Semi-Trailing arm suspension design discussion.

nocones said:

So I guess now is about the time we decide to do Dual A-arms or something not Semi Trailing Arms.

Stay strong on the 'something not dual A-arms' bandwagon. STA actually makes a surprising amount of sense for a small, rather stiffly sprung, very low CG, $2k Challenge car.

One other thought I don't think has been discussed yet is the IRS trade-off between anti-squat and anti-lift. While the anti-squat line is between the wheel center and pivot axis, the anti-lift line is still between the contact patch and pivots axis the same as for a live axle.  With trailing arms this means that to get good anti-lift you have pro-squat, but to get anti-squat you get a lot more anti-lift. The shorter the arms, the worse it gets. I'd wonder if the car might be better suited to getting the anti-lift under 100%, and living with some pro-squat.

Is the concern about pro-squat a concern about "launching" in particular?  Or is it a concern about transient dynamics at any/all speeds?

sleepyhead the buffalo said:

Is the concern about pro-squat a concern about "launching" in particular?  Or is it a concern about transient dynamics at any/all speeds?

Both. I think launches get bad with "pro-squat", but so does accelerating out of a corner. 

Certainly some shock tuning can help with the rates of change, but having the car try to lift it's rear wheels away from the road surface when accelerating doesn't seem good to me. 

In reply to Robbie (Forum Supporter) :

A 3rd spring or some type of 'z-bar' could mitigate your pro-squat geometry concerns.