I have a 1992 Honda CB750 NighthawkAnd I was wondering is there a rule of thumb about upgrading tire sizes?OEM calls for 140/70-17 for my rear tire and I would like to go 180/55-17. Is this safe or even attainable?
The simple and fast answer is no, you can't fit a tire that size. The wheel rim is too narrow for the tire to have a good profile for tire contact on the road and it wouldn't fit in the swing arm as it is too wide regardless of the rim size. with a very open budget you could have a new swing arm fabricated to accept the tire but then will there be enough clearance for the chain to fit between the sprockets, I suspect there would not be the clearance needed. The cost would probably be around the price of a new bike already fitted with the tire size you asked about. I also have to wonder why you want to fit such a wide low profile tire??
