yes factory tires are same size, no the 180 is NOT ment for our bikes because we have a 4.5'' rear rim width. safely we can fit 150/70R17, 160/60R17 170/60R17 those are all acceptable to fit on our rims safely. the 180 width tires are fitted usually on a 5'' 5.25'' or a 5.50'' rim, will the the 180 fit ? YES i have use a 180/55/R17 one time it was a BT-021 i got for free. the rear of the bike sat up higher and tire side walls stuck out farther because of the wider tire. being safe ? i rode with it on but that doesnt make it ok, as long as you dont ride a passenger, throw a knee down in the corners i think its not recommended but do what u gotta do. i kept my pressure at 38 psi in the rear for the 180 tireOkay so I know the standard size on the XJ6 is 160/60/17 (I assume FZ6r is exactly the same).
A friend has some part-worn tires that are 180/60/17...
Obviously this is not the standard size, and isn't ideally fitted...but have you any experience? Would it be safe?