stick your camera in manual decide what iso/shutter you want ( shutter being your dominant decider as you are shooting motorsport) and point the camera at the grass.
shift the aperture until you get a correct exposure on your metering scale, now point your camera at the area you wish to shoot - ignoring the metering scale.
This is called a substitute light reading, but the reason you use the grass is that to the camera grass is a mid tone and depending on your cameras exposure latitude this gives the best chance of getting shadow and highlight detail.
one more trick you could try is an SLR reading, SLR standing for Subject Luminance Range.
To get the SLR for any given subject, you spot meter from the brightest part of your scene, and spot meter from the darkest part - note the two extremes in exposure and pick a happy medium and go for that, thus depending on your cameras exposure latitude again. Problems come when the SLR is out of your cameras latitude, so if the difference from dark to highlight is 8 stops ( which is possible on a bright winters day with a mid day sun) your camera can struggle, thus why most people will shoot precious jobs in RAW.
Shooting in RAW you can use a technique known as "expose right". i.e over exposing on the shoot and bringing the highlights back in with your RAW software.
I use a D3 which supposedly has a 7 stop latitude.
