Sigh, another alignment thread gives me another chance to complain about Sheldon's string alignment method. It can tell you something is off but not what. Park makes a tool that will do a better job (their Frame Alignment Gauge) but the front end needs to be checked first. The most important aspect of alignment is that the seat tube is exactly 90º to the BB threads. If it isn't, your pedals will not be perpendicular to the ground and that crookedness can introduce knee issues. This seat tube alignment accuracy is the foundation for framebuilders to make the rest of a frame.

To check if a seat tube is leaning, use some kind of straight edge (a 4' level works and isn't that expensive) placed against a bottom bracket cup with the axle removed. Use a small ruler to measure the distance from the level near the BB and again near the seat lug. They should agree of course. Next do the same thing along the down tube. If something is off, I recommend taking our frame to your local builder and let him fix it for you. The accepted industry standard is within 3mm. All of us good builders keep tolerances well within less than half a millimeter.

Now that you know the front end is checked and correct, you can see if the dropouts are equidistant from the centerline of the frame. The flaw in Sheldon's method is that he assumes the front triangle is correct. The Park tool works great for this but so does your recently bought 4' level. The straight edge is placed against the head and seat tube and the distance to the inside of a dropout is measured. Flip the tool to the other side and measure to the other dropout. You are good if they are the same distance.

Here is a picture of Dave checking the rear triangle alignment on the frames we made in Bucha Ukraine. This is where the Russians tried to stage their attack on Kyiv and did so much destruction. This picture was taken in 2009 when he was a seminary student. I wonder how his life has been after the Russian invasion. Eventually I took over a tool that works better than a level. Instead of using a ruler to measure, we taped M5 threads into the level and a bolt in the threads could be turned to check distance.


using a level to check rear triangle alignment

checking the drive side to see if the distance is the same as the non-drive side