You should look into filling your tires with Nitrogen. I live in AZ. and we get very hot summers and cool winters. I was tired of fooling around with changing tire pressure as the seasons change so I asked a friend that is in the tire biz. what my options were and he suggested Nitrogen. I paid something like $10.00 per tire for the service and it was well worth it. The tires run cooler and do not fluctuate in pressure due to ambient air temps. I have heard that even NASCAR is going to Nitro in all the cars.

 

You can't hardly buy a new BMW or Mercedes around here without them. It's the last thing in the negotiation, "and I'm not paying for THAT!

 

Putting aside for a minute the question of at what altitude do you fly your Merc , let's notch back the rhetoric a bit to look at why some people (me included) say it's not worth while to use nitrogen fills on the street:

a) As mentioned in other posts, the FAA requires an inert (actually non explosive) gas in aviation tires to prevent fires when they blow. They allow nitrogen as the cheapest gas which conforms to this spec (see the link CEB provided, which states: "To eliminate the possibility of a chemical reaction between atmospheric oxygen and volatile gases from the tire inner liner producing a tire explosion..."). Given that airliners have at least dual tires at each position and might survive one blowing; you in your car do not have dualies and you'll get the same outcome when your tire blows, nitrogen or not

b) All gases, 100% nitrogen or plain old air expand in the same way when heated. Even a nitrogen "hype" site like http://www.getnitrogen.org/sub.php?view=nascar agrees with this. The problem is water vapour (sorry that is the way Canuck's spell it). Liquid water turns to vapour as the tire heats and messes with the pressure. The nitrogen crowd say dry nitrogen does not have water vapour and therefore does not have this problem. True, that's why NASCAR uses it. Problem is a NASCAR tire lasts less than an hour and runs a crapload hotter than your tires do. We normal folk wish our tires to last a little longer. That dry nitrogen you filled your tire with doesn't stay dry all that long and over several months gets as wet as plain old air. So except for the short period immediately after you purge and fill your tires you haven't done anything on the water vapour front. And of course you do purge your tires right, not just top them up, otherwise you never have a "dry" fill.

c) From the nitrogen hype site I mentioned before they do the calculations and show that even with nitrogen you can get a +/- 1 psia difference with temperature. Problem is normal atmospheric variation is of the same size, so do you top your tires up on cloudy days and bleed them on sunny ones, because to be a true believer you should be.

d) Altitude; Going up 100m can make a .5 psi difference in pressure. Do you stop halfway up or down that big hill to change the pressure in your tires? I thought not, me either.


I could go on but you get my point. Dry nitrogen can fix the water vapour problem, but only for a short time and there are 2 other causes of tire pressure variation of comparable size which nitrogen does nothing to address.

So instead I check my tire pressures frequently (but not halfway up the hill ) and enjoy my ride using plain old air.

 

"The problem is water vapour"
Interesting situation that (regards to ColdCanuch). When ambient air is compressed, any humidity in the air is condensed out and collects in the air compressor and lines. Down here in semi-tropical Florida, we are constantly draining our shop air pipes of water.
So compressed air used to fill tires could very well be laden with more than what could be considered 100% percent humidity enriched air. Even still, not a good enough reason to screw around with special fill for tires on the street.

As a side bar, the humidity issue is one of the beefs I have about the Airmatic suspension system. There is no provision for water that condenses out of the air when the Airmatic compressor operates. We have replaced many an Airmatic main valve block due to internal corrosion caused by water accumulation in the valve assembly.

Oh by the way, high temp near 80'F today!

 

Thanks for the detailed explanation. However I am already convinced there is little value using the nitro. Since I had no intention of running it in the Merc I was really only interested in trying it in motorcycle tires. And since it did not cost me anything I thought it would be fun to see if there was a difference. Since it also appears to do no harm I figured what the heck.

While the m/c tires are not stressed anywhere near aviation tires they do run much hotter than the tires on the Merc. But as already stated over and over, little to no benefit.

 

I merely run my air pressure higher than recommended. Now that I have snowtires, I am using 38F / 42R. Better fuel economy without significantly impacting ride quality. Plus with sub-freezing weather I do not have to worry about potential deflation.