tire pressure changes with tmp

Was just thinking the other day about my bike tire pressures changing with ambiant conditions, increacing and decreacing in pressure, Could i remove the air from my tires and pull into a slight vacuam then purge with nitrogen gas, then top of my tires with nitrogen gas to specified pressures for a k1200lt????
nitrogen gas has no inert gasses or moisture, this thought may be way out there but im not willing to just do this till I have investigated the topic...matthew

The air you breathe has 78% nitrogen in it already. I dont think going to pure nitrogen will make much difference at all. Finding a pure nitrogen source while on the road would be difficult to say the least if you need to top off the tires. A local tire company has added the nitrogen inflation gimmick to their commercials in an effort to sell tires. I bet if you hounded BMWNA enough, they could come up with special air to install in the tires, for a premium price.

>I bet if you hounded BMWNA enough, they could come up with special air to install in the tires, for a premium price.

Maybe they could put some of that "Perri-air" from Spaceballs in CO2 cannisters?

Roadcrave, the answer is "yes, you could do that". How much a benefit it would be is dubious at best. I do know racer's do that, I've always thought it was more for convenience than anything else.
Personally, I think the easiest way to go about it would be hire a bottle from a local welding supply/gas supply house. Get a hose-fitting made and put it in the garage. (Following the safety guidlines of course. Pressurized containers can be VERY LETHAL) I would think a large bottle would last a year or so. If you ever had to fill up on the road, you could just re-purge when you got home.

Seams like a lot of work, considering my compressor cost ~$100 and will power my airbrush, some small air-tools, and fill my tires.

Matthew,

The relationship between pressure and temperature is essentially the same for all gasses. You'd get the same pressure increase with increasing temperature whether you used air, nitrogen, oxygen, or even helium. At least helium would reduce unsprung weight.

WARNING! The following is only for residents of the kingdom of Geek -

Neglecting expansion of the tire at higher pressure, the pressure is directly proportional to temperature. If you double the temperature, you double the pressure. There's an equation for this, but you have to express pressure in atmospheres (1 atm.= 14.7 psi) and temperature in degrees Kelvin (K = (F-32) x 5/9 + 273). The equation is

P2 = P1 x T2/T1,

where P1 and T1 are the original pressure and temperature, and P2 and T2 are the final pressure and temperature. If P1 = 40 psi, T1 = 40F, and T2 = 100F, the final pressure would be 55 psi.

Sorry for the science lesson, but as a chemist I couldn't resist. I did warn you!

really that was great feedback, sometimes i think to much, does not hurt to ask, i did refrgeration for years and we used nitrogen gas to purge freon system from moisture and inert gases which is very critical to these systems to be clean and noticed that the nitrogen pressure was constant even if heat was applied????matthew

Chris, geez man, thanks a lot for coming in and messing up the truth with facts.
Back in my racing days, everyone used nitrogen because it didn't change pressure when hot, so I wonder what the real story was. Perhaps it had to do with eliminating moisture. Perhaps it was because one could get nitrogen in large portable bottles. Likely it was nothing more than that sanctioning bodies allowed nitrogen in the pits as it is non-flamable.

I do some refrigeration in my line of work, and we purge with nitrogen to remove the excess moisture, and to pressure test the system before we apply vacuum and then charge the system. Removing the moisture is important to us since the equipment is running at -30 C. I will clog the capillary tube and render the system useless if not removed. Your tires dont really need that kind of precision, unless you are racing, where a pound or two difference makes the handling change dramatically at 140 mph.

Chris is that Boyle's law that determines temp/pressure relationship? It has been a few years and a few thousand brain cells since my leat chemistry class.

Nitrogen is prepared commercially by cooling air until it liquifies, then slowly raising the temperature and collecting the various gases as they evaporate at different temperatures. Since nitrogen turns into a gas a -195.8C, you can bet there won't be any water present! There won't be any oxygen, either (BP = -183C), so flammability isn't an issue. Helium would be a better choice, but it would be much more expensive.

Loraz, it sounds like you're a fellow geek.

Boyle's Law - At contant temperature a fixed mass of gas occupies a volume inversely proportional to the pressure exerted on it.

Charles Law - At constant pressure, the volume occupied by a fixed mass of gas is directly proportional to the absolute temperature. [degrees Kelvin]

Dalton's Law - The total pressure exerted by a mixture of gases is the sum of the partial pressures of the various gases.

These laws are according to Ma Nature, so there is no need to call in the geek police if you are not aware of them.

I guess you could call me a Geek. there are others that would use stronger language though

10% Increase Hot Over Cold

Originally posted by roadcrave nitrogen gas has no inert gasses

Click to expand...

Nitrogen IS an inert gas.

The way to PROPERLY inflate your tires is to fill them up to the number on the side. That's the FULLY LOADED pressure. Let's say your tire's sidewall says, "Max load 350 pounds at 42psi." Fill it up to 42 psi stone cold. Ride the bike til the tires are warmed up and measure again. The CORRECT PRESSURE is when the HOT pressure is 10% greater than the cold pressure. In other words, if you had it at 42 cold, when it is hot, it should be 46. If it is less than 46, then let some air OUT. That will make it run warmer and the pressure will rise. If it is higher than 46, add air to make it run cooler.

Repeat this a few times to learn what pressure is required to suit your riding style on your bike with your loading. And remember to adjust accordingly when you add or subtract a passenger or significant luggage load.

Oh... you can use nitrogen, nitrous oxide, dry air, wet air, or just about anything except helium or hydrogen and this will work just fine.

Tire pressure changes with altitude, too.

lkchris said:

Tire pressure changes with altitude, too.

Click to expand...

Sorta.

A tire pressure gauge measures is the difference between internal and external air 'pressure'. As the external air is thinner at higher at altitude, the gauge will display a higher reading if the tire was filled and checked at a lower altitude.

I'll never forget my goldwing riding neighbor returning to Reno, where I once lived, from the bay area where he had last checked the air pressure. He struggled to understand how his tires "gained air".

Reset

Originally posted by knary A tire pressure gauge measures is the difference between internal and external air 'pressure'.

Click to expand...

Sorta. Depends on the gauge. Digital gauges with a zero-set button retain the reference at which they were last zeroed. You have to manually reset them to zero with changes in altitude, or even significant barometric pressure.

Tire pressure?

Is that on the center stand, side stand, or rolling?