so i had the top down today and was driving down I40 West. i noticed that once i got up to 70mph, everytime I passed a bigger car or a bigger car passed me, my S would sway back and forth a little bit...and it kinda gives you that twist in the pit of your stomach feeling and it *feels* like its the backend getting loose....im guessing because its so light it just sways...has anyone ever lost complete control of the backend from a similar situation?

MODERATOR EDIT: I merged the OP's two threads as they are directly related.
Cliff's notes: He has 225s on the front and is hoping that the wheels are in the right positions front to back. --CKit

 

check your tire pressure. I had a similar thing happen to me when A tire shop put on tires for me and had the rears at 48 psi....needless to say I was pissed.

 

mine is rock steady, as it should be. Like GT said check your pressures and are your tires worn out?

 

brand new tires...just got them 3 days ago...im gonna go check the pressure right now....how long does that "coating" last on new tires?

 

Could be alignment. If you've got less toe-in than appropriate on back (especially) it will feel unstable.

Steve

 

okay guys...i just found out/realized something really interesting....so before i got my back tires replaced they were potenza s03's that were 205s!! now i went to check my tire pressure and i just now realized that the front tires (which i didnt have replaced) are potenza re750s that are 225!!!!! so i think someone may have had the tires on the car rotated...so what should i go about doing now? is there a way to measure so i know which rims should be on the back and which ones shoudl be on the front?

 

is there a way to determine which rims are meant for the rear and which ones are meant for the front? (OEM of course) ...because prior to getting my rear tires replaced...the rears were potenza s03s 205/50 and the fronts are still potenza re750 225/50 ....so it looks like someone may have rotated the tires on my car before i bought it

 

without knowing your full tire sizes, the wider tires should go in the back.

and having different front/back tires isn't generally recommended, especially when they're from different performance classes like re750 vs s03

 

Wider tires on the back! The hub centers aren't the same.

 

Check the rim sizes too. The wider rims go on the back. The hubs aren't the same size and you won't get a secure fit with the wrong rim on the front.