This may help:
From
Revzilla Tire Guide :
Can I mix radial and bias-ply tires? Can I switch from bias to radials?
Again, we respect a customer’s right to choose, but we only recommend sticking with a manufacturer’s recommended tire construction type.
In general, radial tires offer lower temperatures (leading to longer life), stiffer construction, and the ability to have sidewalls with a lower aspect ratio, resulting in less flex. Bias-ply tires offer a softer, more compliant ride and, typically, a little lower price. Their other main advantage is load-carrying capability. In a given size, you’ll typically see a bias handle more weight. It explains why Harley (a big player in the heavy cruiser market) and certain touring bikes use them.
Interestingly, for some manufacturers, a mix of a bias front and radial rear is the setup from the factory.
From Metzler Catalog :
IMPORTANT NOTE REGARDING TIRE UPGRADES
Metzeler allows builders and owners to mix radial rear tires and bias ply front
tires when the following conditions are met:
> All Metzeler tires must be used on the proper permissible rim size, see chart
enclosed to verify correct rim size and tire fitment.
> Mixing radial rear tires and bias ply front tires is allowed only when fitting a
stock Harley-Davidson® with the proper custom width wheels for the tire
application. (see application chart) OR when fitted by a custom manufacturer (i.e. American Ironhorse). OR if listed in this fitment chart!
> FITTING RADIAL FRONT TIRES IN COMBINATION WITH BIAS PLY REAR TIRES
IS NEVER ALLOWED!
> Metzeler tubeless tires may be fitted with Metzeler tubes. Metzeler tube type tires should NEVER be put into service without a Metzeler tube.