Dave: I check my tire pressures on the bike before every ride and with the car, I check the oil level and tire pressure in the AM before the commute to work at least once a week. Takes all of 2 minutes. Like I said, it's marketing hype praying on the desire for us to exchange responisibility and due dilligence for more convinence. Having a compressor at home is the business!
While I was in college I worked for Goodyear Tire an Rubber Co. I did a lot of different things but one of my jobs was to evaluate tires returned under warranty and determine the cause of failure. Over 75%, way over 75% of the tires were what we classified as "Run Flat". In the industry that was the term for a tire that was underinflated to the point it had a catastrophic full circumference structural failure of the sidewalls. You have all seen them, a car sitting by the side of the road with the side walls gone, torn to shreads. That did not happen after the tire blew out, it was the cause of the tire blowing out. It is caused by one thing, underinflation. The sidewalls flex so much that they overheat and exceed the temperature and structural limits of the tire. Z rated tires tires suffer this fate quite often. To make a tire take enough heat to get a Z rating the mass has to be reduced and one of the things they do to reduce that mass is to reduce the inner liner, (the interior lining of non pourous rubber that is there to make the air stay on the inside) to a minimum. No one here has any idea how often we (back at the dealer) have cars brought in on a flatbead with a destroyed tire and an angry customer yelling about defective tires. Funny one of the items I almost never see in a clients car is a tire pressure gauge. People laugh about the new cars having a tire pressure monitoring system. I am glad they have them, the life it saves might be mine. The really sad thing about TPMS systems is that when the system warns them that a tire is low they come to the shop to see what is wrong with the car. In Germany I understand it is a serious traffic offense to have a flat tire, your fault or not. We should do the same thing here, some of those people who died in Explorer roll overs would still be alive.
Quite an interesting thread so far... Regarding nitrogen in car tires. I'm in the airplane business and we use N2 in the tires because of the low moisture content, which leads to a lower chance for corrosion to get a toehold. Dry air is usually proclaimed just fine, too, by those who do the proclaiming. As we all know, corrosion is not good as it can lead to a structural failure. Corrosion can also make you buy a very expensive wheel before you really wanted to. Aircraft wheels are often magnesium and about the only thing magnesium wants to do is return to being a component of seawater. A little extra moisture just helps with the plan. As to the claim of not having to check tires pressures as often in a car using N2, I respectfully submit that in the normal use of a street car, one would have to make very precise measurements to see any difference from using plain old shop air. I think that the demise of the full service gas station has led to many more tire failures among the general population.
When filling race tires with N2 the benifit can only be seen if the are completely evacuated under vacuum. I made a vacuum pump hook up that has an air tight seal to the valve stem and let it go for 45 min's on each tire prior to filling. Everyone that has broken down tires has seen a small puddle of water inside the carcaus from time to time. Water will turn to vapor under a sustained vacuum. The 355, 360 and F40 wheels hold the bead for at least the 45 min's I put them under vacuum. Only then will any benifit be seen from the use of N2. At track events in the Rocky Mountain area where the humidity is low I see about a 14-15# growth in pressure without evacuation and N2 and about a 3-4# growth with N2. Back in the midwest where the humidity level was far higher and the shop compressors would spit water out of the lines by the days end, the results were more dramatic due to the amount of water or water vapor that was put into the tire when inflating. Dave PS I have yet to find any of my customers that wants to go through process of doing this to their street car, and I keep 2 tanks of N2 in the shop.
Of course there is a marketing angle included here, but it IS beneficial to run nitrogen. As said here, most people on the road don't check their tyres often enough, if at all, and these are the people that will benefit the most. Most tyres get replaced because the edges are worn off, and more often than not, this is due to running around on too low pressures. Nitrogen in a road car preserves correct pressures for much longer. Of course, if you can fill it in a vacuum you will get a better fill, but just to deflate and refill with Nitrogen will give a large % of the potential gain. I'd guess 90% of the gain FWIW, but this is a guess based on experience. In racing, Nitrogen gives it's biggest advantage on the first laps. Often, pressures start so low that you risk damage to the tyre if you were to push it or ride kerbs, so with Nitrogen, you can start with a higher pressure, still maintain your ideal hot max, but push that bit harder than the air filled guys on the crucial first laps, without damaging the tyre. It's teams that explore these areas that excell, especially in ultra close championships.
The primary benefit of nitrogen is even internal pressure over time. Heat increases with friction over time, say by mid lap on an average F1 circuit nitrogen comes into play. Which, on average, would be 50 seconds. By that that time, you would be fast asleep and your "mistress" would be a mere wrinkle of a balloon due to an air leak. Sorry Tom, but you left the rake in grass .
In F1 the tyre has a large part to play in the suspension. as ferrarifixer says the pressures are very low, about 1.1bar when at operating temperature so a few psi make a huge difference in handling, better handling = better lap times so the teams exploit any advantage they can. I have to admit that I didn't know that N2 was as easily available for road cars as it seems from this thread (mental note: I must get out more).
Not just F1, also in sports and GT racing where pressures are up around the 30psi range, it's just as important. eg, on a 360C with factory rec pirelli slicks, 30psi is a reasonable ball park target hot pressure. If you use bad air, 30 psi hot can easily be 18 or 19 cold. But under 20 the sidewalls will roll too much and damage the tyre on the out laps, especially if you get forced wide or make a mistake and ride the kerbs, you'll even damage the rim simply due to flat tyres.
Dave this is good stuff. My aerospace wheel and brake shop concurs and it fits my race experience too. The only way to get close to the controlled environment required for aerospace is to use dried shop air or multiple refills of N2. I do this in the field by filling to max pressure and emptying to almost flat but swith positive exhaust pressure from the tire before refilling. It does not reach the pure N2 of a partial vacuum but it has improved the tire temp variation and iincreased the race life. All of this is a complete waste of time and money for garage ridden F cars that are driven onece or twice a week at most and often parked all winter. In fact to those owners looking for make work, I have another more valuable suggestion: buy a home useable lift, and spend that N2 time cleaning and polishing all of the underneath of the car. The park it on top of mirror tiles. make sure you keep the tiles with you come trade in time for your 430, 612 or ENZO 2 so that you get the extra couple of dimes. As compared with the N2 exercise, much more valuable and think of all the bling points you will get !! Keeps the cholestrol and blood pressures down - or so I am told. OTW use air, keep them filled to factory spec Winter and Summer and check the tread regularly for construction debris and use the spare time to drive the sucker.
Agreed. Vacuum is the right way to do it (with a larger pump, it'll go quicker). Debatable whether it helps the street driven car, but at low cost, why not? Mandatory for a race car, though many racers don't use it and get lucky. Yes, it's definitely an additional profit source, but keeping the water out is a good thing. I wouldn't do it on a road car if it werent so convenient for me. Best regards, Rob Schermerhorn
My vacuum pump will turn the tire octagonal in about 5 minutes. I just leave it go that long so in the event there is a puddle or water it has the required time to turn that into vapor. Dave
To those who dont consider N2 of any benifit, I would disagree. As I too have spent some time around aircraft, I have been taught its benifits. First of all, its cheap as hell. You can buy a tank with a regulator used for a reasonable amount, and filling it is very cheap. In addition, a small tank can last a long time around a shop. As far as vacuuming it down, its not necessary. Fill it and empty it a couple times and there wont be much oxygen left inside. Oxygen is the stuff you dont want in the tire. It oxidises rubber. For a garaged car that isnt driven a lot its probably more valuable than on a race car, in that your tires wont oxidize inside. You ever seen those little rubber balls inside a tire after you dismount it? They are rubber oxide. Aircraft also have gas struts that hold the plane up, and N2 keeps the seals from deteriorating, and as has been said, it doesnt change pressure much with heat, so the plane sits at its correct height over a wider temp range. That all being said however, I just use my "air" compressor. On your blow up doll, N2 may not be advantageous, as she is a vinyl doll, and pure N2 would seriously incapacitate her. In addition, I believe at about .069 bar, your doll will blow a rod.
