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Old 07-19-2023, 05:39 PM   #15
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WOW! Has this caused a fire storm. Loaded or unloaded volume of a tire is too small to make a measurable difference in pressure.

Try measuring the pressure of a tire 10 times in a row and see how often you get the same reading within .1 PSI.

The RESOLUTION may be .1 PSI but the ACCURACY is somewhere between 1% and 3% when new depending on the brand. Over time the accuracy degrades a bit.

Repeatability is the ability of the person making the measurement to do it EXACTLY the same each time.

Unless you are checking pressure for a racing team it "AIN'T THAT CRITICAL"!
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Old 07-19-2023, 06:42 PM   #16
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Quote:
Originally Posted by twinboat View Post
An uncapped water bottle is a bad example, there is no pressure there.

When you add weight to a tire the tread flattens but the sides bulge, so same cubic feet of air. No psi change.

Hit a huge pothole, does your TPMS send an alarm, does the tire explode, no. It may damage the tire and wheel but the psi stays the same.
You totally missed the point I was trying to make, and that is displacement. In the water example, pushing in the side of the plastic bottle displaces some of the volumetric capacity of the bottle, and thus causes the overflow.

In the tire, it too experiences a displacement in volume inside, albeit a very small amount. Since the gas/air cannot escape because it is a sealed off container, the only possibility is for that same amount of air to be slightly compressed....and we all know that compression of the gas/air will cause an increase of pressure. In the case we are talking about (tire loaded vs. unloaded), as I stated in my previous post, it will be totally negligible and probably not detectable unless you have specialize equipment. But it still doesn't change the physics of compressing a gas and increasing the pressure when volumetric capacity is decreased, no matter how the decrease in capacity is achieved.
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Old 07-19-2023, 10:02 PM   #17
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Man.. boy oh boy..... I have been doing this wrong for so long.


When I get to a long uphill grade, I take the unneeded air from the front ties and put it in the rears because of weight shift. Then at the top of the hill I take the air from the rear tires and put it in the front tires, again for weight shift.


Now everyone is saying I dont have to do that??? WOW!! That will cut down on how long it takes to get someplace.
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Old 07-20-2023, 08:35 PM   #18
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My tires read the same on jacks or not.

What does make a real difference is if the sun, even the morning sun, is hitting the tires.
An hour of the morning sun raises my tire pressure.

My tires rarely need air and I use a TMPS system but when I do check and adjust the tires I make sure they are overnight cold and not in the sun.
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Old 07-22-2023, 07:35 PM   #19
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Folks this isn't the Indy car series, inflate to Federal Tire Placard pressures and have a carefree trip. Isn't what you do when driving your car or pickup?
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Old 07-23-2023, 09:43 AM   #20
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Folks this isn't the Indy car series, inflate to Federal Tire Placard pressures and have a carefree trip. Isn't what you do when driving your car or pickup?
The Federal Tire Placard on my 2005 Newmar Mountain Aire says 125 psi for all tires.

That number is patently ridiculous. My coach would ride like a buck wagon at those pressures.

125 PSI in my Toyo 295/80 22.5 tires would support 27,760 lbs in the rear and 15,660 lbs in the front.

The rear axle is rated for 20,000 lbs. The front axle is rated at 14,200 lbs.

I weigh 19,700lbs in the rear and 12,900 lbs in the front. Based on the Toyo inflation charts I run 85 PSI in the rear and 100 PSI in the front.
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Old 07-23-2023, 04:23 PM   #21
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Quote:
Originally Posted by bentjm View Post
The Federal Tire Placard on my 2005 Newmar Mountain Aire says 125 psi for all tires.

That number is patently ridiculous. My coach would ride like a buck wagon at those pressures.

125 PSI in my Toyo 295/80 22.5 tires would support 27,760 lbs in the rear and 15,660 lbs in the front.

The rear axle is rated for 20,000 lbs. The front axle is rated at 14,200 lbs.

I weigh 19,700lbs in the rear and 12,900 lbs in the front. Based on the Toyo inflation charts I run 85 PSI in the rear and 100 PSI in the front.
Similar to our weights and the resulting pressures recommended by Goodyear. Much better ride than at max load pressures recommended by Tiffin!
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