I believe "SG" is "side g's", which is a measure of force inflicted on the side of the car. There is also a "FG" which I would take to mean as "forward g's", which would be the force felt on the front of the car. I'm no expert -- that's just my assumption.
However, it takes a long time to download and they aren't quite as "good" as the one above so you may want to skip it. Although "Steering wheel gives out, bus goes over railing (dual lense camera)" is pretty good. Be sure to press 'Rear View' and watch it a 2nd time (I like the way the passenger climbs back into his seat after the crash ).