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In my link above, refer sandbox6688's post half way down 1st page, shows set ups for all 5 races. It helped me beat all bar the 3rd race, for some unknown reason I came 12th on high speed ring (but that was only during champ series, I had beat it before to get the gold on track).
B Spec Guide: http://www.gamefaqs.com/boards/941103-gran-turismo-5/57378570