I had been having a lot of problems with them going out of balance. I wasn't sure what was wrong. Were they throwing wheel weights? Wearing unevenly during burnouts? I had them rebalanced a few times, then switched tire shops doing the balancing, bit the vibration still came back. It is hard on your nerves driving home from the drag strip with a new driveline vibration. Finally, one day I marked the wheels and tires with dial-in on a long shot. I didn't expect to see any movement.