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Determining Proper Tire Inflation - A Confusing Experience

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Ron Dittmer

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Determining Proper Tire Inflation - A Confusing Experience
« on: September 23, 2019, 11:21:34 am »
This topic always has me scratching my head and wonder if I am alone.

Our PC is equipped with these tires. Michelin LTX M/S LT225/75R16
They are the originals with over 38,000 miles and now 12.5 years old.  I will be replacing them before our next big trip.

Here is the max-load condition of our PC, weighed on a truck scale.  Note the following
- front axle places 1630 pounds on each front tire
- rear axle places 2055 pounds on each rear tire.


According to the Michelin chart here
- 1630 pounds per front tire states they need 41 PSI.
- 2055 pounds per rear tire states they need 62 PSI


When I inflate the front tires to 41 PSI, they look terribly under-inflated.  My rear tires don't look as bad, but still so.  Because all tires look so low, I always add more air, inflating the front tires to 65 PSI (24 PSI extra) and the rears to 67 PSI (5 PSI extra).  Doing so, then they look better, still under-inflated, but better.  The rear tires have worn evenly, the front tires would have worn evenly except my front shocks were bad for a while which messed them up.

Am I the only one adding extra air?

Michelin provides a different chart for RVs, the primary difference is weighing each corner, taking the heavier of the two and using that PSI figure  for every tire on the axle.  But since I have not yet found a place to weigh each corner, I resort to "axle weight" alone.

I wonder if there is that much of a difference between the heavier corner weight and axle weight divided by two.  To you who have weighed axles and corners, what are the differences you see?
Ron (& Irene) Dittmer

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keelhauler

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Re: Determining Proper Tire Inflation - A Confusing Experience
« Reply #1 on: September 23, 2019, 03:33:29 pm »
The correct way to to weigh each corner. Otherwise you are taking a guess.
If you weighed with a trailer that would throw everything off. Weight with full tanks and passengers, no trailer.
There are places around the country that can do the 4 corners.

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donc13

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Re: Determining Proper Tire Inflation - A Confusing Experience
« Reply #2 on: September 23, 2019, 04:03:17 pm »
Ron,

I agree with keelhauler, fully loaded, water, fuel, stuff, you and your wife.   Each corner is best, but axle weight is "ok"

I would go with manufacturer reccomend pressures.   After all, they know their product better than you or I do, so why second guess them?

The "look" of a radial tire is really a poor way to judge how well inflated a tire is.   Tread wear and handling are far better indicators.

You already know my opinion on running tires beyond 7 years no matter how good the tread is.
---
Don and Patti

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Ron Dittmer

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Re: Determining Proper Tire Inflation - A Confusing Experience
« Reply #3 on: September 24, 2019, 12:57:33 pm »
In my opening post, I stated "max load condition".  That is a full tank of gas, full tank of fresh water, full tank of propane, all our stuff, cases of extra water, cases of soft drinks, more jugged water, full fridge and pantry, and us in the front seats.  We even had our Jeep Liberty hooked up.  It was truly our max load condition.

I need to find a place that will weigh corners as well as axles.  I was hoping some people here (especially 2350 owners) had both "axle" and "corner" weights to compare.

I wholly agree that "looking" at tires for inflation is not right.  But something is wrong when at 41 psi, I see so much tire resting on the road and the sidewalls bulging there, looking like it's going flat.
« Last Edit: September 24, 2019, 12:59:45 pm by Ron Dittmer »
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2 Lucky

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Re: Determining Proper Tire Inflation - A Confusing Experience
« Reply #4 on: September 25, 2019, 05:54:21 pm »
I've had Michelin's on all my trucks as long as I could afford them, installed at various pro retailers, and have never seen or been shown a chart like you show here. I can only guess that is a minimum inflation.
Tires should be inflated to the vehicle manufacturers recommendation as per the sticker on the door frame. My 2010 E450 2551 is 75psi front, 80psi rear, or the max shown on your chart.
Surprised you made it 38k miles and 12 years, shows the power and value of Michelin I guess!   

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CalCruiser

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Re: Determining Proper Tire Inflation - A Confusing Experience
« Reply #5 on: September 26, 2019, 05:19:20 pm »
Way back in the 1990's Ford pinned the blame on Firestone for the Explorer rollover deaths.
It was actually Ford's' fault because they lowered the inflation pressure on  the tire placard to 26psi for  a smoother car-like ride, causing the tires to be under inflated for the weight of the truck. That lead to overheating and tread separation.

I run 65psi front/ 60psi rear as specified on my E350 sticker, but the GVWR is only 11,500 lbs.
Goin' where the wind goes...

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Rick Leddon

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Re: Determining Proper Tire Inflation - A Confusing Experience
« Reply #6 on: September 27, 2019, 11:27:20 am »
I'm getting ready to go to the PC reunion. Discount tire checked my pressure, the fronts were 75 and the rears 80. Those are the pressures noted on the door jam. Costco had done them in June and must have inflated to 75/80. I concerned I am dealing with it in too basic of a way. I have not weighed the RV, it is a 2910T. I do everything I can to keep weight down.

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Re: Determining Proper Tire Inflation - A Confusing Experience
« Reply #7 on: September 27, 2019, 12:41:38 pm »
Costco or any reputable dealer would not install tires that are under-rated for the vehicle.   The tire pressures on the door jamb are correct. Weighing is important to be sure you are not exceeding the load limit of the tire installed. Just stop at any weight station when you start on your trip. You can always jettison water, the food, the dog, the kids, (anything but the beer) if needed.
Dougn
PS  Have Fun!

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garyg

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Re: Determining Proper Tire Inflation - A Confusing Experience
« Reply #8 on: September 27, 2019, 01:12:24 pm »
This topic always has me scratching my head and wonder if I am alone.

Our PC is equipped with these tires. Michelin LTX M/S LT225/75R16
They are the originals with over 38,000 miles and now 12.5 years old.  I will be replacing them before our next big trip.

Here is the max-load condition of our PC, weighed on a truck scale.  Note the following
- front axle places 1630 pounds on each front tire
- rear axle places 2055 pounds on each rear tire.


According to the Michelin chart here
- 1630 pounds per front tire states they need 41 PSI.
- 2055 pounds per rear tire states they need 62 PSI


When I inflate the front tires to 41 PSI, they look terribly under-inflated.  My rear tires don't look as bad, but still so.  Because all tires look so low, I always add more air, inflating the front tires to 65 PSI (24 PSI extra) and the rears to 67 PSI (5 PSI extra).  Doing so, then they look better, still under-inflated, but better.  The rear tires have worn evenly, the front tires would have worn evenly except my front shocks were bad for a while which messed them up.

Am I the only one adding extra air?

Michelin provides a different chart for RVs, the primary difference is weighing each corner, taking the heavier of the two and using that PSI figure  for every tire on the axle.  But since I have not yet found a place to weigh each corner, I resort to "axle weight" alone.

I wonder if there is that much of a difference between the heavier corner weight and axle weight divided by two.  To you who have weighed axles and corners, what are the differences you see?