Best GXP A/S tires
On The Tree
Joined: Jan 2009
Posts: 177
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From: Brownsburg, IN
Good idea, the noise is like a droning sound that just annoys you a little at around 40ish if you don't have the radio on. It's worse when the weather is bad I've seen. If you have snow built up in the fender wells and the wheels rub that its HORRIBLE. Oh well, take it to the manual car wash and spray em down like i do to get all that crap off there.
Teching In
Joined: Oct 2008
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I have the Kuhmo Platinums on my GXP...They are pretty awesome. Much better than the stockers in the snow. Just got em a month ago, so no summer performance data, but from others experiences, I wont be dissapointed. Too many issues with the F1's on GXP's. The platinums are supposed to be a higher quality tire from Kuhmo, designed for higher end cars.
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From: Glen Ellyn, IL
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From: Glen Ellyn, IL
Maybe its just a GXP thing with the noise. All the reviews on tire rack don't say anything about significant noise. In fact the only place I have read about noise is here on ls1tech.com
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From: Glen Ellyn, IL
The nitto invo's do come in the size for the fronts, but not the rears. I think some people forget that the topic of this thread is about GXP tires: 255/45 18 up front, 225/50 18 in rear.
You have 225s in the rear? Montes have 235s all. Once I get some new rollers I'm stepping up to 255s all around.
Teching In
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From: Cleveland
- Using two cars with the same powertrain, one with 235s all-around, the other with 255s front/225s rear, the split-tire size car produced lap times 3-4 seconds per lap quicker, on average, at Grattan Raceway (where a good lap is in the 1 min, 30 second area)
- Projected tire life on the GXP is for all four tires to wear at about the same rate, versus most FWD cars, which normally use the fronts up sooner. This means the car is better balanced, getting "stick" from all four equally
- The GXP is styled so as not to call attention to the tire/wheel width difference
- Projected tire life on the GXP is for all four tires to wear at about the same rate, versus most FWD cars, which normally use the fronts up sooner. This means the car is better balanced, getting "stick" from all four equally
- The GXP is styled so as not to call attention to the tire/wheel width difference
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From: Glen Ellyn, IL
This is what Car & Driver had to say:
Pontiac Grand Prix GXP - Road Test
Pontiac rewrites the front-drive-performance rulebook.
BY TONY SWAN, PHOTOGRAPHY BY AARON KILEY
October 2005
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 front-wheel-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 pound-feet 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 rear-drive 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.
Pontiac rewrites the front-drive-performance rulebook.
BY TONY SWAN, PHOTOGRAPHY BY AARON KILEY
October 2005
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 front-wheel-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 pound-feet 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 rear-drive 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.
