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Torque steer is not only caused by unequal length drive shafts. That is one of the primary means, but by far not the only. The reason that unequal length drive shafts cause torque steer is that they are at different front view angles. The different front view angles cause a difference in torque about the kingpin axis. (there is a sin theta component of the driveline torque that acts about the kingpin axis and there are different "thetas" when you have unequal length shafts.) With equal length shafts the thetas are equal and the sin theta torques are equal and opposite at each wheel and therefore cancel each other out.
However even with equal length driveshafts there are times when the halfshafts are not at equal angles. (For example cornering) At these times torque steer will still be there regardless of the shafts having equal lengths.
Another cause of torque steer is the fact that the torque delivered to the left and right wheels may not be equal to start out with. We did a study here at GM a while ago and found some interesting things. Unequal length shafts are offten so since the differential of the car is not in the center. To make "Equal" length shafts often times an intermediate shaft is used on the side that is further away. The intermediate shaft comes horizontally out of the differential. When it is the same distance away from the centerline of the vehicle as the "close" half shaft it ends and has the opposite side halfshaft mounted. By doing this both half shafts are of equal length, and sit at equal angles when the car is level. However the side with the intermediate shaft has a different torsional spring constant than that of the side with only the halfshaft. The torsional spring constant difference causes a the two sides of the vehicle to have different lag times. In steady state it does not matter, but in transients the lag can be almost two seconds. So when you stomp on the gas the torque delivered to the two wheels is not equal and this causes a net moment about the kingpin axis and the vehicle steers.
Another source of torque steer comes when the traction available at the two wheels is not equal. When this happens again there is a net moment imbalace about the kingpin axis and the vehicle will steer. The tracion can be different at the wheels for a variety of reasons. Most obvious would be cases where the coef of friction is different on the two sides of the vehicle. (Split mu) But there are other reasons as well. If the load on the left and right tires is not wequal, the torque output will not be equal even if the coef of friction is the same. The load on the left and right wheel is rarely the smae amount. Differences range in magnitude from 50 to 200 pounds on typical vehicles. (Due both to asymetrical CG and "fights" in the suspension)
So how the hell do you get rid of torque steer? Spindle length is the key. If you search the 9-3 board I derived the equations for torque steer in a previous post. Shit I got to go to a ten o'clock meeting. Will finish this later...
-Joe
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