For road vibration, I'll start by mentioning tires. If you suspect it could be a tire then simply switch the wheels back to front and you will soon know, even side to side to narrow down which one. Tires of course need to be properly balanced and even occasionally re-balanced. All new tires will be slightly out of round, the question is how much is acceptable for road use. Manufactures have varying degrees of quality control, but it doesn't mean they catch everything. In the normal case, a dymanic balance can eliminate out of round vibrations at all normal road speeds. For more advanced cases, you need to have them load force balanced to simulate road conditions. I now always recommend paying extra for load balancing, which includes indexing the tire to the rim. A load balance will help keep tire wear more even, keeping its balance and ultimately lasting a little longer. When a load balance can't get the wheel balance within spec, it tells you how much of the problem is due to the wheel rims and how much is the tire. If the rim is within spec then the tire should be returned under warranty, accompanied by the load force balance printout. When the wheel is out of spec, it's time to search for a straighter wheel unless you can find a rim straightener. I've had two such out of round tire returns in my latest batch of eight Continentals and one in a previous batch of four BF Goodrich that could not be brought into load spec and had road vibration at certain speeds. One place wanted to do the warranty return using a prorated mileage formula as it took a few weeks to note the problem under highway driving conditions -I almost lost my cool that time.