> Dan Penoff wrote: > I loaded probably 400-500 pounds of bricks into a little UHaul > trailer and hooked it up to my 1991 Ford Escort wagon. > Thinking that it was best to have the load in the front of the > trailer, I stacked the bricks up against the front wall ahead > of the axle. > > I got out on I-43 and started to drive, accelerating up to the > speed limit. > > The trailer started whipping around like a crazed cat, > ultimately taking hold of the car and spinning it around in a > complete circle at least once before I ended up on the median > facing in the opposite direction on the same side of the road > I had been on.
Was there so much weight on the hitch that the car's steer axle was unloaded? If not, there was still a lot of mass far back on the car, and it has inerta! The key to trailer stability is to have at least 10% of the mass in front of the ground pivot point. (wheels) If you happen to be driving in a perfecly straight line with zero forces on either side (impossible in the real world) then the mass distribution won't matter. With more mass behind the pivot than in front, the mass imbalance means that any side-to-side intertia will apply a force to the tow vehicle that aggravates the situation. That is, if the car turns to the left the trailer pushes the back of the car to the right, so now the trailer is not following directly and has to shift to the left. When it does, the trailer then pushes the back of the car to the right and again the trailer is out of line and has to swing back. It's a positive feedback situation. The solution is more mass in front of the ground pivot. But too much weight on the hitch imbalances steering and braking for the tow vehicle. To sovle that, a weight distributing hitch assembly allows the pivotal mass and the ground weight to _not_ be the same. Thus the ground weight is shifted to the trailer and steer and away from the drive axle. An axle scale would show not enough weight on the hitch. But because the _mass_ is correctly distributed, the resulting in steering and braking balance is correct. Or at least much closer. -- Philip _______________________________________ http://www.okiebenz.com For new and used parts go to www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
