I just put on a Michelin Bopper front tire on my Z20b, and the handling is much better. Gives me more confidence to ride the scooter. It's a 120/90L-10 bought from here. I also bought a Michelin S1 for the rear, size 100/90J-10, but have not installed it yet. $79 including shipping for both. These are the ones previously recommemded by usatracy. The front has about 10% larger diameter, which partially corrects for the speedometer error. My top indicated speed dropped from 50 mph to 45 mph.
I bought some motorcycle tire irons to try and install myself and felt like I was banging my head against the wall. Could not even get the tire iron under the bead. I ended up taking it to an auto tire dealer, and they did it for me for $5.
Any other tires anyone has tried? Results?