1st Gear Boost - not sure, but something like 'more power at low speed' or just VERY grippy start (Cadrona, Landstalker, Greenwood)
2nd Gear Boost - this one gives more power at higher speeds, once car starts rolling, best example Sabre. Slow start with wheelspin, but later kicks in
Offroad Ability 2 (installing Offroad Wheels on the vehicle give Offroad Ability 1) - vehicle acts better on sand or other very soft offroad areas, while offroad ability 1 is for dirt roads or other solid offroad
Hidraulic none - cant have hydraulics, or even if it got, they have no effect (Dozer, Dumper, Monster, Duneride etc..)
Halogen Lights - not sure, maybe brigther lights, needs checking.. some ppl also said few cars have more 'blue' lights
Proc Rear First - no idea
Use Max Speed - vehicle cant go faster than value set in 'TOPSPEED' but seems like doesnt work or is used only for slow vehicles (Dumper, Monsters, Duneride... they all go max 110, Forklift, Sweeper, Mower, all go 60
Swinging Chassis - some cars have shaking ass, like Buffalo, Sabre etc. this flag means these cars