Even with a full 4 watt mobile CB rig and a mag mount antenna like the Wilson if you go down to the far end as a support vehicle you can go beyond your reception range.
As noted if on a crew get a good CB not the cheapest you can find. Do not go cheap on the antenna it is your "ears". Good quality antenna, if mag mount place it near the center of your vehicle roof if you can. The roof provides the "ground plane" that the antenna needs to be effective. More is better. Use large conductor size on your power leads, if you have a choice to make sure you don't have power drop on transmit. Solder all connections on the electrical side and seal with liquid electrical tape.
Get someone experienced in CB/ham radio to help you tune the antenna, to a low SWR (standing wave ratio).
Do not trim the antenna when the car is located close to buildings or over head wires, and make sure if you use a mag mount antenna that it is as far as practical from things like luggage rack cross bars. They will seriously miss-tune the antenna, and make it impossible to get a good SWR tune.
SWR is a measure of how efficient the antenna coax cable transfers power to the antenna and now efficient the antenna can be delivering signal to the radio. Properly tuned the antenna should deliver a SWR at or below 1.2:1, with a proper setup you can get it very near 1:1 which is ideal. Any SWR over 1.5 will seriously impact your ability to pick up weak signals at the far end of the course, or to talk back to the pits and starting line from down course.
If you have problems getting the antenna to tune due to poor mounting limitations you can add a counterpoise to the ground lead at the antenna cut for just slightly longer than 1/4 wave (about 104 inches) and tape it to the car body. I use the flat ribbon conductor Radio shack sells for speaker wire and get a near perfect SWR with a 102 inch whip mounted on a luggage rack bar to avoid drilling holes in the body.
If you are willing to spend just a bit more to get a CB radio that has a reputation of being reliable and bullet proof look at the Galaxy DX-949 they have been building radios for CB since the 1970's. The radio uses older but very mature and reliable designs (not modern super tiny surface mount components) which means it is repairable and rock reliable. It is bigger than many of the modern radios, but also offers SSB on a 40 channel rig which can talk much farther than standard AM CB.
The course safety announcements will of course be made on AM channel 1 or 10 (usually) but having SSB to your team base could be the difference between being able to talk to them and not if you have problems far from the primary pits and starting line area.
Several of us who go out to Bonneville are HAMs and would be happy to help if you need more personal info on radio choice and mounting. It can be an intimidating subject and sometimes individual constraints like no holes drilled in the car body etc. make it difficult to get a setup which you can really depend on.