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Discussion Starter #1
OK, so my driver's side plate says 36 psi front (!) and 30 psi rear.

Is this an AWD thing? I'm used to pressure in the 28-34 range, and higher in the rears for RWD sports cars.

Has anyone monkeyed with the pressure at all? If yes, what handling effects did you notice?

Any insights as to the higher pressure fronts?

Thanks,
Chris
 

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STi speedo reading high, actual speed low...

yeah, even my previous wrx was a 32/29 thing...

just follow what is says on the doors.

btw, i have 2 diff gauges. and they differ by 5 psi!!!! so stick with one and dont worry about it. just maintain it.
 

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I'd never take the dealer's word on something like that. The manufacturer printed what they did for a reason and that is what they will stick to.

Remember the Ford Explorer/Firestone crap? Yup, people took em to court over the accuracy of those door numbers. Most times....they are exactly what you should be using.
 

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Higher Tire Pressures

Higher tire pressures will reduce the contact patch of the tire. Thinking this through, it means less grip if the tire is over-inflated, best grip if it's just right, and good very low speed grip if underinflated (think offroad rock-crawling). Higher pressures will also reduce punctures to an extent. The air inside the tire will push back, rather than give into, outside pressures, like from rocks, gravel, etc.

One other note, higher tire pressure will reduce rolling-resistance. The contact patch is smaller, therefore there is less friction between the tire and the ground. This will allow the engine to move the car a little bit easier at high speed. Just think of riding a bike with flat tires. Hard to pedal, huh?

Speaking of which, everyone catch Lance Armstrong on July 5th on OLN. He's our Subaru spokesman, after all. I think his tires are about 120 psi. No wonder he's so fast. In excess of 60 mph downhill! Good choice by Subaru!

Out,
TerraJumper :)
 

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Never heard of that before. My car is FWD and is obviously front heavy...but all my tire pressures are the same.

And I'm sure it isn't for the reasons Terrajumper added. Obviously they aren't shooting for less grip...and if they were concerned about gas mileage, they wouldn't have made the STi. ;)

Anyone......the deeper meaning? What's Subaru thinking here?
 

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My only guess is since the front is heavier. The only problem with this reasoning though as Rob pointed out is most cars don't do this. The other problem is it would mean the car is very unbalanced.

For instance on my truck I run 33 psi up front and 27 in the rear. This isn't stock mind you. I do this because I run 33x10.50 15's and the contact patches will not be flat if I run more air. My point is that my truck is extremely front heavy. In ice it gets real interesting because even in 4 wheel drive the back wants to pass the front.

So in summation my post brings no new insight to this post, and can be seen as a weak attempt to justify talking about myself :p
 

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Discussion Starter #11
Hmmmm..."unbalanced". This reply probably belongs in the handling forum.

At the risk of starting a flame war, that is kinda my fear. Now, I am an AWD newb, and I love my STi, but...I have noticed my 10 year old RWD MR2 Turbo (mods) actually feels better (yeah, I know, give my STi to you and keep driving the MR2 :wink: ).

Seems like whereever the diff is set, the handling is a little, uh, "squirrely", and with a lot of understeer (until you get on it coming out of the turn - but you don't always have that luxury on the street, traffic, etc). STi steering could use more "feedback"/road feel too, IMHO. Hence the question about tire pressure. On the bright side, it totally freakin' smokes my MR2, even with its HP mods :wink:

Now, I'm taking it in to get the radio tomorrow, and I'll have them check my alignment - that could be an issue.

Chris (donning flame suit)
 

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You probably shouldn't be worrying about the diff at all. Set it to auto and leave it. The algorithm is smarter than all of us and can change things more efficiently/more quickly.

The front diff seems to be a feature that even AWD experts are having to learn to drive properly. While most of us might want to get off of the gas in a turn, it seems the fastest way to drive this car around a corner is to at least stay on the gas at the sam pressure.

If you really have the handling problems you appear to be having, take it in and have it checked out. I haven't driven the car myself, but I do know that the car felt very stable and not in a least bit squirrelly when pushed.
 

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Discussion Starter #13
Thanks, CloNeGTS, for the info. I really should have even further qualified my post - it really does stick like a SOB, and especially in the wet - I just couldn't believe that :)

I think what's working me the most is the "feel" issue - I just can't get nearly enough of a sense of what the car is actually doing through the steering wheel. The 350Z had this problem (test drove it) *real* bad - hence, no Z in my driveway :wink: The Evo had better feel, but you see which car I bought - despite a nasty dealer experience. I just laugh my ass off every time I drive it - I guess that'll fade :wink:

It *does* seem like you can just mash it, and let the DCCD sort it out - and you can even feel it doing it - hmmm...maybe that's what I mislabeled "squirrely". I have a problem with "faith" though. Sometimes I find I'm fighting the steering a bit, almost like a torque-steer thing - but I'm not the best driver on the planet, so...I guess I have a lot to learn - but hey that's gonna be a blast. May monkey with the pressure a bit (more rear, less front) - I've also seen the swaybar recommendations since I posted this. Wife won't be letting me do that for awhile :cry:

Thanks again,
Chris
 

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Chin Spoiler Detachment

cby1, you can do things with the STi that would have your Mr. Two spinning like a top! (literally)

I don't want to track my STi just yet (only 1350 miles) where one can truly test its capabilities, but my past experience with Subies on the track has been awesome. I did power around a corner today from a stop, and it was pretty fun! Highly recommended. :)

I think the other part of what you're feeling is that the STi is fatter than Oprah at a BBQ giveaway. Same problem with the 350Z. Both cars serve as platforms for stupid SUVs, and we pay the penalty in pork.
 

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yeah, I am very anxious to get a chance to 'test' out what people have been saying. Subaru know-alls like Glenn Wallace and a few others who have been around STis from Japan for years have been saying all along that the magazines and everyone else doesn't know how to drive this car yet. Glenn, for example, still contends that you just have to know how to work the car...and then it will take the EVO in tests with no problem.

I sure don't have a feel for it yet, but from the sound of things....you should pretty much have your corner speed determined at entry, and then just keep your foot in it. Now this isn't to say that you won't end up in the dirt if you are maintaining too high of a speed, but if you are at the right speed, you shouldn't be just coasting. Acceleration isn't necessary, but keep the torque moving through that diff so that it doesn't transfer that power in on ya.

I can't wait to learn this car......come on phone....RING!
 
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