There has been discussion over the years as to how accurately BMW forks need to be aligned for proper operation. This drawing is a roughly-accurate approximation of the alignment of my fork tubes, as seen looking up at the lower ends of the fork tubes. You get the best view if you view the page at actual size because it was drawn on a scale of 1:1 (Change the magnification of the image until the ruler at the left is approximately accurate when viewed next to an actual ruler held up to the screen).

      The two yellow-filled circles indicate the perfect alignment of the tubes (.000” error) in the X and Y planes. The open red circle above shows the amount of error I measured in those planes before I started the alignment procedure, being approximately .017 off in parallel, and one leg being about .070 or .080 or so off (estimated- it might have been a bit more than that) in the Y plane.

      It doesn’t look like much here, and in real life the ‘directional error’*1 was only about .072 inches (less than one tenth of an inch!). The approximate azimuth of the error being shown in the diagram by the direction of the arrow*2, but that was enough to make my forks lose about 50-75% of their perceived compliance, and only regular application of silicone spray on the for- boot felt wipers got them to work very well at all. Also consider the fact that in the middle of the fork tubes where the sliders spend most of their lives, the error was only about half that, or .036” out of alignment.

      The amount of adjustment shown here (the difference between the before and after alignments) got the fork assembly to go from teeth-jarring, wrist-wrenching stiff to pavement-absorbing smooth.

      I am sharing this with you (and I wrote this document) because so many of the procedures in various manuals and journals simply do not address the small amount of error that can cause the forks to work poorly, and I have not seen any of them effectively address how to correct those errors.

      I don’t know the answer to the question posed at the top of this page, but I can say, from my limited personal experience, that the amount of error pictured here was way too much, and correcting it made a huge difference.