Jim
09-01-2007, 01:39 PM
How does it work?
Whiteline KCA395 - Lancer EVO VII-VIII-IX front roll centre adjusting kit - Part 1
The following psots by Jim Gurieff have been taken from a forum thread appearing on Evolutionm.net forums at http://forums.evolutionm.net/showthread.php?p=3833998 . It follows a discussion on the capacity of KCA395 to enhance advanced suspension setups inlcuding coil-overs. These posts help explain the underlying geometry, why the kit was designed and how it works. It provides a practical explanation and overview of the basic principals of roll centres, roll axis and roll couple.
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Posted 22nd December 2006
Looks like we have an apology to make to our WRX supporters
We targeted the EVO first because quite frankly, it has a bigger problem in this area. And by "this area", we mean front roll centre, not "ball joint extenders", "camber curve correctors" nor any other issue that may be addressed by other products currently in the market. That is, the copy of the bulletin for KCA395 at the beginning of the thread refers to a solution specific to the front roll centre problem we perceive on the EVO but we don't want to get involved in interpreting other manufacturers products and claims.
All strut based systems are prone to migrating roll centre issues due to the nature of the underlying geometry. In the EVO, front roll compounds and accentuates front roll forcing people to adopt all sorts of "band-aid" solutions to what is fundamentally a geometry problem. Our race testing on Project EVO showed the classic symptoms that was backed up by some measurements so we went to the drawing board (no experience with ball joints etc) and worked out a possible solution. Made some prototypes and everyone seemed happy (Project EVO had best times in slalom and technical sections in Dutton 2006 national tarmac rally series :banana: ). Next job was to do some durability testing before pushing the production button.
So I guess that's the good news, in our minds the WRX is not drastically affected by the roll centre problem. The other good news is that we are working on a product for the WRX but the bad news is that we're a few months away from being able to release details of the products contents and configuration.
Sorry its not more positive news but that's where we are at.
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Posted 2nd Jan 2007
Robbi suggested that I might like to jump in and answer some of the questions on this thread. Unfortunately our office has been closed until today so I apologies for the delay.
I'd like to go through some of the issues raised in point form;
- We don't like to refer to these products as a "ball joint extender" or "spacer" kit as that implies that we've simply added some bits to a kit of standard parts which is not true. The replacement hardware has been designed specifically for the job by well established tier 1 ball joint suppliers that use FEA during the production engineering process. To my knowledge they are not OE suppliers but we have test fitted many sets here before release and are comfortable with the longevity and integrity of the interference fit between alloy arm and housing. We also clocked many months of trouble free road and competition kilometres before approving production.
- Joe Henry is correct in saying that this is a very sensitive area and that's why the amount of RC change we deliver is less than 10 mm. That's right, not 38 mm or 25 mm but LESS than 10 mm. This is not "rocket science" but it is our own proprietary recipe and we would prefer not to disclose the exact numbers. What I can confirm is that the design process did include mapping the roll centres, centre of gravity and roll axis meaning it was done front and rear. This was then modelled via simulation software to ascertain the level of migration relative to various static ride heights and roll angles. The critical thing here is that the front to rear relationship and resultant roll axis first needs to be properly understood before one can work out a sensible solution at the front.
- Continuing on that theme, the problem with simply lowering ride height on this and most other strut based cars is that the RC plunges exponentially with compression. That is, the further you compress the outside strut the more it lengthens the roll couple (referred to as "torque arm for roll" by Joe Henry) which serves to magnify the trait in a continuing loop. Hence, lowering the static ride height without adjusting the RC puts the car further in to the danger zone requiring larger and larger springs and or bars to try to hold up the nose. Fitting the KCA395 allowed us to use softer spring rates to promote wheel articulation and maximise the contact patch.
- Roll centres, roll couple, roll axis and all these related themes are one of the real brain-teasers of suspension setup and geometry change but they are fundamental to the basic design and behaviour of the chassis. To a degree, the innate chassis balance of a vehicle is determined by this relationship. AYC however is about torque distribution or power delivery and its effect on balance under power or acceleration. That is, a poor roll centre outcome will affect the chassis, balance and driver at all stages of the corner from entry to exit. AYC however is designed to maximise power delivery to the road with a resultant affect on chassis balance. As quoted by Mitsubishi itself, "Super AYC 6 traction control" with the word "traction" being the key. Changes to roll centre will therefore be felt irrespective of AYC but AYC can mask roll centre, balance and geometry problems... enough said there I think :-wink.
- The KCA395 is designed to work with stock wheels and brakes. That is, it does not impinge on either or on sensible upgrades to either.
Like all active torque distribution or traction systems, AYC has a bearing on how the car drives. The Impreza STi uses DCCD with the current generation also incorporating a yaw sensor. We had to purchase one to keep ourselves current with the dynamic behaviour as it does have an impact however it does not change the basic geometry of the car. Needless to say we have conducted many race tests with Project EVO on various settings using various components before signing off on the parts. However, thinking about this logically, the lack of a stock AYC system on US cars would suggest that fixing stuff like the roll centre would become even more important.
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Whiteline KCA395 - Lancer EVO VII-VIII-IX front roll centre adjusting kit - Part 1
The following psots by Jim Gurieff have been taken from a forum thread appearing on Evolutionm.net forums at http://forums.evolutionm.net/showthread.php?p=3833998 . It follows a discussion on the capacity of KCA395 to enhance advanced suspension setups inlcuding coil-overs. These posts help explain the underlying geometry, why the kit was designed and how it works. It provides a practical explanation and overview of the basic principals of roll centres, roll axis and roll couple.
---------------------------------------------------------------------------------------------------------------------------------------
Posted 22nd December 2006
Looks like we have an apology to make to our WRX supporters
We targeted the EVO first because quite frankly, it has a bigger problem in this area. And by "this area", we mean front roll centre, not "ball joint extenders", "camber curve correctors" nor any other issue that may be addressed by other products currently in the market. That is, the copy of the bulletin for KCA395 at the beginning of the thread refers to a solution specific to the front roll centre problem we perceive on the EVO but we don't want to get involved in interpreting other manufacturers products and claims.
All strut based systems are prone to migrating roll centre issues due to the nature of the underlying geometry. In the EVO, front roll compounds and accentuates front roll forcing people to adopt all sorts of "band-aid" solutions to what is fundamentally a geometry problem. Our race testing on Project EVO showed the classic symptoms that was backed up by some measurements so we went to the drawing board (no experience with ball joints etc) and worked out a possible solution. Made some prototypes and everyone seemed happy (Project EVO had best times in slalom and technical sections in Dutton 2006 national tarmac rally series :banana: ). Next job was to do some durability testing before pushing the production button.
So I guess that's the good news, in our minds the WRX is not drastically affected by the roll centre problem. The other good news is that we are working on a product for the WRX but the bad news is that we're a few months away from being able to release details of the products contents and configuration.
Sorry its not more positive news but that's where we are at.
-----------------------------------------------------------------------------------------------
Posted 2nd Jan 2007
Robbi suggested that I might like to jump in and answer some of the questions on this thread. Unfortunately our office has been closed until today so I apologies for the delay.
I'd like to go through some of the issues raised in point form;
- We don't like to refer to these products as a "ball joint extender" or "spacer" kit as that implies that we've simply added some bits to a kit of standard parts which is not true. The replacement hardware has been designed specifically for the job by well established tier 1 ball joint suppliers that use FEA during the production engineering process. To my knowledge they are not OE suppliers but we have test fitted many sets here before release and are comfortable with the longevity and integrity of the interference fit between alloy arm and housing. We also clocked many months of trouble free road and competition kilometres before approving production.
- Joe Henry is correct in saying that this is a very sensitive area and that's why the amount of RC change we deliver is less than 10 mm. That's right, not 38 mm or 25 mm but LESS than 10 mm. This is not "rocket science" but it is our own proprietary recipe and we would prefer not to disclose the exact numbers. What I can confirm is that the design process did include mapping the roll centres, centre of gravity and roll axis meaning it was done front and rear. This was then modelled via simulation software to ascertain the level of migration relative to various static ride heights and roll angles. The critical thing here is that the front to rear relationship and resultant roll axis first needs to be properly understood before one can work out a sensible solution at the front.
- Continuing on that theme, the problem with simply lowering ride height on this and most other strut based cars is that the RC plunges exponentially with compression. That is, the further you compress the outside strut the more it lengthens the roll couple (referred to as "torque arm for roll" by Joe Henry) which serves to magnify the trait in a continuing loop. Hence, lowering the static ride height without adjusting the RC puts the car further in to the danger zone requiring larger and larger springs and or bars to try to hold up the nose. Fitting the KCA395 allowed us to use softer spring rates to promote wheel articulation and maximise the contact patch.
- Roll centres, roll couple, roll axis and all these related themes are one of the real brain-teasers of suspension setup and geometry change but they are fundamental to the basic design and behaviour of the chassis. To a degree, the innate chassis balance of a vehicle is determined by this relationship. AYC however is about torque distribution or power delivery and its effect on balance under power or acceleration. That is, a poor roll centre outcome will affect the chassis, balance and driver at all stages of the corner from entry to exit. AYC however is designed to maximise power delivery to the road with a resultant affect on chassis balance. As quoted by Mitsubishi itself, "Super AYC 6 traction control" with the word "traction" being the key. Changes to roll centre will therefore be felt irrespective of AYC but AYC can mask roll centre, balance and geometry problems... enough said there I think :-wink.
- The KCA395 is designed to work with stock wheels and brakes. That is, it does not impinge on either or on sensible upgrades to either.
Like all active torque distribution or traction systems, AYC has a bearing on how the car drives. The Impreza STi uses DCCD with the current generation also incorporating a yaw sensor. We had to purchase one to keep ourselves current with the dynamic behaviour as it does have an impact however it does not change the basic geometry of the car. Needless to say we have conducted many race tests with Project EVO on various settings using various components before signing off on the parts. However, thinking about this logically, the lack of a stock AYC system on US cars would suggest that fixing stuff like the roll centre would become even more important.
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