Re: Tire pressure question

[Clem Z.]

depends on the humidity in the air at the time

the compressors are running since they pull in that air to compress. the NEXTEL CUP race cars pick up sometines 7# even using nitrogen because of the amount of moisture in the atmosphere when the tires were mounted. the tire temp reach 200+ degrees in the right front and since these radial tires act like a spring as the pressure goes up so does the spring rate causing the handling of the car to change. 1/4# of pressure change in the tire can change the spring rate 20#

[Duke W.]

Re: depends on the humidity in the air at the time

PV=nRT. Whether the contained gas is dry nitrogen or air with some water vapor, pressure will increase the same amount with a given increase in temperature at constant volume.

In road racing I see 8-10 psi increase in radial tires.

Duke

[Clem Z.]

if it does not depend on how much moisture

is in the gas how does a steam engine build pressure?????

[Peter L.]

Re: if it does not depend on how much moisture

The steam engine typically uses a sliding piston in a cylinder that is moved by the expansion action of the steam (water in the gas phase) which is generated by boiling water in the boiler of the engine. The steam or gas phase water pressure to drive the piston is manipulated by valves.

[Duke W.]

Re: if it does not depend on how much moisture

Steam behaves like an ideal gas - just like air, but it really has to be superheated. Otherwise it's a two phase mixture, both vapor and tiny liquid droplets. Steam condensing in to tiny liquid droplets is what you see coming out of a tea kettle or the exhaust from a steam locomotive. Clouds are also tiny water droplets suspended in air.

Superheated steam is a colorless, odorless gas, just like air. Look at the exhaust from the Shuttle main engines when it takes off. liquid hydrogen and LOX combust to form superheated steam. All the fire and smoke is from the strap on solids. The exhaust from the main engines is transparent, but it has some visible shocks because the nozzles overexpand at sea level pressure.

Duke

[Terry F.]

Re: It's a load of bull...

This is laughable. It is all about $5.00/tire and some kid thinking he's got something special going on now that he can say his tires are nitrogen filled. I guess I should go out and buy a tank of nitrogen.

Terry

[Dick W.]

Re: It's a load of bull...

I guess that I will add my limited knowledge about the subject. According to the 9/18/06 issue of Transport Topics, Michlein issued a "postition paper" that confirmed nitrogen's low permeability-the gas escapes the tire carcass much slowly than regular air does-and lower temperature running qualities. However, they concluded that the benefits do not outweight the additional cost. The Tire Retread Information Bureau has stated it's support also for the use of nitrogen. The benefits include "a more stabel, consistant tire pressure, cooler running tires, longer tread life, less oxidation of components, and reduced rim and wheel corrosion." The use of nitrogen results in less tire aging.

There are at least a few measurable benefits from the use of nitrogen. The airlines use it exclusivily, and as Clem mentioned NASCAR teams also us it.

[Terry F.]

Re: It's a load of bull...

I could see the justification in racing and the airline industry. When I was in the Airforce I seem to recall the tires being remanufactured. Not certain of that though. I worked around B-52's. Those were some rock hard tires to kick. Interesting though. Terry Terry