The factory manual has a spec for the amount of offset that the rear tire is allowed with respect to the front, seems like "acceptable" was from 5 to 8, or 8 to 13 mm toe displacement--some ocd mofo can look it up exactly. It has always seemed to be a violation of the laws of nature that you can't align the centerline of the front and rear tires exactly. They make a special tool for the measurement that most dealers don't have, but i've just used the string method to verify that this is the case and to try to correct the situation.
The further that the rear tire is offset to the left of the front, the worse will be your front left-side wear patch due to the need for constant pushing with your left-hand to make the bike run straight down the road. Try to ride with no hands and the bike starts turning to the right immediately.
This seems to be related to the design of the BMW single-sided swing-arm--all my chain bikes are perfectly aligned front and rear, even the SSSA of the honda hawk, vfr and ducati 916. They still have a bit of left-side wear patch due to the extra distance travelled in left hand turns, but it is not nearly as noticeable as on the K bikes.
Some years ago when i was actively trying to solve this problem i machined the front motor mounts on the engine and used shims to try to bring the rear into alignment with the front. Probably got it down to about 2 mm of offset, but couldn't get it all out. It did help reduce the wear patch but i got tired of messing with it. i prefer that a bike run straight when i let go of the grips. On a long flat clear slab on interstate it gives your wrist a break to be able to set the throttle lock and steer by shifting your weight with your knees against the tank...
2016 Edit Note: So the OCD mofo is me, and i downloaded the old 2V kbike manual and grabbed some screen shots. The 4V may be where i read about the greater offset values but i don't have that manual.
