The most significant learning experience I had in regard to this issue was the time I handed a *perfectly* aligned bike to a customer and he proceeded to berate me because it didn't look straight to him. I knew that it absolutely was aligned correctly to within a mm, but I got out my tools to loosen the stem bolts and f**k up the alignment until it looked correct to him, in his parallax view.
Because what actually matters is that it looks like it's in alignment to the person riding it. And a perfectly aligned wheel/stem just doesn't look like everything is straight to some people, on some bikes, sometimes. EOS.
Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
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