What size is the 3.00 x 18 in the new tire math? I'm hoping to put a BT-46 Bridgestone on to replace the original tire from 1975. Would that equate to a 90/90-18M/C ?
There are conversion charts published for converting inch to metric tire sizes. For example:
www.cyclegear.com/assets/0002/8205/Tire_Size_Convertion_PDF.pdf
Alternately, the Bridgestone site for the BT46 shows the "standard" rim width for each tire size, as well as the acceptable width range for each size. I believe the standard rim width is what is used to measure the advertised tread width and overall diameter.
www.bridgestone.com/products/motorcycle_...oducts/detail/pr176/
The rim/wheel size should be stamped on the wheel. Many KZ wheels were 2.15" width, but I don't know what you have. Once you find the wheel width, you can look at the standard width and width range for each tire size and get a sense for what will fit. I personally bumped the tire sizes up a bit beyond the "standard" width, but you may have issues with fender and chain guard clearance if you push it too far.