturer know that I changed all 6 tires from a 235/80/22.5 H tire to a 275/70/22.5 G tire?
That statement is for Original Equipment tires and any like sized replacements.

The OE tires set the standard for replacement tires. That standard is to use replacements that provide equal or greater load capacity compared to the OE tires. Adjustments are often needed for the recommended tire inflation pressures of the replacement tires to meet the minimum load requirement of the OE tires. Once set, a notation should be made in the vehicle owner manual to reflect the recommended inflation pressures for the replacement tires.

Don稚 forget to register the new tires.
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Old 01-11-2016, 07:13 PM   #11
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The vehicle mfg has NO CLUE how I will load my coach! Triker56 has it right.

Weigh it, use the TIRE MFG tables and inflate to those numbers plus any fudge factor you choose.

I routinely have four corner weights at either a rally or an Escapee CG that has a SafeWeigh because my load out may vary from year to year.
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