Date: Sat, 07 Jul 2007 18:56:51 GMT From: still me <wheeledBobnospamo.com> Subject: Re: 338 hp saab 900 2-door
On Fri, 06 Jul 2007 20:32:36 GMT, Bill Bradley <senator2nospamAMearthlink.net> wrote: > It's a torque issue. The tires put a force to the pavement (braking, >turning, accelerating). The force is not through the CG, so it creates >a torque with the height to the CG as the torque arm (the lower the CG, >the less the torque). The only way that the torque can be balanced is >by re-distributing the weight force of the car on the tires. Since >acceleration creates a clockwise torque that diminishes the force on the >front tires [in extreme cases even lifting them off the ground] and >increases the force on the rear. Braking does the opposite. Wheel >base [or track for turning] and the location of the center of gravity >are also factors since they effect the torque arm for the normal force >on the tires. Adding to that... In a car, there's also the issue of sprung and un-sprung. A car is not a fixed position weight. The unsprung suspension is relatively fixed but the body is a movable weight. As you accelerate, the springs allow the body to move up in the front and down in the back effectively increasing the weight on the rear of the car and decreasing the weight on the front. While the front tires may lift slightly as you described, the amount is usually minimal. More of the traction reduction is generally attributed to the shifting of the body upward in front and downward in back In a FWD car, stiffer rear springs can help with this issue. (Actually, they help contain the shift in RWD too, but it's not an unwanted effect there). A stiffer rear sway bar will help with the issue that one wheel tends to come up if you accelerating but not going in a straight line (but it will not decrease the overall effect).
