I've always ridden bias ply tires, mostly on Harleys.
Here's some comments about radial tires as found on the new GL with it's new stiffer chassis and wider rear wheel.
Dunlop: "Bias and radial tires have significantly different dynamic properties. They deflect differently, create different cornering forces, have different damping characteristics, as well as other differences. In order for radial tires to be introduced into the two-wheel market, it was necessary to change certain characteristics of the motorcycle. The introduction of the radial tire led to such things as modified frames, wider wheels, new steering geometries and suspensions."
Pirelli: "As motorcycle engines and chassis have advanced, so have tires. Traditionally, motorcycle tires were bias ply, which means the carcass was made up of body cords at an angle directionally. Flash forward to the present, and you’ll see a radial design in many tires, where plies are laid from bead to bead instead. This leads to many advantages:
• Heat dissipation: Radial tires displace heat better, which increase longevity and improved wear
• Sidewall Flexibility: By construction, radial tires sidewalls are not stiff as bias-ply tires. This allows the sidewalls to contour to the road better, improving surface area to the section or tread.
Bias-ply tires are still sticking around, but for good reason. Due to the stiffer sidewalls, bias-ply tires come standard on many heavy cruisers and touring bikes. The lack of flex works well for bikes designed to carry passengers and/or luggage."
Michelin: "Due to their soft sidewalls, the crowns of radial tyres stick to the road on contact. Their imprint, shorter but wider than that of a bias tyre, provides added grip when leaning in heavily on corners. The pressure of the air in contact with the tyre surface is distributed more effectively with radial tyres, which results in more even tread wear over time.
Radial tyres also provide greater comfort at higher speeds, once again as a result of their soft sidewalls, which absorb the impact of imperfections on the road surface. On the other hand, bias tyres are able to carry a greater weight because their sidewalls are more rigid. At high speeds, bias tyres can become so deformed that their performance is affected.
Ultimately, bias tyres are suitable for vehicles travelling at moderate speeds, with small to medium-sized engines and flexible chassis. They are also suited to heavy motorcycles or those that are heavily loaded.
Radial tires are needed for more powerful vehicles with very rigid chassis and for more sporty purposes."
Radials seem to be a big advantage when the bike is designed for them.