We get a lot questions about what is the lowest a vehicle can go. It has been a tough question to answer since at one time the cops would actually measure from the center of your headlight to the floor. We were unable find out any information to back this up. This last weekend I had a fun 8 hour traffic school class that was able to shed some light on the California State law regarding the legal ride height.
The law states (Cut & pasted from the California DMV website):
V C Section 24008 Modification of Vehicles
It is unlawful to operate any passenger vehicle, or commercial vehicle under 6,000 pounds, which has been modified from the original design so that any portion of the vehicle, other than the wheels, has less clearance from the surface of a level roadway than the clearance between the roadway and the lowermost portion of any rim of any wheel in contact with the roadway.
Basically not any part of your vehicle can be lower than the measurement of the lowest part of your rim to the ground. Makes sense right? Just in case if a tire blows out, your not Fred Flintstone-ing with a Fast and Furious floor board on the road.
This law is only confirmed for the State of California. Please check with your state for the current law regarding minimum ride height.