I'd notice the thread on my pusher tire starting to look a bit "thin". Measured it today and it was at 3/32" (2.38mm). Legal minimum, as I recall, is 2/32" (1.58 mm). Got almost 7000 (6984) kilometers from when I changed out the pusher to K37s back at the beginning of the year. Not bad.
I setup the tire changer, got out my tire changing tools to include the Mojo Lever and the No-Pinch Tire Tool and with the help of Miles, my youngest son, got to work. I used the onboard tool set, found I was missing one tool, now added to the tool roll.
Bottom line, the sidecar tire which had 12/32 (9.52 mm) thread left when onto the pusher wheel and conversely, the pusher tire went onto the sidecar wheel. Seems the sidecar wheel experiences the least wear over time on my rig. Makes sense, most the weight/work is done at the pusher. The front tire has like 8/32" (6.35 mm) thread left so I left it alone for now.
Saved myself a drive downtown where the moto shop is located with a onsite tire changing service, along with the fee of $25/tire or $50.
Time was about 3.5 hrs working with my son. It was enjoyable, in spite of the drudgery that is tire work. The tools, help inmensely. Win-Win all around.
No inner tubes pinched because of the use of the no-pinch tool. Love that tool! I did break two of the rubber strips used to cover the spoke heads on the wheels. I had spares. I also covered with a layer of duct tape on top of the new strips.
Found the pusher and sidecar hubs splines dry and starting to rust! I'd greased them at the 20,000 Km service too....so I re-greased them and the wheel splines of course.
Everything went back together with no issues, tires held air, and no extra parts left over.