When does roll center needed adjusted?

[float_6969]

So my setup is as follows; S14, NISMO S-tunes (25mm drop F, 15mm drop R), new MR Hard Rubber bushings on all pivoting suspension points, ES diff and subframe bushings. No STB's (yet) or ASB's (yet).

This isn't much of a drop, but I can already tell that the front and rear LCA's are almost horizontal. My understanding of the suspension on these cars is that they start to loose negative camber once the arm goes past horizontal. My questions are;
-Should I worry about the RC with such a little drop?
-Can it hurt anything if I adjust it anyway?
-For the front I would probably use the MR roll center adusters because they're 20mm, and I'm 25mm in the front, unless you guys have a reason not to?
-What about the angle on the steering rack, do I need to adjust that back too?
-What about the rear? only lowering the angle of the RLCA doesn't make sense to me. Wouldn't it be better to raise the subframe 15mm to offset the drop in ride height? Can you raise the subframe 15mm?

I know it's a lot of questions, thanks for the input.

[Def]

Probably not that big of a deal, and I don't think the MR roll center adjusters do anything. They don't adjust the pivot relative to the ball joint tapered shank IIRC. They just move everything up.

The rear you can install solid/urethane (that are modded) bushings that raise it up against the body. I would not use solid bushings on a car that's street driven often. 10-15 mm is roughly the range you can move it up.

I wouldn't worry about adjusting the tie rod height with minor amounts of RC correction up front.

[float_6969]

I think you're right about the MR adjusters. I think they basically move the control arm down in relation to the spindle/strut. Although I just had a thought. If they move the FLCA down, wouldn't that help with preventing loosing camber when the car rolls over? Wouldn't help with roll center, but it would help with keeping camber gain down, right? Any other options for a stock FLCA? But you said it's not a big deal, so I probably don't need to worry about it, just an idea.

I have ES poly bushing in the subframe now. I assume it would be as simple as removing 10-15mm off of the top of the bushing? Do I need to shorten the metal sleeve too?

Good to know about the tie rod height too, thank you.

[PoorMans180SX]

McPherson strut only loses camber when the strut to control arm relationship goes acute, or smaller than 90 degrees. With the control arms level, the strut is still angled in, so you're fine.

Yes, just take the material off the top. If you shorten the metal sleeve you're probably just need to make the space up on the bottom with washers anyway, haha.

[Sleepy_Steve]

McPherson strut only loses camber when the strut to control arm relationship goes acute, or smaller than 90 degrees. With the control arms level, the strut is still angled in, so you're fine.

That doesn't quite read right to me.

Did you mean when the angle goes obtuse? It starts out acute from the factory with the control arm angled down and the strut angled in to clear the wheel.

[float_6969]

Yea, I'm trying to wrap my head around that, and it doesn't make sense to me. In my mind, it seems to me that if the FLCA is angle "down", that as the spring compresses and the arm travels, that the ball joint would move "out", increasing negative camber until it becomes parallel with the ground. As it continues to travel, the ball joint would move "in" and loose negative camber.

Maybe I'm missing something?

If this description is accurate, don't you also loose negative camber when the body rolls? What is the relationship between camber loss with body roll, and camber gain with suspension compression (with the arm below parallel). ie Do they cancel each other out, or is the overall camber change towards negative, or towards positive?

From the amount of negative camber everyone runs on the front of S-chassis cars, I'm assuming the overall camber change is toward positive camber, but how many have FLCA's that are near the factory setting so negative camber is gained during compression?

[Jason M]

I've measured actual camber gain & loss at multiple different kpi levels, & the amount of camber gain/loss within the usable range of kpi & ride height is probably minimal, even with no roll center correction. At best you might see .2-.3 degrees camber gain per inch at full droop, and .2-.3 degrees loss/inch up near the bumpstop. In the normal range of motion around normal static ride heights, it's probably a safe bet to excpect zero camber gain or loss.

Caster has a much larger effect on camber change, but only while turning the steering wheel. Kpi also has an effect on camber change while turning the steering wheel, but it only starts to effects things after about 15-20 degrees of wheel angle.

The amount of static camber that everyone runs is primarily to compensate for body roll, & wheel/tire deflection under load.

[Umai Kakudo]

If you haven't red them yet see these to help general understanding: http://www.motoiq.com/tech/the_ultim..._handling.aspx

This is the Roll Center specific one: http://www.motoiq.com/magazine_artic...ll-center.aspx

[float_6969]

If you haven't red them yet see these to help general understanding: http://www.motoiq.com/tech/the_ultim..._handling.aspx

This is the Roll Center specific one: http://www.motoiq.com/magazine_artic...ll-center.aspx

OK cool, lots of good info there. I've got some reading ahead of me!

[Def]

I think you're right about the MR adjusters. I think they basically move the control arm down in relation to the spindle/strut. Although I just had a thought. If they move the FLCA down, wouldn't that help with preventing loosing camber when the car rolls over? Wouldn't help with roll center, but it would help with keeping camber gain down, right? Any other options for a stock FLCA? But you said it's not a big deal, so I probably don't need to worry about it, just an idea.

I have ES poly bushing in the subframe now. I assume it would be as simple as removing 10-15mm off of the top of the bushing? Do I need to shorten the metal sleeve too?

Good to know about the tie rod height too, thank you.

The arm itself doesn't matter, it's the virtual arm formed between the inner bushing and the outer balljoint pivot. You can put a 6" long extension between the arm and the balljoint pivot and it won't make any difference.


As far as camber loss/gain, it happens when the arm itself goes beyond 90 degrees relative to the strut KPI line. So the arm has to be pointing upwards a bit before you lose camber with travel. That said, it flattens out severely as that angle goes very close to 90 deg.


On the ES bushings, yes, you have to cut the tops off and the metal sleeve.

[float_6969]

Yea, I knew it was the actual pivot point that mattered, although Megan now has a bunch of info on their site about roll center and are claiming that they make 2 different styles of RC correctors, one for ball joints mounted in the knuckle, connecting to the arm (upside down compared to our), and one with an actual longer shank. IDK if it's true or not, and IDK what the quality is like, but if it's as good as the bushings I just bought, I think they would be a viable option for a minor drop like mine.

I figured the sleeve needed shortend too, thanks.

[PoorMans180SX]

Cool fact of the day, they copied the roll center description out of my thread on zilvia. I called them and made them put my name at the bottom

[float_6969]

I saw the screen name at the bottom and thought it was cool that they gave credit, too bad you had to contact them, lol!