Sway bar as front lower control arm locating device

J

Jeffyoung

Well-known member
I've not read the rules in a bit, and should of course, but if I recall I have to keep a sway bar that acts as a control arm locating device. Mine (EP TR8) does that and does it poorly.

But I can modify the sway bar right? So I can cut out the middle section and just have the remainder of the sway bar operate as a tension arm, which I think was the intent of the rule, and then add an adjustable blade front bar?
 
The rule is a little bit open to interpretation the way it's written, but if you're looking for more front roll resistance, you can just add an additional bar, as that is allowed. If the stock bar is already too stiff, then I think you'd be okay to do what you are suggesting the way I understand it, but I'd request a clarification through crbscca.com
 
I can't speak for Jeff, but I think he's looking for more adjustability rather than necessarily more stiffness.

The TR8 has a goofy front suspension design. It's a strut type suspension, but instead of a lower A-arm, it's got a lower I-arm. Then it uses the front sway bar to sorta-kinda act as the other leg of an A-arm to locate and stabilize the lower end of the strut, in addition to acting as a sway bar. The factory set-up is about as stable as a wet noodle.

I don't think the rules say anything about a minimum diameter for a sway bar. You could cut out the center section of the sway bar and tack in a 1/16" rod in its place, then add your adjustable front bar. No idea if it would be legal or not, but it's a possible work-around.
 
I had a few late 70's BMW 320i coupes which had the same type of front suspension - coupled with the semi-trailing arm rear suspension it was an absolutely unpredictable beast at the limit. Was going to build one as an F Production car, but then thought better of it and built the Civic in my avatar instead. Probably the best racing decision I've ever made :LOL:
 
What Jeff is describing is the classic Ford McPherson strut suspension, which (for economy and simplicity) reduced the number of parts and unibody attachment points to an absolute minimum. The Ford Fiesta shared that design, which as noted uses the sway bar for fore-aft suspension control. (I used to own a street TR8 and a street Fiesta, never really looked at the front suspension on the TR8 but did on the Fiesta.)

Speaking of the Fiesta, it used a typical small diameter shallow U shaped sway bar which did a poor job of fore aft control. At one point my Fiesta developed a significant sideways pull - which a savvy body/frame/alignment guy "fixed" by using a hose clamp to bias the sway bay to one side at the frame mount bushing. Clever fix (it worked) but shows the flimsiness of the design.

I'm not looking at the Prod rules right now but I'm sure that sway bar (ARB) is free but suspension type and attachment points are fixed, Not sure how all of that interacts when the sway bar is also a suspension arm.

My GUESS without poring over the rules (dangerous of course) would be that you absolutely can reinforce the ARB and its mounting to stiffen things, if that's a goal. Not sure if you can:

A) add a second ARB, adjustable or not.
B) sever the existing ARB, at which point it's not an ARB anymore

I'm sure that you COULD modify the existing ARB in such a way that it could be garage adjustable if not cockpit adjustable wrt ARB stiffness.

^ I think that this comment is useful food for thought but hardly a definitive answer
 
Ford Capri ( one from Germany, early to mid 70’s) used the same as your TR8. Look at Burton Racing (you’ll need to search for it but it’s Burton Motorsports maybe but in England) catalog for pictures of a kit they sell to upgrade, race … may give you some ideas re fab’ing up your own.
 
Thom Asay said:
Any pictures of what Group 44 did? I can’t imagine they went stock.
Click to expand...
Also Ken Slagle. Worth looking into but remember that the rules change and back then everything Prod was "full prep" with typically looser suspension allowances, and IMSA even looser I'd think. I can't remember what year it became legal in Prod to move pickup points - probably AFTER the TR8 race cars were built.
 
the way i read it, looks like you have to leave it in the same locating points , but I would make a sway bar that is really 2 suspension locating arms with a small " sway " bar connecting the two so that you can call it a sway bar. then add another sway bar to really resist the roll.

I could help you draw up something for you in 3d cad if you need help

Plucker
 
just make them as a locating arm with spherical mount at both ends and bolt a u shaped sway bar to them and it is a sway bar assembly ! 80's mustangs had a rear sway bar the bolted between trailing arms. copy that idea ?
 
So here's the relevant rules section:

1. Suspension control arms are unrestricted, provided the quantity of these items remains as stock.
2. Suspension bushings, bearings and ball joints are unrestricted. Tapered holes can be drilled or reamed, to allow a bolt to be used in place of a ball joint.
3. Any anti-roll bar(s) and rear axle traction bar(s), rear axle panhard rod and watts linkage can be added or substituted, provided its/their installation serves no other purpose. The mounts for these devices can be welded or bolted to the car. These devices and their mounts can not be located in the trunk or driver/passenger compartment unless fitted as stock. Rear axle traction bar(s) used to control axle housing rotation must be solid bar or tube.
4. When a cars anti-roll bar also acts as a suspension locating device, the bars attachment points and pivot points on the chassis and suspension control arms must remain in the stock location.
5. Bump stops and bracketry are unrestricted.
6. Wheel bearings and hubs are unrestricted.
 
I would thus say that Mr. Plucker's summary above is legal. I will restate:

Produce an alternate anti roll bar (ARB) that primarily serves as a good suspension location link. It has to have the stock mounting point but doesn't have to use an identical mount - just one in the same place in all 3 axes. It should have some amount of a crossbar so that it is still an ARB.

^ This solves the suspension location issue but probably isn't the easiest design to make adjustable. If you want easily adjustable and/or cockpit adjustable, make the main ARB crossbar quite light and add a SECOND ARB that is adjustable.

It's POSSIBLE that it would be legal to omit the crossbar on the "original" ARB (that is now primarily a stiff lower link section). That's getting into a grey area IMO, could be argued to be a violation of clause 1 because now you've added a control arm (as it's plainly nor an ARB any more). You could ask SCCA tech svcs if there is precedent on this.
 
Do you know how you want to distribute your roll stiffness in the front? Stiffer bar, softer spring. Softer bar, stiffer spring. Something in between.

If you think you could do stiffer bar with softer spring but still wanted some adjustment, it could work well to use a nascar style bar so you got a really rigid “control arm” with extra backing from the tube. Then softer springs and a second soft bar with adjustment. Major stiffness change by changing the tube bar and fine tuning with the smaller second bar.
 
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