Cheers all. The Cheng Shin has been a great tyre and has seen hard cornering action around the Derbyshire/Yorks Dales and Yorks Moors!
I am a bit handy with the throttle so this may account for the middle wear a bit.
Bike passed its MoT six weeks ago and no concerns were raised about the tyre?? As for pressures, anything beyond 30 psi at the rear and it squirms a bit on white lines and heavy braking. However, I wouldn't go lower than 28 r and 26 f. I'm going to nip over to another tyre place for their opinion. In the meantime, I'm going to order a Mitas to see how they perform. To be honest, I do expect a bit of weave and squirm from the bike, especially as I do like to chuck it around a bit. My main issue (as you would imagine) is whether it all stays on the road!!
By the way, I did put the original recommended pressures in the bike at first only to be told by a white faced fitter this wasn't a good idea.
The reason, all motorcycle tyres differ from those produced 60 years ago and require the pressures recommended by the manufacturer of the day. 60 years ago, the tyres needed lower pressures, now they need higher pressures due to the changes in the way they are constructed - just a thought.