Is there any problems with changing wheels

I've just recently changed my wheels but when i'm driving it doesnt feel very smooth, I have the right size wheels on and i've tightened them up well enough. It feels particulary un-smooth on the front wheels. What could be the problem does anyone know? could it be the counter balance?

out of balance maybe, or a different tread/wear pattern that just feels different...I dunno, those are just my thoughts...