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Setting up my rear suspension arm lengths and location

 
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QwkTrip
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Joined: 17 Feb 2004
Posts: 3942
Location: Peoria, IL

1989 Pontiac Firebird

PostPosted: Sun Mar 15, 2015 8:16 pm    Post subject: Setting up my rear suspension arm lengths and location Reply with quote

I have adjustable everything and a shorter torque arm than stock. Car is also lower than stock. I can measure the length of torque arm if you need it. I need advice how to set up the geometry of the rear suspension. I want to hook up hard but still have decent cornering and not compromise braking.

- pinion angle. What is a good static pinion angle to start with?
- torque arm front mount height. Recommendations?
- control arm length. I assume I just center the tire in the wheel well and make sure the car tracks straight.
- control arm mount height at axle. What is a good static angle to start with?

I have a 12 bolt axle and gear set if that matters.
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Dewey316
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Joined: 08 Jan 2004
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Location: Bringing the tech

1990 Chevrolet Camaro RS

PostPosted: Mon Mar 16, 2015 5:55 am    Post subject: Reply with quote

Here is the import thing, luckily, the length of the T/A is the thing that really matters, the height of the mount doesn't. The fore/aft I/C location is done with the T/A length, the I/C height is a function of the LCA.



The (anti)squat is figured from the where the I/C is compared to the line drawn between the rear tire contact patch, and a point where the C/G height crosses the front axle plane.



so, That is the basics.

Good news, torque arm mount height means diddly squat (pardon the pun) in how you package this.

LCA mount, with the shorter torque arm, you are almost for sure going to have possitive A/S, going with the rear mount lower than the front, will give you more. Going at parallel to the ground usually gives good handling, since you end up with a more neutral roll/steer, but I would start with the rear just slightly lower, and fiddle until you like the feel of the car.

Pinion angle is sort of black voodoo magic, the reason for a negative pinion angle, is so that under load the output shaft and pinion align. Common setting is in the -2* to -4* range. you have a shorter and stronger T/A than stock, so your deflection should be less, BUT, you have a boat load of power to act on that arm. I would go in the lower end of that for street tires maybe even in the -1* to -2* range, if you are hooking it hard, go higher.

You got it on the control arm length, center and square is what you want. The roll steering effect and I/C creep are less the longer, but when we are talking 1/8", its negligible, so don't even consider it as a real tuning option.

--John
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Twilightoptics
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Joined: 13 Jan 2004
Posts: 9191
Location: Auburn , WA

1987 Chevrolet Camaro IROC-Z

PostPosted: Mon Mar 16, 2015 10:14 am    Post subject: Reply with quote

I'm with stupid
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QwkTrip
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Joined: 17 Feb 2004
Posts: 3942
Location: Peoria, IL

1989 Pontiac Firebird

PostPosted: Mon Mar 16, 2015 12:08 pm    Post subject: Reply with quote

Thanks, guys!

I drew up some graphics during lunch and was coming to the same conclusion about cause-effect. But I had no idea if I was doing it right, and didn't know what is a good starting point for control arm position. You boiled it down some something simple for me to apply. Thumbs up

So what you're saying is my control arm drop brackets are probably not a good idea with the short torque arm. Remove the brackets and use stock mounting points at first? I'm going to make a lot of torque and I'm a little concerned about the suspension being overwhelmed if I dial in too much anti-squat. Since my torque arm is a fixed length, all I can do is play with control arm height at rear mount and see what happens, right?
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Dewey316
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Joined: 08 Jan 2004
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Location: Bringing the tech

1990 Chevrolet Camaro RS

PostPosted: Mon Mar 16, 2015 12:13 pm    Post subject: Reply with quote

pretty much. If you have lowering springs in the rear, use the brackets, stock height...check your LCA's and decide, i would still tend to look for slightly lower rear mount on the LCA's, whatever route gets you there.
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QwkTrip
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Joined: 17 Feb 2004
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Location: Peoria, IL

1989 Pontiac Firebird

PostPosted: Mon Mar 16, 2015 4:46 pm    Post subject: Reply with quote

Best tech on the web is right here. Our little group rocks. Thumbs up
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