I to was concerned with the switching of Tyre production to china and I thought that I would contact Metzler with regard to Quality and Quality Control.
I received an E Mail from them (a year or so ago) which I attach for you information. Now I know that many fellow Tossers on here will say "well yes, they would say that wouldn't they". So for what it's worth here it is :-
Dear John,
Thank you for your email,
We have a Factory in China since last couple of years now that start to produce*Pirelli/Metzeler*tyres, and we can assure you that they are the same quality that are made in Germany as the same high quality and technology equipment installed, I hope this has helped.
*
Regards,
Mannie
Contact Centre
Pirelli Metzeler Moto UK