What is the extra effort needed to ride on 2inch tyres instead of 1 1/4 inch

[johnk]

Has anyone any information on the rolling resistance of tyres on tarmac. I'm trying to find out how much longer my Hybrid with 2 inch tyres would take to do an hours ride on my road bike with 1 1/4 inch tyres. They are both about the same weight. I expect most effort used is overcoming wind resistance.
Thanks

[trevgbb]

read pages 14 to 16 of the tech info download here
http://www.schwalbe.co.uk/c-downloads-schwalbe-catalogue.html