This is typical of a tire pull. It's not exactly a defect, just a difference in rolling resistance. If the two front tires are a different brand, all bets are off. It's not likely they will roll the same.
Based on your dandy observation that it didn't pull before the rotation, that should eliminate an alignment problem. (Your car is alignable for a pulling problem and for tire wear issues by sliding the upper strut mount sideways). There are two things that can be done to prove what a genius I am. :)
The shop that did the rotation might offer to switch the two front tires at no charge to put your mind at ease. After doing that, most likely the car will pull in the other direction. Every once in a while you will run into a pair of tires that will go straight when they're rolling in the opposite direction. Standard procedure is to keep the driving tires on the same side and switch the non-driving (rear) tires side to side when moving them to the front. Now they're rolling backwards compared to before. The only reason for using that standardized pattern is so the next guys will rotate them in the same pattern and not rotate them back to where they were last time.
The second, lesser-known test is to drive at highway speed, carefully let go of the steeing wheel, (be ready to grab it), observe the pull, then hit the brakes relatively hard. During braking, a tire pull will cause the car to pull in the other direction. This only works on front wheel drive cars because you can compare the forces on the tire while braking AND while tugging the car forward.
If you do indeed find a tire pull, you can live with it until the next rotation if it isn't too bad, or you'll have to switch the tires back. I've owned many tires with a pull including a set from a mass merchandiser in the mid 1970s. The pull was so bad, you would end up in the ditch within a few seconds of letting go of the steering wheel. Switched them front to rear and left them there. Never had a problem after that, and they wore like iron. Never rotated them once after that, and they all wore evenly at the same rate. Lasted well over 40,000 miles before I wore them out on the race track!
Wednesday, March 3rd, 2010 AT 9:48 AM