90/90 21 bias front and 200/50 18 radial rear. Metzeler say it's cool to mix as long as the bias is in the front and the radial in the back. Is this so??

 

I would assume it's so if Metzler themselves say so.

 

True enough Deucedog. What I should have asked is, are any of you using bias front and radial rear Metzeler tires and how is the performance??