Put a 200 Avon on my 97 sporty- the only thing I had to change was the :frame,front end, tank, front tire, oil tank, forward control, handlebars-------------etc,etc,etc. Leave it alone unless you have too much time on your hands-not to mention about $6000 for the above custom parts. Did I mention Jockey shift , foot clutch and new up swept pipes? Its a work in progress- but then I have an o5 softail deluxe to ride.
IMHO you wont nitice the 150 tire and will have spent about $1000(paint incl) for your troubles.

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I disagree that wide tires ride rougher......they actually take up more surface area, and absorb some of the smaller impacts...Even if the hit more bumbs (Wider track to expose to bumps- it softens the blow).....Ride a 60's chopper with that skinny *** O-Ring tire, them ride one of todays with a 240, 250, 300,330.....Today is smoother!

BRUCE