Nitrogen question.

I'm really clutching at straws now! I've recently had two new rear Michelin Pilot Sport N1's fitted and the four wheel geometry done - both by my local OPC. Since I've had the car back it just doesn't seem to handle like it used to. If I wiggle the steering at around 30 mph the front end of the car just seems to wallow around like a big bloody jelly - it's as if the tyres are running at about 20psi (they aren't). When they fitted the tyres they said that they were going to fill the tyres with nitrogen. They said that they didn't fill the existing front N1's with nitrogen. I'm assuming that I therefore have normal air in the front and nitrogen in the rears. A silly question, I know - but could this be the cause of the problem? I'm going back there tomorrow (lamb/slaughter) to get two new front N1's fitted and a (free) four wheel geometry done in the hope that this will improve things. It's worth mentioning that the fronts are 6 years and 22K miles old - so I'm going on the assumption that part of the problem could be that the rears are brand new and the fronts are 6 years old and as such the two sets of tyres have differing 'malleabilities'? Also, the fronts have suffered a degree of inner shoulder wear in the past as the car was running too much negative camber for a while - which is the main reason I'm renewing them. The car has M030 suspension and I've made sure that they know about this. The pre and post print outs of the four wheel geometry that were given to me after the rears were fitted all seemed to be within their limits. Any suggestions would be appreciated. Adrian.

new geo and front set will probably solve everything, odd though

That does sound odd. If the fronts are 6 years old, they have to be replaced by law anyway (check the DOT). I doubt that's the cause of the issue though. I also don't think it's anything to do with the nitrogen fill up (which, I understand is because it helps keep a more consistent psi under extreme driving conditions). Did this problem occur after the rears were fitted? Personally, I would try running the front and rears on a slightly lower psi than recommended, as most 996 seem to prefer this....but only after you've replaced the fronts.

IMHO you need to change the fronts. You will find that new fronts will transform the car, I'm a massive believe in fresh rubber all round, even though the fronts havent worn they will be well past their best. When you have done so I look forward to hearing how much in love with your car you are again, thats how confident I am on this :thumb: :grin:

Not true 'If' tyres have been stored for in excess of 6 years they should noyt then be used There is no legal maximum age for tyres on a vehicle Though there is a guideline that suggests the replacement of tyres once they reach ten years old as a matter of course

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incidentally, i have seen a geo from an opc - and, well, it was awful. a proper geo soon sorted it. make sure you get the printout.

Hi Matt. There is a lot more to this topic than meets the eye. I'm yet to submit any of my experience so far to this forum as I'm waiting to see what the outcome of tomorrow is. Suffice to say that the journey with the OPC thus far has been 'emotional'.

Sorry, I thought that it was actually a legal requirement. Everywhere you look talks about not using tyres more than 6 years old: Porsche 996 manual (in bold) for example: IN NO CASE SHOULD TYRES BE MORE THAN 6 YEARS OLD Then you've got a couple of threads on it here: http://www.wisebread.com/are-your-new-tires-really-6-year-old-ticking-time-bombs http://www.carbibles.com/tyre_bible.html You're quite right, it's not law, but equally something that I wouldn't take the risk with personally....but nothing to do with 6 years storage, just the age. This quote is particularly interesting: "in June 2005, Ford and GM admitted that tyres older than 6 years posed a hazard and from their 2006 model year onwards, started printing warnings to this effect in their drivers handbooks for all their vehicles." So I stand by my earlier statement about the age of your front tyres potentially affecting the performance of the car, but I think it's more likely to be: a. Machine wasn't aligned when geo was done b. Tyres are slightly mis-shapen (unlikely) c. Alloy damage d. Over-inflated tyre (ie. actual compared to recommended - recommended is too high a psi IMO).

a. Machine wasn't aligned when geo was done I specifically took the car to an OPC as I'd been warned by others that some places don't get their Hunter geometry equipment calibrated as often as they should and that this can result in false readings. I have to say that on paper (literally) the post-alignment readings are all within the parameters that Porsche set for M030 Sport suspension - but it doesn't feel right and that's what counts here. I have to admit that I've done very well out of my front tyres. They're showing signs of micro-cracking on the outer shoulders due to their age but I've not been concerned about it as I never thrash the car and even if I did they're nowhere near 'letting go'. From my experience I think it's very easy to get baffled about tyres and their condition and as such, people can be 'bullied' in to forking out for new ones prematurely.

People use nitrogen because the tyre will deflate less on this compared to air. It's to do with the transfer of oxygen, which is 21% of air, which passes more easily through rubber than oxygen. So after you first fill tyres up with air you will notice they deflate at an increased rate then every time you top up with air there will be more nitrogen and relatively less oxygen to further deflate the tyre and so on. At some point you will achieve stability or close to except for 'normal' gas loss from the tyre. There isn't any difference between N2 and O2 chemically that will cause a difference in inflation or handling as both gases observe the same pressure law (Boyles Law :wink: ) As to the ageing of rubber, it is well known that the cross-linking of rubber ('vulcanisation' -nothing to do with Star Trek :starwars: (I know this is SW so don't comment)) which deteriorates with time. The bonds break . So if you are relying on tyres keeping you alive at some point I personally wouldn't use old ones. How old 'old' is is up to you. Dr Pete PhD Chemistry :judge:

This nitrogen s**t is all bollox, on a newly mounted tyre do they suck all the air out first and then fill with N2? Do these companies offering this have a bottle of N2 to do this or do they 'separate' air to extract the N2?

Think about it Damian. There is 1atm of air to start with, then you added 'x'atm more of nitrogen. The original amount of O2 will be much less than 21% because of it. Not so if you inflate using air. It will still be 21%

Good point Regardless there's little or no value in doing this, if you are constantly changing your pressures on track or to meet the requirements of the ambient weather conditions you're slowly diluting this mix

:agree: Wouldn't pay extra for N2 cos I check my tyres regularly anyway