AudiOn19s

You'll have to bear with my stupid questions but to the shims move the outer portion of the arm directly in and out in relation to the car..or do they offset the arm front and back as well?

Caster (at the top mount) is effected by moving the strut forward or backward in relation to the car...camber is obviously in and out.

Personally I'd think that the shims shouldn't effect caster at all as long as the bottom of the arm is simply moved out from the bottom of the car and not forward and backward but I"m not familiar with how the shims work.

p.s. I doubt that any of these adjustments would have any effect on your corner balance values as you're not changing height any.

p.p.s. You can do a similar mod to the E46 M3 to gain negative camber and I did it on my car before I bought proper camber plates. The mod on the M3 also causes caster changes but I couldn't really notice the difference. However I did eventually upgrade to good camber plates because they're readily available for that car AND it allows me to switch between track and street settings with relative ease now.

Larry Herman

Here's the deal. If you look at the lower control arm, when you install the shims, it moves the arm out, which requires the front locating strut to be lengthened as well. Since this cannot happen, it pulls the control arm forward forward slightly and increases the caster. If you fabricate an adjustable locating strut, then you can correct this condition. Alternately having a fully adjustable upper strut mount could correct this as well.

As far as rotating the strut goes, there are 3 pins and 6 holes. The correct procedure is to press out the pins and push them into the other holes. Then you turn the strut 60 degrees, which keeps the hole in the same fore-aft plane (hence not affecting caster) and moves the hole inward about 25 mm or so IIRC, giving you additional camber. If this does not happen, then you have placed the struts in the wrong position.

Let me know if you have any more concerns about this.

LVDell

Thanks Larry. I'll print this thread off for my mechanic. I want to make sure I do the "right" thing. So, what does the shim do in "layman" terms. I understand that the shims push the control arm "outward" but I am confused how it moves forward? When I talked to Greg at Synergy (before he left) when I did my initial setup, he suggested either shims or control arm replacement. However, there was NO mention of strut top rotation.

I am so confused. It all makes so much sense that it is confusing me

Larry Herman

Dell, I wish that I could get my hands on a picture of the suspension. It would be very clear then but think of this, the control arm is trianglated by the front locating arm. That is what keeps the lower control arm from moving forward or backwards. It attaches at the 2/3rds point through a big bushing. It forms a triangle with the car.

Think of a right (90 degree) triangle standing on it's base. If you lengthen the vertical side, the upper "point" will be pulled one way or the other, and you will have less than a 90 degree triangle. You must lengthen both sides to keep it a right triangle. If you need to talk to me, PM me with your number.

boqueron

Dell,

I have rotated the struts after discussing this same question with lots of people here in Rennlist. I was reluctant but...: A very succesfull mod ! ( and unexpensive ) . All - including caster - 100% right afterwards. The shop that aligns my car works solely for racing cars, no doubt about their final alignments...

If you are not modifying your car height much, you should not find any problem ..

boqueron

Dell,

I recovered this - long - thread on this "rotating" question..https://rennlist.com/forums/showthre...6&page=3&pp=15

LVDell

Larry....PM sent.

Thanks B for the link to the other thread.

multi21

I did this as well on my M3 with no ill effects.

Greygt3

I'm going through this right now. I had to shim my left side to get the front camber to equal the right 2.1. This threw the caster out off wack. So I'll either have to slot the upper mounts on the left or rotate the top. I just did a DE this past weekend with the 2.1 front and 2.8 rear camber settings and the car could use some more camber front and rear. I am using cups. Keep the info coming this is good stuff.

LVDell

Wow that's a buttload of camber in rear. Don't see how you would need that much. You could use more in the front though as you pointed out.

LVDell

Why would the caster change when you are moving the strut inward? You are NOT moving it fore or aft. That doesn't make sense.

Rad.......care to chime in (since you were cited )???

AudiOn19s

Hopefully Rad will chime in. As I understand it the strut is not centered in the 3 bolt holes in the top mount hence when the mount is rotated a change in orientation of the top of the strut itself. If the top mount is not turned and the existing mounting slots in the strut towers are slotted further you're correct that there would not be any caster change only camber change...but how I understand it is that as soon as the top mount is turned to utilize the other 3 mounting holes it changes caster values.

But again...Larry and I believe Mike K have stated that they did not see this caster change so maybe I'm mis-informed. I did not go with the GT3 monoballs fearing the caster change problem.

LVDell

From what I understand (and I have had lengthy discussions with others on this) that 2 things are up for discussion but the facts are already there so I don't understand where some of the misinformation comes from.

1. Using shims will increase your caster angle. By shimming the control arm you move the strut FORE from changes in the leading arm (think triangle....change the length of one leg the angle changes). No way around that.

2. Rotating the strut mount (not the strut itself) moves the strut INWARD not FORE or AFT. Doing this keeps caster constant and changes the "floor" of your camber setting to ~ -2.5degrees. From what I understand this is why the strut mount top is predrilled with 6 holes NOT 3 like the rest of the 996 line soas to allow for adjustability.

Anybody else care to chime in?

DavidNR

Dell,

You are correct. Shims increase camber and caster, upper strut mount rotation changes camber only.

AudiOn19s

Great...all of this conflicting information. If I'm wrong about this I'm sorry for the misleading information.

Now I've got to go spend more money on the GT3 monoballs and test this caster change theory out for myself....cause I need more negative camber in the front.

Andy