They can be different for different tyre makes and even the different versions of the same tyre, hence the confusion.
It's always best to check the manufacturer's recommended settings for that particular tyre and use that.
Here's some links:
Avon:
http://www.avon-tyres.co.uk/motorbik...&model=&year=0 Bridgestone:
http://www.bridgestonebikersclub.co.uk/guide/ Dunlop:
http://www.dunlopmotorcycle.eu/dunlo...nder/index.jsp Metzler:
http://www.metzelermoto.co.uk/web/default.page Michelin:
http://www.michelin.ie/motorcycles/ Pirelli:
http://www.pirelli.com/tyre/gb/en/mo...E&segment=road