maybe it is too soon to speak.
i decided to store my 18" SSRs for the winter and
mount the stocks with my Falken 512s. the stock setup
was giving me major concerns since i was getting the "shimmy"
at about 75-85 mph.....this was before i took them off for the 18".

i tried the stocks this morning and the shimmy/vibrations disappeared.
can anyone explain this?? i had the stocks in the garage for about
3-4 weeks. the only main difference i know is that i personally mounted
the stocks. the lugnuts were all hand tightened by me as well.

 

Sounds to me like you had a bent front rim that found it's way to the rear. You won't notice the vibration now because it's not feeding it through the drivetrain. That would be my guess based upon my own experiences. It could also be an out of balanced wheel problem

 

could be...but i made sure i placed the front ones in the front again.
the reason i know is due to all the brake dust left from when i took them off.

 

Strange indeed!

 

3PUTT,

I had a similar experience (the opposite- smooth wheels turned into shakers) with my Z28 that just had the brakes checked and the dealer took off the wheels, but when they reinstalled them they just did it with the air gun. When I went back they checked a service bulletin which pointed out vibration could result from improperly torqued lug nuts.
After they were hand torqued the lug nuts the vibrations disappeared.
Good tire shops hand torque the lug nuts. I've also heard that rotor warpage is attributed to uneven lug nut tightning.