photographing motor sports in a manner which creates visually appealing imagery is challenging and it helps to have an understanding of each type of race so you can better predict the action
many races are run in early afternoon which makes high overhead sunlight problematic from a photography aesthetic perspective
the trick is to gain variety and portray movement while ensuring the driver or some other part of the image (eg. pit stop crew) is as sharp as possible, and much of this requires a well practiced panning technique with a camera with very fast autofocus (preferably continuous AF although in some situations S-AF will work well)
if you can see the manufacturer markings on the tyres, then these need to be blurred by using a slowish shutter speed to demonstrate movement - this is not an issue if shooting a car front on in which case you can use faster shutter speeds and wider apertures
position yourself so as to avoid annoying backgrounds