Help! Slight vertical bounce with new wheels/tires
 

My problem:

I upgraded my stock wheels to 18x9 +35 with 255/35 Bridgestone Driveguards. At first this was really wobbly and bouncy. It turns out they forgot to get hubcentric rings to put on the car. A few days later these were put on. This helped quite a bit, but there is still a little bit of bounce that turns into vibration at high speeds.

Does everyone deal with this going this wide? Could the Driveguards just have really stiff sidewalls?

I'm still at stock height. Could I possibly be rubbing slightly on my springs/struts?

If anyone could point me in the right direction for my next step, that would be awesome ...

Bridgestone has a 30 day Buy and Try policy so I'm contemplating getting rid of the tires for something else if that will solve the problem.

Thanks!

After a quick search, I found this