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      11-17-2005, 09:51 PM   #1
robinli
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Correct tire pressure?

Hi,

Please forgive my ignorance. I got my car (e90 325xi SP) and just changed to winter tires. For the OE all season tires, I measured the tire pressure. The front is 30 and rear is 36. These are exactly the same as specified in the manual. Now, I got the winter tire on, I measured the front is 28 and the rear is 30. I did not get the winter tires from a BMW dealer. Should I increase the pressure to 30 front and 36 rear? Is tire pressure, tire specific?

Please help.
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      11-17-2005, 10:35 PM   #2
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What is your tire size? Proper tire pressure will vary with model, tire size, expected load and speed. Check the manual for your 325xi - it will tell you the proper pressure based on these variables.

Having just put on 225/45/17 snow tires all around on my 330i sport pkg., I used 29/36 for normal load and speed under 100mph. My manual does not include the 'xi' tire pressures, but I'm gonna guess that 30 is too low for the rear - s/b more like ~35.
.
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      11-19-2005, 12:54 PM   #3
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Tima -
I have a 330i sport also and the manual says 33/41 for speeds < 100mph on our cars for 225/45/17. Where are you getting your numbers?
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      11-19-2005, 09:05 PM   #4
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I have a 325i (non sport) with the 205/55R16 Tires.

The BMW recommended (both in the manual, and in the driver door sill) pressure for this size is 33 front / 41 rear, which is what I have them set at.

Interestingly, when I got it from the dealership, they were set to 33 front / 35 rear.
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      11-19-2005, 10:02 PM   #5
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Quote:
Originally Posted by tima

Having just put on 225/45/17 snow tires all around on my 330i sport pkg., I used 29/36 for normal load and speed under 100mph. My manual does not include the 'xi' tire pressures, but I'm gonna guess that 30 is too low for the rear - s/b more like ~35.
.
May I ask why u don't have all 4 tires same pressure?
Sport package has different size fronts & backs so pressure is different.
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      11-20-2005, 01:32 AM   #6
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Quote:
Originally Posted by petesamprs
Tima -
I have a 330i sport also and the manual says 33/41 for speeds < 100mph on our cars for 225/45/17. Where are you getting your numbers?
Hi Pete

Right now I am looking at p. 103 of the .pdf version 330i manual (non-idrive) downloadable from this site. That page covers tire inflation for 330i w/ sports package.

Looking at the line that reads: 225/45 R 17 91 H M+S

For traveling speeds up to a max. of 100mph for psi/kPa it lists:
front: 29/200
rear: 36/250


I do see that speeds over 100mph for max load with luggage it lists:
front: 33/230
rear: 41/280


Without looking right now, I'm 98% confident that my printed manual sez the same - at least for the first set of numbers. I checked it with the shop that mounted my runflats so they could get the right pressure.

Hope that helps. And congrats on the car!
Cheers!

[edit: just dawned on me that I can post a snippet from the manual... here 'tis]
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Last edited by tima; 11-20-2005 at 01:49 AM.
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      11-20-2005, 01:34 AM   #7
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Quote:
Originally Posted by Barry626
May I ask why u don't have all 4 tires same pressure?
Sport package has different size fronts & backs so pressure is different.
Hi Barry,

Please note I'm talking about the 225/45/17 Dunlop MST runflats I have mounted for winter. They are the same size all round. Sorry for any confusion.
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      11-20-2005, 07:09 AM   #8
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Quote:
Originally Posted by tima
Hi Barry,

Please note I'm talking about the 225/45/17 Dunlop MST runflats I have mounted for winter. They are the same size all round. Sorry for any confusion.
Yes I know but why 29 for front & 36 for back since tires are all same size.
I believe chart in manual is only for summer tires not snows?
Which would mean the snows would have different pressure...
same in all 4 tires. Yes/No?
I have 225/45/17 Blizzak and all 4 have same pressure.
Not runflats does that make a difference?
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      11-20-2005, 11:44 AM   #9
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Barry - I think you might be confused. Just because your have 4 tires of the same size on doesn't mean the tire pressure is the same. Check the manual - in both cases (same all around and staggered setup that came w/ sports pkg) the rear has more pressure.

And it doesn't matter if we're talking winter tires or summer. The manual is talking about both.
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      11-20-2005, 02:07 PM   #10
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petesamprs is correct, it doesn't really matter if you have the same size tires front/back or not, all of the BMW recommendations have more pressure on the back tires (regardless of your specific configuration). I beleive this has something to do with more pressure in the back because that is the drive axle, and a bit less in the front because that is the steering axle, allowing more rubber to contact the road and providing better steering control.

Disclaimer: I am no tire expert, so I could be mistaken here.
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      11-20-2005, 08:44 PM   #11
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Tima - I rechecked my manual and it says 33/41 for 330 with sports for <100mph for 225/45/17.

I could take a picture of it and post it if I knew how to do that. btw, mine is an october build.
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      11-20-2005, 08:54 PM   #12
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speaking of tire preasure...


I had a flat today and the tire monitor said nothing about it.
I thought it had a system that tells you when you have a flat???
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      11-20-2005, 11:55 PM   #13
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Tima - Here's the pic of my manual

Not sure why it's different from yours.
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      11-21-2005, 01:25 AM   #14
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36 psi front
41 psi rear
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      11-21-2005, 11:58 AM   #15
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What's the final word on this? It is very weird that the online and paper manual have different numbers for just this tire combination on the 330 sport. Which is correct?
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      11-21-2005, 12:14 PM   #16
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I am running the 33/41 setup as per manual for my 225.45.17.

I am so paranoid of underinflation in winter (as temp goes down the air condenses and pressure decreases a bit), that I am running the highest possible setup answer.

As air condenses, my tires will have a little less pressure, which could actually help with traction without resulting in underinflated tires on the coldest of days.
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      11-22-2005, 12:55 AM   #17
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Guys thanks much for the info. really appreciated.
This forum is full of good info. for sure!

I've been running all 4 snows with 29.5.
Will never know why rear is 36 on 17 inch & same with 18 inch.
You would think smaller the tires less air they would need?

So bottom line is I have a 330i with sport package.
I've using 225 45QR 17 fronts should be 29 & rears 36 correct?

Over 1000 miles on my snows surely running them 29.5 didn't hurt them?
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      11-22-2005, 10:53 AM   #18
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Tire pressure is also posted on the well of the driver's side door.

As you're entering the car, look down and to the right. Front and back are usually different (even with the exact same tires on all 4 wheels). Good to know because it's always nearby when you're filling the tires.

I wound't sweat it if you're off by a pound of two.
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      11-22-2005, 06:12 PM   #19
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Quote:
Originally Posted by petesamprs
What's the final word on this? It is very weird that the online and paper manual have different numbers for just this tire combination on the 330 sport. Which is correct?
I checked my printed manual and it shows the same as I posted from the .pdf manual available here. My car is from a March '05 build.

A good question, Pete... looks like different specs for the same scenario - 225/45/17 330i ZSP. Hmmmm.... I am out of town w/ limited access at the moment, otherwise I would call BMWNA and ask them, but will inquire when I return - unless someone else learns an answer sooner. Don't know if E90Fleet frequents this forum - he might know. I agree one doesn't want to run under-inflated.

Fwiw - over the past couple days I've put on ~1000 miles on the 225/45/17 Dunlop MST runflat (snowtire) - one day in the dry, the other all day in the rain. Mostly interstate driving 70-85mph. This with the 29/36 pressure. The car performed well, and as far as I can tell the tires are fine.

To Barry626
Quote:
I've been running all 4 snows with 29.5.
Will never know why rear is 36 on 17 inch & same with 18 inch. You would think smaller the tires less air they would need?
Not sure the tire size is the factor here as much as pressure within a volume - psi (pounds per square inch).
.
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      11-23-2005, 01:45 AM   #20
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Appears there are now 2 different manuals for the e90.
One that says 33/41 for 17 inch tires has to be wrong?
Same manual says 32/36 for 18 inch tires, how can there be more in 17 inch?

I will stick with my manual that says 29/36 for 17 inch, makes more sense.
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      11-23-2005, 11:32 PM   #21
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I live in minnesota,and in the winter i run 35 all around,it seems to work better.If temp,is not a problem,the 29 front and 36 back,thats what i use in non-winter.
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      11-24-2005, 11:43 AM   #22
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33/41 is definitely too high unless ur running with full load all the time + <100mph. I use 30/36 for my 17" summer. As for 16" winter I am using 30/34 as I thought 36 at cold when its minus 20 outside is just too high once the tire warms up.
And the drive axle always require higher pressure than the other axle regardless of tire size. Placement of engine (front vs rear) also makes difference to recommended tire pressure
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