Originally Posted by
cny-bikeman
There would be lots of ways to do it, the primary object being to measure the distance between a line drawn down the middle of the fork column and the center of the dropout. Actually, I just thought of a method while typing this which I believe would work.
- Place the fork on a level surface, pointing the rake down.
- Take a short level that has a groove for placing it on a pipe (common on 9" levels) and place it on the fork column, tape it if you like. If a threaded fork make sure the level is secure against the unthreaded portion.
- Lift the fork column up until it is level.
- Measure the distance from the bottom of the column where the level is to the table/surface (at the end OK if unthreaded).
- Add 1/2 of the fork column O.D. where the level is, subtract distance from the dropout center to the table.
I would think this method would be accurate within 1 mm.
I may be old-school, but my mechanic's brain is still working!
The problem with this method is that it relies on your accurate judgement of the bubble being truly centered, and you have to do that twice - once for table and once for the fork, which doubles your possible error. I'd suggest taking the level part out of it:
It would be better to place an object under the steerer tube that is easy to change the height, and then move it up and down the steerer, measuring the height of the horizontal steerer off the table until that height is the same wherever the object is placed. At that point the steerer and table are parallel to each other, and you can take your measurements, adding for steerer centerline and subtracting for the dropout.
This method also avoids trying to get a 2 foot level to remain firmly in contact with 6 inches of steerer.