What you are experiencing is not a balance issue. If it were out of balance you would get a shimmy, typically around 55-60 mph but it can occur at other speeds as well. Your pull is what we refer to as a tire pull and is being caused by one of your tires. You can drive it a bit and see if it quits but it probably will not. If you want to know which one it is I suggest that you cross rotate the fronts and see which way it goes. USUALLY the pull will follow the bad tire. If it pulls right and you cross rotate the fronts only and now it pulls left, you have a bad tire on the left front. That is hands down my single biggest cause of pulling on Volvos, bad tires. Your options usually are to live with it, re-rotate it to the rear, buy 2 new tires up front. I say 2 so that you keep them matched in tread ware. When you replace tires one at a time it does not take long before you have 4 tires wearing at four different rates. It is bad enough when you have two new ones up front and two older ones on the rear.

Mark