Mumford Linkage

[Lonnie-S]

My build is going to be a street car, not a race car, so that is the performance context for me.

I started out with a Mumford link in mind on my live Ford 7.5" rear axle. However, the more I learned about what can be done with a Panhard Rod in terms of it mounting geometry the less interested I became in the complexity of the Mumford link. Body roll is minimal with these Locost cars as are bump and droop. I built quite a bit of adjustability into both mounting ends of my Panhard rod: chassis and axle.

In terms of roll center height, torque effects and the like, I believe it gives me quite a bit for a simpler setup. Of course opinions differ and if you have a race car things might look differently to you.

Cheers,

[Bent Wrench]

I believe a Panhard may be tolerable as the arm length is greater and sweet spot within the normal travel on a Locost makes it fairly predictable.

If ones driving skills surpasses the suspension design, a different setup may be installed easily enough.

Keeping it simple now has it's advantages... and is lighter!

There can be elegance in simplicity..

[Driven5]

The problem with panhard's is that it does not work the same for turns in the opposite direction.

A Mumford or a Watts will have the same performance in right or left turn.

Unless the L/R weight distribution is 50/50, then the car (assuming equal L/R wheel rates) inherently does not turn identically both directions. With a longitudinally mounted engine, accelerating or decelerating has unequal L/R inertial effects. With a live axle, being on or off throttle also causes unequal L/R tire loading. And I have yet to run a circuit that has an equal amount of left and right turning, as there tends to be ~360* more of one than the other... So with all of this in mind, are we sure that equal L/R reactions through the axle's lateral locating device is even desirable? On the street might it be desirable to balance out another imbalance? On the track might it be fastest to favor one direction slightly over the other? Note that it wouldn't be hard to add a second set of mounting points, so that the Panhard could be flipped depending on which direction the track is being run.

Perhaps most Locost designs do not normally need a lower roll center than a Watts can provide?
And those that cant tell the difference simply install a Panhard.

The main reason we don't want to run higher roll centers on independent suspensions is 'jacking'... However, solid (live and de Dion) axles do not suffer from jacking effects the way independent suspensions do. This means that solid axles are able to run significantly higher roll center heights without ill effect. So with all this in mind, are we sure that chasing independent-like (anti-jacking) roll centers are what we even want for solid axles? I've seen referenced where a race car was converted from a (Watts) live axle to independent, which and lowered only the rear roll center by more than half, and yet doing so with no change to the front suspension did not upset the previously achieved balance.

[LoadOS]

Race car designs don't consider front and rear roll centers in a vacuum, they are considered together as a side view roll axis.

Sometimes you need a Mumford link to get the roll axis where you want it (at the rear).

For anyone confused by how the Mumford link works, consider the two bell cranks like sections of two symmetrical X shaped bell cranks with the pivot in the center:

If the points of the X are 7, 9, 5, 1 and 3 on your keypad, 5 is the center pivot. In the picture up in the thread, the left bell crank is between points 1, 5 and 3, the right bell crank is points 7, 5 and 3, the central link connects point 3 on the left link to point 7 on the right link. The center pivots are offset left and right but are typically at the same height on the chassis. Because of the ~symmetry of the bell cranks the Mumford link locates the axle side to side but does not add any roll stiffness or wheel rate.

The roll center becomes where the two outer links intersect