Rims On 95 Buick Centry

iight i just put some 18 inch mossa rims on my car...and i am havein a problem after one day of drivint...now i am hearin that my problem is that i need them ballance but idk....anyways after bout a half a day of driving they my car started shaking and makin a knockin noise .....now when i am accelerating and slowin down there is lil to no problem but when i try to stay at one speed is when the problem occurs...some one plese let me kno :banghead:

i would get them ballanced or realigned, i had the same problem, got them re ballanced and the were fine, what speeds though? highway speeds you will notic it if its unballanced or unalligned