Put the ISO as low as possible like 50-100 and ramp the aperture up as depth of field doesn't matter when the bg is out of focus. Stick it in manual and dial The aperture to f8-16 and the shutter speed to 1/30th-1/250th depending on the speed of the vehicle and the available light, fast moving vehicles like f1 you can get away with higher speeds and you get more keepers but I like to be around 1/80th to 1/125th with panning IS on the lens activated works a treat, higher keepers but less effect depends where you want to be.
It's not an exact science and a little bit of experimentation at the start of the event is a good idea to get the exposure dialled in and shoot lots of frames and it soon comes.
Also technique is key. Arms into chest left arm tucked in left hand supporting the lens and use your face to support the camera, sort of fun stance left foot forward and right foot behind and hold your breath. Making yourself as much of a support as possible, pan with the car as it comes and start to lay down the frames as you feel the car entering your ideal composition.
Also other techniques like back button focus where you disconnect the metering/shutter from the AF. So you use the rear AF button on the back of the camera to continually focus/track the car and the shutter button to lay down the frames when you need. Takes some getting used to but once you get the hang of it your keepers will be 50%+ instead of <10%.
Lastly the AF you can select the zone af, where it selects 9 AF points to keep the car where you need it to be, then change the AF mode to what ever is suitable so in terms of cars a subject that accelerates and decelerates quickly dial that in and the cameras AF will work the way you want it to.
The techniques are quite advanced but I think it's worth doing it right from the beginning rather than trying to change techniques that may be less suitable.
Hope that helps
