Pressure in new tires?

[Uzi]

I just bought a new set of Michelin Sport Pilot A/S 205/55 16" for my
2002 WRX. The decal on the door says to inflate tires to 32/29
front/back. The guy at the tire store said to leave them at 35/35
because he was worried this specific tire would wear unevenly and that
seeing it was getting colder here the inflation would drop in any case
(as if I couldn't add air and remove it as necessary during my regular
bi-weekly tire checks).

So, what should I set the pressure in my tires to? Should I listen to
the guy at the tire store, or follow the guidlines on the sticker?

Thanks.

 

[mulder]

I just bought a new set of Michelin Sport Pilot A/S 205/55 16" for my
2002 WRX. The decal on the door says to inflate tires to 32/29
front/back. The guy at the tire store said to leave them at 35/35
because he was worried this specific tire would wear unevenly and that
seeing it was getting colder here the inflation would drop in any case
(as if I couldn't add air and remove it as necessary during my regular
bi-weekly tire checks).

So, what should I set the pressure in my tires to? Should I listen to
the guy at the tire store, or follow the guidlines on the sticker?

Thanks.

You can adjust the pressures up and down to suit your preferences for
ride vs. handling, but it's important to maintain that 3-psi
differential from front to rear. Too much in the rears relative to the
fronts can promote excessive oversteer in the WRX.
Perhaps try 35/32 F/R and make adjustments from there.

 

[Jim Stewart]

I just bought a new set of Michelin Sport Pilot A/S 205/55 16" for my
2002 WRX. The decal on the door says to inflate tires to 32/29
front/back. The guy at the tire store said to leave them at 35/35
because he was worried this specific tire would wear unevenly and that
seeing it was getting colder here the inflation would drop in any case
(as if I couldn't add air and remove it as necessary during my regular
bi-weekly tire checks).

So, what should I set the pressure in my tires to? Should I listen to
the guy at the tire store, or follow the guidlines on the sticker?

If it were me, I'd leave them at 32/29 and
check the tire wear at the next rotation
interval. Underpressure tires will show
more wear towards the sidewalls, Overpressure
shows more center wear. You won't see too
much difference over the rotation interval
and you can adjust the pressure then.

 

[xtranet]

I just bought a new set of Michelin Sport Pilot A/S 205/55 16" for my
2002 WRX. The decal on the door says to inflate tires to 32/29
front/back. The guy at the tire store said to leave them at 35/35
because he was worried this specific tire would wear unevenly and that
seeing it was getting colder here the inflation would drop in any case
(as if I couldn't add air and remove it as necessary during my regular
bi-weekly tire checks).

So, what should I set the pressure in my tires to? Should I listen to
the guy at the tire store, or follow the guidlines on the sticker?

I would go with what is written on the tire's sidewall. Some tires
nowadays
have a max psi of 44psi.

My take...

Max PSI of 44: 38-40 psi
Max PSI of 35: 30-32 psi

 

[l.lichtman]

I have always understood that increasing tire pressure decreases the
slip angle (improves the grip.) If that is true, then increasing
pressure in the rears would make the car UNDERSTEER. Only thing is, I
don't know whether All Wheel Drive makes a difference.

 

[Here and There]

I have always understood that increasing tire pressure decreases the
slip angle (improves the grip.) If that is true, then increasing
pressure in the rears would make the car UNDERSTEER. Only thing is, I
don't know whether All Wheel Drive makes a difference.

Increasing tire pressure makes the contact patch smaller which
reduces available grip but makes the tire firmer and more responsive.
Although going in either direction is not linear and depends on
rubber compounds and tire construction.

Generally increasing rear pressure will *increase* oversteer.
However, if the tire is sloppy at lower pressures and prone
to snap oversteer as the tire loses its shape. Increasing
pressure will make the loss of grip more progressive and
more predictable leading you to believe you are getting
more grip.

Recommended pressures on the door sticker are for
comfort rather than handling. As someone has already
said, they should be used as a low starting point.
Work up in pressure (cold) until the ride becomes
stiffer. That point will vary with tire construction
and age. I have found that point to vary with
different brands of tires in the same size on the
same car, based on my own preferences.
Keep the same ratio of pressures as on the sticker unless
you are on the track experimenting with the handling
and looking for optimum balance rather than a safe
dose of understeer as is typical for recommended pressures.

The number on the side of a tire is a max (cold) for
that tire, and has nothing to do with any particular
application of the tire or the car and rim on which
it is mounted. Don't use that number for anything other
than not inflating it to a higher pressure than that number.

My regular daily driving pressure is usually 5 to 10 psi
above the sticker/manual recommended pressure.
Autocross pressures up to 15 psi above recommended.

 

[Rick Courtright]

I just bought a new set of Michelin Sport Pilot A/S 205/55 16" for my
2002 WRX. The decal on the door says to inflate tires to 32/29
front/back. The guy at the tire store said to leave them at 35/35

Hi,

My experience (limited, of course!) with Michelins is they seem to
respond better to slightly higher pressures than some other brands I've
used (mirroring advice from a tire dealer friend to always run Michelins
at 2-5 psi higher than the door sticker.) OTOH, they've often seemed
"slippier" across the board of pressures I used, where some brands were
"sticky" at lower pressures and lost a little as they were inflated
higher, others became more "sticky" at higher pressures. As a general
rule, I'll run about 2 psi over the door sticker's "everyday"
recommendation, and usually maintain whatever frt/rr differential is
recommended. Only time and driving will tell, but if you're checking
pressure bi-weekly, you should be able to give yourself enough time to
get used to one "feel" before trying the next.

Good luck!

Rick

 

[Uzi]

As a general
rule, I'll run about 2 psi over the door sticker's "everyday"
recommendation, and usually maintain whatever frt/rr differential is
recommended.

Good luck!

Rick

I've been running them at 3psi higher keeping the ratios between front
and rear. I kept the ratios because I had read somewhere that handling
could be affected, but I couldn't remember if it was oversteer, or
understeer. Thanks to 'Hear and There' for clearing that up. It seems
to work fine at 3psi over the sticker. I'll try varying it higher. I
did notice a lighter colour band of dirt in the center of the rear
tires as if that part of the tire wasn't making complete contact, or
as much as the the outer portions of the tire. There wasn't a similar
band on the fronts which are at a higher pressure, though. I just
noticed it as I parked the car for the day, so I'll see if it is
something that varies with tire pressure.

Great tire, though. I never had any complaints with the OEM RE92's,
but the difference these tires make is tremendous. So much quieter and
steering response is instantaneous, but not twitchy. The RE92s seemed
wobbly and vague in comparison and didn't inspire the confidence the
Michelins do. The car feels like a different vehicle with the
Michelins on.

The main reason I asked the question is the tire guy initially ordered
the wrong tires. I asked for the pilot's and more than once asked him
to confirmation yet he managed to order and install on the car
Michelin Energy MXV4's. Don't ask me why he thought I'd want grandpa
touring tires on my WRX, nor why he was surprised I wasn't happy with
'his' selection of tires for my car. At that point I wasn't going to
take his word for what the tire pressure should be.

Thanks, guys.

 

[Edward Hayes]

My Forester S is run with 2-3 lbs higher than door recommendations and
is a good compromise. I too maintain the recommended pressure
difference. One thing not mentioned and I think is very safety related
is "how does the vehicle act at the tire break- away-point"
Generally, the higher the pressure to sharper the break away, meaning
there is less and less warning before the tire slides sideways in a
sharp turn. Many less experienced drivers are VERY surprised when this
happens too quick and I think that is one of the reasons why Subaru
picks "their pressure" and not for the soft ride. Just my thoughts on
the subject. ed

 

[James Meyer]

I just bought a new set of Michelin Sport Pilot A/S 205/55 16" for my
2002 WRX. The decal on the door says to inflate tires to 32/29
front/back. The guy at the tire store said to leave them at 35/35
because he was worried this specific tire would wear unevenly and that
seeing it was getting colder here the inflation would drop in any case
(as if I couldn't add air and remove it as necessary during my regular
bi-weekly tire checks).

So, what should I set the pressure in my tires to? Should I listen to
the guy at the tire store, or follow the guidlines on the sticker?

Thanks.

The WRX is an all-wheel-drive vehicle. It's *very* important to
maintain the same tire circumference on all four wheels. For example, if you
have half the tread left on all your tires and one is damaged beyond repair, you
should replace *all* the tires at once.

There is a slight front-to-rear weight difference on your car with more
weight on the front. The "rolling radius" of a tire is affected by the weight
on that axle. That's why the slight (32/29 is slight) bias front to rear is
recommended. It's to make the tire circumference the same front to rear.

The decal is there to tell you important stuff. Not just to make the
door jamb interesting reading.

Jim

 

[Here and There]

The WRX is an all-wheel-drive vehicle. It's *very* important to
maintain the same tire circumference on all four wheels. For example,
if you have half the tread left on all your tires and one is damaged
beyond repair, you should replace *all* the tires at once.

The tire companies recommend ensuring less than 1.5 inches of circumference
for AWD/4WD vehicles, while in the U.S. people report here that Subaru
insists on 1/4 inch. Do the math.

There is a slight front-to-rear weight difference on your car
with more
weight on the front. The "rolling radius" of a tire is affected by
the weight on that axle. That's why the slight (32/29 is slight) bias
front to rear is recommended. It's to make the tire circumference the
same front to rear.

Tire companies quote Revs per Mile because with radial tires the revs per
mile is virtually constant. The distance travelled by the tire under
load is dependent on the belt length. The variable is load which
causes tread squirm, which has a very small variance. (less than 1%)

The sticker recommendations are to create a similar size contact patch
from front to read based on weight ratio. While the revs per mile is
fairly constant, the size of the contact patch is directly related
to the weight on the wheel and the pressure in the tire.

The decal is there to tell you important stuff. Not just to make
the
door jamb interesting reading.

Jim

Information is more valuable when you know how the numbers
are actually derived and why they are important.

 

[bigjim]

Dont worry about the sticker. I find 32psi front and rear is best on my
04 OBW. Good handling and mileage. 35 psi feels different in the rain.

 

[tom klein]

i am NOT an expert, so i'll stay away from the technical stuff.

my preference is to overinflate 10% over the door sticker, purely fora
little extra fuel economy. that works out to about 3 psi, which should
be well within safe limits.

but a dramatically overinflated tire (like the way they ship new cars)
can be VERY dangerous - on my first new car ('86 accord 2-door) i
didn't notice how overinflated the tires were, until the first stretch
of wet highway, when it started hydroplaning at about 70 km/h! it
seems the dealer had missed a thing or two in the pdi.


........ tom klein

 

[R. Gerard]

I have always understood that increasing tire pressure decreases the
slip angle (improves the grip.) If that is true, then increasing
pressure in the rears would make the car UNDERSTEER. Only thing is, I
don't know whether All Wheel Drive makes a difference.

This is good question! Does AWD make a difference? Anyone know?

When I took my BMW 328i to a weekend Safety Handling Course at a
local track, the lecture portion covered tires. The response to one
question was almost uniformly wrong. The question was: In snow, repeat
snow, are you better off to have your tires a bit over-inflated or
under-inflated?

Almost everyone answered under-inflated. Wrong! The correct answer
is a bit over-inflated.

Wonder if that applies to AWD. BMWs are or course rear-wheel drive,
although they are available, in some models, as AWD.

Bob