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      05-06-2012, 12:08 AM   #1
SMJ2012
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tyre pressure

hello, my X1 run flats have 225/94 17 number and this corresponds to 2.2 /2.6 bar and 220/260KPA pressure. (as per the drivers door sign)

is it correct to convert these to 32psi and 38psi.
is it notmal for dual pressure tryes with the back being inflated more?
why is this? is 38 normal for a RFT?

thanks
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      05-07-2012, 12:29 PM   #2
hookah66
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BMW tire pressures are different between the front and rear wheels, this is to compensate for rear traction bias. In other words, BMW x traction will put larger torque on rear wheels, unless they start to slip and then transfer the torque to the front wheels as needed. Even in my rwd e93, the rear tires pressures are recommended at 41psig, and front at 33 psig. Is nitrogen available in your neck of woods? It is getting more popular here in US, and I put it on all of my vehicles. It really softens the harsh ride of the RFT's. By the way, nitrogen was always used in racing, aviation and in the military vehicles.
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      05-07-2012, 05:09 PM   #3
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Ok, before my X1 I had a Ford Focus Mk1, and along with a new set of tyres the fitter decided to add nitrogen. I abhorred it - it made my car wholly unstable. It was much better after I bled them and refilled normal air. I'm not the only one who's found problems with nitrogen.

After that horrific experience there's no way I'm filling my X1 with nitrogen. To improve my ride quality I may fit regular tyres instead of the runflats when my motorplan ends.

Last edited by manicm; 05-07-2012 at 05:17 PM..
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      05-08-2012, 10:02 AM   #4
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Adding nitrogen? Why bother - normal air is 78% nitrogen anyway! Sure nitrogen is inert whereas the oxygen in air is an oxidising agent (hence can maybe degrade rubber) but my guess is that you will wear out the tyre by driving on it long before you need to worry about any deterioration or hardening of the rubber compounds within the tyre! I could be wrong of course and I am certainly no expert but adding nitrogen sounds more like a gimmick to me!
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      05-08-2012, 02:03 PM   #5
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I understand there is resistance in adding nitrogen in a passenger vehicle. As a fleet operator we had great success, i.e. less tire wall deterioration, preservation of TPMS, etc... Here in US, Price Costco a large discounter have also seen less customer complaints in the tires they sell which is filled w/ nitrogen. This is a relative new trend not yet well known by the consumers.... and yes, nitrogen cost more than air. On the other hand, Tire Rack a very large mail order outfit abhors the use of nitrogen gas in tires.
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      06-24-2012, 01:11 PM   #6
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We have 50K kilometres on our X1 xdrive 20d (2010). It is currently on second set of tyres (normal HP's). Pressure of 2.4 bar all round works very well . Tyre wear is even all round, unlike the first set (run flats) done at 2.2 front and 2.6 back.

Tyre pressure definitely remains more constant with Nitrogen as a top up of pressure is needed once every 6 - 8 weeks.
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      06-24-2012, 05:37 PM   #7
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On our X1 with 225/45 R18s we're using 2.6 front and 3.0 rear. Less pressure just feels less sharp in handling
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