So where's your hugger rubbin' on the tyre? From your desription it sounds like it's at the front?
The 180 tyre is obviously narrower, but they tend to have a higher profile than 190's, so whilst the wheelbase won't be affected, the radius of the tyre will be.
Not sure on a solution, don't know what a longer chain would do to the handling other than slow the steering slightly, but if you do find a bit of clearance then bear in mind that when the tyre's spinning round it'll enlarge a bit more with the centrifugal effect!
I've followed a gsxr1000 once doing XXXmph when his back tyre ripped the hugger off and made a nice mess of his back end.
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