what is a fxst? if it 's a super glide model a 140 is about as wide as you can go , maybe a 150 , just remember that some tire's are wider then other's even if there the same size , Avon is a bit wider them the metzler & both are the 150 X16 & both of these are just a bit wider then the dunlop HD tire at the same size ,the tire might fit the frame good but watch the side of the belt
