Roll center adjustment

I am trying to optimize a fwd (corolla) strut car for packed dirt/gravel. I may or may not lower the car depending on conditions.

So I have 4 questions;

Is it ok to use roll center adjusters (available as a 20mm ball joint spacer for my application) without lowering the ride height?

With the proper grade hardware can I just make these spacers myself in varying thickness sets to apply to potential ride height changes or do you just get what you can out of your geometry and leave it?

What determines how far is too far using this sort of adjustment?

Does this change the effective spring rate?

This will be in a club racing environment.

Hi Deric, roll centre isn't really an absolute so it's hard for me to give you specifics. The best advice I can give is to test and see what the effect of roll centre change is on the handling so you can assess what's best. In general terms though roll centre adjustment is more important when the car is lowered so at stock ride height you may find that raising the roll centre height makes things worse.

You can buy extended ball joints to correct roll centre on some popular applications from the likes of whiteline but of course you're kind of stuck with whatever adjustment they offer. Both our race cars use aftermarket suspension arms and a spherical bearing with a stud that locates in the taper in the hub which allows us to make spacers to adjust the roll centre. The limiting factor here is the strength of the stud in the hub since the further the arm is spaced down, the more bending force is applied to the stud. No, it won't alter your effective spring rate.

i´m driving fwd rallycar

How i can low roll center on rear beam axle without lowering ride heigth?

Unfortunately with a beam axle you're limited in what you can do with the roll centre height as it is fixed at the centre point of the beam. However you can still affect the handling by altering the front roll centre height instead.