Air pressure question

[Secret Chimp]

The door jamb panel on my car recommends that both the front and rear tires be inflated to 32 psi. My Outback back in Seattle had a higher pressure for the fronts, and I'm wondering if I should do the same for my car. The sidewalls squish out noticeably more, and I'm wondering if I'd be doing myself a favor in terms of tire wear and steering response I inflated them to 33 or 34 psi instead.

[S204STi]

I think so, yes.  Leave the rears at 32 but bump the fronts up to 34.  It will help reduce wear on the shoulders of your front tires, though some will occur naturally due to scrub during turns, but it will help at least.  Also I think autoXers tend to run higher front pressures for better handling characteristics, though that part may be more subjective in the real world.  Either way that's what I do with cars that come through my bay unless it's a 1-ton truck that specifies 55psi in the front and 80psi in the rear...but that's another story.

[Pancor]

Unless you're using OEM tires, a little (and only a little!) more pressure in the front is allright.  I'd consider this more an effort to preserve  responsive handling than tire longevity, however.   

[S204STi]

Unless you're using OEM tires, a little (and only a little!) more pressure in the front is allright.? I'd consider this more an effort to preserve? responsive handling than tire longevity, however.? ?

Que?

[Pancor]

Que?

I'm going to assume you meant "pourquoi?", and my reasoning is that the manufacturer's recommendations should really only apply to the tires that came from the factory.  Most people don't replace their OEM tires with ones carrying the same load rating, so why use the same air pressure?  Some manufacturers specify different pressures front/rear, and some don't....?

[93JC]

Why are you looking at the doorjamb anyway?

Look on the tire sidewalls.

[Pancor]

The tire sidewall usually only carries the "max" pressure rating, which you should only use if you intend to load all four tires up to their maximum load rating, which would be absurd....

[S204STi]

I'm going to assume you meant "pourquoi?", and my reasoning is that the manufacturer's recommendations should really only apply to the tires that came from the factory.? Most people don't replace their OEM tires with ones carrying the same load rating, so why use the same air pressure?? Some manufacturers specify different pressures front/rear, and some don't....?

Ah, I follow you now.  True, load rating plays a major part.  However, when I worked for Nissan every Altima was rated for 29 psi yet would chop its tires to sh!t unless you bumped them up to 32psi or more in the front, and that was with brand-new cars.

In Car and Driver's abortion of a tuner mag ("Speed" was it?) they actually had a very relevant article on how to get the perfect tire pressure for your car, in which you rub some sort of visible element such as chalk on the shoulders of your tires and drive the car around.  See if it was scubbed off beyond the edge of the tread, in which case more pressure is needed, etc.

[Pancor]

Ah, I follow you now.  True, load rating plays a major part.  However, when I worked for Nissan every Altima was rated for 29 psi yet would chop its tires to sh!t unless you bumped them up to 32psi or more in the front, and that was with brand-new cars.

In Car and Driver's abortion of a tuner mag ("Speed" was it?) they actually had a very relevant article on how to get the perfect tire pressure for your car, in which you rub some sort of visible element such as chalk on the shoulders of your tires and drive the car around.  See if it was scubbed off beyond the edge of the tread, in which case more pressure is needed, etc.

That crayon-scrub method would work for autocross or track use, but if you used that for normal granny driving, you'd end up having a pretty high pressure!  That Altima situation is interesting, however!

[S204STi]

The tire sidewall usually only carries the "max" pressure rating, which you should only use if you intend to load all four tires up to their maximum load rating, which would be absurd....

I agree, that is a bad idea.  All that is going to happen is your tires will wear out in the center of the treads quicker than the rest, and you will have miniscule contact patches.  Yay.

[AutobahnSHO]

Why are you looking at the doorjamb anyway?

Look on the tire sidewalls.

that's a max rating, not what you should actually use.

[93JC]

Really? I thought they had recommended pressure on there too.


Meh. I just inflate it to 30ish psi, check for wear, and don't worry about it.

[etypeJohn]

Really? I thought they had recommended pressure on there too.


Meh. I just inflate it to 30ish psi, check for wear, and don't worry about it.

Well, they don't know what you are going to put those tires on.

My theory is when in doubt follow the automobile manufacturer's rcommendations.  Of course that only applies if you are running OEM sized tires. 

[JWC]

Well, they don't know what you are going to put those tires on.

My theory is when in doubt follow the automobile manufacturer's rcommendations.  Of course that only applies if you are running OEM sized tires. 

Key words here...OEM sized tires.  The recommendation on the door jamb is based on the vehicle's load rating with that particular sized tire.  It is a compromise for handling, wear, and ride comfort.  The more air, the stiffer the ride.  Unless a customer specifies a preference, we bump tire pressures by 3lbs in our shop. 

[The Pirate]

Yeah, my car specs 29psi up front, and 28psi in the rear.  I run them at 33psi and 32 psi, respectively.