I know this is an old thread but I just experimented with these and they worked great.
Bought some 28x9 slicks used. Had a hell of a time getting them to balance. 2 tire shops later I was ready to give up. They told me the tires were defective or I had a bent rim. Anyway long story short I tried the method below and it worked very well.
I only broke the bead on one side of the rim too so I couldn’t of accidently rotated the rim and caused an in-balance situation. (all wheel weights were removed prior, vibration was still present)
I put 4.5 ounces worth of the heavy airsoft rounds in each of the tires and the car never felt so smooth at speed, what a difference! I know it sounds like a gimmick but it was night and day with these slicks.
After seeing the video below I decided to give it a shot figuring I couldn't hurt anything.
I've had my slicks balanced for years. (spin balanced at install) And the ride quality at 130+ was always a little ruff to say the least. I still have slight vibration at the speeds but it is the smoothest I've ever felt the car since running slicks. It felt like my old radial days!