The heated visor article is in GC's files for a future magazine. Heated anything (I did my own jacket too) is just about getting the right power spread over the right area (10-15W for a visor, 50-60W for a jacket, maybe 20W per grip). Under power it and it doesn't work, too much power over too little area and things melt or burn. This sets the wire diameter for the length you need and Bob's your uncle.
Google Nichrome resistance wire, the UK supplier has a nice element calculation tool.
Andy