tire pressure- what's the right value for an 02 530i?

Hi:

I've just taken the summer tires 234/45-17Y off my 2002 530i. I now have my
Hakapellita 1 215/55-16T tires on.

In the manual, and on the door, it tells me to use 33 psi front and 41 psi
rear based on "std temperature".

The auto shop that I trust, and does BMW and Porches work, told me to use 35
psi, front and rear.

My dealer didn't give me a number; they just said follow the book ;(

So what do others do? I live in Canada and winter tires are a must. In the
summer we get over 30C and in the winter it can be colder than -30C. Thus
it's important to check tire pressure at least evert season.

Also do others de-rate their tire pressures during colder weather or do you
keep the pressure constant regardless of season/temp. Since the current temp
is -2C/29F, I used 31f & 39r. There are much lower numbers on the door
pillar for non USA/CAN drivers. I don't know why.

Please post any updates to this NG. Thank you.

- Walter

"Walter" > wrote in message
. ..

Let's see if we can resolve this "question of ages" once and for all.

1-The only absolute when it comes to tire pressures is the maximum. This is
the number stamped on the sidewall by the manufacturer. It should never even
be close to what you inflate the tire to, it is just a warning that the tire
is not meant to be inflated over that figure. This is the only number that
comes into play as far as the tire is concerned.

2-As far as the VEHICLE is concerned, this is where the confusion arises.
The manufacturer will indicate recommended pressures for front and rear
based on the load of the vehicle. The more people or stuff you put in the
car, the higher the number will be. This is only a GOOD STARTING POINT.

3-From the starting point, you may want to increase or decrease the pressure
depending on what you are trying to achieve. Comfort, life of the tire,
increase or decrease understeer by adjusting either the front or the back
tire pressures, etc. I'm not going to go into detail about these objectives,
especially altering handling characteristics, because unless you are driving
in a manner where you are cognizant of under/oversteer, it probably won't
matter enough to you to try and change it. If you are aware of these things,
then you should know, or know how to find out, the changes that need to be
made to alter the handling to your preference.

4-The whole idea of cold or hot inflation temperatures is also much
overdone. Tire pressure will vary according to, ultimately, the temperature
of the tire and the air in it. Again, it won't make much difference if you
inflate your tire to x lbs. hot or cold, unless you can detect it. Also,
unless you are inflating the tire in the Arctic and driving it in Death
Valley it won't be critical. The easiest thing to do about this is just
inflate the tires to a starting pressure, get them up to operating
temperature, then adjust the pressures to achieve your intended result. Note
these pressures when warm, then note them when cold, and these will be your
desired pressures whether you check them in your driveway when it's been
cold all night, or after you are driving for 6 hours and pulling into a gas
station.

5-Very important. NEVER NEVER trust the pressures as indicated by gas
station pumps. You could guess the pressure just as well by kicking the
tire. Buy yourself a nice digital gage and be confident.

6-If all of this sounds too complicate, just use the pressures as indicated
on the car door jamb, which are always cold inflated pressures.

Ok?

"Walter" > wrote in message
. ..
> Hi:
>
> I've just taken the summer tires 234/45-17Y off my 2002 530i. I now have
> my Hakapellita 1 215/55-16T tires on.
>
> In the manual, and on the door, it tells me to use 33 psi front and 41 psi
> rear based on "std temperature".
>
> The auto shop that I trust, and does BMW and Porches work, told me to use
> 35 psi, front and rear.
>
> My dealer didn't give me a number; they just said follow the book ;(
>
> So what do others do? I live in Canada and winter tires are a must. In the
> summer we get over 30C and in the winter it can be colder than -30C. Thus
> it's important to check tire pressure at least evert season.
>
> Also do others de-rate their tire pressures during colder weather or do
> you keep the pressure constant regardless of season/temp. Since the
> current temp is -2C/29F, I used 31f & 39r. There are much lower numbers on
> the door pillar for non USA/CAN drivers. I don't know why.
>

Since the tire pressure will effect the handling of the car and wear of the
tires, its best to go by what the car manufacturer says. Go by what's on
the inside of your door. Also, check your tire pressure weekly. I've seen
coworkers who never check their tires have flats this time of year when the
temperature gets real cold compared to when they had them filled up last
summer.

Kyle.

"Kyle and Lori Greene" > wrote in message
...
>

>
>Tire inflation pressures also fluctuate with changes in the outside air
>temperature. This occurs at a rate of about 1 psi for every 10°F (plus or
>minus). So the tires you set correctly with an 80°F ambient temperature
>will be under inflated by 6 psi at 20°F.

That's pretty dramatic. Do you think that the calibration stamps at petrol
stations from leading suppliers such as Shell or BP are unreliable?

In the UK there is an increasing number of pumps that one can preset on a
digital display. Air is pumped in until the set point is reached.

Are these also no good?

DAS
--
For direct contact replace nospam with schmetterling
---

"tech27" > wrote in message
o.verio.net...
[...]

> 5-Very important. NEVER NEVER trust the pressures as indicated by gas
> station pumps. You could guess the pressure just as well by kicking the
> tire. Buy yourself a nice digital gage and be confident.
[...]

Dori A Schmetterling wrote:
> That's pretty dramatic. Do you think that the calibration stamps at petrol
> stations from leading suppliers such as Shell or BP are unreliable?
>
> In the UK there is an increasing number of pumps that one can preset on a
> digital display. Air is pumped in until the set point is reached.
>
> Are these also no good?
>
> DAS

I personally would not (do not) trust them, since they would vary from
station to station. Nor do I suggest checking the air pressure at a gas
station anyway (unless you live there) since you will have driven some
distance to get there and the tires will no longer be "cold".

I always check tire pressure in my own driveway after sitting (at least)
overnight. I use the same handheld pressure gauge every time so its
absolute accuracy is unimportant. I have a small air compressor (picked
up (inexpensively) at a department store many years ago) to adjust the
pressure as needed.

-Fred W

Although I am given a manufacturer's pressure adjustment for warm tyres I
can never tell how warm they really are after 50 miles or 200 miles
(presumably there is an equilibration point somewhere).

So I always measure cold (the recommended practice, of course) or 'near
cold' as I don't think that a short gentle drive makes much difference to
the temp. (Or does it?)

DAS
--
For direct contact replace nospam with schmetterling
---

"Fred W" > wrote in message
...
> Dori A Schmetterling wrote:
>> That's pretty dramatic. Do you think that the calibration stamps at
>> petrol stations from leading suppliers such as Shell or BP are
>> unreliable?
>>
>> In the UK there is an increasing number of pumps that one can preset on a
>> digital display. Air is pumped in until the set point is reached.
>>
>> Are these also no good?
>>
>> DAS
>
> I personally would not (do not) trust them, since they would vary from
> station to station. Nor do I suggest checking the air pressure at a gas
> station anyway (unless you live there) since you will have driven some
> distance to get there and the tires will no longer be "cold".
>
> I always check tire pressure in my own driveway after sitting (at least)
> overnight. I use the same handheld pressure gauge every time so its
> absolute accuracy is unimportant. I have a small air compressor (picked up
> (inexpensively) at a department store many years ago) to adjust the
> pressure as needed.
>
> -Fred W
>

If you are driving from your house to the corner gas station, the tires will
remain cold for the purposes of this discussion.

I would put more faith in the digital type of filling hose, but I carry my
own tire pressure guage in the car. I happen to own a compressor, so I have
the luxury of being able to fill my tires at home if I want, but if I
managed to get away from the house and notice I have a low tire, stuffing in
30psi is good enough for the vast majority of people. It is reasonable that
all cars take 30psi as the default tire pressure, then as the tires get
older, this can be adjusted up or down a few psi to acheive proper
treadwear.

If you have been driving for 50 miles, then the tire pressure will be raised
as a result of the heat build up, but even if you put in 30psi while hot,
the tires should remain in the range of 25 ~ 28psi when cold, and this is
fine for everybody by racers.

My advice is to always put equal amounts of air in both tires on the same
axle. In a perfect world, we would put air in all 4 tires at the same time,
but in the real world we tend to air one tire only - especially if the
weather sucks, our hands are clean and we are on the way to a meeting, our
suit is freshly pressed and out of the cleaners, or any number of crappy
excuses for doing a half-assed job - but we should always at least do both
tires on the same axle. If you put 30psi in the left rear, then also put
30psi in the right rear. Same for the front, whatever you put in the left
front, put in the right front as well. If you have the time or inclination
to do the other axle, then fine, but always do both ends of the same axle at
the very least.

Most cars take 30psi both front and rear under the majority of "normal"
operation conditions. Sure, there are exceptioins to the rule, but the
exceptions are just a few pounds, and over the life of the tire, a few
pounds isn't going to make much difference, and if it is, you can see it by
looking at the tires and adjusting the air pressure as needed. Tires leak,
so overfilling by a pound or two will take care of itself in a couple of
weeks.

Undefilling causes the tires to wear on the edges (both edges of the same
tire), overfilling causes tires to wear in the center. Alignment causes only
one edge to wear (one edge on one or more tires), and frequent rapid
accelleration causes the rear tires to wear on the inside edge (inside edge
of both tires). Mixing improper air pressure with alignment or accelleration
styles can influence the wear patterns I described.








"Dori A Schmetterling" > wrote in message
...
> Although I am given a manufacturer's pressure adjustment for warm tyres I
> can never tell how warm they really are after 50 miles or 200 miles
> (presumably there is an equilibration point somewhere).
>
> So I always measure cold (the recommended practice, of course) or 'near
> cold' as I don't think that a short gentle drive makes much difference to
> the temp. (Or does it?)
>
> DAS
> --
> For direct contact replace nospam with schmetterling
> ---
>
> "Fred W" > wrote in message
> ...
> > Dori A Schmetterling wrote:
> >> That's pretty dramatic. Do you think that the calibration stamps at
> >> petrol stations from leading suppliers such as Shell or BP are
> >> unreliable?
> >>
> >> In the UK there is an increasing number of pumps that one can preset on
a
> >> digital display. Air is pumped in until the set point is reached.
> >>
> >> Are these also no good?
> >>
> >> DAS
> >
> > I personally would not (do not) trust them, since they would vary from
> > station to station. Nor do I suggest checking the air pressure at a gas
> > station anyway (unless you live there) since you will have driven some
> > distance to get there and the tires will no longer be "cold".
> >
> > I always check tire pressure in my own driveway after sitting (at least)
> > overnight. I use the same handheld pressure gauge every time so its
> > absolute accuracy is unimportant. I have a small air compressor (picked
up
> > (inexpensively) at a department store many years ago) to adjust the
> > pressure as needed.
> >
> > -Fred W
> >
>
>

No. I've never seen one that is any good, but then all I ever see are the
ones with a stick type reading on the business end of the air hose. I've yet
to see a digital display type, but in any case I would still check the
pressure with my own guage.


"Dori A Schmetterling" > wrote in message
...
> That's pretty dramatic. Do you think that the calibration stamps at
> petrol stations from leading suppliers such as Shell or BP are unreliable?
>
> In the UK there is an increasing number of pumps that one can preset on a
> digital display. Air is pumped in until the set point is reached.
>
> Are these also no good?
>
> DAS
> --
> For direct contact replace nospam with schmetterling
> ---
>
> "tech27" > wrote in message
> o.verio.net...
> [...]
>
>> 5-Very important. NEVER NEVER trust the pressures as indicated by gas
>> station pumps. You could guess the pressure just as well by kicking the
>> tire. Buy yourself a nice digital gage and be confident.
> [...]
>

"Jeff Strickland" > wrote in message
...

All correct. Just a FYI - for normal driving set the tire pressure when
cold. When we track the cars, we inflate to around what we think we will
want, then take 3 or 4 laps to heat up the tires to racing temps, then pull
in and immediately check and adjust the pressures to what we want to run at
given the chassis settings, type of track, etc.