Traction Bars?

[Morphius]

I assumed that we were talking about accelerating, not braking

My 2g is 1500 miles away, so I can't go crawl under it, but if I recall the 'compression arm' is bowed to provde clearance for the wheels when you articulate the steering. Doesn't the 'compression arm' see tension on acceleration and compression during braking?

I'd agree with topstreet on the design of the compression arm. A bend like that doesn't lend it's self to being stiff. I would say, in addition to flex in that rear bushing, there is likely some amount of flex in that arm.

I do understand it would be complex to come up with a different mount scheme or method to attach an additional bar.

 

[jtmcinder]

Yes, the bend is to go around the tire's inside edge when steered. Straight bars must either restrict steering or have a sharp angle, which shrinks the base of the triangle. That's why the arm on a 2G is curved.

As to the idea that the compression arm on a 2G ever bends, you've got to take one off and look at it to see how crazy this idea is. On the down-side, it weighs a ton and it's 50% unsprung, so it isn't helping grip on rough pavement, to say the least.

Yes, a leading-link compression arm (as on a 2G) is under tension when accelerating and compression when braking. A trailing-link arm (as sold for 1Gs) is the opposite.

- Jtoby

 

[Morphius]

Dug this up off the RRE's site, for discussions sake.....

 

[wret]

This might help put it into perspective.

Jtoby, are saying that if the busing were replaced with a spherical bearing that the arm would hang limp and possible drag on the road? If so, would it be possible to limit the bearing movement enough to prevent this but still allow steering movement? I remember ACM saying that a spherical the mounting points, in single sheer, would not take the pressure of a bearing over bumps.

 

[jtmcinder]

I don't remember Charles saying that and I can't see the problem wih bumps. The problems are (1) the twin ball-joints and (2) the non-coaxial nature of the inboard pick-ups which cause (3) the two lower arms to move forward and backwards, as well as up and down.

The picture, however, makes it clear that the inboard pick-ups aren't as far off-line as I thought and was implying. If the compression arm's pick-up could be moved just a little bit (and rotated, of course), then you'd be close to the arrangement required for a true lower A-arm. This would open the door for swapping in a single lower ball-joint and connecting the two arms together, producing a true A-arm in all respects. That would then allow you to use single-axis inboard bearings, if you wished, but, more important is the joining of the two lower arms to eliminate the issue of the compression arm rotating.

For those in SM, you could actually do this, with a few changes. Keep in mind that SM allows you to do anything you wish to the arms and knuckle ... anything other than the actual pick-up point. So you create a new knuckle with a single lower ball-joint and fab a true lower A-arm with sphericals on the inboard ends. The only issue I see with all this is whether you are forced to use the original, funky inboard bolt-on bar for the compression arm. Because this thing is thicker on the ends than the middle, it isn't clear to me how to get a solid bearing onto it. Of course, you are allowed to grind off a pound, so it could probably be done.

Withe regard t the OP's question, this would keep the huge triangle of the 2G's front (making an additional traction bar unneeded), which also possible dropping a lot of unsprung weight from the front, which would be great for grip on uneven surfaces. Of course, all of this assumes that the front suspension is over-engineered and these changes won't make it too weak.

- Jtoby

 

[underradar92]

I would think that adapting something like this to the offending pivot would solve this dilemma. These things have a reasonable amount of angular travel and are available in a lot of sizes up to 2" and 20mm i.d.'s. They are available @ http://www.mcmaster.com/ .

 

[jtmcinder]

There are already at least two people who can press a spherical bearing into the lateral arm for you. And they could, if they wanted to, tell us the source for bearings that fit perfectly. The issues that I see as being problems are (1) getting a bearing to fit on the funky bolt-on shaft that connects the compression arm to the chassis, and (2) coming up with a single lower ball-joint knuckle. Solve these and then get Polk to make a tubular true A-arm and you're golden.

If you aren't limited by certain rules (e.g., SCCA Solo2 rules), then the bolt-on shaft issue is easily solved. But the amount of work involved in converting the knuckle to a single lower ball-joint is pretty serious. And, yet, it could knock 20# off the unsprung weight and eliminate the longitudinal slop (which is what this thread is supposed to be about).

- Jtoby