Thread: The Roofus Special

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J., I'm assuming moment center means instant center, the pivot point on a ladder bar system. Thank you for elucidating.

Originally Posted by J. Robinson

Flipper - You're a man after my own heart. Being an old stock car racer, I like cars that handle GOOD. I build my cars to drive and I flog them pretty hard sometimes, too. Back in '06 we drove my coupe on a 2400 mile loop up through the midwest. The curvy roads through the western North Carolina mountains were an absolute blast! Even though it's a beam axle, my coupe has torsion bars up front and coils in the rear (fully adjustable on all four corners) with NASCAR style truck arms in the rear. It handles like a dream; I would love to put it through a timed Gymkhana course sometime and see how it stacks up against the Camaros and Mustangs...

Tech - Yes, the center torque arm is like a ladder bar. It transfers the torsional force of the rear end housing to its front mounting point. This becomes the lift point or "moment center" of the rear axle. The rear end is located fore & aft by the short outer bars (radius rods) and laterally by the panhard bar. This system can be tough to dial in for drag racing because the front pivot point of the center link is usually too low and too far forward to provide good "bite" off the line. For overall handling, though, it can be a great system... I have a picture and a diagram of this system in my file cabinet at school. I will try to remember to get it tomorrow and post it here.

Since I don't currently have floors to get in the way, raising the torque arm mount is not really an issue.

In a perfect world, what would the best set-up look like?

Also, are the locating arms short to induce steering from body roll?

So, what are the opinions on building a car without a traditional style frame under it?

Too early in the build to pass judgement?

Is this thing just too far out there?

There will be lots more angles installed before the plating begins. Some of the plating will probably be bead rolled for even more strength (and style).

Tech - Yes, I meant "instant center". ("Moment center" is the suspension axis around which the body rolls in a turn.) In this type of suspension, the "instant center" is a fixed point determined by the front pivot of the long torque arm.

Flipper - Yes, the short arms induce rear-steer with body roll. The length of the arms affect how much rear-steer is input (longer arms input less) and the angle determines whether it is negative or positive steer. I'll post pics later if I can find them.

OK, guys, here are the pics I have. I took the photo and did the drawing about 20 years ago for a catalog I was helping to edit. The company went out of business a long time ago, but I still have the pics & drawings I did. I edited out the company's name and phone info...

Notice the long center "torque arm" is supposed to reach all the way to the rear u-joint area (transmission crossmember) and has a shackle type mount that is made from a female Heim joint mounted in rubber. The short arms are considerably shorter, but could be any length you desire. As I stated above, the longer they are, the less rear-steer they induce. When viewed from the side, if the short bars run uphill from the rear axle to the frame they will induce positive steer and make the rear of the vehicle "loose" in a turn (good for running on dirt tracks). If they run downhill from the rear axle to the frame, they will induce negative steer and make the rear of the vehicle "tight" in a corner (better for asphalt).

That's interesting. I just saw this 1st Gen Camaro torque arm setup in the new Hot Rod.


BMR Fabrication

Very cool J., thanks a lot.

Originally Posted by 39Deluxe

That's interesting. I just saw this 1st Gen Camaro torque arm setup in the new Hot Rod.


BMR Fabrication

That's a really cool bolt-in conversion. It uses a telescoping joint at the front instead of a shackle arrangement. Notice it has multiple holes in the bracket for the short arms so that rear-steer input can be fine-tuned. Nice!

Originally Posted by J. Robinson

That's a really cool bolt-in conversion. It uses a telescoping joint at the front instead of a shackle arrangement. Notice it has multiple holes in the bracket for the short arms so that rear-steer input can be fine-tuned. Nice!

That one has all three links mounting at roughly floorpan level.

Is that ideal? or a comprimise for a stock floor Camaro? Is it better if you went above the driveshaft with the front mount?

I'm not sure, Flipper... Very good question. I would guess that it's a compromise for the stock floor and mounting hardware. If you look under a 3rd generation Camaro, the long arm runs beside the driveshaft, not under it. I'm not sure it would make a huge difference, though, unless you moved the front pivot point up and back a lot which would affect weight transfer under acceleration/deceleration.

When you move the instant center up and back, it improves traction for launch/acceleration (suspension loads), but, if ya go too far, can cause wheel-hop on deceleration (suspension unloads). I think I would follow the Camaro's example and mount the center link beside the front u-joint.

Note also, on a 3rd gen Camaro at stock height, the short arms run slightly downhill from the rear axle to the subframe mounting points. That gives the stock Camaro a slight negative input from the rear-steer. I've never talked to any GM designers, but I would guess they designed it that way because the 3rd gen Camaros are slightly nose heavy and need the negatve input to control oversteer (loose condition). For your application, I think I would keep the short arms as level as possible and lengthen them to about 2/3rd the length of the long arm. That way the rear-steer input would be minimal and controllable. My reasoning here is that your car is a lot lighter than a stock Camaro and your weight distribution will be about 50-50; you therefore don't need a lot of rear-steer input under normal driving conditions. If you can somehow incorporate it into your design, it would be nice to have multiple mounting holes so that you could adjust the angle of the short arms. That way, if you ever want to run it through a Gymkhana or flog in on a dirt track at one of the vintage meets, you could dial in the rear suspension to your liking.

How about multiple mounting holes for the torque arm also?

There is no reason you couldn't have multiple mounting holes for the torque arm. If you raise or lower the front of the torque arm, though, you would have to adjust the rear heims to maintain pinion angle. If you are suggesting holes to move the pivot fore or aft, the arm would have to be made adjustable lengthwise...

No, up and down on the torque arm with LH/RH threaded heims on the rear bars. Maybe LH in the front heim and RH in the rear heim. Weld a nut on the bar itself to fit a wrench to turn the bar after loosening the heim lock nuts.

Originally Posted by techinspector1

No, up and down on the torque arm with LH/RH threaded heims on the rear bars. Maybe LH in the front heim and RH in the rear heim. Weld a nut on the bar itself to fit a wrench to turn the bar after loosening the heim lock nuts.

That torque arm "bar" is a piece of 2x3 tubing that is secuerly attached to the rear end in at least 4 places. I don't think it would easily adjust.

Jim I'm enjoying the build keep them coming!