Ok I am posting this in the suspension board as well as the wheel and tire section because it could be one or the other. Im not sure. OK I have a 95z28 and over the weekend I put on new rims with new tires, 18 front 20 rear, and a new adj panhard rod. When I dorve the car to work today it felt like it was shifting around like I was driving on a wet road. Could this be because of the new panhard rod? New tires? Or something else? Also I did not have an alignment after getting the new tires. Do they need to break in first? The rear tires have 295/25/20s on them, the front has 285/35/18. Any help is greatly appreciated.

 

could just be groove wandering. thats a lot of rubber of front

 

Common problem with wide tires. The edges of the tires ride up and down the grooves in the asphalt from the 18-wheeler tires. Feels like the car is darting side-to-side continuously. Incorrect tire pressure may make it feel worse, so you might want to experiment a bit with tire pressures.

Rubber-band thin tires make sense on a car with a sophisticated fully independant suspension. The suspension can compensate for road irregularities. But put those same thin sidewall tires on a solid rear axle vehicle like an F-Body, and they probably hurt handling a lot more than they help. That will only worsen the "wandering" in grooves in the pavement.

 

As the others have stated, what you are experiencing is the most frequent complaint regarding wide tires, particularly on cars with a (relatively) primitive suspension like the F-bodies.

I've found also that the particular tires you have on the car also are a contributing factor, with some tires causing this phenomenon more than others. For example, the OEM Goodyear Eagle VR50s on my old '87 IROC-Z were better than the replacement Goodyear GSCs (which were horrible for groove wandering). The BFG Comp TAs were an improvement. The OEM Goodyear tires on my '00 SS were ok, but the OEM Firehawk tires on my '99 TA Firehawk were horrible. Now that I have a new set of Goodyear F1 GS-D3 on the car (for summer) and a set of BFG gForce KDWS (winter) things are better.

My fiance's Acura RSX is a much easier car to drive, with its narrower OEM tires, and independent suspension.

Check your tire pressure, and try rotating your tires (if they are the same size, front & back, obviously). You might have a tire that is out of round.

And get an alignment check, too.