Swapping OEM suspension bits to MY04 wagon
15 March 2005, 10:10 AM
#1
Swapping OEM suspension bits to MY04 wagon
Anyone know which bits can be donated to an MY04 wagon from other Imprezas?
I'm looking at changing roll bars, roll bar links and alloy wishbones. I'm OK about the roll bar links, but can anyone confirm:
The front end of the MY03/04 wagon has the same parts as the GC8 classic saloon. If so then will the front alloy wishbones and roll bar off a classic saloon STi fit?
Is the MY03/04 wagon rear roll bar shape used in any other car, but in a thicker section - or can mine only be beefed up using aftermarket ones?
I have been looking around for a dead buegyed STi wagon to donate parts but they are very very rare, so perhaps something off a classic might work?
Nick
I'm looking at changing roll bars, roll bar links and alloy wishbones. I'm OK about the roll bar links, but can anyone confirm:
The front end of the MY03/04 wagon has the same parts as the GC8 classic saloon. If so then will the front alloy wishbones and roll bar off a classic saloon STi fit?
Is the MY03/04 wagon rear roll bar shape used in any other car, but in a thicker section - or can mine only be beefed up using aftermarket ones?
I have been looking around for a dead buegyed STi wagon to donate parts but they are very very rare, so perhaps something off a classic might work?
Nick
15 March 2005, 01:00 PM
#3
Thanks Austen.
I'm going to try and keep to Subaru gear from breakers, rather than nice whiteline or Perrin stuff, as I am a tight with my money.
I'll measure the bars I have at the moment and the ring a breaker.
The NASIOC guys are saying that stiffening up the front bar only is dialling out understeer on the Impreza.
It goes against what I was brought up with, but there was a thread on the camber changes through the full front suspension travel of an Impreza, which explained the reasoning - so I may try that first.
Nick
I'm going to try and keep to Subaru gear from breakers, rather than nice whiteline or Perrin stuff, as I am a tight with my money.
I'll measure the bars I have at the moment and the ring a breaker.
The NASIOC guys are saying that stiffening up the front bar only is dialling out understeer on the Impreza.
It goes against what I was brought up with, but there was a thread on the camber changes through the full front suspension travel of an Impreza, which explained the reasoning - so I may try that first.
Nick
15 March 2005, 01:07 PM
#4
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You need to stiffen up the rear to dial out the understeer!!! Thw whiteline adjustable rear ARB is only £65+vat from Demon tweeks (with SN discount), the none adjustable is only about £50 i think, probably cheaper than a breakers!!
15 March 2005, 05:37 PM
#6
I've had to sort out the dross, but these two statements sum it up.
They also appear to say that the front roll bar swap is more beneficial to the newage cars than classics.
Anyone comments? Are the statements valid for UK cars over the US models?
<<The other guys mentioned it earlier, but I'll try to explain better here.
What happens with the WRX is that under compression, the struts do not pick up additional negative camber like you would with a well-designed double a-arm design. In fact, some have mentioned that under compression the struts will actually pick up of positive camber which is exactly what you don't want for maximum grip.
Combine that positive camber gain under compression along with body roll and now you've got a huge postive camber gain which puts the tire on the shoulder and you've lost your contact patch and you end up with a large loss of traction and understeer.
Reducing the amount of roll in the front keeps the front tires planted flatter on the ground and the net gain is more grip even though you are increasing weight transfer at that end.
If the WRX had a perfect camber curve (or even just a half-way decent one) adding a stiffer bar up front would increase understeer. But because it lets the outside tire lean so far over anything we can do to keep it flatter will increase grip.
As mentioned, because the front a-arms are shorter than the rear lateral links, the the front suspension will pick up more positive camber than the rear under the same amount of compression. In addition, stock, the front camber is either 0 or slightly positive and the rear camber is around 1.5* negative. A simple alignment getting as much static negative front camber as possible (usually 1-1.5* with stock parts) and some rear camber bolts setting the rear to 0.5* or so will go a long ways towards reducing understeer.
This is one reason why it's a bad idea to lower the WRX (or any other strut-based car) so that the a-arms are above parallel. The further above parallel you get the arms, the more positive camber you get for a given amount of suspension travel as the arm follows it's arc closer to the center of the car. In addition, having the arm above parallel can decrease the effective spring rate as centrifugal force will cause the outside arm to dive worsening an already bad situation.>>
and <<The older body style Imprezas like you have actually came with stiffer springs and very tiny rear swaybars in comparison. Body roll on a stock setup wasn't near the problem that it is on the GD* chassis cars. Thus, your notable difference between what you have experienced and what those in the GD* chassis cars have experienced with regards to swaybars and effect. The body roll just wasn't there and quite the same problem on the older cars; not to mention that the car was notably lighter as well. Weight distribution I'm not sure about; that might be a factor as well perhaps.
As for the *best* handling GC RS I've ever driven (around town and on an autox course) it had a 25mm front and 24mm rear bar, along with the V5 STi struts and some springs.
Subieworx is right about the front bar and it's reduction in understeer. What happens in the case of the larger front bar == less understeer is that it's actually loading up the tire more, which is where the reduction in grip comes from that folks think about and read about in their "How To Setup A RaceCar" suspension books. But the soft springs and camber curve benefit far more than the small reduction in grip: So it's a gross effect of -1 (grip reduction from load) and a +4 (from fixing camber curve issues.) Your net effect is a +3. >>
Nick
They also appear to say that the front roll bar swap is more beneficial to the newage cars than classics.
Anyone comments? Are the statements valid for UK cars over the US models?
<<The other guys mentioned it earlier, but I'll try to explain better here.
What happens with the WRX is that under compression, the struts do not pick up additional negative camber like you would with a well-designed double a-arm design. In fact, some have mentioned that under compression the struts will actually pick up of positive camber which is exactly what you don't want for maximum grip.
Combine that positive camber gain under compression along with body roll and now you've got a huge postive camber gain which puts the tire on the shoulder and you've lost your contact patch and you end up with a large loss of traction and understeer.
Reducing the amount of roll in the front keeps the front tires planted flatter on the ground and the net gain is more grip even though you are increasing weight transfer at that end.
If the WRX had a perfect camber curve (or even just a half-way decent one) adding a stiffer bar up front would increase understeer. But because it lets the outside tire lean so far over anything we can do to keep it flatter will increase grip.
As mentioned, because the front a-arms are shorter than the rear lateral links, the the front suspension will pick up more positive camber than the rear under the same amount of compression. In addition, stock, the front camber is either 0 or slightly positive and the rear camber is around 1.5* negative. A simple alignment getting as much static negative front camber as possible (usually 1-1.5* with stock parts) and some rear camber bolts setting the rear to 0.5* or so will go a long ways towards reducing understeer.
This is one reason why it's a bad idea to lower the WRX (or any other strut-based car) so that the a-arms are above parallel. The further above parallel you get the arms, the more positive camber you get for a given amount of suspension travel as the arm follows it's arc closer to the center of the car. In addition, having the arm above parallel can decrease the effective spring rate as centrifugal force will cause the outside arm to dive worsening an already bad situation.>>
and <<The older body style Imprezas like you have actually came with stiffer springs and very tiny rear swaybars in comparison. Body roll on a stock setup wasn't near the problem that it is on the GD* chassis cars. Thus, your notable difference between what you have experienced and what those in the GD* chassis cars have experienced with regards to swaybars and effect. The body roll just wasn't there and quite the same problem on the older cars; not to mention that the car was notably lighter as well. Weight distribution I'm not sure about; that might be a factor as well perhaps.
As for the *best* handling GC RS I've ever driven (around town and on an autox course) it had a 25mm front and 24mm rear bar, along with the V5 STi struts and some springs.
Subieworx is right about the front bar and it's reduction in understeer. What happens in the case of the larger front bar == less understeer is that it's actually loading up the tire more, which is where the reduction in grip comes from that folks think about and read about in their "How To Setup A RaceCar" suspension books. But the soft springs and camber curve benefit far more than the small reduction in grip: So it's a gross effect of -1 (grip reduction from load) and a +4 (from fixing camber curve issues.) Your net effect is a +3. >>
Nick
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