اقتباس:
أما فى حالة الانزلاق, و فى الأنظمة ذات الدفع الرباعى المستمر و ليست تلك التى تبدل العزم حسب الحاجة, تتشابك قوى الاطارات نظرا لأن تناسب زاوية الدوران قد فقد مع الانزلاق, و بذلك يساعد الدفع الرباعى على دوران السيارة حول نفسها, و يعمل وزنها الثقيل على تكبير عزم الدوران, مما يؤدى غالبا الى صعوبة بل استحالة التحكم فى السيارة
العربية تلف حوالين نفسها ده في الاحلام (باذن الله)وعن تجربة مش بالكلام اقتباس:
Advantages and Disadvantages
Traction and Grip :
Apparently, 4-wheel drive brings traction and grip to higher level because the tractive effort is shared by 4 wheels instead of two. This enable higher cornering limit, especially in rough roads and wet condition. Since it was introduced in 1980 to rally cars, 4WD proved its superiority in this aspect.
Weight penality and power loss :
Because the driving mechanism of the additional wheels has frictional loss, 4WD consumes a little bit more power than 2WD cars. Anyway, this is still a fraction compare with the increased weight. Most 4WD systems weigh 50kg-100kg more than a 2WD system, thus deteriorate acceleration as well as fuel consumption.
Steering tendency :
As mentioned in our study of Handling, in theory, permanent 4WD cars generate neutral steering tendency, thanks to the tractive force sharing by all 4 wheels. However, in reality this become much more complicated. Steering tendency can also be corrected by weight distribution, the adjustment of camber and castor, the choice of different size tyres in front and rear etc. Moreover, it is widely agreed that a slight oversteering, if could be accurately controlled by throttle and steering, is even more satisfying than neutral steering. In contrast, most 50:50 permanent 4WD cars can hardly enable oversteering, unless in really slippery surface.
Steering feel :
Depends on tuning, some 4WD cars deliver less steeing feel, since the presence of torque in the front wheels may generate slightly torque steer. However, most modern 4WD cars overcame this problem.
اي تتلخص العيوب في فقدان جزء من العزم + ثقل الوزن + التكلفة
