Nagging Question About Tire Pressure

[David40]

Lets say you are working with a tractor or other vehicle that weighs around ten thousand pounds. You have one of the wheels off and you fill it to about 60 psi which would be about right for a Class E tire. You put the tire back on and lower the vehicle to the ground. You check the tire pressure and it's still 60 psi. You have just added 2,500 pounds of weight to the tire. Since the tire is now being squeezed by that additional weight why doesn't the tire pressure go up?

 

[ILENGINE]

Because the volume of the tire didn't change. The bottom of the tire deflected but the rest of the tire could grow in size to compensate.

 

[Oddjob]

Lets say you are working with a tractor or other vehicle that weighs around ten thousand pounds. You have one of the wheels off and you fill it to about 60 psi which would be about right for a Class E tire. You put the tire back on and lower the vehicle to the ground. You check the tire pressure and it's still 60 psi. You have just added 2,500 pounds of weight to the tire. Since the tire is now being squeezed by that additional weight why doesn't the tire pressure go up?

Here are my thoughts as a non-engineer: Because air compresses too easily. There’s a lot of room between air molecules. When you squeezed the tire with the weight of the tractor, the air molecules just moved into the empty spaces. That’s why if you get air in your brake lines you get a soft pedal and poor braking, hence the need to bleed brakes. Your tire psi probably did go up a little, but not enough to register on your air gauge.

 

[Auto Doc's]

Study physics.

Air and hydraulics are not the same. Air acts in a passive cushion manner. Hydraulics transfer power using liquid which is not compressible. They both have many uses but should not be confused.

 

[Oddjob]

Challenge accepted. Because it has been about 56 years since my last physics class, I went to the internet and looked it up. Air is compressible, but as I said, there is a lot of room between molecules so it doesn’t compress very easily. Fluids are not incompressible. Even hydraulic fluid, expressly designed to resist compressing, does in fact compress slightly.

 

[Skippydiesel]

As a retired agriculturalist, I am wondering about a tractor tire that is being inflated to 60 psi ???
Could be some sort of loader I suppose.

 

[sgkent]

I would have thought there would be some minor increase because the tire volume should be reduced. A Google AI of the question answers that there is a subtle increase that is barely measurable with most non-scientific gauges.