Roll Center Adjusters

[260DET]

Ones for the front, they fit between the suspension ball joint/control arm and the strut bottom, sometimes called bump steer spacers.

 

Anyway, my question is - are they a good thing for a much lowered road/circuit car? If so, what effect on the handling do they have?

 

My car has had the inner control arm pivot points moved up ~30mm, at static ride height the control arms are very slightly lower at the outside. If the adjusters are a good thing, how thick should they be?

 

Basically I'd like to reduce body roll without going to heavier anti-sway bars, springs, etc.

[2126]

As I understand it from my investigation into this issue, you should not require the spacers as you have already relocated the inner pivot points 1.18" (30mm) upward. Also, with your car at static ride height, it is a good that your links have a downward slope (outer end lower). If you visit Jim Cook Racing's website, they have a pretty good illustration and explaination regarding the roll center issue and using the spacers. Remember that the explaination is realtive to a Z that has not had the inner pivots relocated. Hope this helps!

[JMortensen]

IMHO it will be beneficial even though you already have the pivots raised, but you'll need to deal with the bumpsteer issues again (assuming that you did when you raised the pivots). You'll either have to raise the rack or lower the outer tie rod ends.

 

The spacers change the camber curve, caster curve, and the roll center. Your sway bar end links will most likely also be in a better position with spacers in. I'm sure there's more, but those are the advantages I can cite off the top of my head.

 

As for thickness, you generally find 3/4" or 15/16" being sold for Z's and some REALLY big ones sold for 510s. I have seen some that I would swear were 1.5". At that point the strength of the bolts starts to scare me a bit. Maybe I'm overly cautious on that one, but I'd stick to a 1" spacer or less. I know I'm running a 3/4" right now and John Coffey ran a 15/16" one.

[johnc]

My car has had the inner control arm pivot points moved up ~30mm, at static ride height the control arms are very slightly lower at the outside. If the adjusters are a good thing, how thick should they be?

 

Since swapping these spacers is a simple, trackside thing I suggest you make up 3 sizes and use part of a test day to determine what works best on your car. That's what I did and why I ended up with 25mm thick spacers on a front suspension that did not have the LCA pivot relocated. I even been known to run different thickness spacers on tracks that have significantly more important turns in one direction then another.

 

Basically I'd like to reduce body roll without going to heavier anti-sway bars, springs, etc.

 

Try increasing track width with wheel spacers.

[260DET]

Thanks all, very useful info. In the Jim Cook Racing site its said that with a lowered Z the front roll center can end up below ground level, not a good thing.

 

What I might do is try to locate the relevant suspension points on a sheet of paper and work out from that where the present roll center is.

[260DET]

My green Z exiting a 180 degree fairly tight third gear corner onto a straight which goes away to the left. Moderate body roll, probably a touch of power oversteer, not as much front wheel turn angle as it may appear, the front spoiler is not wide enough to cover the outer part of the tyre tread. Look OK? Well better than the yellow one eh

 

[johnc]

Looks fine except, somehow, you slid over into the passenger seat!

 

Do you drive this car on the street?

[ww]

Nah! He's just leaning into the corner!

[260DET]

First rule of cornering - always get on the inside

 

Yeh it gets driven to and from with the R tyres stacked inside, not a daily driver although it could be with air con.

[johnc]

Yeh it gets driven to and from with the R tyres stacked inside, not a daily driver although it could be with air con.

 

Then it looks like you have the car setup well.