Watts linkage question

In one of my old HOTROD magazines, I noticed a model T hotrod that utilized Watts linkage in the rear suspension. Can anyone tell me why Watts linkage (2 rods) is preferable to the usual panhard bar (1 rod) ) on coil spring rear suspensions. I noticed Speedway Motors sells a Watts linkage kit. Thanks.

 

With a Watts, the axle moves straight up and down ( in relation to the car's centerline ), with a Panhard it moves at an arc.

 

Because the diff can only move straight up and down when it travels. A panard bar makes the diff travel in a small arc. The Watts link keeps the diff perfectly centered in the ch***is, and ICW parallel 4 bars, you also get no pinion angle change, either. Gary

 

The axle always stays dead center.

 

most t's have such short suspension travel, a panhard will suffice. watts is cool, but not really necessary on street car. i run a panhard on a jeep with about 10 inches travel, and it works fine on it too.

 

Thank you all for the responses. Very helpful.

 

Another point, is that with a panhard bar, the rear roll centre is the height where the bar crosses the car centre line.
The roll centre rises as the body rolls one way, and falls when the body rolls to the opposite side. That cannot be right!!

A Watts linkage has none of these problems.