I have a 95 civic dx aftermarket 15 inch rims. My problem is it shakes a little it starts at 15mph and goes and goes. I put new tires on it and it went away a little I could not go faster then 70 with out it shaking to bad and now about 80mph I dont know what to look for. Someone said wheel spacers but there not to big right? Does the offset of the rim make a difference? Is there any things I could look for to decrease what it could be?

 

check for a broken motor mount.

 

Are all tires matching. Are your tires balanced. And is there any wear on the inside of the tires? If there is uneven wear it either needs to be alligned or you need to check your suspension. 15 inch rims shouldn't make any big difference from the stock 13 or 14 rims but if the car is lowered or if your not aligned or balanced your going to get terrible shaking. My car did it when ever I hit speeds of 60+ but I noticed my tires were wearing away and I got new tires mounted balanced and alligned and now it drives great.

 

Sounds like a bent rim in the rear.