Recommended tire pressure: what psi do you use? - Subaru Forester Owners Forum
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post #1 of 30 (permalink) Old 10-15-2008, 03:10 PM Thread Starter
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Recommended tire pressure: what psi do you use?

I've got an '08 Forester with 16" factory Yokohama tires/wheels. The door placard says 29 Front and 28 rear, with incremental adjustments based on load. Living in Minnesota with so many temp fluctuations, that's impossible to maintain, so in the colder months I've been keeping all 4 at 32/33 psi cold pressure to allow for extreme temp changes. Now, my dealer techs say they like them all at 36 psi cold pressure in the winter months, and on a sidenote they say they've discovered they get more even tread wear than with the factory recommendations. If you go from tech to tech, you'll get many opinions, and some say that 36 psi is way too high. Today, I added air for the first time in months, because overnights have brought my cold pressure to around 31, and with gauge inaccuracies, and more cold nights to come, I thought I'd try their advice. I pumped all four up to 36 psi, but this was after driving, so the cold pressure is probably going to be around 33-34.
QUESTION:
I'm wondering what you all set yours at, and if a hot pressure of 36-37 psi could damage anything, like the suspension or anything else due to "tire hop."
I've only driven it one day that way, and most days my cold pressure has been around 32-34 throughout the whole summer. I thought it rode pretty well that way, but the slight increase today made every bump seem a little rougher out there. I'd appreciate your input,
Thanks...
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post #2 of 30 (permalink) Old 10-15-2008, 03:19 PM
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I believe I ran my stock Geo at 36 all around. It rides a little rougher, but it wore better and had less sidewall roll when cornering.

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post #3 of 30 (permalink) Old 10-15-2008, 03:30 PM
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We use bar here instead of psi. Normal for forester according to the marking at the door is around 1.8-2.0 when the car is not full of people or luggage.
I think the tires gets too little pressure then so I fill 2.5bar on all 4 tires. Works for me. The tires look better and it does not feel weird on the steering then.

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post #4 of 30 (permalink) Old 10-15-2008, 03:36 PM
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2-3 psi above specs, usually...

The Michelins on my 96 Outback rolled 67K because I was attentive to pressure. I changed them only because the sidewalls had begun to crack.

I usually inflate 2-3 psi above the numbers on the placard.

If you want to experiment with tire pressure, you'll want to inspect the wear patterns after you've run them a while at a certain pressure. Maybe you know about this? Assuming the wheel alignment is set properly, greater wear on the edges means overinflation, but greater wear in the center means underinflation.

If you don't like the ride with higher pressures, that's a good reason to back off a little. I don't think 36 psi will cause damage but may exacerbate rattles.

I remember something about using nitrogen gas in tires. Maybe someone else knows more?

Colder weather does reduce pressure, but 1 or 2 psi isn't much to worry with. Make sure the tires seal well at the rim bead. I had that problem with my Outback and the factory alloys.
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post #5 of 30 (permalink) Old 10-15-2008, 04:25 PM
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Quote:
Originally Posted by SageGForester View Post
Assuming the wheel alignment is set properly, greater wear on the edges means overinflation, but greater wear in the center means underinflation.
I thought it was the other way around?

HOW TO READ TIRE WEAR
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post #6 of 30 (permalink) Old 10-15-2008, 04:32 PM
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I ran 36 front and 32-34 rear on the geos. My current tires are 38/36 and my previous tires were 42/40. Find what you like, as long as the cold pressure is below the max specified on the sidewall.

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post #7 of 30 (permalink) Old 10-15-2008, 04:39 PM
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I run about 32 front and rear.

Be careful what you wish for.
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post #8 of 30 (permalink) Old 10-15-2008, 04:42 PM
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Quote:
Originally Posted by fx4me View Post
I thought it was the other way around?

HOW TO READ TIRE WEAR
It is.

Look at the side walls--over inflation is less dangerous than under inflation. Higher inflation will yield less rolling resistance but a rougher ride.

Tire pressures on the side walls are cold. When hot you can get 6psi or more of growth. Depends on the temperature delta and the construction of the tire (does it expand with the pressure increase in a linear manner?)
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post #9 of 30 (permalink) Old 10-15-2008, 04:45 PM
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Whoops

Quote:
Originally Posted by fx4me View Post
I thought it was the other way around?

HOW TO READ TIRE WEAR
It certainly is.

Worn edges, underinflation.

Worn center, overinflation.

Inability to think clearly may be the result of either.
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post #10 of 30 (permalink) Old 10-15-2008, 05:58 PM
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haha I know, I was just politely correcting him. :)
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post #11 of 30 (permalink) Old 10-15-2008, 06:06 PM
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It was extraordinarily polite

Quote:
Originally Posted by fx4me View Post
haha I know, I was just politely correcting him. :)
Compared to all that could have been said, which is not to promote any other ideas.

As I said, fuzzy thinking can come from either overinflation or underinflation or from too much television.
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post #12 of 30 (permalink) Old 10-15-2008, 08:03 PM Thread Starter
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Quote:
Originally Posted by quickshoe View Post
Higher inflation will yield less rolling resistance but a rougher ride.
Thanks for all your replies. In reference to higher pressure, is a rougher ride the only consequence? What I mean is, if the ride is rougher, isn't the abuse on the vehicle itself more aggressive? You hear much more rattling from the likes of the dash board and the cargo area, so couldn't other important components be experiencing unusual wear and tear?
Thanks again.
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post #13 of 30 (permalink) Old 10-15-2008, 08:19 PM
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32 to 34 here.


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post #14 of 30 (permalink) Old 10-15-2008, 08:37 PM
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31-32 here....had them up to 35-36 once and was to rough of a ride. At the recommended 28-29 was too squishy.

03 2.5x AT
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post #15 of 30 (permalink) Old 10-15-2008, 09:25 PM
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Quote:
Originally Posted by bjp forester View Post
Thanks for all your replies. In reference to higher pressure, is a rougher ride the only consequence? What I mean is, if the ride is rougher, isn't the abuse on the vehicle itself more aggressive? You hear much more rattling from the likes of the dash board and the cargo area, so couldn't other important components be experiencing unusual wear and tear?
Thanks again.
It will help improve cornering, and yes it'll be a little rougher ride. But I don't think my car got any more rattley than it was before...
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