I checked my tire pressures today, and I wondered. Why is the pressure the same when the wheel is off the car as when it is on the car? Wouldn't the car's weight compress the tire, increasing the air pressure?
I checked my tire pressures today, and I wondered. Why is the pressure the same when the wheel is off the car as when it is on the car? Wouldn't the car's weight compress the tire, increasing the air pressure?
How accurate is your gauge?
I think my head just asploded.
Perhaps the same reason that front tires can have the same psi as the back tires, but look more deflated: The pressure acting on the inside of the tire remains constant, but the shape of the tire changes.
I dunno, I pulled that out of thin air... I'm going back to my beer now
Perhaps the wheel does not sit on air but in fact hangs from the bead at the top of the tire?
well, the shaft on a bicycle rim is infact supported by the spokes connected to whatever part of the rim is up
http://grassrootsmotorsports.com/forum/grm/tire-pressure-hoist-vs-on-the-ground/3231/page1/
done
Well, this doesn't answer your question but I found it while looking.
http://auto.howstuffworks.com/question506.htm
As to your question I would have to say that the bulge at the bottom of the tire doesn't reduce the volume of the tire enough. The pressure probably does change, but not enough to measure with a conventional tire gauge. That is my SWAG. If you find out, post it here. I would be interested to know myself.
These are "forbidden questions". Ones that should not be asked, for if they are answered, and the obvious flaw in the universe is exposed, the fabric of the universe will rip apart and will cease to exist!!
Ok, figured it out. Tires aren't stretchy like a balloon, so when weight is put on them, they deform, instead of shrink. That way, the volume is the same, and pressure is the same.
No, not-stretchy means surface area remains more constant, not internal volume. The balloon that stretches rather than deforms is more likely to maintain constant internal pressure.
But the most likely answer is that the pressure change is too small to be measured by the instruments that you have. You either need a more precise instrument, or to apply significantly more force to the wheel than the weight of the car alone.
Ah, ok.
Go to the drag strip and talk to a Super Comp racer. They have gauges that go from 0-10 psi and are ridiculously accurate. You can see the shape of the slick change and the pressure move when they lower the rear of the car onto the ground (most dragsters are warmed up on stands in gear).
Next question to ponder Tommy.
If the air is holding the car up, how can the pressure be uniform inside?
I'd say that it shouldn't change enough to notice for the simple fact that you're not changing the amount of air in the tire.
I know it's more complicated than that, but that's just what i would imagine.
OK, how 'bout this? If a tire holds 32 psi at sea level, what will the pressure be at 10,000 feet?
mw wrote: http://grassrootsmotorsports.com/forum/grm/tire-pressure-hoist-vs-on-the-ground/3231/page1/ done
Hello??? As mw posted, this has been discussed to death. Sorry, I forgot my meds today. 
Hey...cut the kid some slack before he goes running to his daddy and has you banned from the forum...
Just kidding Tommy...and I think the air question was a very good one.
If the air in the front tire is on a westbound train, traveling at 87 mph and the air in the rear tire is on an eastbound train traveling 73 mph...
pinchvalve wrote: If the air in the front tire is on a westbound train, traveling at 87 mph and the air in the rear tire is on an eastbound train traveling 73 mph...
...and both are experiencing an airspeed of 99 mph, and the rails are a treadmill how long will it take to acheive escape velocity?
What if the tire is on a frictionless roller?
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