STR Prep - Suspension and Alignment
Registered User
Joined: Oct 2011
Posts: 22
Likes: 0
Originally Posted by daytrip00' timestamp='1328307780' post='21382069
EDIT: Actually... looking at the first picture, now I'm not so sure...
I think this is the relevant pic:
Registered User
Joined: Sep 2008
Posts: 2,380
Likes: 0
From: Arizona
I wouldn't consider a ball joint re-locator any different than using a eccentric bolt to push the knuckle away from a strut on the lower hole or towards the strut on the upper hole. The lower ball joint acts like the lower hole on a strut and the upper ball joint acts as the upper hole. If an eccentric bolt is legal, so is a ball joint that moves the knuckle the same way. The only 2 "geometry" benefits of the ball joint is that
1.) You could potentially gain or subtract caster. Not sure if a caster adjustment is legal if your car doesn't already have a caster adjuster knob or bolt.
2.) it general sits lower on the knuckle so depending on the design, it could therfore widden the track width by a greater amount than most eccentric bolts do but I'd need to see some math to prove that with our current parts vs say the next top competitor runnig struts. Possibly an unfair advantage. Kinda comparing apples to oranges though for suspension setups.
IMO, IT'S a mod class. The rules should be written in a manor that evens the playing field for gaining camber.. . If it needs to change, it needs to change.. .
1.) You could potentially gain or subtract caster. Not sure if a caster adjustment is legal if your car doesn't already have a caster adjuster knob or bolt.
2.) it general sits lower on the knuckle so depending on the design, it could therfore widden the track width by a greater amount than most eccentric bolts do but I'd need to see some math to prove that with our current parts vs say the next top competitor runnig struts. Possibly an unfair advantage. Kinda comparing apples to oranges though for suspension setups.
IMO, IT'S a mod class. The rules should be written in a manor that evens the playing field for gaining camber.. . If it needs to change, it needs to change.. .
Registered User
Joined: Jan 2011
Posts: 796
Likes: 1
A race car engineer friend of mine says this commenting on this thread I pointed to him:
"[t]he relevant dimension is from the pivot point of the joint itself (which we cannot see) to the seating area (or basically to some dimensional position the knuckle). It looks like that dimension is probably shared between the two and if that’s the case, it would be legal. When installed, yes, the upper control arm will look inclined from the chassis going to the ball joint in comparison to the stock ball joint… but it really doesn’t matter if the upper control arm is inclined or declined, the imaginary line you would connect to determine roll centers would be from the inner pivot of the lca to the ball joint pivot. that dimension pretty much remains unchanged… on a roll center adjuster, you are basically making the knuckle pivots (upper and lower ball joints) further apart. With these ball joints, the distance between pivot points on the knuckle remains unchanged (assuming pivot point to seating area is the same which it looks pretty close in that regard). . . ."
Sounds legal to me
"[t]he relevant dimension is from the pivot point of the joint itself (which we cannot see) to the seating area (or basically to some dimensional position the knuckle). It looks like that dimension is probably shared between the two and if that’s the case, it would be legal. When installed, yes, the upper control arm will look inclined from the chassis going to the ball joint in comparison to the stock ball joint… but it really doesn’t matter if the upper control arm is inclined or declined, the imaginary line you would connect to determine roll centers would be from the inner pivot of the lca to the ball joint pivot. that dimension pretty much remains unchanged… on a roll center adjuster, you are basically making the knuckle pivots (upper and lower ball joints) further apart. With these ball joints, the distance between pivot points on the knuckle remains unchanged (assuming pivot point to seating area is the same which it looks pretty close in that regard). . . ."
Sounds legal to me
Joined: Feb 2010
Posts: 480
Likes: 3
I wouldn't consider a ball joint re-locator any different than using a eccentric bolt to push the knuckle away from a strut on the lower hole or towards the strut on the upper hole. The lower ball joint acts like the lower hole on a strut and the upper ball joint acts as the upper hole. If an eccentric bolt is legal, so is a ball joint that moves the knuckle the same way. The only 2 "geometry" benefits of the ball joint is that
1.) You could potentially gain or subtract caster. Not sure if a caster adjustment is legal if your car doesn't already have a caster adjuster knob or bolt.
2.) it general sits lower on the knuckle so depending on the design, it could therfore widden the track width by a greater amount than most eccentric bolts do but I'd need to see some math to prove that with our current parts vs say the next top competitor runnig struts. Possibly an unfair advantage. Kinda comparing apples to oranges though for suspension setups.
IMO, IT'S a mod class. The rules should be written in a manor that evens the playing field for gaining camber.. . If it needs to change, it needs to change.. .
1.) You could potentially gain or subtract caster. Not sure if a caster adjustment is legal if your car doesn't already have a caster adjuster knob or bolt.
2.) it general sits lower on the knuckle so depending on the design, it could therfore widden the track width by a greater amount than most eccentric bolts do but I'd need to see some math to prove that with our current parts vs say the next top competitor runnig struts. Possibly an unfair advantage. Kinda comparing apples to oranges though for suspension setups.
IMO, IT'S a mod class. The rules should be written in a manor that evens the playing field for gaining camber.. . If it needs to change, it needs to change.. .
Lateral adjustment makes sense for camber. Longitudinal adjustment, if there was any, would change caster. Moving the entire ball joint unit doesn't change anything but the shape of the arm. What I am speaking of, is the distance from where the ball joint pivot, to the flange/plane/point on the ball joint shank where the upper portion of the knuckle lands. Under one interpretation of the current rule, that distance must remain stock. If you can picture an upper ball joint with a really long shank, you might visualize how such a part would put the upper arm in a steeper part of the camber curve. Generally this "height" is not adjustable but through the use of spacers on a special ball joint or rod end.
Do the Skunk2 arms use factory ball joints? If not, is the installed distance from the ball joint pivot to the top of the knuckle, exactly the same as stock?
Registered User
Joined: Sep 2009
Posts: 558
Likes: 24
From: littleton, CO
So do the SPC's affect roll center of the upper arm? for those saying they don't, i almost agree with you. however that would mean the hardrace and j's roll center spacers do nothing. and in reality the shank that connects the ball joint to the knuckle is what needs to be lengthened...
i have no conclusion :/
I like the SPC because it allows me to adjust the track width front and rear. j's and hardrace only make front wider.
But if these do change that rollcenter geometry, then we are hurting our suspension performance by running them, basically doing the exact opposite of what the lower spacers are supposed to correct.
i have no conclusion :/
I like the SPC because it allows me to adjust the track width front and rear. j's and hardrace only make front wider.
But if these do change that rollcenter geometry, then we are hurting our suspension performance by running them, basically doing the exact opposite of what the lower spacers are supposed to correct.
Registered User
Joined: Jul 2007
Posts: 1,376
Likes: 2
So do the SPC's affect roll center of the upper arm? for those saying they don't, i almost agree with you. however that would mean the hardrace and j's roll center spacers do nothing. and in reality the shank that connects the ball joint to the knuckle is what needs to be lengthened...
i have no conclusion :/
I like the SPC because it allows me to adjust the track width front and rear. j's and hardrace only make front wider.
But if these do change that rollcenter geometry, then we are hurting our suspension performance by running them, basically doing the exact opposite of what the lower spacers are supposed to correct.
i have no conclusion :/
I like the SPC because it allows me to adjust the track width front and rear. j's and hardrace only make front wider.
But if these do change that rollcenter geometry, then we are hurting our suspension performance by running them, basically doing the exact opposite of what the lower spacers are supposed to correct.
The J's & Hardrace lower roll center adjusters are different because the ball joint assemblies fasten to the knuckle. The SPCs are effectively connected to the control arm, not the knuckle. The roll center change occurs when you change the vertical distance between the upper ball joint _rotation center_ and the lower ball joint _rotation center_. The other dimensions do not matter. That was part of the "chili joint" joke....the dimensions of the upper ball joint don't matter if the rotation location stays the same, relative to the knuckle.
Here's a graphic that shows the dimension that is critical to the roll centers. This dimension needs to remain unchanged to be legal per the STR rules. The black points represent the rotation centers of the ball joints. The red line is the distance between the two centers that needs to remain the same as the OE setup.
Registered User
Joined: Jul 2007
Posts: 1,376
Likes: 2
Good discussion here, just need a little more info about the SPC joints.
Registered User
Joined: Jan 2011
Posts: 796
Likes: 1
Ok, so I already pressed the OEM ball joints into the arm earlier today, but here are pics that should nonetheless provide useful in speculating whether the roll center remains unchanged. Both were fully articulated and the SPC was placed in an orientation identical to how it would sit in that arm. The SPC seemed to be about 5mm higher than the OEM, but the angle of articulation was virtually identical.
