Rear anti-roll bar
 

I've got a Prodrive rear anti-roll bar on my blob, and I'm trying to work out its size.

Ive got receipts from the previous owner for bushes that are 21mm, so I'm guessing (no sarcasm pls) this is a 21mm bar?

Would it be worth upgrading to a bigger Whiteline anti-roll bar, as shown in the link below, or shall I stick with the Prodrive bar? I was thinking 24 or 22mm would help with a bit of roll.

http://scoobyworld.co.uk/catalog/ind...lf2un08j5fo4r6

Cheers
Jack

The 21mm bar will be the one usually fitted to an RB320 which is already an upgrade. (Std OEM 20mm for STi)

%age increase in stiffness
http://www.subaru4you.co.uk/images/p...rstiffness.jpg

The rb320 21mm bar has two settings also so you can increase tension again on it by using inner most fitting hole for droplinks

Not in an Impreza but I've tried the RB320 ARB in a FSTi.
Works best on the soft hole (with a 20mm OEM front ARB), spoils the balance on the hard one.
Roll isn't necessarily bad as you can feel what the car is doing and can be more progressive on the limit.

https://cimg9.ibsrv.net/gimg/www.sco...49f8d05294.jpg

I've just had confirmation from the previous owner it is the 21mm bar from the RB320, so I will leave that for now and play around with the settings.

I agree, roll does help, but coming from two seaters I love the feeling of being completely flat all the time. Don't get me wrong, the scooby is planted, but where it has so much grip and you can go so fast, it naturally gets roll.

Is it relatively easy to change the settings? I've changed the bushes on the roll bar, so I'm guessing you just take it out of one hole by removing the bushes?

Would there be a difference upgrading to a 22mm roll bar, or would it be best to make a bigger jump?

The table in post 2 (assuming scoobynet has caught up) shows the various increases in stiffness when you change ARB's

That's a really handy table. Thank you!

I've recently just upgraded to a SuperPro adjustable 24mm rear bar, and honestly the difference is fantastic, feels much more planted and predictable, currently set up on the middle setting.

I went with SuperPro as the Whiteline products tend to suffer very badly with corrosion, but if I were you I'd have a play with the bar you have, and if it doesn't make enough difference for you then look to upgrade to a bigger bar.

^ 24mm rear with std front can make for tail happy car

True, but it all depends on how the rest of your suspension is setup too. I haven't found mine to step out at the back at all since the change, I guess it also depends on your driving style and how much your trying to push it.

I may look into the front to in the future but for now I'm quite happy with how it handles, and as it's adjustable its just about playing around until you like it.

moving to the inner bolt hole is the equivalent of fitting a 22mm bar

https://www.scoobynet.com/suspension...-roll-bar.html

Not quite. There's much more of a difference than that :)

It's more of an exponential thing. Have a look at Don's chart and see how much of a % increase there is from bar to bar

dont quite grasp what you are saying? i understand the % increase table what im saying is you will get the same percentage increase on a 21mm bar on 2nd setting as you would with a 22mm on a standard setting hence no point him upgrading to a 22mm bar unless it also has more than 1 setting

I found these articles a few weeks ago and found them interesting. If fitting a fatter rear ARB is your thing you may want to think twice.

http://www.pcadynamics.com/magazine-articles/

If you want to really reduce the feeling of roll then you need to go for thicker bars all round, not just on one axle. There may be tradeoffs that come with that, such as reduced compliance.

Lowering the centre of gravity would ultimately reduce the roll, but I want to keep the RB320 suspension really. Might look into 24mm on the rear, as that's what I feel lift in some corners. The front is pretty planted to be honest.

Can I just ask why are guys fitting stiffer ARBs?

I race RC cars and set up theory is pretty much the same.

If you fit a stiffer ARB then you take grip away from the end you've fitted it to.

If you fit a stiffer ARB on the rear, you're taking grip away from the rear. The rear is going to want to slide more.

If 4WD has a tendency to understeer, if you're taking grip from the rear, does that reduce the understeer at the front or will the whole car just slide more?

Over lowering the centre of gravity will increase roll - unless you address the roll centre at the same time. The rb320 front spring/Bilstein, as a combination, are as low as you can go - or you'll have no bump travel.

If you're lifting the inside rear wheel, with your sping/damper, soften the rear bar.

The rear will have less grip, but as the chassis is relatively stiff, there is also a diagonal effect from the rear bar, helping front grip.

Don't make the balance completely neutral, on a road car, or you'll come unstuck during emergency braking, lift-off oversteer and/or slippery conditions.

The short answer is you will have overall more grip

Longer answer is most road going cars are set up by the manufacturer to understeer, and fitting larger anti-roll bars will achieve two man things - balance of under and oversteer at the limit and an increased roll resistance, with an overall increase in grip

Larger rear bar fitment may sound like sacrificing rear grip, as the the stiffer bar will load the rear wheels more unevenly, however, as the rear resists roll more, the front resists less, and the front wheels will be more evenly loaded, increasing their grip, and overall grip

As the roll stiffness increases, chassis roll is reduced, reducing the effects of 'roll-camber' (loss of static alignment geometry, going into positive camber etc)

You could also reduce the front bar's stiffness to achieve the same, but the roll camber would reduce grip and spoil the handling

Car set-up is a personal thing, and there's many different ways to achieve your goal. I don't like understeer for example and prefer a car's rotational balance to be right under the driver's seat

The article in the URL I posted above specifically deals with the RB320 suspension, have a read and see what you make of it :thumb:

Am confused. I mentioned going for thicker bars on both axles, not lowering.

And you talked about reducing the feeling of roll, which is not the same thing as feeling "planted". In fact, increasing the size of the rear bar relative to the front will make the rear feel LESS planted.

What exactly are you seeking to achieve?

I'd suggest you'll have less overall grip.

You've intentionally redistributed some grip to the front - good.

But, the larger rear bar is destablising the contact patches, on both rear tyres - no such thing as a smooth road - dampers work constantly.
The larger rear bar is coupling the motions between both sides of the rear suspension. That will have a negative impact on braking, traction and comfort - the bigger the bar/worse the road, the greater the inherent instability.

On a road car, you don't want a neutral chassis, near the limit. A previously recoverable situation, becomes an accident waiting to happen.

Chassis tuning is a lot down to personal preference - a different driving style suits a different chassis set-up. There's many ways to skin a cat

Petter Solberg liked the RB320 with its rear bar set on stiffest - bit more rear bias balance (said it was the best road car he'd driven - we don't know what else what else he drove though ;) )

The S203 was set-up by STi to have a touch of entry corner understeer (which could be easily throttle controlled), those are just two examples

Personally, I like a neutral balance, and I think you'll find many do YMMV :)

Edit: I'm not saying I want a 100% neutral balance at the limit, and I understand what you're saying - the rear could easily overtake you in certain situations, usually just when you don't want it, but a good measure to help turn the car.

The car turns with much less steering input, negating to a large extent the effect of the roll resistance on the dampers/springs

For what it's worth, the STi pink rear ARB that the S203/S204 cars use is 21mm.

Agreed with bonesetter, handling/rotational balance is something personal and everything is relative and depends on a driver's experience amongst other things.

@ 2pot, why do you consider a neutral chassis at the limit as an accident waiting to happen?

The average driver will tend to lift off when a car understeers hence understeer may be seen as a "safer" behaviour, something that isn't necessarily true.

To control lift off oversteer though, lifting off or breaking (which is what most people tend to do) will make the situation worse.

When I first went around the Nurburgring with my 07 WRX wagon (Prodrive springs, 22mm front and rear ARBs, Whiteline ALK and upgraded droplinks) the car was so understeery that was scary (Toyo T1R tyres didn't help being soft like a bubble gum). You had to trail brake hard while turning in to make it turn (on all fours) which was much easier to control than understeer.

Ditto, this is not something you do at the road and I don't fancy a car that has sudden lift off oversteer without warning or being on my toes when it's wet but my 205 GTi modified by Skip Brown Cars is the best example I can give about a car that is planted while still retaining line adjustability mid-bend via the throttle.

Although a standard car's nickname was "widow maker" as many of you may have heard, the Skip Brown Cars modifications (Bilstein inverted dampers revalved in house, different springs, thicker rear ARB, thicker torsion bar and negative rear camber kit) made the car much more planted while still being able to adjust your lines mid-bend so progressively and accurately. Without one driving the car it is impossible to describe.

The thread should be moved under Suspension.

Agreed.

It was very easy to tripod my 205 GTi once the suspension was upgraded. Nothing wrong with tripoding though as the car had much more grip compared with the OEM setup.

Road car - Give yourself a margin for error - whether it's your error or someone else's.

Classic (manual) Subaru 19/20
Prodrive P1 19/20
Classic WR99 Prodrive/Bilstein kit 19/18 (stiffer rear springs)

Rear 21 or 22 - Dry, smooth, roads - more front grip.

If the roads are undulating/uneven or conditions are poor, soften the rear bar - increasing the margin for error.

As is the front ARB........

Brand: STI
Product: Stabilizer - Rear Impreza GD/GG
Part Num: ST204104S200

SPECIFICATIONS:
Application: Rear
Diameter (mm): 21
Color: Cherry Red

PRODUCT NOTES:
-Impreza (GD/GG) G-Type: When installing, STI lateral link set, and STI bracket link set are required (sold separately)


Brand: STI
Product: Stabilizer - Front Impreza GD/GG
Part Num: ST204104S010

SPECIFICATIONS:
Application: Front
Diameter (mm): 21