Roll Centre / Bump Steer mod - worth doing?
 

Having read a few posts recently about lowered cars and alteration of roll centre potentially resulting in more rather than less roll, I'm wondering whether it's worth investing in one of these Whiteline kits given that I'm running on Coilovers that sit a little lower than the Prodrive spring and WRX shock combo I had before:

http://www.camskill.co.uk/m10b346s26...it_GC8_Impreza

Anyone had these / care to comment?

So you've lowered more than 1 inch...?

The extended ball joints are a worthwhile addition and will reduce roll centre

I wouldn't bother with the track rod ends. They seem to increase bump steer. Lowering the steering rack is the better option. Are you getting bump steer?

Not getting a terrific amount of bump steer; I was more looking for something to eliminate roll further and get the car to corner flatter.

I already have front and rear ARB's (with the rear on hard and the front on medium, both are 22mm whiteline jobs), solid rear droplinks, an ALK and a front strut brace fitted.
I'm running BC coilovers with not much clearance between tyre and arch when running 18's - i.e. I haven't slammed the car, but yes it's more than likely lowered by more than an inch.
IIRC the Prodrive springs drop the car around 25mm, and I've probably gone around another 10-15mm lower again (just because it looks meaner ;)).

When I had my Coilovers refurbed I purchased some ball joints since I thought I might as well refresh whilst everything else was off.
I then found out that my current ball joints were extended ones like the whiteline ones in the link (mine are probably zero sports) so I decided to keep for now.

Doing a bit of research, the Whiteline ones have had a few reliability issues in the past and they don't seem to add as much extension as the zero sport ones do:
http://shop.edoperformance.com/zeros...r-p-11877.html
(I haven't seen any side by side measurement tho)

The zero sports ones are just too expensive but I have seen that APEX sells something similar:
http://www.apexperformance.co.uk/cat...4e36c45e516f73

These are what I would probably get when mine fail.
Btw I am running the Zero Sports Ball joints with regular track rod ends no problem.

That's quite alot of lowering. You're almost up to 40mm drop.

You're running 25mm rear arb and 23 (?) front. This sounds great. I have the same set-up along with sticky rubber and love the combo. That's quite a bit (but not too much) arb roll resistance.

When I fitted a RCC kit to my New Age it sharpened the front up a treat.

Other things to check are front to rear ride heights and rake, and of course alignment settings, not just that these are correct, but dialed for what you want

Edit: Edited in light of Arnie's response below

Well, as much as I'm anathema to that much lowering in general (geometry issues and travel issues, depending on the damper) the one advantage damper styles like the BC have is the amount of travel is not affected by how low you set them. The entire damper cartridge is lowered when you raise and lower it. The actual stroke is not compressed at all. So you don't lose any travel when you lower them.

But Bonesetter is absolutely right, travel is pretty limited on these struts.

Good work :thumb:

The Zero Sports ones are mega bucks for sure, but the Apex kit looks like the ones to go for.

TBH, I've lost faith in Whiteline kit. A while ago production was farmed out to Asia and with it a lowering of tolerances and R&D budgets. Shiny expensive bits?

Thanks for putting the BC lowering issue right. So although stroke travel isn't affected, the suspension will still be into, or will on cornering, the 'bad' part of the camber curve (?), ie bottom arms level etc (sorry haven't explained well)

Yup, exactly. The geometry will still be compromised though travel hasn't. One's ride height is a personal thing. Kinda depends on what you value more, performance or aesthetics. Though there isn't an "ideal" ride height, as it depends on so many things, from a performance standpoint, I've found that a good Classic ride height setting starting point is front 350mm rear 345mm (measured center of hub to bottom of arch). As the front ride height goes lower than this your front roll center drops significantly leading to more body roll as well as the camber curve going to "positive". This means that as you corner camber will no longer be negative, rather positive and you'll be cornering on your sidewalls. Using ball joint Roll Center Adjusters such as the Whitelines allow you to lower the car while maintaining decent geometry. Though its not a cure-all for a completely slammed car, it can help.

Though a lower center of gravity is a desirable thing, for a proper handling car, its not as simple as just lowering the car. Just decide if you want "the look" or actual performance.

Thanks guys, very interesting to hear.
I actually didn't intentionally lower the car that much to begin with, just over-estimated how low the Prodrive springs took the car I think!

The rear actually sits a little higher and I was thinking I should take it down a bit more.
Just to be quite sure, I'll try and measure the hub--> arch distance as suggested and check what it is. Whilst I do like the low look, if it reduces the drivability of the car I'd rather raise it 10mm and enjoy it more - after all, this isn't a Corsa, it's a Scoob ;)

As per Arnie on the height. With the 'off the shelf' available roll centre correction kits, the car will drive quite nice at 350-355mm front and 340-345mm at the back. This is for a New Age too (your scooby is a bug, right, or have I dreamed that?).

Here is a pic of my new Age JDM from a while back. I took the handling on as a project as when I bought the car it had been over-lowered to F340/R325 :eek: It drove awful on any kind of real road - crashing and banging.

Here's a pic of the car at its final height front 350 and rear 335. I tried for a little more on the rear but the adjuster collar became stiff and just wouldn't go any more (this was on Tein Superstreet coilovers, but it's common for the collars to seize after a winter, esp the 'cheaper' sets. If you adjust yours clean the thread AS MUCH as possible before, so they're COMPLETELY spotless)


https://lh4.googleusercontent.com/-z...%252520001.JPG

Informative thread and comments. :)

Yes indeed mate it's a bug :).
Your pic's interesting....the pics below should give you an idea of how low mine is:
https://lh4.googleusercontent.com/-b...0/IMAG1492.jpg....
and at the front on its own:
https://lh6.googleusercontent.com/-X...0/IMAG1509.jpg
Admittedly, it probably needs dropping a little at the back and raising at the front to get it a bit closer to what you've got there, but that pic - assuming that's what it looked like after you'd finished with the ride height(?) - looks nice without being overly slammed, or too high - in other words - just right :).

Sorry I don't have any more recent ones just side on...

I'm also interested to see people saying just go for the ball joints - so the consensus is not to bother with replacement track rod arms then?
And...does this compromise ride quality at all? Yes I know I'm running coilovers already - which is why I'm asking :lol1:

These are ride height specs I typically use for setting up various Impreza's:

Classic front 350mm rear 345mm
01-04 front 370mm rear 360mm
05 front 380mm rear 360mm

typically much higher than what aestheticists tend to use.

As far as the tie rods go, I'm pretty curious to see where Powerstation get that the Whiteline one's increase bumpsteer. Its the first I've heard of it. I'd personally run as the manufacturer intended and use their tie rods. At the very least, I think I'd trust that Whiteline would have properly engineered their tie rods to do what they claim on the tin!

Love your Bug Eye, by the way!

I fitted this kit to my Partners JDM Forester, which had been lowered before we bought it, I found the kit made a big difference, and even the missus noticed it felt more stable in the corners, it reduced the front end roll, keeping the car a lot flatter in the corners giving more grip, obviously the Forester is still higher then most Impreza, but an noticeable difference none the less

Mark :thumb:

:thumb:

Thanks, the car drove extremely well. It had the benefits of low CofG and the suspension and chassis well sorted to match

Your bug (very nice looker btw - bet you don't stand on the brake pedal too hard lol). It could do with being matched front to rear a bit more though (front higher), and of course your toe will need resetting to suit

As for height, with what you have at the front the front roll centre will be almost below the ground. Sometimes this creates some strange handling characteristics as well as the distance between the COG and RC being a bit on the high side, increasing the tendency to roll at the front. The RC correction ball jt's will reduce this roll couple. I'm going to stick to my guns on the track rod ends :)

I've just ordered the Whiteline roll center/Bump steer kit for my newage. Even though I'm not a fan generally of Whiteline products I didnt think there looked a lot wrong with this kit.
I looked at if I needed to correct the Roll center/bump steer situation when I re-hashed my front suspension but me and the bloke that was helpeing me (who just happens to be a suspension guru that mainly works as a adviser to touring car teams) felt that the angles that the steering arms and wishbones were working through were just about optimum at the ride height I was running at. I'd like to have gone a little lower but on the bump stops my 18's were kissing the inner wing.
As I am now tubbing the inner wings I'll be running lower hence the need for the Whiteline kit.
Cheers Martin

I love this forum. It's very helpful sometimes.

I'm about to upgrade my suspension on my ver.5 Type R. One thing I'm thinking about buying is the whiteline roll centre adjustment kit. But it seems that people have different thoughts about the track rod ends, if they do what they suppose to do. Some say they actually give more bump-steer, the opposite to what they are suppose to do. And that you should only get the ball joints.

What are your thoughts about the track rod ends??


I don't know if i need the roll centre adjustment kit at all. I can't remember if I got bump-steer now or not. But I think it will help because my car sits kinda low.

I like the hight of the car now but I'm going to measure the hight from the hub to the fender to see where I am with that. If I'm to low I think I will raise it to the hight you are recommending.

But here is some pictures so you can see how low it is.

http://www.djfoto.se/bilder/subba/martin/_MG_9821.jpg

http://www.djfoto.se/bilder/subba/host/2.jpg

http://www.djfoto.se/bilder/subba/2011.05.21/4.jpg

Immaculate motor mate :thumb:
I don't personally get much in the way of bump steer, but it's the roll centre I have concerns about, so I may well look at that modification on mine.
Either way, looks like I should look to reduce the ride height at the rear on mine, but potentially raise the front a little too.
Once I've done that, I'll re-evaluate the roll and see if I think it still needs doing.

Thanks for all your feedback guys, as well as your positive comments on the car - gratefully received :)

Wow. That's clean, well done :notworthy

I'm convinced the track-rod ends are dubious. That's the first thing. The Impreza can cope well with some bump steer, and it rarely has a negative effect. There are chassis tuners who say the WL track rods make the bump steer worse. I've heard this from 3 sources, including Prodrive. For what it's worth, I wouldn't personally bother with them

What is much more important is to raise the roll centre to match your lower CoG on the lowered car. This reduced roll couple is a worthwhile upgrade. The Apex ones suggested by Fleetwood above look good

Thanks =).

Okey. I'm thinking about this kit from super pro. Looks similar as the Apex.

http://www.scoobyparts.co.uk/acatalo...O_RCA_KIT.html

As I understand it, the current WL ball joints come without a liner, but am not 100%. If this is the case, then WL really have sold out and must be grouped in with the rest of the Asian rubbish

The SuperPro ball joints will reduce the roll couple a little more than the WL's :thumb: and SuperPro stuff is well made

Okey. Maybe i should avoid buying WL stuff then.
Planing to buy this WL stuff.

BSF20XZ - 24mm WHITELINE Adjustable Front ARB
BSR20XXZ - 24mm WHITELINE Adjustable Rear ARB
KSB750 - WHITELINE SUBFRAME LOCK KIT
KCA319A - WHITELINE ANTI-LIFT KIT

Is there any others that make these things?

You're confusing me now (easilly done btw, so don't worry :) )

You say you are going to avoid buying Whiteline, yet you have posted a WL shopping list

The thing I would say is slow down a little. It is usually much better to add one upgrade at a time. This way you understand what difference each thing makes, and this is also more fun too.

Other thing is, is there any aspect of your car's handling you are not happy with? What are you hoping to achieve?

Re: ARB's. I have a Type R, with a 24mm rear set on middle, and a 22 front on firm. This, to me is alot of anti-roll, and in fact I was advised to go 22mm rear ONLY for road use...

I forgot the question mark =). It was a question about if i should avoid WL stuff completely. And I meant that is there others than WL that makes the arb's and anti lift kit?

Edit: After some searching i found CDF makes anti lift kit. And the other arb's i find is not adjustable like the whiteline.


Well for me to buy one thing at the time will be more expensive, more shipping cost to me in Sweden. That is why i want to buy saveral things at one time.

I want less roll,more grip. Better handling on the car. I want it to be natural not understeering or oversteering.

I'm going to the track with the car also, not just the road. So I decided for a 24/24 arb combo after advice from Arnie1 and after reading the following.


"Simply sticking a thicker ARB on the rear will not cure the Imprezas awful handling, sure traditional thinking has long held that if you want to fix understeer you want the rear to step out more. While this does appear to work to some extent to improve balance it doesn't reduce understeer so I feel this is the wrong way to approach.
Sure CONTROLLABLE oversteer with the back stepping out is fun, and a good thing, but the front is still going wide. As part of this traditional thinking folks scream get a bigger rear bar, and leave the front alone or go smaller. I have to disagree on this. Here's why -

First, let's look at the technical reason. The dynamic camber curve for the mc'pherson strut setup is very poor it's a basic design problem. all setups have their good and bad points. What happens is this - you enter a turn at speed. Your ourside front corner gets loaded with weight. That weight compresses the suspension. When the suspension compresses the camber of that wheel, where that tire is loaded, rolls toward positive camber. If you're running very little static negative camber this will actually start to make the inside edge of the tire light, reducing the width of your effective contact patch that resists lateral acceleration. This lose of traction results in that "push" or understeer condition. This is why folks who are more into performance run a decent amount of negative front camber. Sure, they give up some straight line accel and decel grip doing this, but that's more than offset by the fact that they can maximize the width of the contact patch in turns to help resist higher slip angles due to lateral acceleration. If you lower the car any with springs or coilovers that camber curve gets worse as does bumpsteer.

A thicker FRONT front swaybar will increase the effective spring rate of the wheel without effecting the ride spring rate. In other words, it will help keep the suspension from compressing so much at the loaded corner. Less compression means less loss of camber. Less loss of camber means that you can tune to, and maximize the contact patch of the tire to resist that push. Now, one of the things you need to consider - just like you can't make something from nothing, you can't make a good contact patch if you have nothing to give it to begin. Because the suspension will still compress some you need some negative camber in the front to start with.See, this stems from my philosophy that move oversteer does not necessarily mean less understeer. The front is still pushing. I feel the fix for this is to setup the front end of the car to truly reduce understeer as much as possible. This will make the front tuck in more, and while your tires will be resisting more lateral acceleration taking more grip from straight line acceleration (think traction circle), you'll be able to unwind from the turn faster thus getting you back toward the acceleration portion sooner than your competition. In other words, you'll be able to drive a tighter, and more controlled line.

Additionally, by reducing understeer as much as possible you won't have to set up the car for so much oversteer. This will also lead to more control, a tighter line, and the ability to accelerate sooner.

Now, that's great an all, but if you're looking for a simple answer as to what size bar to get then here it is (I'm giving these in terms of whiteline bars as I am most familiar with them):

Rear - 22mm to 24mm, but if you go to 24mm then you really want to think hard about upgrading your springs. If you go higher than 24mm then you are taking the wrong approach and trying to fix shortcomings of your springs with swaybars, and this is not the right way to do it. Get a proper spring for what you do, and then fine tune with a swaybar.

Front - for the street and mild autocross, and mild track work look at 24mm up front. If you start to get into it more then 26mm is good (WL makes a 24-26 adjustable front). These are also very good sizes if you are not a smooth driver as they won't make things too "darty" with super quick tuck of the front end into the apex. For autocross junkies or track whores who are smooth overall and can anticipate the "dartiness" then look at the 27 to 29mm front bar."

I would go with what Arnie recommends. It would be best to start another thread too. Happy fettling :)

Cheers guys.
In that case I suspect I'll go for the ball joints (I've heard good things re the Superpro stuff like you guys), drop the back a little, possibly raise the front and then get a pro geo setup.
Might even try it at the weekend as I'll have some free time.

Now here's the thing - I've been to a few so called specialists in Berkshire who reportedly do geo setups.
I know for a fact that one of them just dials in the standard STI manufacturer settings.

I've had the Prodrive settings done by my local dealer, which I actually thought were pretty good and definitely improved turn in, but would anyone else care to make any recommendations? I'm already running camber bolts at the rear so have a bit of play.

I'm in Bracknell, so East Berksl / West Surrey is ideal.

Hi there

not sure if James@GRD or Jimmy@JS Engineering http://www.jsraceengineering.com/

can help you with setup


Jura

Have look through this thread which has some good stuff in it

I usually 'work with' the geo aligner in coming up with settings. In other words I have a pretty firm idea of what I'm after when I arrive.

For my Type R weekender/ B-road muncher, I dial a slightly more 'fast road' setting to my daily wagon...