11110001 - 09 July 2008 01:40 AM
Can't believe no one has an answer to this... hmmmm
There was not a 'prime' and 'option' tire as we know them today when 'slick' tires were used; this is a recent development in use only since the inception of the current grooved tires and the single supplier Bridgestone.
Previously, a tean had choices in compounds, but had to decide on one to run the entire race on, excepting wet conditions, of course. Here is an article on this aspect:
27-06-2006 Tyres crucial at Indianapolis
http://www.f1technical.net/topics/6?sid=63ed65bf038cf777e5fa1f4304d43659
Google; it's a beautiful thing. Try it, you might like it.