Car goes sideways under hard acceleration

[Cpt_Impossible]

Some background:

2003 G35 Coupe 6MT with sport package 70,000 miles, no suspension mods.

Two days ago I had new tires put on (225/45/18F:245/45/18R) Hankook Ventus Evo V12. On the way home I noticed that the car just felt off. Not just taller and more squish at low speed turns like you would expect. The car felt sluggish when shifting the weight with the steering wheel. Like the wheels would turn, then the car would turn. Way more than the normal body roll (I've been driving the car for 2 years).

It drives straight in a straight line under normal conditions. No unusual vibrations at freeway speed. I noticed under hard rights at speed, I would get a chattering in the drive-train. I thought this may be the traction control confused by the new tires. Also under hard acceleration, the cars back end feels like it is all over the place. It doesn't seem to be losing traction and fishtailing like a normal rolling burnout, it feels like its floating around. It is VERY unnerving.

I am wondering if they bent something when they lifted the car to swap the tires out, of if anyone has any advice as far as what to look at. I don't see any suspension parts obviously broken in two or sway bars dangling, the lugnuts are tight. The wheels seem to be solidly connected.

I am taking it to Infiniti on Wednesday for the airbag recall, but in the mean time am paranoid about driving in it as it feels possessed.

[Cpt_Impossible]

Just jacked all four corners up one at a time. All the suspension components seem intact. No visibly torn bushings or arms. All four wheels don't have any play other than to spin. Only odd thing that I noticed was that the driver's side front tire was not quite true. It would catch the ground about 1/4 of its circumference when the tire was jacked just off the ground.

An alignment is done from the wheel not the tire right? So changing the tires shouldn't put the car noticeably out of spec unless there was something seriously wrong with the old tires (evenly worn).

[Cpt_Impossible]

I would think if those were my problems, they would be present during freeway driving. The floating feeling is only under hard acceleration. I drove at 50-60mph for 20 minutes and it felt fine just cruising. No shimmy or unusual tracking.

I'm thinking it could just be mostly the casting oils on the tire surface still. My appointment with Infiniti isn't till Wednesday, we will see if it starts to go away on it's own before then from some gentle driving (hopefully).

Any other thoughts?

[DrDan]

Check your rear tire inflation. Make sure they are at spec and equal side to side.

[Cpt_Impossible]

Yeah, I got the problem figured out the other day...

When I was handed the keys at the tire shop I was told by the tech "it's 35 all around like factory" and my invoice said that they had filled it to 35F 35 R in the notes. After more test driving it, Was able to get the traction control to consistently interfere and the back end was still floating. I could drive at about 20mph and toss the wheel back and forth and after a few seconds, the back end would slide as the weight would shift back and forth. Something was clearly not right. So when I got back to my garage I finally decided to check the tire pressure, just in case they were wrong...

Driver Front: 33.8
Passenger Front: 34
Driver Rear: 76.1
Passenger Rear: 83.5

I checked it again, and checked my other car just to make sure the digital gauge wasn't wrong. Took pictures of all readings just for proof before letting them down to 35 (a full minute per tire of air letting). After the store brushed me off and refused to refund what I had paid them for their negligence, I spoke with corporate VP who gave me a full refund and rebalanced the backs at another location.

[kmckis1029]

wow 76 and 83 psi is way off... how you almost double the psi? what if the tire exploded?

[audtatious]

Yeah, that's pretty high. Why wasn't your TPMS going off?

I have the same brand on my coupe (and Ventus S4's on the sedan) and have not had any real issues other than noticing they will spin a tad easier from a start when the blacktop road is moist (in comparison to the factory tires).

[Cpt_Impossible]

I don't have tpms in the 03 Coupe.

[audtatious]

Ah. I missed where it was a '03.