>> I' was thinking about buying a harley davidson 883iron.
"Buying a Harley" are generally not associated with "Thinking." Thinking has you on a little 250cc bike such as the littlest V-Star or a Ninjette. Anything larger involves a large grin and "OOooo... I can have...."
>> is it safe to drive bikes on the roads?
A motorcycle is a smaller target, quicker, more agile, no blind spots, and generally much safer, meaning ability to avoid a collision, than a cage. In a collision it is safer to be inside a nice steel crash cage.
A bike is safer to drive, a car is safer to crash. You have to do your own risk assessment.
>> is it true that harleys' crash ratings are lower than sport bikes?
True, but meaningless. Corvettes are crashed a LOT more than Cadillacs -- but that is simply a reflection on the idiots that buy 'Vettes. Sport bikes, like 'Vettes, have better performance and should be safer. Statistics often, but not always, lie.
>> does harley d's sound has any impact over the car drivers?
Not enough to matter. There is no valid reason to run open pipes.
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About the only thing I really know about Harleys is that my little Suzuki Savage is cheaper, 200 pounds lighter, far quicker, and nearly as fast as a 883 Sportster. And it takes most of the aftermarker Sportster parts!