Displacement activity is when you tidy your workshop instead of painting the house, and displacement activity is when you rebuild John's unicycle instead of Getting On With his high racer. But unicycles are quicker to build than high racers, and with four-inch cranks and a twenty-inch wheel, his unicycle has actually worn out his knees. Besides, what else am I to do with all those knackered 26 inch mountain bike rims?
Is there anything of interest to state about building a unicycle? - Discarded front fork, vice, large pipe to bend the fork legs straight, couple of lumps of mild steel sawn and filed and drilled and tapped 8mm metric to accept the original axle bearing mounts, slots in the fork ends with an angle grinder. Of course it came out dented and slightly wonky, but with the original wheel in place, wedged before tack-welding, everything ended up parallel and square and proper and nice and whatnot and besides nobody ever admires workmanship on a unicycle because there isn't anything to admire.
You always thought you were the single worst wheel-builder in the world. You were wrong. First I laced it with a cross-over where the valve lay. Next I laced it so the right-hand rim holes pointed at the left-hand flange. After that I got it right but found that the spokes wouldn't tighten because of a dismal failure to consult WISIL's spoke length calculator. Then I found that the only spokes I had that would marry the large flanges of the original hub, necessitated a four-cross pattern. I laced eighteen spokes with a set of long nipples after getting the calculator measurements wrong, and replaced them all because I only have one matchbox of long nipples whereas I have a full coffee tin of or'nery ones. I used up quite a lot of vocabulary while doing these things.
When it was finished he found he could no longer hop on, and we learnt that there is a whole technique to mounting that you have to re-learn when the seat is three inches higher up and you can't start off with a foot flat on the floor. But after half an hour he managed it, and now, with those cranks and that rim, he reports it's like riding a seven-inch divided by four-inch crank times a twenty-six inch wheel, so that's about a 45 inch gear.
He now zooms. Previously only his knees zoomed.