Tire pressure question

[Gus]

On my tires there's a notice saying "max pressure 44 psi", while on the
driver's side pillar the manual for the Subaru Outback refers you to a
sticker, which indicates pressure of between 29 psi for front wheels and
29 - 35 psi depending on number of passengers.

I was wondering if the sticker is "recommended" or "minimum" psi. I'd think
it means recommended, but this seems substantially lower than the max psi
shown on the tire so wanted to check. Any help appreciated.

In case it has any bearing, its a 2002 H6 Outback with alloys.

Cheers,

Gus

 

[Phil]

I run mine on 35 / 36 psi without any adverse affects. In fact I think the
mileage is a little better than running them at the lower pressure.

 

[mulder]

On my tires there's a notice saying "max pressure 44 psi", while on the
driver's side pillar the manual for the Subaru Outback refers you to a
sticker, which indicates pressure of between 29 psi for front wheels and
29 - 35 psi depending on number of passengers.

I was wondering if the sticker is "recommended" or "minimum" psi. I'd think
it means recommended, but this seems substantially lower than the max psi
shown on the tire so wanted to check. Any help appreciated.

In case it has any bearing, its a 2002 H6 Outback with alloys.

Cheers,

Gus

The pressures shown on the sticker are the recommended cold pressures.
The max pressure stamped on the tire is the highest safe cold pressure
as rated by the tire manufacturer and you shouldn't run the tire at or
near that pressure for normal use.

 

[Gus]

The pressures shown on the sticker are the recommended cold pressures.

The max pressure stamped on the tire is the highest safe cold pressure
as rated by the tire manufacturer and you shouldn't run the tire at or
near that pressure for normal use.

Got it. Thanks!

 

[ric_man]

On my tires there's a notice saying "max pressure 44 psi", while on the
driver's side pillar the manual for the Subaru Outback refers you to a
sticker, which indicates pressure of between 29 psi for front wheels and
29 - 35 psi depending on number of passengers.

I was wondering if the sticker is "recommended" or "minimum" psi. I'd think
it means recommended, but this seems substantially lower than the max psi
shown on the tire so wanted to check. Any help appreciated.

Just got back from a defensive driving course, and was told that
pressure depedns on who you talk to. Marketers who try to push nice soft
rides will go for lower pressures, whereas tire engineers will
reccommend higher pressures.

Saying that, the course suggested to inflate to 35-36psi for normal city
driving, and if you're travelling long distances under load, then
inflate to 40psi. Keep in mind, this is for modern cars / tires. I
wouldn't try this with cars from the 80s.

It was also mentioned that it's far easier to get a blowout at lower
pressures than at higher pressures, as tires will deform much easier and
therefore create friction at lower pressures (don't ask the physics on
it... I didn't pay much attention to the tire bit about the course -
which was probably a mistake since on reflection, they're the most
important part of the car).

HTH,

....Ric

 

[Edward Hayes]

The door sticker is Subaru's recommended COLD pressure for this tire
on this vehicle. The tires max pressure is the max. safe pressure for
this tire-period. Your owners manual is your friend and not the
general public.

 

[ric_man]

The door sticker is Subaru's recommended COLD pressure for this tire
on this vehicle. The tires max pressure is the max. safe pressure for
this tire-period. Your owners manual is your friend and not the
general public.

OK... I see your point, but the "new" information was communicated to me
via the Subaru Defensive Driving course:
http://www.melbourne.subaru.com.au/AboutInteractive/AID020.asp

You'd think they know what they were saying...

This leads me to think that they market cars one way, but they suggest
you set it up another way to get "more" out of it...

....Ric

 

[Edward Hayes]

WOW. Now that surprises me if indeed it was a "Subaru sponsored
Defensive Driving Course" I do know that owners who race competitively
raise tire pressure. The door recommendations are supposed to be the
best all around pressure with respect to safety, ride and tire life. I
think if you're unsure what pressure to run in your Subaru you might
consider emailing Subaru at www.subaru.com and ask the question.
Please let us know what you are told. Ed Hayes

 

[Carl 1 Lucky Texan]

WOW. Now that surprises me if indeed it was a "Subaru sponsored
Defensive Driving Course" I do know that owners who race competitively
raise tire pressure. The door recommendations are supposed to be the
best all around pressure with respect to safety, ride and tire life. I
think if you're unsure what pressure to run in your Subaru you might
consider emailing Subaru at www.subaru.com and ask the question.
Please let us know what you are told. Ed Hayes

I see no reason to consider any single pressure ideal for the majority
of drivers due simply to the fact that vehicle use can be so
dramatically different from day to day, week to week. Of course it is
unreasonable to make adjustments to pressure every time the car is used
- so the practicality of the issue lies somewhere between considering
the 'door/manual' pressure as a good minimum cold pressure - probably
yielding a comfortable ride and decent, fairly even wear with good
handling for average driving, and the sidewall pressure being considered
the max cold pressure (though the engineers probably have a huge
safety margin built in)useful for a heavily loaded vehicle driving at
high speeds (this includes track day as well as moving day). There are a
lot of folks with plenty of experience using slightly (5-10%) higher
pressures than the recommended number from the manual and they
experience no significant wear problems. Perhaps a silighly harsher ride
sensation. That is my experience anyway. Even on my one track day, I was
under the max pressure on the sidewall.

It's better to UNDERSTAND what tires and the stuff related to them are
all about rather than blindly follow a static number for something as
dynamic as automobile tires. Considering what they have to do and the
environment/punishment they endure - they are amazing objects really.

(where does all that worn off tire rubber from millions of cars go? hah!)

Carl

 

[ric_man]

(where does all that worn off tire rubber from millions of cars go? hah!)

Doing "number 11s" on the streets around where I live...



....Ric

 

[Monique Y. Mudama]

It was also mentioned that it's far easier to get a blowout at lower
pressures than at higher pressures, as tires will deform much easier
and therefore create friction at lower pressures (don't ask the
physics on it... I didn't pay much attention to the tire bit about
the course - which was probably a mistake since on reflection,
they're the most important part of the car).

You can test it out for yourself by riding a mountain bike on gnarly
trails with underinflated tires. The resulting phenomenon is called a
"snake bite", as the matching punctures on both sides of the tube (where
the rim made contact because there wasn't enough pressure in the tube to
prevent it) resemble, well, a snake bite.

Granted, that's a fairly extreme example, and probably not exactly
what your teachers had in mind. I suspect that car tires (which of
course are tubeless) are designed to have maximum structural integrity
with the shape they have when properly inflated, and when they're
underinflated that shape is compromised.

 

[Clamstrippe Fecadunker]

I see no reason to consider any single pressure ideal for the majority
of drivers due simply to the fact that vehicle use can be so
dramatically different from day to day, week to week. Of course it is
unreasonable to make adjustments to pressure every time the car is
used - so the practicality of the issue lies somewhere between
considering the 'door/manual' pressure as a good minimum cold pressure
- probably yielding a comfortable ride and decent, fairly even wear
with good handling for average driving, and the sidewall pressure being
considered the max cold pressure (though the engineers probably have
a huge safety margin built in)useful for a heavily loaded vehicle
driving at high speeds (this includes track day as well as moving day).
There are a lot of folks with plenty of experience using slightly
(5-10%) higher pressures than the recommended number from the manual
and they experience no significant wear problems. Perhaps a silighly
harsher ride sensation. That is my experience anyway. Even on my one
track day, I was under the max pressure on the sidewall.

It's better to UNDERSTAND what tires and the stuff related to them are
all about rather than blindly follow a static number for something as
dynamic as automobile tires. Considering what they have to do and the
environment/punishment they endure - they are amazing objects really.

(where does all that worn off tire rubber from millions of cars go? hah!)

Carl

tires are amazing indeed.

but they are much much more likely to fail due to
underinflation than overinflation. the higher the
pressure, the smaller the contact patch and also
the less flexure the sidewall must endure per
rotation. the latter is what causes failure due to
underinflation, the sidewalls overheat and rupture,
usually catastrophically.

the only downside I can
imagine of running 10 or 20 percent higher than
(or any increase so long as it does not exceed
the tire's maximum marking)
the vehicle mfgr. recommendation would be
accelerated wear in the center of the tread,
and obviously a slight decrease in absolute grip
due to the decrease in contact patch area.

often the vehicle mfgr. will recommend a pressure
that is lower than that which provides maximum
grip, sacrificing this for improved ride. in hard
cornering, the lower portion of the tire is bent inward
dynamically as it rotates. this too causes heat buildup.
if the pressure is below optimal (and assuming
the suspension is doing a reasonable job of
maintaining proper camber) the tire will bend so
much that the "good" part of the tread is no longer
in contact with the road. in the extreme the sidewall
will begin to make contact. this is obviously not
ideal or even safe operation.

I would not recommend running more than the
maximum value molded into the tire itself.
the tire companies know what they are doing.
I use their maximum as a starting point and adjust
downward.

YMMV

 

[ric_man]

but they are much much more likely to fail due to
underinflation than overinflation. the higher the pressure, the smaller
the contact patch and also
the less flexure the sidewall must endure per
rotation. the latter is what causes failure due to
underinflation, the sidewalls overheat and rupture,
usually catastrophically.
the only downside I can
imagine of running 10 or 20 percent higher than
(or any increase so long as it does not exceed
the tire's maximum marking)
the vehicle mfgr. recommendation would be accelerated wear in the center
of the tread,
and obviously a slight decrease in absolute grip
due to the decrease in contact patch area.

often the vehicle mfgr. will recommend a pressure
that is lower than that which provides maximum
grip, sacrificing this for improved ride. in hard
cornering, the lower portion of the tire is bent inward
dynamically as it rotates. this too causes heat buildup.
if the pressure is below optimal (and assuming the suspension is doing a
reasonable job of maintaining proper camber) the tire will bend so
much that the "good" part of the tread is no longer
in contact with the road. in the extreme the sidewall
will begin to make contact. this is obviously not
ideal or even safe operation.

That about sums up things that were said during the defensive driving
course...

....Ric