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Discussion Starter #1
2003 GT
MM coilovers. Front 375 Lb, Rear 250 Lb, Koni Yellow SA
MM front control arms, standard offset
MM bumpsteer kit
MM rear "sport" lower control arms, new stock uppers, new differential bushings
MM panhard bar

I am getting ready to install my new MM coilovers. I know I read somewhere that there is a maximum angle that should not be exceeded on the rear control arms. However, I can not remember what that is. I think I recall that if we say "0*" is level to the ground, you do not want to go beyond that. Is that correct?

Thanks,
Ted
 

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Discussion Starter #2
Maybe it isn't the control arm angle that is the issue... Maybe it is the pinion angle (trans - driveline - pinion) that I need to be concerned with? Or is it both?
 

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The rear lower control arm angle has a direct impact on instant center. It is a very important part of the whole package. If you have a lot of adjustment in the upper control arms for changing instant center, then setting the lowers to zero is a good starting point. But with your set up, you can not change the angle of the upper control arms easily, so dropping the back of the lower control arms an inch or so can provide an easy way to change instant center in the car. If you do not know what the instant center is or how it affects the chassis, STOP. Do not do anything until you understand what these adjustment actually do.
 

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Discussion Starter #4
I have a rudimentary understanding of instant center. However, I have no idea how to make any adjustment to it as the stock 4-link has the mounting points for the upper and lower control arms fixed. Ultimately, among other factors, I believe that you want the IC of the rear differential to be set at the halfway point between the minimum and the maximum travel? I am probably completely wrong. Can you please elaborate or point me to something that will help educate me?
 

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If you don’t have adjustable uppers, I’m thinking you may be able to change that geometry with the lowers, but I’ve been told ideal is to make the lowers parallel to the ground and use uppers to move the I.c. Forward to the ideal position. However, I had someone much smarter than me on suspensions mentor me in getting the relocation kit. Hoping he chimes in here to speak more intelligently on the subject.
 

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I’m also worried though that by changing the length on the lowers to get ideal geometry, your obviously going to be changing pinion angle....
 

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I am using the Baseline Suspensions Outlaw kit in the rear of my car along with adjustable lower control arms by Wolf Racecraft. All that being said, I also have lowered the mounting point of the lower control arms at the differential by 1"
Obviously, everyone is going to have to adjust for what your own car wants. My set up works for me, but it is small tire (26X8.5) drag racing only.
http://www.baselinesuspensions.com/kits/outlaw.htm
 

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Discussion Starter #8
For what it it worth, my application is for open track (HPDE for now). The car will be driven to and from track. So, to complicate this a little, I am considering installing a torque arm. With a TA the upper control arms are removed. So, in that case, how is IC addressed?
 

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By the adjustment of the lower control arms, or the adjustment (if there is any) of the torque arm. A torque arm rear suspension is better for road racing than a 4 link suspension. For drag racing the 4 link is far superior.
 

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Discussion Starter #10
I just spoke with Maximum Motorsports about the IC and torque arm. With the torque arm, the IC does not change. The IC is fixed at the front point of the torque arm where it attached to the body. That's cool.
 

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It is correct that the IC of a TA rear suspension is fixed in a plane at the front of the TA, sort of. The MM TA design has a barrel shaped bushing at the front of the TA. This allows the TA to plunge in and out of the crossmember a little bit. As the TA plunges, the IC moves forwards and backwards a tiny bit. This is required for a TA rear suspension to not bind up, if other control arms are also restraining the axle assembly. There is no adjustment for the IC location with the MM TA.

The bigger and more important point here is that it absolutely doesn't matter. The IC location determines almost nothing about the rear tire forward traction during launch. What determines this is the amount of antisquat in the rear suspension design. The IC location affects the amount of antisquat, but there are an infinite number of IC locations that will all result in the same amount of antisquat.

This is sort of like tuning the handling of a car by only looking at the spring rate at one end. It is meaningless without considering the opposite end of the car.

I've attached two drawings. One shows how to find the IC location and calculate the AS% for a 3-link or 4-link rear suspension. The other drawing does the same for a TA rear suspension. In both situations, the IC can be anywhere along the AS line and the amount of AS will be the same.
 

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Discussion Starter #12
Then, is it safe to say that in the case of open track driving / racing that the effect of the IC / anti-squat are controlled satisfactory then with the TA / PHB / MM LCA's and coilovers (Koni SA with 375 front / 250 rear)?
 
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