Legality has nothing to do with it. Safety is what you should be concerned with. You should never ever mix Bias & Radial tires on the same vehicle. This will cause the vehicle to handle in an unsafe manner. The handling characteristics of Bias Ply and Radial Ply tires is so very different that it is unsafe to mix them.
manufacturing process of bias & radial tires
Radial ply tires and tubeless tires are made from rubber, fabric, and steel.
Radial tires are worlds beyond bias ply tires. In radial tires, the steel chords are placed in a criss-cross pattern. Whereas bias ply tires are placed flat across the face of the tire. Bias ply tires are much, much harder for the engine to turn and are much harder for the suspension to compensate for. Bias ply tires are almost no longer used. That goes for America at least.
The Simple answer: Radial Tires Roll down the road easier. How and Why is quite complicated
Bias ply tires get a flat spot from sitting but I have yet to see a radial tire do that.
1995
Bias ply Tires (called cross ply in the UK) due to the construction of the internal belts actually had the trad squirm as the tire went around. Radial tire construction corrects this problem. Radial tires are also made of more advanced "Rubber" compounds that wear better
bias ply, belted bias, and radial.
Radial tiers have a lower rolling resistance than previous types of tire Resistance is energy, in tires resistance creates heat. Radial tires construction and the materials they are made of create less heat and roll easier. And if you need a more detailed explanation you need to look at Bias Ply tires (called Cross Ply in some countries) and Radial tires to see why it makes a difference
You should get radial tires because if you go to www.mud-throwers.com it lists all of the disadvantages and advantages. So you should spend a little more money on the radial tires.
Because bias ply tires are constructed with more material than radial tires. More material means less flex which equates to a higher rolling resistance.