Hi Guys,

I am wondering if there are any memebers here that are running our GXP Rims (or other) using the 18X8 Rims all around with the 255/45/18s.

I have spoken to one member and he advises that it works well for him and that he is happy..

Any other GXP'ers ?

Thanks..
Frank

no, but I would love to do that....i was reading that the reason that they are stagered like that is for oversteer and torque pull or something. I dont really remember any more.....

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2006 GP GXP : K&N Forced air Intake, Dual Magnaflow Exhaust with Silverline Dual Resonated Tips, 20-30% Tint, Double Pin stripe down side. Diablo Audio Hellfire 1000.1, JL Audio Setup w/ 300/4, One 13W7, ZR650, VR690, Cleensweep setup, 2f SPL Cap.

It was to help make it the best handling Front wheel drive. If you dont care about the car handling as good at the limit there is nothing else stoping you. The basics is this. A FWD car with equal size tires pushes when you try to hussel through a corner. The rear tires never let go or slide. The reason is with an equal contact patch the rear tires never have a chance to let go. The larger front tire helps with more traction with the power of these cars. Then with narrower tires on the rear of GXP they alow to rear to act more like a RWD car actually letting the rear slide a bit. Which help eliminate some but NOT all of the understeer/Push of a GXP.Very simple thing that really does work. i have tried it lol. They tested on a race track and with the setup on our cars it was able to make a lap like 3 seconds quicker. Plus if you drag race u already have a lower rolling resistace tire in the rear since it is narrower.

Long read, but it explains things....

The obvious part of the formula is obviously far from new: Cram a big ol' V-8 in there,
make the car go faster. Detroit has been doing this since the '60s. But what may not be so
obvious is that there's a big asterisk to the formula when you start applying it to a frontwheel-
drive car. The footnote reads something like this: "Put enough power through a
front-drive system, and the driver will find himself turning right or left when he was
planning on straight ahead."
It's called torque steer, and it's the major limiting factor in front-drive performance cars.
Despite various engineering advances, the problem persists in cars such as Acura's
otherwise superb TL, which sends 270 horsepower through a six-speed manual
transmission to the front wheels via a helical limited-slip differential. But in the Grand
Prix GXP, with more horsepower (303 at 5600 rpm) and a lot more torque (323 poundfeet
at 4400 rpm), torque steer is not a serious issue. There are hints—a little tugging
when the driver cracks the throttle at low speed—but no real wrestling.
How'd they do that? By adopting a measure no one else has ever put into production.
More in a minute. But first, another front-engine, front-drive problem, one that's even
more chronic than torque steer. With a design that puts all the heavy powertrain hardware
up front, front-drive cars invariably have a pronounced forward weight bias, 64/36
percent in this case. As a consequence, the front wheels carry more than their fair share of
the car's mass, diluting the ability of the tires to transmit steering inputs. Worse, the front
tires are also required to transmit power to the pavement, and all things being equal, the
poor things just can't handle their multiple assignments as well as the front tires of reardrive
cars. The result is understeer. The faster the driver herds the car into a turn, the
more it wants to go straight.
Pontiac's solution to these two inherent front-drive directional control problems—
understeer and torque steer—is unique. Instead of four tires of equal size, the GXP has a
lot more rubber up front than at the rear:
Bridgestone Potenza RE050As, 255/45-18 front,
225/50-18 rear.
"We wanted a car to run with BMWs," says
program engineering manager Phil Minch. "But
we were limited by the W-car architecture, in
other words, by front-wheel drive.
"The rear end never lets go when you have the same size tires all around. So we put our
computer guys on it, and they came back with a recommendation for a smaller rear tire,
to give the car better balance."
This is a radical departure from conventional wisdom, and the idea proved out in initial
testing. But there was a nasty side effect: Increasing the contact patch at the front
amplified torque steer. However, after experimenting with a number of different tires
from a variety of manufacturers, Minch and company decided the problem lay in the tire's
construction-the way the plies were wrapped-and not the footprint. With sufficient
application of power, the tire sidewalls distort, thus affecting directional stability.
Bridgestone, the supplier of choice, was initially reluctant to accept this theory, but when
the GXP team achieved improved results using an off-the-shelf tire from another maker,
the Bridgestone people got to work and developed a tire that delivered the desired
performance.


From Car and Driver article about the GXP.

yup that posting above was the one I remember reading....

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2006 GP GXP : K&N Forced air Intake, Dual Magnaflow Exhaust with Silverline Dual Resonated Tips, 20-30% Tint, Double Pin stripe down side. Diablo Audio Hellfire 1000.1, JL Audio Setup w/ 300/4, One 13W7, ZR650, VR690, Cleensweep setup, 2f SPL Cap.

Thanks Guys..

Your input is much appreciated.

Frank

That IS a good read. I have to imagine that would be good advise for ANY front drive high power vehicle.

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One Big Ass Mistake America

I have said it before, our GXP, bought from a dealership GM Certified Used had the wide (front) rims and tires all around. I don't know why, but this dealership had about 6 of these come through in like a 2 month period. I don't even think they ever had more than 1 new one, but anyway............somehow somewhere along the way someone put the wide ones on the back.

I caught it when I started reading about the car after purchase (bought it on a whim) and checked the size. No problem...looked good, and couldn't tell a problem driving it. THEN we went on a trip. Loaded the trunk with luggage and in-laws hopped in the back seat.........then we started hearing the rub.

On turns.....hard acceleration.........bumps.....the sound of rubbing tires. After a couple hundered miles it was obvious on the outer sidewall where the tire was rubbing on the fender lip.

So.....no load in the rear all is good. Two adults and luggage=problems.

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Missing the Monte......Rocking the GXP!!!

Take it back make them eat there CERTIFIED BS. lol Tell them its not and ask to make it right and to fix it

My car was GM Certified too. When i got it home i was showing the tires to a friend and noticed that the diver front rim had a 225/50/18 tire mounted instead of the normal 255/45/18 .The passenger side was correct. I took it back and didnt leave without them mounting 2 brand new tires on the front of the car. Dirk, do you have the 18x8 or the 18x7 rim min the back with the 255's mounted? I'd take it right back man.