Rustam
04-03-2006, 03:52 AM
If you thought about what I said a bit deeper you would realize that essentially I was explaining what makes cars squat... Have you ever asked yourself this question? For every force of action there is equal but opposite force of reaction - I guess this should sound familiar. In initiation of forward motion the input pinion exerts downward force on the ring gear at the point of their contact. This is the force of action. The ring gear exerts opposite upward force on the input pinion and therefore on the pinion shaft, which, being in direct contact with differential housing bearing exerts the force on the housing itself - cocking it up. The differential housing being in direct contact with the car respectively cocks up the car, making it squat. This force now is the force of action with respect to the car - is counteracted by the force of reaction at four points - two points of support on the front springs and two points of support on the rear springs. The rear moves down as the rear springs compress providing more force of resistance. The front elevates lessening the support of the springs in effect becoming "heavier" and providing this weight at the point of center of mass of the car. (If your springs are well balanced this motion occurs around the point of center of mass which is marked by very familiar symbol within BMW roundel - two blue sectors and two white sectors denoting the point of center of mass and as such standing to represent the pursuit for dynamic balance - side note). Only when these forces are just enough to counteract the force that cocks up the pinion shaft, the differential housing, and therefore the car - does the car start to move forward. Now to lessen the effect of squatting one can install stiffer springs - the back will not go down as much and the front will not elevate as much. Another way to lessen the effect of squatting as should be obvious at this point is to make the ring gear have larger radius so as to make less effort in applying the force of action to initiate motion and respectively, experience less force of reaction that cocks up the car.
Of two identical cars able to achieve given speed but having different rear differential ratios which one will accelerate faster? The one that has greater ratio - surely it does not do that by taking longer time squatting before actually moving does it???
Have you ever seen cars racing on drag strips experiencing a pickup of the nose - so much so that a railing is put together at the back to resist this motion? Why does that happen? Ever asked yourself? You really think that smaller ring gear requiring obviously more torque would alleviate this effect?
Your car squats so much because you have smaller gear ratio at the rear differential and that's the end of it...
Of two identical cars able to achieve given speed but having different rear differential ratios which one will accelerate faster? The one that has greater ratio - surely it does not do that by taking longer time squatting before actually moving does it???
Have you ever seen cars racing on drag strips experiencing a pickup of the nose - so much so that a railing is put together at the back to resist this motion? Why does that happen? Ever asked yourself? You really think that smaller ring gear requiring obviously more torque would alleviate this effect?
Your car squats so much because you have smaller gear ratio at the rear differential and that's the end of it...