to beat this game you should only need to achive about 80 points in each field, IE ~80 machine points, ~80 course points, ~80 battle points.
this is an about number because bspec racing also requires alot of other factors! people can do it with lower some will require higher because of their low skills.
-you will need to activly manage your racer... this is required for a few courses for sure! by lowering the speed before tight corners(turns) so that your guy doesnt go off the road.
-you will also need to tune your cars! tune so that your car wont go off the road and turn better... get better acceleration on tracks with lots of turns, and higher top speed for tracks with more strait aways... tune the LSD so your driver makes better turns at faster speeds (and better turns overall). brakes is huge part, not to much brake power cause that will make you unstable, especially at high speeds.
this is all esential parts to managing your driver.... not only that but you will need to train your drive to achive better scores.
i made a tutorial for this, check it out at
www.gamefaqs.com in the gt4 section! its not the best but it will help most.