I'm building a singlespeed mtb, using an old diamondback frame with horizontal dropouts and 132mm rear spacing. I'm just using the 7-speed cassette hub that came with the bike, and using a cog with spacers mounted on the freehub body.
I removed a couple of spacers from the drive-side axle and stuck them on the non-drive-side axle, since the cassette lockring will be able to nearly touch the frame and I don't need to worry about the chain since the cog will be near the middle of the freehub body.
This allows me to have minimal dish in the rear wheel.
My worry now: is there too much exposed axle (i.e., distance between the bearings and the dropout) on the non-drive-side? This wouldn't be a worry for road riding, but more exposed axle on the non-drive-side could be a problem for off-road riding with lots of bumps, causing the axle to eventually bend and then need to be replaced.
So I'm asking a question about optimization between two factors:
1) I would like the rear wheel to be as close to dishless as possible - equal spoke tension, stronger wheel, more likely to last a really long time without breaking spokes or coming out of true. I accomplish this by switching spacers from the drive-side to non-drive-side axle (so effectively moving the hub body over with respect to the rim) and then re-dishing the rim.
2) The further over I move the hub body (and it's not as if I can do it all that far; this is limited by the cassette lockring hitting the inside of the dropouts), the more spacers there are on the non-drive-side axle. This means increased distance between the non-drive-side bearings and the left rear dropout, and as this length grows, the bending moment on that section of axle increases. Too much bending moment, and your axle ends up bending, and will eventually need to be replaced. This is the reason freehubs are superior to freewheel hubs on multi-speed bikes, because freewheel hubs leave a long distance of exposed axle between the drive-side bearings and the right dropout (and it's extra-problematic on the drive-side, because there it's dealing with horizontal force from the pulling of the chain on the sprockets, along with vertical force from rider's weight and hitting bumps).
I suspect that with 36 spokes the wheel is already plenty strong without having re-spaced anything, and it'd be prudent to move a spacer back over to the drive-side. But I'm really not sure.
Does it look like too much exposed axle on the non-drive-side?