Tire pressure, again

galager · 12-23-2009, 11:54 AM

I hate to post about this, but I'm a little perplexed. Both the door card and the owners manual recommend a tire pressure of 36 psi front and 44psi rear. I have an '09 3.0 z4 with base suspension, stock tires are 225/45 17 all around. These are the highest numbers I have ever seen recommended in any car.

I just bought run-flat snows mounted and ready to go from tire rack, they are 205/50 17's. On the tire it states max inflation pressure is 44 psi. I was concerned about inflating tires to 44 psi, so I called tire rack and they recommend 32 front/35 rear for this car which sounds normal to me and that's what I went with. I just find it hard to believe that BMW inflates tires to 44psi...especially when that's the max pressure of a lot of tires, including the BMW approved (they have the star on them) run flats I just bought and the Yokohama avid S4's I have on another car.

Z_Victor1 · 12-23-2009, 04:04 PM

The US pressures are a little different to the UK ones recommended by BMW.

These figures are copied DIRECTLY from the sticker affixed to the door-jamb on my 35i..........
Note, these are NOT the maximum pressures. They are the pressures recommended by BMW (BMW do not recommend under-inflation of the tyres).

I understand that this does not exactly answer your question BUT it will give you an idea behind their thinking.

Interestingly, no reference is made by BMW to different pressures for load and/or speed.

Note, the HIGHEST pressure quoted is 3.1 bar

2.4 = 34.8 psi
2.6 - 37.7 psi
2.7 = 39.2 psi
2.9 = 42.1 psi
3.1 = 45.0 psi

__________________________________________________ ____
225/35 R19 88 Y XL front 2.4 bar
225/45 R17 91 W front 2.4 bar
255/30 R19 91 Y XL rear 2.9 bar
225/45 R17 91 H (M+S) front 2.4 bar + rear 2.9 bar
225/45 R17 94 V (M+S) XL front 2.4 bar + rear 2.9 bar
__________________________________________________ ____
225/40 R18 88 W front 2.6 bar
255/35 R18 90 W rear 3.1 bar
__________________________________________________ ____

255/40 R 17 94 W rear 2.7 bar
__________________________________________________ ____

I currently run my fronts (225/45 R 17s) at 2.4 bar and the rears (255/40 R17s) at 2.7 bar and she rides beautifully.

FWIW, our road surfaces are pretty awful (cr*p to you and me)

Good luck!

Memphis1 · 12-23-2009, 04:11 PM

Quote:

Originally Posted by galager

I hate to post about this, but I'm a little perplexed. Both the door card and the owners manual recommend a tire pressure of 36 psi front and 44psi rear. I have an '09 3.0 z4 with base suspension, stock tires are 225/45 17 all around. These are the highest numbers I have ever seen recommended in any car.
I just bought run-flat snows mounted and ready to go from tire rack, they are 205/50 17's. On the tire it states max inflation pressure is 44 psi. I was concerned about inflating tires to 44 psi, so I called tire rack and they recommend 32 front/35 rear for this car which sounds normal to me and that's what I went with. I just find it hard to believe that BMW inflates tires to 44psi...especially when that's the max pressure of a lot of tires, including the BMW approved (they have the star on them) run flats I just bought and the Yokohama avid S4's I have on another car.

1. the psi on the sticker is the maximum... it depends on the load and on the speed.
2. if they're not the tires that came with the car go with what tirerack said. maybe 2psi higher because of the cold weather.

jadatis · 12-24-2009, 08:19 AM

Came by this topic when searching with Google for Tire-pressure.
Been busy with calculating tire-pressure with use of the formula the European tire- and car- manufacturers also use to calculate the advice pressures for cars.
Learned myself Excell to make spreadsheets for it.
Translated a few from Dutch to Englisch to go worldwide with it.
http://cid-a526e0eee092e6dc.skydrive...0tyre-pressure
In this map spreadsheet and exsamples for re-calculating tire-pressure when other then original tires are placed.
Can also be used to check the original and see if you can go lower in sertain conditions.

Important for the pressure is the load the tire must carry, and the speed the car is driven. a little bit but seldomly the case the camber-angle above 2 degrees gives higher advice-pressure.
In earlier days they gave in Europe the normal advice-pressures, in America never did so. Nowadays also in Europe they dont give normal-advice.
In my spreadsheet I give 3 advices for upto 2 speeds.
For normal advice the sheet calculates back the loads they used for the original and use that for the new tires. But if this is not given this part cant be used. In Dutch I made a spreadsheet to determine these loads yourself, but have not translated it because of the amount of Dutch text.

Yust use my spreadsheet and you will get wiser about tire-pressure.

12-23-2009, 11:54 AM	#1
galager Registered 1 Rep 1 Posts Drives: '09 Z4 3.0 Join Date: Dec 2009 Location: NY iTrader: (0)	Tire pressure, again I hate to post about this, but I'm a little perplexed. Both the door card and the owners manual recommend a tire pressure of 36 psi front and 44psi rear. I have an '09 3.0 z4 with base suspension, stock tires are 225/45 17 all around. These are the highest numbers I have ever seen recommended in any car. I just bought run-flat snows mounted and ready to go from tire rack, they are 205/50 17's. On the tire it states max inflation pressure is 44 psi. I was concerned about inflating tires to 44 psi, so I called tire rack and they recommend 32 front/35 rear for this car which sounds normal to me and that's what I went with. I just find it hard to believe that BMW inflates tires to 44psi...especially when that's the max pressure of a lot of tires, including the BMW approved (they have the star on them) run flats I just bought and the Yokohama avid S4's I have on another car.
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12-23-2009, 04:04 PM	#2
Z_Victor1 First Lieutenant 64 Rep 328 Posts Drives: 2022 G22 M440i 👍 Join Date: Jun 2009 Location: SouthEast UK iTrader: (0)	The US pressures are a little different to the UK ones recommended by BMW. These figures are copied DIRECTLY from the sticker affixed to the door-jamb on my 35i.......... Note, these are NOT the maximum pressures. They are the pressures recommended by BMW (BMW do not recommend under-inflation of the tyres). I understand that this does not exactly answer your question BUT it will give you an idea behind their thinking. Interestingly, no reference is made by BMW to different pressures for load and/or speed. Note, the HIGHEST pressure quoted is 3.1 bar 2.4 = 34.8 psi 2.6 - 37.7 psi 2.7 = 39.2 psi 2.9 = 42.1 psi 3.1 = 45.0 psi __________________________________________________ ____ 225/35 R19 88 Y XL front 2.4 bar 225/45 R17 91 W front 2.4 bar 255/30 R19 91 Y XL rear 2.9 bar 225/45 R17 91 H (M+S) front 2.4 bar + rear 2.9 bar 225/45 R17 94 V (M+S) XL front 2.4 bar + rear 2.9 bar __________________________________________________ ____ 225/40 R18 88 W front 2.6 bar 255/35 R18 90 W rear 3.1 bar __________________________________________________ ____ 255/40 R 17 94 W rear 2.7 bar __________________________________________________ ____ I currently run my fronts (225/45 R 17s) at 2.4 bar and the rears (255/40 R17s) at 2.7 bar and she rides beautifully. FWIW, our road surfaces are pretty awful (crp to you and me) Good luck! Last edited by Z_Victor1; 12-23-2009 at 04:19 PM..*
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12-24-2009, 08:19 AM	#4
jadatis Private 12 Rep 86 Posts Drives: No BMW Join Date: Sep 2009 Location: Holland Europe iTrader: (0)	Came by this topic when searching with Google for Tire-pressure. Been busy with calculating tire-pressure with use of the formula the European tire- and car- manufacturers also use to calculate the advice pressures for cars. Learned myself Excell to make spreadsheets for it. Translated a few from Dutch to Englisch to go worldwide with it. http://cid-a526e0eee092e6dc.skydrive...0tyre-pressure In this map spreadsheet and exsamples for re-calculating tire-pressure when other then original tires are placed. Can also be used to check the original and see if you can go lower in sertain conditions. Important for the pressure is the load the tire must carry, and the speed the car is driven. a little bit but seldomly the case the camber-angle above 2 degrees gives higher advice-pressure. In earlier days they gave in Europe the normal advice-pressures, in America never did so. Nowadays also in Europe they dont give normal-advice. In my spreadsheet I give 3 advices for upto 2 speeds. For normal advice the sheet calculates back the loads they used for the original and use that for the new tires. But if this is not given this part cant be used. In Dutch I made a spreadsheet to determine these loads yourself, but have not translated it because of the amount of Dutch text. Yust use my spreadsheet and you will get wiser about tire-pressure.
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