Tire Pressure...

[sx460]

Lets say I inflate my tires to 35 psi. If I put 1500 pounds of weight in the bed, will the tire press increase or stay the same?

[ZZebes]

stay the same, tire pressure is static. the only way tire pressure can change is when it heats or cools and the air expands or contracts and thereby increases or decreases the static pressure

[silveradoHO]

Stays the same. You still have the same amount of air in the same amount of space.

[snoman]

stay the same, tire pressure is static. the only way tire pressure can change is when it heats or cools and the air expands or contracts and thereby increases or decreases the static pressure

 

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No exactally. It will increase slightly because the tire will compress some under load and reduce the area/volume for the air in it. It will not be a large shift and you will need a very accurate gage to see it but there will be a shift. It was a good question though.

[ken1mod]

Snoman is correct, the pressure will increase. Next question. Will tire pressure change with changes in altitude?

 

This is fun.

 

Ken

[MustGoFaster]

given that a tire is not a solid object, and a function of it's mesaured pressure is due to differential between the atmosphere and the inner surface of the tire, as you lower the exterior pressure, the tire will expand slightly within the limits of the materials, lowering the pressure

[ken1mod]

Mustgofaster is correct. Altitude does matter. If you fill your tires to 35 psi at sea level and drive to 18000 feet (the only numbers I recall) outside pressure will drop from 14 psi to 7 psi and your tires will now read 42 psi if temperatures are the same. Half the atmosphere is below you at 18000 feet.

 

Ken

[snoman]

Lets not forget tempature either. Fill your tires up when it is 50 degrees out and check them again and 0 degrees and there will be a noticable drop in pressure (also this is why you check tires cold because pressure does increase when they warm up driving and this is foactored into cold pressure rating.)

[Draenor]

Lets not forget tempature either. Fill your tires up when it is 50 degrees out and check them again and 0 degrees and there will be a noticable drop in pressure (also this is why you check tires cold because pressure does increase when they warm up driving and this is foactored into cold pressure rating.)

 

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Every 10 degree difference equals 1 PSI change

[ken1mod]

Gentlemen,

 

You will note from my last post, "if temperature is the same". You betcha. temperature does matter. Boyle's law as I recall.

 

ken

[overlord1]

Gentlemen,

 

You will note from my last post, "if temperature is the same".  You betcha. temperature does matter.  Boyle's law as I recall.

 

ken

 

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I am absolutely anal about tire pressure and even bought a $100 digital tire gauge similar to those used by racing teams. I check my tire pressure weekly without fail (first thing in the morning when the tires are stone cold). I was surprised to find the tires on one side of my truck to be consistantly 1.5-2 PSI higher than the other side simply because the sun was shining directly on them while the tires on the opposite side were in the "shade". I have checked them repeatedly and it is always the case. I imagine the difference after driving for several miles would be even more pronounced.

 

Ed

[asepgrad98]

if a tire explodes in the woods and no living creature is around to hear does it still make a sound??

[snoman]

I was surprised to find the tires on one side of my truck to be consistantly 1.5-2 PSI higher than the other side simply because the sun was shining directly on them while the tires on the opposite side were in the "shade".  I have checked them repeatedly and it is always the case.  I imagine the difference after driving for several miles would be even more pronounced.

 

Ed

 

 

When driving the tempature difference would basically go away because while tires are generating heat from fricton and flexing (and at a higher rate than from sunlight) they are also radiating it into the slip stream as they cut through the air.

[ken1mod]

I think it is great to see people "anal" about tire pressure. It is a number we live or die by every day. Good for all of us with a non pin-stop gauge. these are gauges where the needle sits in a band of color, floating, not against a stop pin. When the gauge is in the band with no pressure on it, you know the gauge is within its guaranteed accuracy.

 

When I did my 141 mph speed run, I knew my tires were spot-on.

 

Google non-pin-stop gauge.

 

Tire pressure rocks.

 

Ken

[pm26]

OK, let's simplify this a bit. The following equation applies:

 

(P1) x(V1)/(T1) = (P2)x(V2)/(T2), where

 

P1 = initial pressure

V1 = initial volume

T1 = initial temperature in Kelvin or Rankin

 

P2 = final pressure

V2= final volume

T2 = final temperature in Kelvin of Rankin

 

An example:

 

If the initial tire pressure at 75 degrees F is 35 psi, what will the pressure be at 120 degrees F? Assume the volume remains the same.

 

Answer: Since V1 = V2

 

P2 = P1 xT2/(T1) = 35 x 580/( 535) = 37.9 psi

 

So, as you drive, the pressure in your tires increases about 3 psi as the tires heat up (moderately to 120 deg F in this case).