Like 412 said, they "pre-run" the course before their desert truck races it. Sometimes also off course, to go ahead to set up the next pit, or be "chase trucks", which follows behind the race truck with extra parts,fuel,tools etc... I will further divulge....
These trucks are purpose built (like rock crawlers, mud trucks etc)...Built for high speeds through mostly open desert terrain. The difference from the race truck being they are also loaded with spare parts,tools,fuel, tow straps, tires etc...to support not only itself, but also the race truck. So they are usually less capable than the race truck, but much more useful.
During prerunning, they will note stuff like any blind or gnarly sections (huge ruts, hidden boulders, etc), and sometimes plot the course itself to avoid any missed or wrong turns, and find the best line.
Its like how racers get to practice laps, except its a 1000 mile lap lol
common platform:
-long travel suspension, like 8" to 2 feet!(usually most of the truck is hacked up and every inch utilized for suspension, but pre-runners may compromise to save bed space for payload, or have toolboxes and racks instead of shower towers
-lots of lighting
-cooling upgrades, like a huge radiator in the bed (desert is brutal and hot!). and of course engine mods of various degree.
-usually fiberglass bodywork, and flared or bulged fenders/bedsides to swallow up all that tire and suspension. These trucks are wide and low for stability, and all about "downtravel".
-And the infamous pre runner bumper. These are made to help keep the front end smooth over impacts (and hold lights), and make great bushwackers!
If you want a chub, check out Terrible Herbst's trucks.
They can be 2wd or 4wd, although the prerunners are usually 4x4, because they may have to venture off course, or pull out a stuck (or inverted) race truck that did....
The top class is called trophy trucks...the buggys are up there too. Then there's various classes below it down to basically stock vehicle class. Motorcycles and now UTV's have their own categories as well.
Now Im wondering if they make prerunner utvs lol
If I lived in rocky mountains or dense woodlands, I would build a rock crawler.
If lived in southern swamp lands or northwest rain lands, I would build a mud truck.
But being I live in the mostly desert and beach sands of Socal, my ranger is very much pre runner oriented.
I am far from it being an actual respectable pre runner, because its still mostly stock...But the things I can and plan to do are pre runner based. In my opinion, pre runners are more badass than the race trucks, because the race trucks need support, pre runners are the support. Im going for overlander/prerunner hybrid, something minimally hacked up, that I can hit the desert in solo in with relative confidence, yet be capable enough to have some fun.
Sorry if that was long winded, pre runners are awesome.