Did a quick search and they do a 21 90/90 �60-�70 and a few 17" �80ish, options for the rear, so you can get them to fit the Z.

You got me thinking now, they'd be a good choice for the Z if you're not doing any serious off-roading and lots of road work. Be interesting to see how they compare with the 'dual tyres' for wear and price.

Might get a set when the tyres that came free with the bike wear out.