Now it is time to design the outer wheel spacers. There is one on each side of the wheel for four, total. The design force is the axle tension with lubed threads having a 0.015 coefficient. There are two faces for each spacer for eight, total. The inside faces push against the bearing inner races and the calculations for the internal spacer will work for those. Alloy 6061 T6511 aluminum will work OK.
One spacer is trapped between a die case aluminum fork leg and the wheel bearing. The outer face of the spacer is larger to reduce the pressure on the softer fork leg material. The calculations are similar to those recently posted.
The story is different for the spacer on the other side of the wheel. The outside end of the spacer bears on the shoulder of a widened section of the axle. There is not much load bearing area and design pressure is 32,400 psi. Yield strength of alloy 303 annealed stainless steel is 34,800 psi. 34,800 / 32,400 = 1.07 That is a very low factor of safety. It is like getting a D- in school. Passing, yes, but barely. Aluminum 6061 T6511 has a 35,000 psi yield strength with a 1.08 safety factor. That is not good enough. Triumph uses steel for these spacers on all of their bikes I have worked on, so there is a clue to what I need. Steel rusts and is inappropriate. Structural titanium has a 141,000 psi compressive yield strength with a 4.35 safety factor. The spacer is made from that and another problem is solved.
Structural titanium is often called Ti-Al-4V due to its primary alloying constituents, aluminum and titanium. In many ways it is easier to machine than the stronger stainless alloys and it resists corrosion, is lighter, and much stronger. It is very easy to get a much smoother finish than stainless. The finish on the spacer is cut with roughing bits. It is better than I can get on stainless with finishing bits. It is my "go-to" metal for a steel substitute when making bolts, spacers, and other small items.