I've run my TKCs right down now, the rear is just under legal limit and the front blocks are very wedge shaped.......... I've been riding my X for a few weeks, but jumped on the Z for a couple of days and nearly shat myself. I must have been riding round what are very nasty wear effects. I had noticed that the front under braking felt like it had started to feel like it was stuck in a rut, well it is so bad now that the bike needs over correcting to make it pull up straight. The rear is letting go with just a whiff of dampness, which at this time of year is almost all the time. When cornering it feels like its falling into the corner and then it hits a 'ridge' at which point it just feels like its going to go down.
Obviously I have run the tyres to their limit and beyond, but its worth noting that unlike more road biased tyres these need to be changed before they get to the legal limit.