i know this does not help but I just can't figure out why it is not recommended. a radial tire will warm up faster than a bias ply, but don't know of any reason why it would cause your bike not to handle correctly.
if you figure out why not from here post back and let me know.
I would really check this out fefore running different kinds. With Autos, back when we could first get Radials in the States from Sears no less, in 1968 I got just rears. Didn't even make it home before turning around and getting the fronts. Caused a very noticable terrible mismatchin handling. And that was with 4 wheels. Would be very careful with motorcycles.
In the early days then, they would recommend put on rears first cause the traction was so good with radials they wanted understeer rather that oversteer.
GM came out with a statement in 1969 saying they had no plans to ever run radials. Hell of a world.
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sglide18 DO not try this at (home) in 1976 i put a 15" VW radial,widest i could find at the time,on back of 69 sportster W 17" bias-ply on front.Luckly i tried it out on 4 lane,with no traffic.At 70mph bike started swapping lanes tried to use brakes to slow down,made it worse,had to ride it out,kinda hairy!!!! that was then don't know about now!!!