Originally Posted by Bradley P

I measured ERD at two spots 90 deg apart on the new rim and got 606. Salsa claims 605. This was measured by taking two of the spokes that measure 295mm from thread tip to bend, inserting them into diametrically opposed holes and threading them fully on to the nipples. I pulled them tight and measured across the two bends, about 16mm.

The wheel is threaded as a X3. If it were threaded as a X2 there would be 10mm of spokes poking out.

I think I see what is going on here. If everything were perfect, ERD as specified and spokes cut to the ideal length, the wheel would go into tension just at the point that the ends of the spokes became flush with the ends of the nipples.

I rounded spoke length up and they were fabricated 1mm longer than spec so my spokes are about 1.5mm too long. With everything perfect I would need to be able to tighten such that about 1.5mm of spoke protruded beyond each nipple to tension the wheel. The spokes and nipples both have 9mm of thread; it is not possible to tighten the spokes to where there is 1.5mm protruding from the nipple - only flush or slightly beyond.

It seems to me that to allow for tolerances in spoke fabrication, and to allow tension to occur before the spoke protrudes from the nipple, spoke length should be specified as less than the ideal by perhaps 2mm. That still would allow 6-7mm of thread engagement under worse case tolerance stack up. OTOH, were these spokes cut to the requested length, and had I rounded down I think this wheel would have come into tension.