Bigger Roll bars and uk roads
08 March 2015, 05:07 PM
#91
Just thought I'd list my set up for anyone who may be interested.
Car is 54 WRX Wagon PPP and AP 4 pots up front.
225 /17 /45 Pirelli Sotto zero winter tyres on standard Sti rims.
Blue Super Pro (I think) polly bushes, on standard bars front and rear, also on the steering rack.
Camber bolts all round, although not taking advantage of them at the moment.
PCA Dynamics Blue springs on standard struts.
Rear alloy drop links.
Cusco rear roll bar brace, this mounts to the same points as the roll bar and goes pretty much in line with it across the underside of the car but has no real flex in it.
Front -1.25 camber
Rear -1.50 camber
Toe -0 01
Caster is around 3.37 had some problems with this but as the next mod is Classic STI Alloy front wishbones and drop links I've not concentrated on it too much.
Going to be heading for about 5 degrees of caster.
Personally I think this set up is good for the road, very stable in all conditions
and when pushing on, good steering feel, direction changes are vastly improved as is cornering speed.
I still have a small amount of understeer which is easily controlled with the gas, either ease off a little and it straightens up or give it some more and the back starts to come round a little, depending on road conditions and speed, but that is me being a little lairy in the wet, turn in is still very good.
Still have a bit of front end roll I'd like to lose and not sure about the understeer as yet but that can be cured via a little more camber or possibly a slightly bigger Front Roll bar (22mm) I'll wait and see how it feels after they Alloy arms are fitted and add 0.5 of neg camber at the front.
I'm currently set up for winter on greasy winding country roads in one of the Mountain Regions of Croatia and you don't really want an over active back end, had that with my last set up and it was a tad hairy for winter.
As above next steps are hopefully going to be the final part to get it exactly where I want it.
I'll be changing to summer rubber soon and add a bit more camber front and rear as I'll be moving a fair bit faster and loading the suspension up more.
As you can tell I'm no expert but in laymans terms this is a good cheap way to get a WRX handling and steering pretty well for about £300 and the ride is still pretty good too.
HTH.
Car is 54 WRX Wagon PPP and AP 4 pots up front.
225 /17 /45 Pirelli Sotto zero winter tyres on standard Sti rims.
Blue Super Pro (I think) polly bushes, on standard bars front and rear, also on the steering rack.
Camber bolts all round, although not taking advantage of them at the moment.
PCA Dynamics Blue springs on standard struts.
Rear alloy drop links.
Cusco rear roll bar brace, this mounts to the same points as the roll bar and goes pretty much in line with it across the underside of the car but has no real flex in it.
Front -1.25 camber
Rear -1.50 camber
Toe -0 01
Caster is around 3.37 had some problems with this but as the next mod is Classic STI Alloy front wishbones and drop links I've not concentrated on it too much.
Going to be heading for about 5 degrees of caster.
Personally I think this set up is good for the road, very stable in all conditions
and when pushing on, good steering feel, direction changes are vastly improved as is cornering speed.
I still have a small amount of understeer which is easily controlled with the gas, either ease off a little and it straightens up or give it some more and the back starts to come round a little, depending on road conditions and speed, but that is me being a little lairy in the wet, turn in is still very good.
Still have a bit of front end roll I'd like to lose and not sure about the understeer as yet but that can be cured via a little more camber or possibly a slightly bigger Front Roll bar (22mm) I'll wait and see how it feels after they Alloy arms are fitted and add 0.5 of neg camber at the front.
I'm currently set up for winter on greasy winding country roads in one of the Mountain Regions of Croatia and you don't really want an over active back end, had that with my last set up and it was a tad hairy for winter.
As above next steps are hopefully going to be the final part to get it exactly where I want it.
I'll be changing to summer rubber soon and add a bit more camber front and rear as I'll be moving a fair bit faster and loading the suspension up more.
As you can tell I'm no expert but in laymans terms this is a good cheap way to get a WRX handling and steering pretty well for about £300 and the ride is still pretty good too.
HTH.
We need to know your rear diameter
Last edited by bonesetter; 08 March 2015 at 05:08 PM.
08 March 2015, 05:09 PM
#92
'Roll over steer' is a normal term in suspension engineering. This happens when a car rolls 'off its rear grip'.
Indeed, extra caster will increase the loading on the inside front wheel during cornering and increase the negative camber on the outside front wheel during cornering. Do pay attention to the camber gain curve when adding caster as on a lot of cars the camber gain is quicker than the loading increase on the outside wheel resulting in the car momentarily only running on part of the front tyre during turn in. This will provide an unsettling feeling, like driving on eggs.
Remember, Subaru fitted ARBs to the Impreza to suit all types of drivers with all types of tyres and all types of road surface. This compromise does favour a safer under steer bias. As enthusiasts might want a slightly different compromise. Even Subaru used a larger rear ARB on some of the more driver orientated specials. In all forms of motorsport ARB adjustment is used to change a car's balance, where permitted in regulation.
In my experience with my Imprezas, the change from Michelin or GoodYear tyres to Bridgestone or Yokodrama has a much larger effect on comfort than changing to a slightly larger diameter rear ARB.
People running cheaper coilovers normally have much larger problems with unloading of the inside rear wheel not only due to reduced rear droop but also increased stiction as well as higher amounts of lower speed rebound allowing the car to 'hold on to its wheels' in roll mode.
I understand that your experience is different. Showing again this is to do with personal preference, not wrong or right.
Indeed, extra caster will increase the loading on the inside front wheel during cornering and increase the negative camber on the outside front wheel during cornering. Do pay attention to the camber gain curve when adding caster as on a lot of cars the camber gain is quicker than the loading increase on the outside wheel resulting in the car momentarily only running on part of the front tyre during turn in. This will provide an unsettling feeling, like driving on eggs.
Remember, Subaru fitted ARBs to the Impreza to suit all types of drivers with all types of tyres and all types of road surface. This compromise does favour a safer under steer bias. As enthusiasts might want a slightly different compromise. Even Subaru used a larger rear ARB on some of the more driver orientated specials. In all forms of motorsport ARB adjustment is used to change a car's balance, where permitted in regulation.
In my experience with my Imprezas, the change from Michelin or GoodYear tyres to Bridgestone or Yokodrama has a much larger effect on comfort than changing to a slightly larger diameter rear ARB.
People running cheaper coilovers normally have much larger problems with unloading of the inside rear wheel not only due to reduced rear droop but also increased stiction as well as higher amounts of lower speed rebound allowing the car to 'hold on to its wheels' in roll mode.
I understand that your experience is different. Showing again this is to do with personal preference, not wrong or right.
The following prodrive classics had to be capable of driving quickly on undulating B roads, as do we all. Depending on the springs, I don't think the big rear bar stacks up. Each to their own though.
P1 34N/mm 27.5N/mm 19mm/20mm bars
WR99 35N/mm 35N/mm 19mm/18mm bars
I also think, if you're learning in your own car, at track days, and you want to drive home, an amount of at the limit understeer is not a bad thing!
This sums up what I've discovered, and he's forgotten more than I'll ever know, about car set-up:
Originally Posted by johnfelstead 
Setting a car up to handle is far more involved than just choosing the correct dampers and springs, you have to match everything else on the car so that it works in harmony. For example, having the spring rates low and damping high can lead to some very dangerous situations where the suspension jacks itself down onto the bump stops. You also need to choose the bump stops you use and how long they are, bump stops are not what most people think, a last resort to save the damper, they are a very important tuning device that alters your efective spring rates under higher load. My bump stops are used actively to give a rising rate of spring rate up at the upper end of suspension bump travel.
I also played around with suspension ride height and rake settings, the Impreza doesnt like low ride heights at all, it responds well to dialing in some positive rake, this especially improves front end bite on corner entry, it has less effect on set state cornering, changing as little as 3mm in rake makes a huge diference.
You also have to decide what you want from the car. I run my car with 22mm ARB's front/rear with the rear set to fully stiff. This works incredibly well in most circumstances, but on a very bumpy B road its more of a handfull than most people would like. Going back to a stock front and mid rear bar setting makes it much easier to drive on a bumpy road, the fastest aproach to ARB's on bumpy roads is actually to use stock STi bars, but that compromises the car on the smoother roads and track. You can help gain some control back by upping the damping rates, but that takes away some of the balance in other areas.
The point i am trying to make is there is no right or wrong (unless its seriously fubar'd), you need to know what you want and then design the suspension around that. Some things are certain, stiff wheel rates dont work in the UK, ride height needs to be sensible, you have to use positive rake and you must get your geometries setup acurately, running more rear camber than most people have and a very small amount of f/r toe-in to aid stability.
Last edited by 2pot; 08 March 2015 at 05:15 PM.
08 March 2015, 05:45 PM
#93
What do the guys on the P1 forum run?
I think a lot of the P1 guys run thicker than OE rear bars
My P1 (Type R 'P1') set-up runs 20 front on hard (soft setting understeers) and 24 rear on medium
Obliterates all 'shire' roads
I think a lot of the P1 guys run thicker than OE rear bars
My P1 (Type R 'P1') set-up runs 20 front on hard (soft setting understeers) and 24 rear on medium
Obliterates all 'shire' roads
08 March 2015, 06:11 PM
#94
It was reading this and other threads that steered me away from a big fat rear roll bar, I would say my set up is probably the equivalent of fitting an STI bar on the rear.
One point I'd like to make for anyone reading this is that my turn in and ability to hold a line is sooooo much better than it was, direction changes are not greeted with the woaaaaa of my previous set up, it's a good thing I had the AP's for that because they were needed to seriously reduce speed when I came to the bendy bits, that's not necessary now.
Last edited by ditchmyster; 08 March 2015 at 06:22 PM.
08 March 2015, 06:36 PM
#95
What do the guys on the P1 forum run?
I think a lot of the P1 guys run thicker than OE rear bars
My P1 (Type R 'P1') set-up runs 20 front on hard (soft setting understeers) and 24 rear on medium
Obliterates all 'shire' roads
I think a lot of the P1 guys run thicker than OE rear bars
My P1 (Type R 'P1') set-up runs 20 front on hard (soft setting understeers) and 24 rear on medium
Obliterates all 'shire' roads
08 March 2015, 10:00 PM
#97
The RB320 is 20mm front, 21mm road/track adjustable rear (soft setting 20.5mm, hard setting 21.5mm). Due to the softer prodrive suspension for the UK.
I've posted this link already on SN. See if it helps you to see what I'm getting at, with regard to big bars.
FCM Suspension Truth v2.6 - The Hidden Cost of Sway Bars - YouTube
I've posted this link already on SN. See if it helps you to see what I'm getting at, with regard to big bars.
FCM Suspension Truth v2.6 - The Hidden Cost of Sway Bars - YouTube
We re saying the same thing I think.
It's all about the golden mean and finding the balance.
From my experience, 22mm front and back ARBs (that was with hawkeye Prodrive WRX wagon springs - not sure of their rates) was too stiff for my liking, 20mm front and 21.6mm rear (on the FSTi with custom made Bilstein B14s and 5kg front, 3.7kg rear springs) worked perfectly for all conditions).
If you don't use any ARB at all though the car will roll so much more that it will cause loss of grip.
Using too big a bar, you will have more grip on flat, smooth roads but on slippery ones the car will loose grip suddenly without much warning.
Last edited by fpan; 08 March 2015 at 10:17 PM.
08 March 2015, 10:45 PM
#98
To be precise, the rear ARB on the RB320 is 21.6mm in diameter.
We re saying the same thing I think.
It's all about the golden mean and finding the balance (from my experience 22mm front and back was too stiff for my liking, 20mm front and 21.6mm back worked perfectly for all conditions).
If you don't use any ARB at all though the car will roll so much more (unless it has stiffer springs) that it will cause loss of grip.
Using too big a bar, you will have more grip on flat, smooth roads but on slippery (or undulating) ones the car will loose grip suddenly without much warning.
We re saying the same thing I think.
It's all about the golden mean and finding the balance (from my experience 22mm front and back was too stiff for my liking, 20mm front and 21.6mm back worked perfectly for all conditions).
If you don't use any ARB at all though the car will roll so much more (unless it has stiffer springs) that it will cause loss of grip.
Using too big a bar, you will have more grip on flat, smooth roads but on slippery (or undulating) ones the car will loose grip suddenly without much warning.
Can't disagree with the above.Just being a bit tedious on this subject, as I've had some classic springs designed, with alternative bump stops, and trying to understand the seemingly automatic change to 22/24 bars, on UK/NI roads.
Last edited by 2pot; 08 March 2015 at 10:47 PM.
09 March 2015, 08:47 AM
#99
Have you tried a ~24/22 arb set-up?
With OE spring/damper (and decent coiovers) it works very well indeed for UK roads
I have that combo on my current Type R and have used the same on other Impreza's. With sensible ride height, not over-lowered, decent travel it gives plenty of compliancy with control
The rear 24 is set to middle and the front to full stiff. Set the rear to the softest setting and you get understeer. Hard setting and upset the rotation
Here's a good post from the 22B forum
Setting a car up to handle is far more involved than just choosing the correct dampers and springs, you have to match everything else on the car so that it works in harmony. For example, having the spring rates low and damping high can lead to some very dangerous situations where the suspension jacks itself down onto the bump stops. You also need to choose the bump stops you use and how long they are, bump stops are not what most people think, a last resort to save the damper, they are a very important tuning device that alters your efective spring rates under higher load. My bump stops are used actively to give a rising rate of spring rate up at the upper end of suspension bump travel.
I also played around with suspension ride height and rake settings, the Impreza doesnt like low ride heights at all, it responds well to dialing in some positive rake, this especially improves front end bite on corner entry, it has less effect on set state cornering, changing as little as 3mm in rake makes a huge diference.
You also have to decide what you want from the car. I run my car with 22mm ARB's front/rear with the rear set to fully stiff. This works incredibly well in most circumstances, but on a very bumpy B road its more of a handfull than most people would like. Going back to a stock front and mid rear bar setting makes it much easier to drive on a bumpy road, the fastest aproach to ARB's on bumpy roads is actually to use stock STi bars, but that compromises the car on the smoother roads and track. You can help gain some control back by upping the damping rates, but that takes away some of the balance in other areas.
The point i am trying to make is there is no right or wrong (unless its seriously fubar'd), you need to know what you want and then design the suspension around that. Some things are certain, stiff wheel rates dont work in the UK, ride height needs to be sensible, you have to use positive rake and you must get your geometries setup acurately, running more rear camber than most people have and a very small amount of f/r toe-in to aid stability.
With OE spring/damper (and decent coiovers) it works very well indeed for UK roads
I have that combo on my current Type R and have used the same on other Impreza's. With sensible ride height, not over-lowered, decent travel it gives plenty of compliancy with control
The rear 24 is set to middle and the front to full stiff. Set the rear to the softest setting and you get understeer. Hard setting and upset the rotation
Here's a good post from the 22B forum
Setting a car up to handle is far more involved than just choosing the correct dampers and springs, you have to match everything else on the car so that it works in harmony. For example, having the spring rates low and damping high can lead to some very dangerous situations where the suspension jacks itself down onto the bump stops. You also need to choose the bump stops you use and how long they are, bump stops are not what most people think, a last resort to save the damper, they are a very important tuning device that alters your efective spring rates under higher load. My bump stops are used actively to give a rising rate of spring rate up at the upper end of suspension bump travel.
I also played around with suspension ride height and rake settings, the Impreza doesnt like low ride heights at all, it responds well to dialing in some positive rake, this especially improves front end bite on corner entry, it has less effect on set state cornering, changing as little as 3mm in rake makes a huge diference.
You also have to decide what you want from the car. I run my car with 22mm ARB's front/rear with the rear set to fully stiff. This works incredibly well in most circumstances, but on a very bumpy B road its more of a handfull than most people would like. Going back to a stock front and mid rear bar setting makes it much easier to drive on a bumpy road, the fastest aproach to ARB's on bumpy roads is actually to use stock STi bars, but that compromises the car on the smoother roads and track. You can help gain some control back by upping the damping rates, but that takes away some of the balance in other areas.
The point i am trying to make is there is no right or wrong (unless its seriously fubar'd), you need to know what you want and then design the suspension around that. Some things are certain, stiff wheel rates dont work in the UK, ride height needs to be sensible, you have to use positive rake and you must get your geometries setup acurately, running more rear camber than most people have and a very small amount of f/r toe-in to aid stability.
09 March 2015, 11:23 AM
#100
Have you tried a ~24/22 arb set-up?
With OE spring/damper (and decent coiovers) it works very well indeed for UK roads
I have that combo on my current Type R and have used the same on other Impreza's. With sensible ride height, not over-lowered, decent travel it gives plenty of compliancy with control
The rear 24 is set to middle and the front to full stiff. Set the rear to the softest setting and you get understeer. Hard setting and upset the rotation
Here's a <a rel="nofollow" href="http://bbs.22b.com/forums/showthread.php?13338-Suspension-setup" target="_blank">good post from the 22B forum
Setting a car up to handle is far more involved than just choosing the correct dampers and springs, you have to match everything else on the car so that it works in harmony. For example, having the spring rates low and damping high can lead to some very dangerous situations where the suspension jacks itself down onto the bump stops. You also need to choose the bump stops you use and how long they are, bump stops are not what most people think, a last resort to save the damper, they are a very important tuning device that alters your efective spring rates under higher load. My bump stops are used actively to give a rising rate of spring rate up at the upper end of suspension bump travel.
I also played around with suspension ride height and rake settings, the Impreza doesnt like low ride heights at all, it responds well to dialing in some positive rake, this especially improves front end bite on corner entry, it has less effect on set state cornering, changing as little as 3mm in rake makes a huge diference.
You also have to decide what you want from the car. I run my car with 22mm ARB's front/rear with the rear set to fully stiff. This works incredibly well in most circumstances, but on a very bumpy B road its more of a handfull than most people would like. Going back to a stock front and mid rear bar setting makes it much easier to drive on a bumpy road, the fastest aproach to ARB's on bumpy roads is actually to use stock STi bars, but that compromises the car on the smoother roads and track. You can help gain some control back by upping the damping rates, but that takes away some of the balance in other areas.
The point i am trying to make is there is no right or wrong (unless its seriously fubar'd), you need to know what you want and then design the suspension around that. Some things are certain, stiff wheel rates dont work in the UK, ride height needs to be sensible, you have to use positive rake and you must get your geometries setup acurately, running more rear camber than most people have and a very small amount of f/r toe-in to aid stability.
With OE spring/damper (and decent coiovers) it works very well indeed for UK roads
I have that combo on my current Type R and have used the same on other Impreza's. With sensible ride height, not over-lowered, decent travel it gives plenty of compliancy with control
The rear 24 is set to middle and the front to full stiff. Set the rear to the softest setting and you get understeer. Hard setting and upset the rotation
Here's a <a rel="nofollow" href="http://bbs.22b.com/forums/showthread.php?13338-Suspension-setup" target="_blank">good post from the 22B forum
Setting a car up to handle is far more involved than just choosing the correct dampers and springs, you have to match everything else on the car so that it works in harmony. For example, having the spring rates low and damping high can lead to some very dangerous situations where the suspension jacks itself down onto the bump stops. You also need to choose the bump stops you use and how long they are, bump stops are not what most people think, a last resort to save the damper, they are a very important tuning device that alters your efective spring rates under higher load. My bump stops are used actively to give a rising rate of spring rate up at the upper end of suspension bump travel.
I also played around with suspension ride height and rake settings, the Impreza doesnt like low ride heights at all, it responds well to dialing in some positive rake, this especially improves front end bite on corner entry, it has less effect on set state cornering, changing as little as 3mm in rake makes a huge diference.
You also have to decide what you want from the car. I run my car with 22mm ARB's front/rear with the rear set to fully stiff. This works incredibly well in most circumstances, but on a very bumpy B road its more of a handfull than most people would like. Going back to a stock front and mid rear bar setting makes it much easier to drive on a bumpy road, the fastest aproach to ARB's on bumpy roads is actually to use stock STi bars, but that compromises the car on the smoother roads and track. You can help gain some control back by upping the damping rates, but that takes away some of the balance in other areas.
The point i am trying to make is there is no right or wrong (unless its seriously fubar'd), you need to know what you want and then design the suspension around that. Some things are certain, stiff wheel rates dont work in the UK, ride height needs to be sensible, you have to use positive rake and you must get your geometries setup acurately, running more rear camber than most people have and a very small amount of f/r toe-in to aid stability.
It's a great post, that's why I used it in post 92. It covers everything I've found, so far.24/22 - I assume that's a Freudian slip, and you meant 22/24?
Haven't tried 22/24. Started with 19mm front and 20mm adjustable rear. I got as far as adjustable 22/22, and ran out of talent. Then thought "I'll get some higher rate springs made - how hard can it be?"
My issue is, as I've said many times before:
A bigger rear bar is effectively masking the inherent understeer.
By using a bigger, balancing, rear bar, the rear is oversteering more, than the front is understeering - that is a very wide line.
As we're discussing road use, IMO, that's a 19mm-22mm front bar - depending on your roads.
Why not address the understeer first, through alignment, increased caster, bump stops, bigger front bar (I know that's counter-intuitive, but it's stopping the camber going positive) and spring rates.
This, allows a smaller rear bar, which increases grip, independence and comfort.
A bigger front bar helps turn-in. At the expense of high speed mid and exit corner understeer.
A bigger rear bar reduces grip and comfort and moves the balance toward or into oversteer.
You choose the balance.
Can we agree, it's better to use struts than cheap coilovers?
Last edited by 2pot; 09 March 2015 at 12:33 PM. Reason: add reason
09 March 2015, 03:22 PM
#101
I wouldn't get too hung up on rear arb and any inherent compromise
In fact, fitting an uprated rear bar on an Impreza does not so much reduce the rear grip, but increases the weight on the inside front wheel during cornering
- it's the diagonally opposite corner which 'gains' when fitting a thicker arb, (front or rear), thus the rarb will increase overall grip
The rarb also reduces the effects of "roll camber" which as you say gives the outside wheels positive camber under cornering
I prefer a softer spring rate and as much travel as can be. My Forester STi is great at going fast on bad (and good for that matter) roads
How would you alter geometry to 'help' with understeer?
In fact, fitting an uprated rear bar on an Impreza does not so much reduce the rear grip, but increases the weight on the inside front wheel during cornering
- it's the diagonally opposite corner which 'gains' when fitting a thicker arb, (front or rear), thus the rarb will increase overall grip
The rarb also reduces the effects of "roll camber" which as you say gives the outside wheels positive camber under cornering
I prefer a softer spring rate and as much travel as can be. My Forester STi is great at going fast on bad (and good for that matter) roads
How would you alter geometry to 'help' with understeer?
09 March 2015, 08:32 PM
#102
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It's a great post, that's why I used it in post 92. It covers everything I've found, so far.24/22 - I assume that's a Freudian slip, and you meant 22/24?
Haven't tried 22/24. Started with 19mm front and 20mm adjustable rear. I got as far as adjustable 22/22, and ran out of talent. Then thought "I'll get some higher rate springs made - how hard can it be?"
My issue is, as I've said many times before:
A bigger rear bar is effectively masking the inherent understeer.
By using a bigger, balancing, rear bar, the rear is oversteering more, than the front is understeering - that is a very wide line.
As we're discussing road use, IMO, that's a 19mm-22mm front bar - depending on your roads.
Why not address the understeer first, through alignment, increased caster, bump stops, bigger front bar (I know that's counter-intuitive, but it's stopping the camber going positive) and spring rates.
This, allows a smaller rear bar, which increases grip, independence and comfort.
A bigger front bar helps turn-in. At the expense of high speed mid and exit corner understeer.
A bigger rear bar reduces grip and comfort and moves the balance toward or into oversteer.
You choose the balance.
Can we agree, it's better to use struts than cheap coilovers?
A larger front bar can help turn-in. However, when there is little grip available between the road surface and the tyres due to rain, grease, ice etc. it can stop the car turning in altogether.
Comparing parts that reduce comfort, I would place a slightly larger rear ARB quite far down the list, after harder springs, reduced suspension travel, too much rebound, worn bushes, hard tyres etc.
09 March 2015, 11:58 PM
#103
Irrespective of bars transferring diagonally and springs laterally, weight transfer reduces overall grip. The bigger the bar the less the roll, but, the greater the lateral load transfer, whilst cornering
Whichever pair of wheels, front or rear, that resist roll most (stiffest bar/spring combination) will have the lowest traction.
By increasing rear bar size, and therefore the percentage of weight transfer dealt with by the rear axle, that's the end that'll slide first.
Whichever pair of wheels, front or rear, that resist roll most (stiffest bar/spring combination) will have the lowest traction.
By increasing rear bar size, and therefore the percentage of weight transfer dealt with by the rear axle, that's the end that'll slide first.
Last edited by 2pot; 10 March 2015 at 10:01 AM. Reason: add 'but'
10 March 2015, 12:24 AM
#104
A larger front bar can help turn-in. However, when there is little grip available between the road surface and the tyres due to rain, grease, ice etc. it can stop the car turning in altogether.
Comparing parts that reduce comfort, I would place a slightly larger rear ARB quite far down the list, after harder springs, reduced suspension travel, too much rebound, worn bushes, hard tyres etc.
Comparing parts that reduce comfort, I would place a slightly larger rear ARB quite far down the list, after harder springs, reduced suspension travel, too much rebound, worn bushes, hard tyres etc.
The comfort issue was not the bar itself, but the reduction of rear suspension independence, by fitting a larger rear bar.
I'm sure I've mentioned those points before.
10 March 2015, 07:58 PM
#105
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Irrespective of bars transferring diagonally and springs laterally, weight transfer reduces overall grip. The bigger the bar the less the roll, but, the greater the lateral load transfer, whilst cornering
Whichever pair of wheels, front or rear, that resist roll most (stiffest bar/spring combination) will have the lowest traction.
By increasing rear bar size, and therefore the percentage of weight transfer dealt with by the rear axle, that's the end that'll slide first.
Whichever pair of wheels, front or rear, that resist roll most (stiffest bar/spring combination) will have the lowest traction.
By increasing rear bar size, and therefore the percentage of weight transfer dealt with by the rear axle, that's the end that'll slide first.
We even run quite a lot of ARB on formula cars in most of the highest forms of motorsport. Both to fine-tune balance as well a to increase grip (depending on the suspension frequency and grip available between tyre and road surface).
Traction is another story again. I have been writing about grip.
I do think you are making an issue of the reduction in suspension independence on the Impreza when increasing bar diameter by a couple of mm, that most people won't feel or notice.
What most people notice when fitting a slightly larger rear ARB is increased front end grip due to the inside front tyre working harder, faster turn-in and a very slight reduction in rear end grip. Most people like this change in balance that allows most Imprezas to be able to be 'steered on the throttle' better.
Traction normally is not a problem with the Impreza at all unless running huge torque and power.
Last edited by lookout; 10 March 2015 at 08:03 PM.
10 March 2015, 08:45 PM
#106
What most people notice when fitting a slightly larger rear ARB is increased front end grip due to the inside front tyre working harder, faster turn-in and a very slight reduction in rear end grip. Most people like this change in balance that allows most Imprezas to be able to be 'steered on the throttle' better.
Traction normally is not a problem with the Impreza at all unless running huge torque and power.
Traction normally is not a problem with the Impreza at all unless running huge torque and power.
11 March 2015, 12:09 AM
#107
ARBs do not always reduce grip or traction. Quite often they do, but only on the axle it is fitted on.
We even run quite a lot of ARB on formula cars in most of the highest forms of motorsport. Both to fine-tune balance as well a to increase grip (depending on the suspension frequency and grip available between tyre and road surface).
Traction is another story again. I have been writing about grip.
I do think you are making an issue of the reduction in suspension independence on the Impreza when increasing bar diameter by a couple of mm, that most people won't feel or notice.
What most people notice when fitting a slightly larger rear ARB is increased front end grip due to the inside front tyre working harder, faster turn-in and a very slight reduction in rear end grip. Most people like this change in balance that allows most Imprezas to be able to be 'steered on the throttle' better.
Traction normally is not a problem with the Impreza at all unless running huge torque and power.
We even run quite a lot of ARB on formula cars in most of the highest forms of motorsport. Both to fine-tune balance as well a to increase grip (depending on the suspension frequency and grip available between tyre and road surface).
Traction is another story again. I have been writing about grip.
I do think you are making an issue of the reduction in suspension independence on the Impreza when increasing bar diameter by a couple of mm, that most people won't feel or notice.
What most people notice when fitting a slightly larger rear ARB is increased front end grip due to the inside front tyre working harder, faster turn-in and a very slight reduction in rear end grip. Most people like this change in balance that allows most Imprezas to be able to be 'steered on the throttle' better.
Traction normally is not a problem with the Impreza at all unless running huge torque and power.
I have no issue with a starting point of 19mm/20mm on a classic or 20/21mm on a newage, that use poor, undulating roads, assuming correct spring rates - it's a cheap and effective set-up.
But, you've chosen to ignore this - it's not up for debate - it's fact:
By increasing rear bar size, and therefore the percentage of weight transfer dealt with by the rear axle, that's the end that'll slide first.
You've caused the rear to oversteer to compensate for an understeering front.
Sort out the understeer, first.
MacPherson strut front suspension - poor camber curve, you gain more by fitting a bigger front bar, to stop the curve collapsing and maintaining negative camber. Turn-in is more important, than the potential for high-speed understeer.
Should understeer be a issue, balance with a rear bar of an appropriate size - it doesn't have a collapsing camber curve to maintain.
As you, rightly, explained previously the rear bar can help the front. Conversely, by fitting a larger front bar, you've helped the rear.
11 March 2015, 02:24 PM
#108
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What would you all suggest?
Since moving from stiffer bars back to oem my car is super smooth and controlled on undulating and bumpy roads.
But I'm still have a bit to much high speed roll.
Would I benefit from a roll centre kit or going up a spring rate.
I'm on 5/4 at the moment would a 6/5 be more suited?
Since moving from stiffer bars back to oem my car is super smooth and controlled on undulating and bumpy roads.
But I'm still have a bit to much high speed roll.
Would I benefit from a roll centre kit or going up a spring rate.
I'm on 5/4 at the moment would a 6/5 be more suited?
12 March 2015, 04:43 PM
#110
What would you all suggest?
Since moving from stiffer bars back to oem my car is super smooth and controlled on undulating and bumpy roads.
But I'm still have a bit to much high speed roll.
Would I benefit from a roll centre kit or going up a spring rate.
I'm on 5/4 at the moment would a 6/5 be more suited?
Since moving from stiffer bars back to oem my car is super smooth and controlled on undulating and bumpy roads.
But I'm still have a bit to much high speed roll.
Would I benefit from a roll centre kit or going up a spring rate.
I'm on 5/4 at the moment would a 6/5 be more suited?
20/17
20/20
20/21
And under what circumstances does high speed roll happen?
And assuming you've still got the 22mm bars? Why don't you try a 22 on the front, or a 22mm on the rear. And post the results. Would be interesting.
Last edited by 2pot; 12 March 2015 at 04:50 PM.
13 March 2015, 09:57 AM
#111
Should be useful having these attached to this thread.
http://pcadynamics.com/app/download/...he+Insider.pdf
http://pcadynamics.com/app/download/...a+Handling.pdf
http://pcadynamics.com/app/download/...+-+Insider.pdf
http://pcadynamics.com/app/download/...32/Insider.pdf
http://pcadynamics.com/app/download/...10400-TECH.pdf
http://pcadynamics.com/app/download/...he+Insider.pdf
http://pcadynamics.com/app/download/...a+Handling.pdf
http://pcadynamics.com/app/download/...+-+Insider.pdf
http://pcadynamics.com/app/download/...32/Insider.pdf
http://pcadynamics.com/app/download/...10400-TECH.pdf
19 March 2015, 11:45 AM
#112
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Not knowing much about newage bar sizes, when you say you went back to oem bars, is that:
20/17
20/20
20/21
And under what circumstances does high speed roll happen?
And assuming you've still got the 22mm bars? Why don't you try a 22 on the front, or a 22mm on the rear. And post the results. Would be interesting.
20/17
20/20
20/21
And under what circumstances does high speed roll happen?
And assuming you've still got the 22mm bars? Why don't you try a 22 on the front, or a 22mm on the rear. And post the results. Would be interesting.
24mm and 22mm on different settings.
Oem front 22rear makes the front roll more and feel very soft up front.
But slightly nervous at the back end over bumps.
Oem rear 22mm front makes the car turn in better and feel more responsive to steering inputs. But very nervous over bumps at speed.
22 front and back is kind of the same affect depending on what settings there on.
24mm bars are horrid bumping and crashing off undulations and bumps and lifting a rear wheel coming out of driveways ect. Made my favourite roads unenjoyable to drive on finding bumps that I didn't know was there.
Oem front and rear the cars is composed on our roads and so much smother to drive.
Low speed roundabouts ect no roll
Higher speeds corners feels like the car rolls more.
Just fitted a SuperPro roll centre correction kit.
And the car feels just like adding a 22mm front bar. Turn in is more responsive and less initial roll but without the harsh ride.
After all this I personally prefer the oem bars. I know a lot of people like them but for me I like my car working with the road rather than keeping me on my toes.
All a personal preference I guess.
19 March 2015, 09:03 PM
#115
I've tried all combinations of bars.
24mm and 22mm on different settings.
Oem front 22rear makes the front roll more and feel very soft up front.
But slightly nervous at the back end over bumps.
Oem rear 22mm front makes the car turn in better and feel more responsive to steering inputs. But very nervous over bumps at speed.
22 front and back is kind of the same affect depending on what settings there on.
24mm bars are horrid bumping and crashing off undulations and bumps and lifting a rear wheel coming out of driveways ect. Made my favourite roads unenjoyable to drive on finding bumps that I didn't know was there.
Oem front and rear the cars is composed on our roads and so much smother to drive.
Low speed roundabouts ect no roll
Higher speeds corners feels like the car rolls more.
Just fitted a SuperPro roll centre correction kit.
And the car feels just like adding a 22mm front bar. Turn in is more responsive and less initial roll but without the harsh ride.
After all this I personally prefer the oem bars. I know a lot of people like them but for me I like my car working with the road rather than keeping me on my toes.
All a personal preference I guess.
24mm and 22mm on different settings.
Oem front 22rear makes the front roll more and feel very soft up front.
But slightly nervous at the back end over bumps.
Oem rear 22mm front makes the car turn in better and feel more responsive to steering inputs. But very nervous over bumps at speed.
22 front and back is kind of the same affect depending on what settings there on.
24mm bars are horrid bumping and crashing off undulations and bumps and lifting a rear wheel coming out of driveways ect. Made my favourite roads unenjoyable to drive on finding bumps that I didn't know was there.
Oem front and rear the cars is composed on our roads and so much smother to drive.
Low speed roundabouts ect no roll
Higher speeds corners feels like the car rolls more.
Just fitted a SuperPro roll centre correction kit.
And the car feels just like adding a 22mm front bar. Turn in is more responsive and less initial roll but without the harsh ride.
After all this I personally prefer the oem bars. I know a lot of people like them but for me I like my car working with the road rather than keeping me on my toes.
All a personal preference I guess.
However, I said your BC's were your weakest link, and I stand with that
BC's are notorious for having insufficient droop travel leading to tripodding which you report, and many other issues too, some of which you mention, and I have not the time to go into here. This will also limit independence of corner suspension
Do report back of the front arb size as if this is too soft or spring rate too soft, will cause front roll induced "rear lifting"
19 March 2015, 10:07 PM
#116
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Yeah I understand the BC's only a budget option and there may well be more in the way of an improvement by replacing them.
I have been discussing my options with Simon from chevron and there's is something he's working on that could make it on to my car in the next few months if all his testing goes well.
I have been discussing my options with Simon from chevron and there's is something he's working on that could make it on to my car in the next few months if all his testing goes well.
20 March 2015, 01:29 AM
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I have similar set-up to Ditchmeister on my blob wrx wagon with PCA Dynamics springs (same as Prodrive blues) with 2003 STi rear 20mm ARB (Super-pro ARB bushes on rear with whiteline solid droplinks), front is totally standard 20mm ARB except super-pro bushes in the droplinks. This makes it exactly the same as the GB270 set-up.
I have just had approval from Subaru to have the front steel wishbones replaced under the re-call notice that will include new OEM front and rear wishbone bushes. I am now wondering if it would be worth fitting a 22mm front ARB at the same time as would be minimal additional labour.
I mainly drive on broken, poorly surfaced roads in Edinburgh and country B roads, no track days. Reading this thread is starting to put me off the idea of a thicker front ARB as it may cause unwanted harshness, or...would a thicker 22mm bar be fine with the compliant PCA dynamic springs, improve turn-in and make the front more direct?
I have just had approval from Subaru to have the front steel wishbones replaced under the re-call notice that will include new OEM front and rear wishbone bushes. I am now wondering if it would be worth fitting a 22mm front ARB at the same time as would be minimal additional labour.
I mainly drive on broken, poorly surfaced roads in Edinburgh and country B roads, no track days. Reading this thread is starting to put me off the idea of a thicker front ARB as it may cause unwanted harshness, or...would a thicker 22mm bar be fine with the compliant PCA dynamic springs, improve turn-in and make the front more direct?
20 March 2015, 04:24 AM
#118
@ modrich
Funny that as it's putting me off going for a thicker front bar too.
If I do go for one I think it will be an STI one first off, but I shall reserve judgment until I fit the classic alloy wish bones and solid links and get some more castor as it seems they benefit from around 5 degrees, also sticky summer rubber might make a difference.
My roads can be terrible too.
Edit to add, sounds like you need to fit steering rack and roll bar polly bushes and see what you think, mine needs to lose a bit more front roll but that is only when pushing hard, mountain roads and no cops well there are but there's not many places they can stop you and that's only if they could keep up with their 110 bhp Octavia estates 
Seriously though if the front is totally standard that's what needs doing to sort your turn in, what geo settings do you have?
Funny that as it's putting me off going for a thicker front bar too.If I do go for one I think it will be an STI one first off, but I shall reserve judgment until I fit the classic alloy wish bones and solid links and get some more castor as it seems they benefit from around 5 degrees, also sticky summer rubber might make a difference.
My roads can be terrible too.
Edit to add, sounds like you need to fit steering rack and roll bar polly bushes and see what you think, mine needs to lose a bit more front roll but that is only when pushing hard, mountain roads and no cops
well there are but there's not many places they can stop you and that's only if they could keep up with their 110 bhp Octavia estates Seriously though if the front is totally standard that's what needs doing to sort your turn in, what geo settings do you have?
Last edited by ditchmyster; 20 March 2015 at 04:34 AM.
20 March 2015, 09:10 AM
#119
I have similar set-up to Ditchmeister on my blob wrx wagon with PCA Dynamics springs (same as Prodrive blues) with 2003 STi rear 20mm ARB (Super-pro ARB bushes on rear with whiteline solid droplinks), front is totally standard 20mm ARB except super-pro bushes in the droplinks. This makes it exactly the same as the GB270 set-up.
I have just had approval from Subaru to have the front steel wishbones replaced under the re-call notice that will include new OEM front and rear wishbone bushes. I am now wondering if it would be worth fitting a 22mm front ARB at the same time as would be minimal additional labour.
I mainly drive on broken, poorly surfaced roads in Edinburgh and country B roads, no track days. Reading this thread is starting to put me off the idea of a thicker front ARB as it may cause unwanted harshness, or...would a thicker 22mm bar be fine with the compliant PCA dynamic springs, improve turn-in and make the front more direct?
I have just had approval from Subaru to have the front steel wishbones replaced under the re-call notice that will include new OEM front and rear wishbone bushes. I am now wondering if it would be worth fitting a 22mm front ARB at the same time as would be minimal additional labour.
I mainly drive on broken, poorly surfaced roads in Edinburgh and country B roads, no track days. Reading this thread is starting to put me off the idea of a thicker front ARB as it may cause unwanted harshness, or...would a thicker 22mm bar be fine with the compliant PCA dynamic springs, improve turn-in and make the front more direct?
The thicker rear bar will hold-up the front, preserving dynamic geometry, giving better turn-in
No need to bother with the front one
Last edited by bonesetter; 20 March 2015 at 09:15 AM.
20 March 2015, 09:23 PM
#120
Yeah I understand the BC's only a budget option and there may well be more in the way of an improvement by replacing them.
I have been discussing my options with Simon from chevron and there's is something he's working on that could make it on to my car in the next few months if all his testing goes well.
I have been discussing my options with Simon from chevron and there's is something he's working on that could make it on to my car in the next few months if all his testing goes well.
The front OEM ARB in a hawkeye STi is 20mm from memory.