whobble or shakes

[swoop]

I recently changed wheels from one suburban to a newer one that I have bought. The newer burb had skinnier wheels and tires on it and my older one had just the opposite. Slightly wider rims and tires. I changed them out and now I have a whobble around 60 to 70. I didn't notice this whith the skinnier rims so it shouldn't be too much air getting under the front end making this happen would it? I took it to get the tires balanced. The shop said that they were out pretty good. I didn't get the back ones balanced becuase I hoped the problem was with the front two. The whobble definatley becomes better when following close to a bigger vehicle. And it is better at higher speeds. almost smooth at 80. Should I have them rebalanced?