MacPhearson Strut and chassis setup

[Merritt5]

When I read into chassis setup, conventional vs bb/ss, it mostly refers to SLA
type front suspensions. With sla type suspension, you could go in either
direction depending on how you want to drive the car and given the front geometry is optimal.

Since the strut system doesn't allow much camber gain, would it favor a big bar/soft spring setup
over a conventional stiff spring/soft bar?



Merritt

[David Pozzi]

It should. BB/SS requires less camber gain per inch of dive than a stiffer version. Stiff spring needs more/faster camber gain. But roll center movement needs to be compatible

[Merritt5]

It should. BB/SS requires less camber gain per inch of dive than a stiffer version. Stiff spring needs more/faster camber gain. But roll center movement needs to be compatible

Thank you, David for the response.

For the roll center movement, are you referring to it being close to the cg to cause less roll or more so when the car is in dive?

[David Pozzi]

I'd look for the roll center to not go below ground at full dive/full roll. It should be between 1" above and at ground level but not below. As far as lateral migration of the RC I'd like it to move towards the inboard tire or at least not travel towards the outside tire in roll and dive.

[CSG]

Assuming this is on your 93, keeping the rc above ground us tough without relocating the inner control arm mounts

[Merritt5]

I'd look for the roll center to not go below ground at full dive/full roll. It should be between 1" above and at ground level but not below. As far as lateral migration of the RC I'd like it to move towards the inboard tire or at least not travel towards the outside tire in roll and dive.

David, do you use any type of software to check the geometry of your suspension? I know many use performance trends or some type of 3D cad program.



Assuming this is on your 93, keeping the rc above ground us tough without relocating the inner control arm mounts

I know relocating the inner mounts would be needed, so I'm ok with that.

[67King]

Since the strut system doesn't allow much camber gain, would it favor a big bar/soft spring setup
over a conventional stiff spring/soft bar?



Merritt

On a track car, heavier springs and softer bars are the best combo. Problem with a big bar is that while it is great at helping keep the car more flat (which heavy springs will also do), it can cause the inside tire to life, and when that happens, you lose overall grip. As I've gotten more experience, I've gone down in bar size and up in spring rate. The more loaded tire neither knows nor cares how its effective rate comes about, it just knows the total. The roll couple doesn't differentiate, it treats them the same. This is a 944, which has a strut system.

On the street, you won't get into that kind of scenario, the big bar will probably help with ride harshness.