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BMWCurves
01-21-2016, 11:41 AM
After a somewhat lengthy discussion on tire inflation over in The Random E46/ZHP Question Thread (http://www.zhpmafia.com/forums/showthread.php?11957-The-Random-E46-ZHP-Question-Thread&p=468901#post468901) and doing some cursory research, especially in this old Mafia thread on tire pressure (http://www.zhpmafia.com/forums/showthread.php?1579-What-is-the-recommended-tire-air-pressure-for-the-E46-BMW-330-ZHP), I figured I would try and create a central thread on tire inflation info.

First, why is proper tire inflation is important?

To answer this important question, I turn to Tire Rack's expertise:

Advantages of Correct Tire Inflation
Maintaining correct tire inflation pressure helps optimize tire performance and fuel economy. Correct tire inflation pressure allows drivers to experience tire comfort, durability and performance designed to match the needs of their vehicles. Tire deflection (the tread and sidewall flexing where the tread comes into contact with the road) will remain as originally designed and excessive sidewall flexing and tread squirm will be avoided. Heat buildup will be managed and rolling resistance will be appropriate. Proper tire inflation pressure also stabilizes the tire's structure, blending the tire's responsiveness, traction and handling.

Disadvantages of Underinflation
An underinflated tire can't maintain its shape and becomes flatter than intended while in contact with the road. If a vehicle’s tires are underinflated by only 6 psi it could lead to tire failure. Additionally, the tire’s tread life could be reduced by as much as 25%. Lower inflation pressure will allow the tire to deflect (bend) more as it rolls. This will build up internal heat, increase rolling resistance and cause a reduction in fuel economy of up to 5%. You would experience a significant loss of steering precision and cornering stability. While 6 psi doesn’t seem excessively low, remember, it usually represents about 20% of the tire’s recommended pressure.

Disadvantages of Overinflation
An overinflated tire is stiff and unyielding and the size of its footprint in contact with the road is reduced. If a vehicle's tires are overinflated by 6 psi, they could be damaged more easily when running over potholes or debris in the road. Higher inflated tires cannot isolate road irregularities well, causing them to ride harsher. However, higher inflation pressures usually provide an improvement in steering response and cornering stability up to a point. This is why participants who use street tires in autocrosses, track events and road races run higher than normal inflation pressures. The pressure must be checked with a quality air gauge as the inflation pressure cannot be accurately estimated through visual inspection.

Source: http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=1

When should I check my tire pressure?

Air is a gas, and gas expands and contracts with temperature. Note: this isn't technically correct since gas fills the volume of any vessel it's contained in, but the pressure of a gas does increase with increasing temperature if volume stays the same. As a result, the pressure in your tires in the morning will be lower than after a long drive in the sun.

So when should you check my tire pressure?
According to Tire Rack, you should test your tire pressure in the morning, before you drive. This is so the air in tires have had sufficient time to reach ambient air temperature if the car has been driven the previous day, and the air be at the lowest temperature for the day.

Tire Rack has some other interesting information in their article, discussing ambient air temperature, heat due to driving, effects of filling your tires with air at different times of the day. The article is linked below. I'll include some of the important excerpts:

"The tire pressure recommended in your vehicle's owner's manual or tire information placard is the vehicle's recommended cold tire inflation pressure. This means that it should be checked in the morning before you drive more than a few miles, or before rising ambient temperatures or the sun's radiant heat affects it."

"In most parts of North America, the difference between average summer and winter temperatures is about -50° Fahrenheit...which results in a potential loss of about 5 psi as winter's temperatures set in. And a 5 psi loss is enough to sacrifice handling, traction, and durability!"

"As the day's temperatures went from 67° to 85° Fahrenheit, the tire that was kept in the shade went from our starting pressure of 35 psi to a high of 36.5 psi. The tire that was placed in the sun and subject to the increase in ambient temperature plus the sun's radiant heat went from our starting pressure of 35 psi to a high of 40 psi. In both cases, if we had set our tire pressures in the afternoon under the conditions of our evaluation, they would have been between 2 and 5 psi low the following morning."

Source: http://www.tirerack.com/winter/tech/techpage.jsp?techid=73

So when should I fill my tires?
This is similar to checking your tire pressure. It should be in the morning. For those of thus that prefer to drive to a gas station to fill our tires, you will want to keep the driving distance down to minimize the pressure increase in the tires.


Then what is proper tire inflation for our cars (ZHPs)?

ZHP stock tire sizes:
225/40R18 - Front
255/35R18 - Rear

BMW recommends the following tire pressures for these tire sizes on the ZHP:

Normal driving/cargo (4 passengers or less)
Sedans and coupes - 32/38 psi front/rear
Convertibles - 32/36 psi front/rear

Fully loaded (5 passengers and cargo)
Sedans, Coupes, and Convertibles - 39/46 psi front/rear

Note: as previously mentioned, these values are for cold tires.

These pressure values are found in the user manual for a Model Year (MY) 2004 325i/330i, MY 2005 325Ci/325Ci, and MY 2005 325CiC/330CiC. Pictures of the tire inflation spec pages in the manuals can be found here:

Sedans - http://i.imgur.com/zVJZzYP.png
Coupes - http://i.imgur.com/GWACJjF.png
Convertibles - http://i.imgur.com/1y4XW6d.png

I would like to see if any other values are found in other model years, so if any members have a ZHP from a different model year than listed above, feel free to check your user manual and report back!


Why are the pressure values different between the front and rear tires?

That's a good question, especially given that the E46 has 50/50 weight distribution (actual values for a 330i: 50.1/49.9 (manual), 50.6/49.4 (auto)). Although there are several possibilities as to why BMW recommends a higher pressure in the rear tires, the most likely reason is similar to why the ZHP comes in a staggered tire size: promote understeer. BMW may be in the business of taking your money, but they're not in the business of killing its customers (intentionally). Understeer is safer and more manageable than oversteer for the novice driver. Logically, biasing the car toward mild understeer will keep BMWs customers safe and out of trouble. Higher tire pressure in the rear as compared to the front tires promotes understeer. For a nifty, quick and dirty guide on ways to alter your car's handling parameters, see UUC's chart below, paying attention to the first two rows.


http://i.imgur.com/6ZMpxUm.png

Source: http://store.uucmotorwerks.com/articles/swaybar_setup.htm


Well understeer is for gutless commies, what tire pressure should I use?

What tire pressures do you, the members, use?

Post below or PM me your tire size, brand, and tire pressure and I will log it in this post below for everyone to see. I think it will be helpful resource for everyone!


User Table

http://i.imgur.com/X2Z4dq9.png

san
01-21-2016, 12:06 PM
Awesome thread!!
Tire size : F 225/40 18
R 255/35 18
Brand : continental dws 06
Tire pressure : F 32, R 38


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BMWCurves
01-21-2016, 12:36 PM
Added!

wsmeyer
01-21-2016, 12:40 PM
Excellent info. This made me laugh:

"Well understeer is for gutless commies"

I'm partial to the old saying; "Oversteer wins races, understeer wins championships."

BMWCurves
01-21-2016, 12:57 PM
Excellent info. This made me laugh:

"Well understeer is for gutless commies"

I'm partial to the old saying; "Oversteer wins races, understeer wins championships."

True. Ass out is for fun, smooth and clean is for speed.

What's your tire size and pressure?

Vas
01-21-2016, 01:24 PM
My Imola Sedan

Tire size : .
F 225/40 18
R 255/35 18
Brand : Bridgestone Potenza S04
Tire pressure : F 34, R 36

BMWCurves
01-21-2016, 01:33 PM
Will update soon.

wsmeyer
01-21-2016, 01:34 PM
Tire size:
F 225/40 ZR18
R 255/35 ZR18
Brand: Michelin Pilot Super Sport
Tire pressure: F 32, R 36

BMWCurves
01-21-2016, 02:30 PM
Added.

johnrando
01-21-2016, 03:50 PM
245/35 ZR18 x 8.5 (x4)
Michelin Pilot Super Sport
38 PSI x 4

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danewilson77
01-21-2016, 04:21 PM
So....we are posting our tire sizes and what pressure we're running?

Great contribution by the way.

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ELCID86
01-21-2016, 04:32 PM
Yeah I don't necessarily get that. But do appreciate the thread!


---
"ZHP is a garbage option anyway- just some cosmetic upgrades with a different cam and diff to claw back some of the performance lost fitting those hideous and heavy wheels. Any 330 with a 3.46 diff will smoke a ZHP every time. The whole Mafia thing reeks of childish behavior." - an e46fanatic

BMWCurves
01-21-2016, 04:49 PM
I know it doesn't really have much use in real terms, but interesting to see nonetheless what tires/pressures people use.

Lorenzo
01-21-2016, 05:01 PM
Shawn, you wrote 'Sedans and coupes - 32/38 psi front/rear'. But my places says much higher. Anyone know why?

san
01-21-2016, 05:12 PM
Shawn, you wrote 'Sedans and coupes - 32/38 psi front/rear'. But my places says much higher. Anyone know why?

Yours seem to show the max values based on the chart William posted


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Johnmadd
01-21-2016, 05:15 PM
So....we are posting our tire sizes and what pressure we're running?

Great contribution by the way.

Sent from my SM-G925V using Tapatalk


Yeah I don't necessarily get that. But do appreciate the thread!


---
"ZHP is a garbage option anyway- just some cosmetic upgrades with a different cam and diff to claw back some of the performance lost fitting those hideous and heavy wheels. Any 330 with a 3.46 diff will smoke a ZHP every time. The whole Mafia thing reeks of childish behavior." - an e46fanatic

It's a good idea imo, afterwards we can compare tire wear. I will post my size tomorrow, I typically run 32 front and 36 rear on stock size conti dws extreme contacts.

danewilson77
01-21-2016, 05:19 PM
Conti DWS 245/40 ZR 18 97 Y x 4 @ 42 psig.

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RUS_ZHP
01-21-2016, 07:35 PM
Great thread, thanks!
I am running Michelin pilot ss
225/40/18 @ 32 psi
255/35/18 @ 38 psi

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BMWCurves
01-21-2016, 11:56 PM
So....we are posting our tire sizes and what pressure we're running?

Great contribution by the way.

Thanks! I felt it might be useful to have the info consolidated to a single thread.


Yours seem to show the max values based on the chart William posted

Correct, those are the values BMW gives for a fully loaded car i.e. five passengers with cargo.

Table is updated with everyone who posted here.

derbo
01-22-2016, 04:15 PM
Great post.

245/40/R17
Dunlop Star Spec Z1
Tire Pressure: 36psi

My tire pressure is usually 35psi hot on the track but thats a whole different concept that this.

BMWCurves
01-22-2016, 04:38 PM
Added! Anyone else?

slater
01-22-2016, 08:01 PM
i run stock sized michelin PSS, as well as 225/45/17 and 245/40/17 michelin pilot sport AS3, both sets with 32F/38R.

running 215/50/17 michelin x-ice3's with varying tire pressures - trying different values with the new suspension.

BMWCurves
01-23-2016, 01:27 AM
Non-winter tires added.

BMWCurves
01-26-2016, 12:58 PM
Bump for additional members' tire/wheel setups and pressures.

Ssparrow
01-26-2016, 03:26 PM
Michelin Pilot Sport A/S3

Front: 225/40/18 - 35psi
Rear: 255/35/18 - 40psi

BMWCurves
01-26-2016, 04:23 PM
Added!

BMWCurves
02-06-2016, 11:25 PM
Bump.

ecrabb
02-11-2016, 03:10 PM
LOLs at "understeer is for gutless commies".

I'll update once I get my new PSS's and have a few miles to evaluate a couple of different combos.

I am confused about the table posted above and at Tire Rack, though...

The table says to decrease understeer (i.e. increase oversteer), the proper combo would be higher front tire pressure and lower rear tire pressure. Why is that? I thought that as you increased tire pressure, you reduced the contact patch (and traction). If you're raising pressure (and decreasing traction) in the front and running less pressure (and more traction) in the rear, that's going to make the car push/understeer, is it not? Where am I going wrong?

SC

ecrabb
02-11-2016, 03:40 PM
Hmmm... Lots of good info in this thread on Rennlist...
http://rennlist.com/forums/racing-and-drivers-education-forum/398996-why-does-increasing-front-tire-pressure-reduce-understeer.html

I think my intuition is right on this. The table above and that posted on Tire Rack and other places are a gross oversimplification because it really depends where you start, and what the tire's optimal pressure is. This guy said it better than I can...



Originally Posted by RedlineMan
Craig;

Think of graphing tire performance; pressure on the bottom (X), and performance up the side (Y). The graph will look roughly like a pyramid. ...

To say that you always add or always subtract air to get an effect now can be seen to be wrong. ...
+100000000000. It never ceases to amaze me that people say to increase front pressure for more front grip. Like RM explained, if you're already high, more pressure will make it WORSE. Overinflate your street front tires sometime and you'll understand quickly.

Great thread. More people need to understand this issue.

But, then looking at the BMW recommended tire pressures of 32 front/36 rear on the vert are a little counter-intuitive, at least with the narrative that "biasing the car toward mild understeer" is safer for novice drivers. I'm not sure it's the lower front/higher rear that causes that because it isn't just tires that bias the car one way or the other, but also the suspension. If the suspension is tuned to be biased toward understeer, then the tire inflation could be counteracting that. The 36psi on the rear would be making the rear a little less sticky, and the 32psi on the front is making it a little more sticky. Same with the coupe.

Am I completely out in left field here?

SC

BMWCurves
02-16-2016, 10:36 PM
LOLs at "understeer is for gutless commies".

I'll update once I get my new PSS's and have a few miles to evaluate a couple of different combos.

I am confused about the table posted above and at Tire Rack, though...

The table says to decrease understeer (i.e. increase oversteer), the proper combo would be higher front tire pressure and lower rear tire pressure. Why is that? I thought that as you increased tire pressure, you reduced the contact patch (and traction). If you're raising pressure (and decreasing traction) in the front and running less pressure (and more traction) in the rear, that's going to make the car push/understeer, is it not? Where am I going wrong?

SC

Hmmm... Lots of good info in this thread on Rennlist...
http://rennlist.com/forums/racing-and-drivers-education-forum/398996-why-does-increasing-front-tire-pressure-reduce-understeer.html

I think my intuition is right on this. The table above and that posted on Tire Rack and other places are a gross oversimplification because it really depends where you start, and what the tire's optimal pressure is. This guy said it better than I can...



But, then looking at the BMW recommended tire pressures of 32 front/36 rear on the vert are a little counter-intuitive, at least with the narrative that "biasing the car toward mild understeer" is safer for novice drivers. I'm not sure it's the lower front/higher rear that causes that because it isn't just tires that bias the car one way or the other, but also the suspension. If the suspension is tuned to be biased toward understeer, then the tire inflation could be counteracting that. The 36psi on the rear would be making the rear a little less sticky, and the 32psi on the front is making it a little more sticky. Same with the coupe.

Am I completely out in left field here?

SC

Whoops, I somehow completely missed your posts when you originally posted them. I look forward to your review of your PSS and your preferred tire pressures.

As for your oversteer/understeer question, I'll first say I am the opposite of a so-called "expert," but, like any good American, I'll plunge headlong into the discussion anyways. As you say, there's a lot more to handling characteristics than simple tire pressure differences. Engineers definitely build cars today with the average driver in mind and tend to err on the side of understeer characteristics because it's considered safer and easier to handle. My mother's Volvo S40 understeers quite a bit, but I'm sure that's by Volvo's design, despite the tires all being the same size and pressure. My guess for our cars is that the suggested differences in tire pressures are due to BMW wanting to induce understeer and maybe also just a product of different section width tires requiring different tire pressures because of the inherent difference in width. I'm not sure what elements within the E46 chassis promotes understeer. Honestly I don't even notice much understeer in our cars from the factory.

I don't know, I'm talking in circles.

BMWCurves
02-22-2016, 01:14 PM
Updated with slater's new winter setup.

slater
02-22-2016, 01:49 PM
Updated with slater's new winter setup.

thanks... btw, my rear PSS should be listed at 255/35/18's, if you don't mind. :)

BMWCurves
02-22-2016, 03:58 PM
thanks... btw, my rear PSS should be listed at 255/35/18's, if you don't mind. :)

Whoops, got yours and Ssparrow's profile ratio wrong.

BMWCurves
03-02-2016, 01:14 PM
Updated with my new tire size.

CarbonZHP
03-02-2016, 04:22 PM
Anyone care about 19"?

BMWCurves
03-02-2016, 04:46 PM
Anyone care about 19"?

Sure, I'm just trying to populate the list!

BMWCurves
04-07-2016, 04:05 PM
Bump for new members.

Karl Lazlo
04-07-2016, 05:57 PM
2003 330Ci ZSP
F: Mich PSS 255/35-18 42PSI
R: Mich PSS 255/35-18 42PSI

2006 330Ci ZHP
F: Connie ECDW 225/40-18 40PSI
R: Connie ECDW 255/35-18 38PSI

BMWCurves
04-08-2016, 01:17 PM
Added.

MrAdventure
11-01-2016, 08:49 AM
User Table

http://i.imgur.com/vUrQgVL.png

For Winter, I'm switching over to a non-stock square setup of 225/45-17s all around. Should I go with an equal pressure all around like derbo and BMWCurves have done for their setups? Should I go with a similar pressure around 36-38?

I have had the stock tire sizes on the car, until now.

fw_fw
11-01-2016, 10:41 AM
For Winter, I'm switching over to a non-stock square setup of 225/45-17s all around. Should I go with an equal pressure all around like derbo and BMWCurves have done for their setups? Should I go with a similar pressure around 36-38?

I have had the stock tire sizes on the car, until now.

Look in the back of your owner's manual, they have tables that show different sizes and pressures, including for 225/45/17 square, where BMW on a 330Ci recommends 32/39....

BMWCurves
11-01-2016, 11:16 AM
Here is the tire pressure chart from a 2004 owners manual for the E46 sedan

http://i.imgur.com/9DaDgkH.png
http://i.imgur.com/oYnblFp.png

Here is the tire pressure chart from a 2006 owners manual for the E46 coupe

http://i.imgur.com/mWKYWvJ.png

MrAdventure
11-01-2016, 11:52 AM
In the sedan, light load, it's 32/38, heavy load, 39/46.

For some reason that wasn't registering. I was thinking that the pressures should be the same for front and rear. got it, thanks!

BMWCurves
11-01-2016, 11:59 AM
In the sedan, light load, it's 32/38, heavy load, 39/46.

For some reason that wasn't registering. I was thinking that the pressures should be the same for front and rear. got it, thanks!

As a reference to the original post, there's a probable reason our tires are staggered and have different pressures: to promote understeer to keep BMW's customers safe.

Sicily1918
01-07-2017, 12:44 AM
I'm running stock rims w/stock tire size.

Michelin PSS, 34F/40R (I wanted a slightly firmer ride)

dpark
02-10-2017, 07:32 PM
Very interesting thread, but I have a datapoint that is opposite of what is posted in here. So while I enjoy some spirited driving, I also like it when my tires wear evenly. When I got my first 1998 e46 (a 323i) and did the recommended pressures, I balded my rears in the middle of the tire at like 12k miles. I was not a happy camper. I put new rears on, same recommended pressure and they wore out (balded in the center again) about the time the fronts wore out. The fronts also balded in the centers, but at a much slower pace.

Since that experience and up to and including my current 2004 ZHP, I continued to lower my tire pressures until I could get even treadwear. For me, that PSI level is 30 front AND rear. The rears still wear out before the fronts but instead of a 2:1 ratio (two sets of rear tires for every 1 set of fronts) it is now down to 5:4.

I just replaced all 4 tires in the rears were well into the wear bars, and the front were approx 3/32". Wear across the tire was very even.

My guess is I will hear that I am in danger of something bad happening but I have done this for the life of my ZHP and have had zero problems. I can corner aggressively, have used my ABS more than once to avoid an accident, still do high speed runs down the interstate over 100 with no problems and the car tracks well. In general I have no complaints.

What I don't know is how other folks who keep their tire pressures at 35PSI and above don't have terribly uneven wear on their tires. I guess if you are driving a 8/10ths on the street that those PSI levels are warranted, but I just couldn't deal with the bad tread wear.

FYI, the tires on my car have been the original Michelin Pilot Sports, Pirellis, Yokohamas (don't remember the models) and most recently the Conti DWs and DWSes (my most recent set). All have worn evenly at 30/30 PSI

David

az3579
02-10-2017, 09:36 PM
What I don't know is how other folks who keep their tire pressures at 35PSI and above don't have terribly uneven wear on their tires. I guess if you are driving a 8/10ths on the street that those PSI levels are warranted, but I just couldn't deal with the bad tread wear.


35 psi on all four (square setup) for a few years now and have gotten even wear amongst all four tires. I rotate every oil change (about 7500 miles, if I'm not being lazy). Not only do they wear evenly, but I'm getting usually about 25k on a set of high performance summer tires. You shouldn't really be expecting significantly more than that for fast wearing summer tires anyway.

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dpark
02-10-2017, 10:19 PM
35 psi on all four (square setup) for a few years now and have gotten even wear amongst all four tires. I rotate every oil change (about 7500 miles, if I'm not being lazy). Not only do they wear evenly, but I'm getting usually about 25k on a set of high performance summer tires. You shouldn't really be expecting significantly more than that for fast wearing summer tires anyway.

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When I ran 35PSI, my rear centers balded when I still had 50% tread left on the edges. I only got even wear at 30PSI.

Does not matter the tire brand. Running stock size rubber and original wheels. Even 32PSI resulted in uneven wear.

holyc0w
02-10-2017, 10:38 PM
I read somewhere that 255s are on the larger end for 8.5" wide rims. Maybe 245s would provide more even wear?

fredo
02-11-2017, 04:39 AM
Good info here. I'm willing to try 30 PSI on all 4 tires. I run the staggered setup.

ELCID86
02-11-2017, 05:12 AM
Good info here. I'm willing to try 30 PSI on all 4 tires. I run the staggered setup.

Seems low. No?

az3579
02-11-2017, 06:52 AM
Seems low. No?
Seems too low to me, personally.

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BMWM3186
02-11-2017, 09:50 AM
I am running at 34/40 psi on the dws 06s that were put on 10kish ago by the PO. When I bought the car they were inflated to 38/46.

Dave1027
02-11-2017, 11:44 AM
When I ran 35PSI, my rear centers balded when I still had 50% tread left on the edges. I only got even wear at 30PSI.

Does not matter the tire brand. Running stock size rubber and original wheels. Even 32PSI resulted in uneven wear.

I get even wear at 32 psi. Of course that depends on the temperature. If it's 50 degrees in my garage I do have to compensate be subtracting 2 psi.

ELCID86
02-11-2017, 04:06 PM
Good to know.

dpark
02-11-2017, 10:59 PM
I read somewhere that 255s are on the larger end for 8.5" wide rims. Maybe 245s would provide more even wear?

255 was the factory tire size so I stayed with it. Probably because it kept the overall wheel circumference very close to the fronts at 225/40-18

I do agree that according to certain sites: http://www.tyresizecalculator.com/charts/tire-width-for-a-wheel-rim-size-chart that 255 is the max size for an 8.5" rim.

dpark
02-11-2017, 11:03 PM
Seems too low to me, personally.

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Don't disagree (on the low PSI), but my decision was based on getting even wear across the tread and over the course of my first e46, I kept lowering the PSI for each new set of tires I bought until I got the wear I wanted. And 30PSI did it.

If I did any sort of serious racing, no question I would up the PSI, but for daily driving, I have had no problems. I don't go hanging out the rear end around corners, but I don't drive like grandma either.

This is what worked for me.

danewilson77
02-12-2017, 06:46 AM
I am running at 34/40 psi on the dws 06s that were put on 10kish ago by the PO. When I bought the car they were inflated to 38/46.
I think this is close to what the door jam says?

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BMWM3186
02-12-2017, 07:29 AM
I think this is close to what the door jam says?

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Yep, seems like a lot of shops don't know that that the pressure stamped on the door is the max pressure.

az3579
02-12-2017, 09:56 AM
Yep, seems like a lot of shops don't know that that the pressure stamped on the door is the max pressure.
Well the sticker doesn't say it's max pressure. That's why it's so confusing. It makes it seem like that is the actual pressure to set them to.

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BMWM3186
02-12-2017, 06:28 PM
Well the sticker doesn't say it's max pressure. That's why it's so confusing. It makes it seem like that is the actual pressure to set them to.

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Yeah it's stupid, I didnt realize either until I decided to check the owners manual

BMWCurves
06-07-2017, 08:36 AM
Updated.

ELCID86
03-31-2018, 09:30 AM
Had mine done at Costco today. The sticker on the window says they went 32F/36R.