Inertia/supineness of veh. while at high speed / unable to steer

[IT_Q]

(sry if the translation is not very good, but couldnt find it exactly)
ok now the situation: while being at high speed with wheeled vehicles like jeeps/hmmv/trucks (which means being on a road) its almost impossible to steer, if u try 2 do so, u r maybe able to do a 5% curve, if u break down to lower speed the vehcile can be steered normally again

(it neednt to be perfect steerable, but try it for your own, driving with a truck along everon on roads with decent speed is impossible)

i tryed serveral variables but didnt have any success

( wheelCircumference / turnCoef / terrainCoef / maxSpeed / precision / dampersize / steerAheadSimul /steerAheadPlan / predictTurnSimul / predictTurnPlan )

just one thing i have noticed:
the "sport car" or skoda/rapid has a much better handling (along with motorcycle) regarding this issue, but also seems to be more light-weighted as u can easily jump and make a "stop-turn" - so its maybe model-related or anthings like this?

help very much appreciated - thx !

regards