# does a car tire weigh more when it is inflated?

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Weight of Air

Air at sea level weighs about 1.2 kg per cubic meter.

You can find that using the ideal gas law pV=mRT

where

p is pressure V is volume m is mass of gas R is the gas constant for air = universal gas constant/average molecular mass of air T is the temperature in absolute units.

All of those are better in metric units, so p is in pascals, V is in cubic meters, m is in kilograms, T is in kelvins, and R is 8314/28.8 = 288 N-m/kg-K.

At sea level, standard pressure is 101325 Pa, temperature is about 20 deg C or 293 K. For a volume of 1 cubic meter,

m/V = p/RT = 101325 / (288 * 293) = 1.201 kilograms per cubic meter.

Since you wanted to know gallons, 264.2 gallons is 1 cubic meter, and 2.204 lb in one kg, so

1.201 kg/m^3 * (1 m^3/264.2 gal) * (2.204 lb/kg) = 0.0100 lb/gal.

Not a heckuva lot, but not zero.

One thing to notice is that if you put a gallon of air on a scale, (in a wieghtless container, of course) you would measure zero, exactly. That's because the buoyancy caused by the surrounding air exactly counteracts the weight of the air in the container. If you pressurized the air in your gallon container to, say ten times the outside pressure (or 147.0 psi absolute, or 132.3 psi gauge) it would now weigh nine times 0.01, or 0.09 lb. Of course, the container that held all that pressure would have to weigh a lot more than 0.09 lb, so measuring the change would require a very good scale.

So your answer is more than zero but not noticable under small amounts used it tires.

Source(s): ASE master tech w/ L1 cert
• terri
Lv 4
4 years ago

You can't go wrong with 32 psi. Do not run the maximum, it's way too much air unless your car weighs as much as the the tire says it's rated for at the max psi. Everyone always sees the "Max inflation 44 psi" but they never seem to see what follows, "at 1500 lbs" or whatever the weight rating may be for that tire. IE: if the tire says 44 psi at 1500 lbs. that would mean you should run 44 psi if your car weighs 6000 lbs. Does your car weigh 6000 lbs? Not unless it's an F-350 super duty or something of that nature. Look at the weight rating on the tire, then look at the gross vehicle weight on the door placard on your car. It will be way less than the sum of the four tires. While you are looking at the door placard, look at the psi recommendation. It will most likely say something around 28-30 psi. The manufacturers tend to run them a little low because it makes the car ride smoother but you will wear the tires out faster. After all this, you will find that you will want to run your tires right around 32 psi, maybe even 35 but no more than that unless you are carrying sand bags every where you are driving.

• ?
Lv 4
4 years ago

Weight Of A Car Tire

• Anonymous

Not noticeably.

Although when properly inflated (or slightly higher) they will provide less rolling resistance, which makes your car get better mileage.

Low pressure will wear your tires out faster, and cause you to lose mileage.

Yes air does have weight.

34 psi x 212 Cubic inches volume= 7,208 pounds.

Just kidding of course......

YES-Air under pressure has more mass than atmospheric-pressure air. More molecules are pushed into a small space.

Source(s): ASE Mastertech
• Katie
Lv 5