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Terry Kennedy
01-15-2003, 08:29 PM
I'm confused about the optimal tire pressure. This is on a 2003 325XiT (wagon) with factory ContiTouringContact 205/50 R 17 93V CV95 on BMW Type 73 wheels. When I got the car at initial delivery, tire pressure as delivered was 32 front / 35 rear. The pillar rating plate says 35 front / 41 rear. That was in October. Since then I've been keeping them around 34 front / 39 rear.

A couple days ago I hit a disguised crater (full of water) and ruined my front right tire (slow leak, and when I reinflated it there was a pronounced bulge on the sidewall and a very minor bend to the rim of the wheel). So, off to the dealer...

Turns out a new tire and wheel were needed, so I bought a match for the existing ones. [The wheel can possibly be repaired, but the dealer doesn't do that.] But now the car has 32 front / 35 rear again, including the new tire.

I can't fault them for their thoroughness, but I'm confused about the optimal pressure. Again, the pillar plate lists 35 / 41 as the minimum for this tire size and even higher for when the car is heavily loaded. Do they know something I don't, or are they the ones that are confused?

BTW, I checked the pressure with both an Accutire digital gauge and an older pop-out gauge, and they match within a half PSI.

Nick325xiT 5spd
01-15-2003, 08:40 PM
You have RS-As, right?
You should run AT LEAST 40 PSI all around.

Terry Kennedy
01-15-2003, 10:21 PM
Originally posted by Nick325xiT 5spd
You have RS-As, right?
Nope,
Originally posted by Terry Kennedy
factory ContiTouringContact 205/50 R 17 93V CV95 on BMW Type 73 wheels.
Does that change the answer?

Nick325xiT 5spd
01-15-2003, 10:36 PM
Ooops, need to work on my reading comprehension. ;)

And it really doesn't change anything. The contis have much better sidewalls than the RS-As, though.

I'd put 42F, 40R in.

Artslinger
01-16-2003, 06:28 AM
Why such high pressure? I use 32 front / 34 rear pressure in my performance tires and 32 front / 32 rear in my snow tires. I find anything higher and the car rides to harsh for city driving.

Nick325xiT 5spd
01-16-2003, 06:40 AM
The high pressures do two things:
Protect the rims a lot better and prevent the sidewalls from rolling.

It also stiffens the tire up so that the carcass isn't dragged from side to side by the road. If you really want to feel a difference, put 30PSI in a set of S-03s and drive down a highway. Then do the same highway with 40PSI. The first time around, the car will try to throw itself off the road, the second time, the car will track fairly straight.

Ultimately, even if you want a softish ride, the contis are pretty soft tires. 40PSI in them is not NEARLY as harsh as, say 30PSI in a set of S-03s.

I run 38 PSI all around in my HTR+ tires, which is the lowest I can go before I start to get serious sidewall roll in the corners. The RE950s weren't happy below 38, either. The Contis weren't happy in corners, period, but they needed at least 40PSI to feel good. Keep in mind also that even BMW recommends 41 for the rear. The touring is heavy and on skinny tires. 205/50 needs more air than 225/45 to support the same weight.

Artslinger
01-16-2003, 06:54 AM
What would the ideal pressure to use on my car, 325i SP w/Continentals.

Nick325xiT 5spd
01-16-2003, 07:02 AM
Couldn't tell you, no actual experience with the contisports. 40 all around is my default starting point, then I adjust from there. Anything less than 35 was dangerous in the contitourings, but that doesn't carry over to another tire.

vern
01-16-2003, 07:24 AM
The next time you need a new rim and have to go to the dealer to match your existing ones ask him for what they call a take off rim.Thats a new rim that somebody had the dealer take off there car when they took delivery and wanted to upgrade to a different style.Its almost 1/3 the price.For some reason or another they don't charge you the full price because it was taken off another car.
good luck
vern

Dr. Phil
01-16-2003, 07:36 AM
Originally posted by Nick325xiT 5spd
You have RS-As, right?
You should run AT LEAST 40 PSI all around.
:yikes:

I have RSAs and have found 38 around to be ample:confused: Even at that setting bumps are a bit harsh :eek:

Nick325xiT 5spd
01-16-2003, 07:39 AM
Originally posted by PM 325xiT
:yikes:

I have RSAs and have found 38 around to be ample:confused: Even at that setting bumps are a bit harsh :eek:

http://www.bimmerfest.com/forums/showthread.php?s=&threadid=14418&highlight=drive+like+alee

:confused:

Dr. Phil
01-16-2003, 07:41 AM
Originally posted by Nick325xiT 5spd
http://www.bimmerfest.com/forums/showthread.php?s=&threadid=14418&highlight=drive+like+alee

:confused:
:flipoff: :flipoff:

Funny boy ;)

So at 40psi I could drive like you or Clyde :dunno: :D

·clyde·
01-16-2003, 07:44 AM
Originally posted by PM 325xiT
:flipoff: :flipoff:

Funny boy ;)

So at 40psi I could drive like you or Clyde :dunno: :D

Talk to us after you get a real transmission. :flipoff:

Pinecone
01-18-2003, 11:22 AM
The MINIMUM tire pressure you should run is the door pillar number. Lower pressures can cause handling problems and in some cases can cause serious tire problems.

Since you are very unlikely to actually stop and add pressure when you add load (people or stuff) I always run at the loaded tire pressures.

Now for performance, start with the higher of the door pillar numbers and add 2 psi all around. If you want to reduce the understeer add another 2 psi to the fronts (4 psi over highest recommended). But do not exceed the maximum tire pressure as stated on the tire sidewall.

Remember all these pressures are COLD. WHich means overnight, not driven. If you don't have air at home, check the tire pressures at home. Write down how much each tire needs, then drive to the gas station and ADD that much to each tire for what the reading is at the station.

Or buy a compressor. A small portable one will run about $30.

Interesting info, the recommended tire pressure for the Explorer with Firestone tires was 26 psi. And since tires in general lose about 1 psi per week, and most people do not check their tire pressures. And since a modern radial doesn't look low until the pressure is less than about 18 - 19 psi, it is likely that some, if not all, of the tire failures were low pressure related.

And for those who don't know, the number one cause of sudden tire failure (blow out) is low tire pressure. The low pressure allows the sidewall to flex overheating the rubber sidewall.

Terry Kennedy
01-18-2003, 12:05 PM
Originally posted by Pinecone
The MINIMUM tire pressure you should run is the door pillar number. Lower pressures can cause handling problems and in some cases can cause serious tire problems.
Indeed. That's why I was confused by the dealer repeatedly setting 32/35.
Since you are very unlikely to actually stop and add pressure when you add load (people or stuff) I always run at the loaded tire pressures.
IIRC, the lower of the door numbers includes reasonable loads (2 passengers and some stuff in the back). When I fill the back, it is with photography stuff - bulky, but not heavy.

Given our "wonderful" NY roads, I'd rather not have my teeth rattled loose by running at 48PSI all the time.:rolleyes:
Remember all these pressures are COLD. WHich means overnight, not driven. If you don't have air at home, check the tire pressures at home. Write down how much each tire needs, then drive to the gas station and ADD that much to each tire for what the reading is at the station.

Or buy a compressor. A small portable one will run about $30.
I have a compressor, actually. And the aformentioned pair of gauges.

I'm actually pretty good about tires - I'll at least do a full walkaround to visually inspect the tires before each time I pull out of the garage, and often if I'm parked somewhere for a while I'll check before getting in the car (a habit an ex-cop taught me years ago). And I check the pressure at least every couple weeks. Given that my cars are always low mileage (my '95 Talon had a bit over 11K when totalled in 2002, and the BMW has 2650 miles or so since 10/02), checking pressure every couple weeks is sometimes more often than I drive the car.

I was more interested in an explanation for why the dealer was setting the pressure lower than how I interpreted the pillar sticker. Something like "you dolt, you're supposed to look at the column with the triangle symbol, not the one without any symbol" or somesuch. But it seems that the dealer is just confused.

brave1heart
01-18-2003, 12:06 PM
It's really a trial and error. Depends mostly on your driving style. Generally, I like the fronts to be 2 psi higher than the rears at track events/autox and the other way round for street driving. I use 32/34 for the street and 35/33 for the track but that varies depending on the air and track temp. The hotter it is, the lower I like my tires' psi.

Pinecone
01-19-2003, 05:18 PM
Originally posted by Terry Kennedy
Indeed. That's why I was confused by the dealer repeatedly setting 32/35.

..........

I was more interested in an explanation for why the dealer was setting the pressure lower than how I interpreted the pillar sticker. Something like "you dolt, you're supposed to look at the column with the triangle symbol, not the one without any symbol" or somesuch. But it seems that the dealer is just confused.

Most likely your dealer has no clue. The same thing happened with our Roadster. Inspection 1 and they reset the tire pressures, too low.