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