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Rca's (roll center adjusters)


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Im not really that up on the whole chassis tuning fundaments of cars and all that but I've seen these a lot lately on corollas hondas etc etc.

Basically from what i can gather they are to realign the wishbone so is sits level on lowered cars and returns the cars natural state or postion at which it rolls.

Soo, why is it no1 has made a set for ep's, do we not need them? Its just an extended ball joint or plate to go between balljoint and wishbone if i understand correctly.

Edited by morgey
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When you lower a car you also lower the centre of gravity height, when designing a suspension system there is other points called "instant centre's" and "roll centre".



The instant centres are where the upper and lower wishbones essentially cross if you were to continue them (this happens because wishbones are inclined at an angle therefore they will cross if the wishbones were long enough) however we just draw the lines on when designing a suspension/chassis system.



The roll centre is the axis point at which the vehicle body rolls about. This should be as close to the CoG height, if both the CoG and roll centre are at the same position then vehicle roll would be 0. Likewise the further away the roll centre from the CoG height the greater the body will roll.


This is an ideal situation for body roll however this includes further complications by something called "jacking" which I won't go into.



When you lower a car the CoG height decreases but also so does the roll centre height and this is generally moved further away from the CoG height inducing greater body roll therefore using Roll centre adjusters helps bring the roll centre back closer to the CoG height to get body roll back to a normal amount.



I can't say I've ever used RCA's so can't comment whether they work or not or their effect on handling because I've never really lowered a car, likewise when I've designed a suspension/chassis system the ride height has been kept constant. For a road car I struggle to see why spending a couple of quid on some springs or coilovers outweighs the benefit of having the manufacturer spend millions of pounds in R&D and testing :sad:


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Right well i can make sence of that although that seems to be for dual wishbone setup but the principal will still stand.

Also reading on we would need to get an extended ball joint as to move the pivot point of the ball joint down rather than just spacing it out.

So depending on the angle of our wishbones then we should notice the benefit of a set of rca's as it will probably bring the Rc back closer to where it was from factory.

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Right well i can make sence of that although that seems to be for dual wishbone setup but the principal will still stand.

Also reading on we would need to get an extended ball joint as to move the pivot point of the ball joint down rather than just spacing it out.

So depending on the angle of our wishbones then we should notice the benefit of a set of rca's as it will probably bring the Rc back closer to where it was from factory.

Don't the spacer move the joint anyway? I'm not too clued up on them so could be a silly question lol.

if your doing it for the antirollbar then thats easy fixed by shorter abar linkages

It's not the anti roll bar, they don't have no bearing on the suspension geometry. It's to do with the wishbones going at funny angles when lowering.

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Reading the link jay posted it basically states that you have to move the pivot point away from the hub,. Spacing the wishbone wont work as the point of movement will remain the same, there's 2 types of ball joints ones mounted in the hub pointing down they need spacing away from the hub from behind the joint (packer style) or the type mounted in the wishbone pointing up and they need spacing away above the joint (extended balljoint arm)

Edited by morgey
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Sorry to bring this thread up again. But i was at brands hatch recently and i was talking to a chap from super pro. They do roll centre kits but not for the starlet. However he said i could email super pro and get them to actually make a kit if there is enough demand. So before talking about the need for it. I just want to say it is a significant piece of kit. Also roll centres will always change when theres any sort of wheel travel. Its more complicated then it looks. Been doing some kinematic testing recently and been using lotus shark for my project. I think i would be a huge benefit for those who track their cars.

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Might just add this here as it gives a quick guide to roll center adjustment and why



2102011_174131.jpg



2102011_174138.jpg



2102011_174145.jpg



The problem I see with the spacers is that you are not actually lowereing the pivot point. See each line is drawn from the pivoting point. All the spacer does is change the angle of the arm.



Look at the small pic aboce the ball joint base is longer therefore the ball joint pivot is placed further.



What the Starlets need is a ball joint that has a longer shaft.

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