I'll try.
LANDSTAL 1700.0 5008.3 2.5 0.0 0.0 -0.3 85 0.75 0.85 0.5 5 160.0 25.0 20.0 4 D 6.2 0.60 0 35.0 2.4 0.08 0.0 0.28 -0.14 0.5 0.25 0.27 0.23 25000 20 500002 0 1 0
This is the first entry for HANDLING.CFG in SA.
1700 - the weight (kilos)
5008.3 - Turnmass, I think the amount of force to move vehicle.
2.5 - Drag multiplier, I think aerodynamic.
0.0 0.0 -0.3 - Centers of gravity, X/Y/Z. Moving these will affect how well the vehicle stays upright when turning.
5 - Number of gears in transmission.
160.0 - Top speed (kph)
25.0 - Acceleration (I think meters per second), your gas pedal.
20.0 - Deceleration, (I think meters per second), your brakes.
4 - Drive type, 4 (4x4), R (Rear wheel drive), F (Front wheel drive)
D - engine type, petrol (P), diesel (D) or electric (E)
From here you get into steering, suspension limits & flags used by the game.
25000 is value of the vehicle, in $.
If you're not comfortable editing your handling file, I have tuning services available in the trading stalls.
http://www.thegtaplace.com/forums/index.php?showtopic=11534