So i downloaded and modded BritishPoliceMods's Unlocked Scania: 

But every time i try to turn it just filps. I got that it's the handling line, but i can't find one! Can someone help me?!

Try switching what type of vehicle it is in vehicles.ide:

 

firetruk, firetruk, car, FIRETRUK, FIRETRUK, VEH@VAN, VEH@VAN_RI2_LE2, 100, 999, 0.3407, 0.3407, 0.3, 2, 1.5 ,1, noboot+avoidturns+big+truckfirefx+truckenginefx

 

firetruk, firetruk, car, MULE, MULE, VEH@TRUCK, VEH@TRUCK_LE1_RI1, 10, 999, 0.2970, 0.2970, 0.9, 1, 1.5 ,1, noboot+avoidturns+big+ext_requi+truckfirefx

 

Or maybe remove +avoidturns and/or +big?

I'll test it!

Something that could come handy as well: '?do=embed' frameborder='0' data-embedContent>>

Does not work.... Can someone download it and try? Did you fix it?

http://gtaforums.com/topic/464276-car-flip-over-even-changed-handlingdat

 

"i found what make the flip of car -> center of mass.z, you must lower this value in negative, so example if u have -0.05 put -0.2

another example my cavalcade have this values 0.0 0.0 -0.3 < x, y, z ..... and with this 0.0 0.0 -0.62 i have no more flips "

 

It worked! Problem solved.

What I sometimes do. Is mix and match original handling lines until I find one that works. I've got a nice Mercedes in my game but the handling line with it was crap, so I made my own using different parts from different lines. Now it's fine :)