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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.
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.
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?
Last edited by SubieJack; 16 January 2017 at 11:40 PM.
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.
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 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.
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.
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.
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?
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.
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.
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?
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.
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?
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
Last edited by bonesetter; 18 January 2017 at 02:56 PM.
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.
The article in the URL I posted above specifically deals with the RB320 suspension, have a read and see what you make of it
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.
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.
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
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
Last edited by bonesetter; 20 January 2017 at 01:35 PM.
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.
If you're lifting the inside rear wheel, with your sping/damper, soften the rear bar.
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.
16 January 2017, 06:39 PM
Rear anti-roll bar
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