Late response. I've been thinking about that issue for a few months now.

Last year I was running eBay knock-offs of the T1R anti-bump steer kit (J's racing version, TC Race-only version). After a few alignments of trial and error, I felt like they were quite helpful in making the rear end more predictable and forgiving. A few co-drivers confirmed that the car felt like a big Miata, which I credit to a nicely sorted suspension and tire setup. I think those rear-toe control arms were part of that forgiving nature, and we were able to run at or near FTD times in my region (understanding that this is local, anecdotal information that doesn't really mean much on a National level..we all suck down here). The setup was with 380F/320R springs (good) on stock dampers (meh), a custom Speedway front sway bar and the stock 2001 rear bar. Wheels and tires were ASA FR1 and Kumho V710: 245 on 17x8+48F, 275 on 17x9+63 rear.

The best setup with the T1R-knock-offs were when I used the lowest possible toe-control point (most spacers on the hub's toe bolt), moved the cam of the frame's camber bolt the the inner-most position (getting the maximum length of the toe-control arm for smaller arc changes), and adjusting the toe control arm's threaded spherical ends to get to the right toe/camber for alignment that I liked. At this setting, the control arms were about horizontal with my ride height. This might not work as well with the AP2, as the AP2 hub is slightly different (or at least has a different part number from the AP1 rear hub).

A couple months ago I pulled the rear control arms an put the stock ones back in, as preparation for STR. I had the car aligned (-1.5*fr camber, max caster, zero front toe, -2.5* rear camber, 1/8" rear toe-in) and the car has been a handful with the rear sway bar connected. Without the bar, it's been much more neutral but a bit sloppy in transitions (OEM dampening isn't helping here). It's still quick but clearly harder to drive fast.

The way I read the rules, my control arms were legal on the outer (hub) end (spherical versus OEM ball joint had the same metal-on-metal design). The spherical inner joint, however had more metal content than the OEM bushing. That OEM control arm is one of several factors (IMHO) that contribute to the AP1's high dynamic rear toe change (front-to-rear roll stiffness is another factor, along with suspension geometry, tire/wheel stagger, etc). A friend showed me these as a possible way to lower the AP1 roll-steer and still be legal in STR:

http://www.spohn.net/shop/Del-Sphere-Pivot-Joints/

I believe these could be legal if they were grafted onto the inner side of T1R-style arms. It would require removing the Aurora spherical (15mm bolt) and re-tapping the aluminum body for the larger, SAE threaded bolt (0.75"-16). Having the Spohn-bearing suspending in a Delrin housing might satisfy the rules of not having complete metal-to-metal contact in the bushing.

There are of course, a couple unknowns that need to be addressed (besides legality in STR). One is fitting the larger Spohn bearing (1.50") inside the frame mounting point (1.765") and making sure there is enough articulation for the control arm to move freely. Second is the Spohn's inner bearing diameter of 0.750 inches onto a 14mm camber bolt (0.549"). A spacer or shim might need to be machined to bridge the SAE-to-metric dimensions.

Another option would be to cut up my stock control arm, thread the shaft on the bushing side, and stick it onto the adjustable length control arm.

Thoughts on this method are certainly welcome. While not something most STR drivers will need to be regionally competitive, the price makes it low-hanging fruit ($120 knock-off arms plus 2x$40 Spohn bearings). I'm a big fan of making a car easier to drive.

 

20.6 Lbs

https://www.s2ki.com/forums/index.php?showtopic=190919

 

Using those arms is a very grey area. Replacing the upper OR lower arms is allowed with the intent of gaining camber, so you'd have to show that you are gaining camber with those arms. If you can't prove that, then the arms are illegal. Even then, you can't use spacers to adjust where the mount attaches to the hub, so you lose one aspect of adjustability with the aftermarket arms.

 

I don't think you are going to find a way to replace the toe control arms in ST.

"Non-integral longitudinal
arms that primarily control fore/aft wheel movement (e.g.
trailing arm(s) or link(s) of a multi-link suspension) may not
be replaced, changed, or modified."


You especially would not be allowed to add spacers between the ball joint and the arm. You would only be allowed to change the length of the arm. You can do this with an offset bushing on the inner pickup point.

 

See, that rule is the grey area. It's referring to a link or arm aligned to the "longitudinal axis" of the car, hence the "trailing" designation. The arm in question is definitely aligned more towards the lateral axis. It could be argued that the lower arm on the S2000 is comprised of 2 arms. The hurdle is to prove that the mod was done to gain camber and the change in geometry is an acceptable by-product, and not the other way around.

James Yom

 

The BSK is not a gray area. I asked for clarification on this a while back, and was told that they are illegal under the current rule set.

 

This is the same rule under which installing an adjustable toe-control arm on an EF Chassis is illegal.

Sure it probably changes camber when you adjust it - but there is no allowance for a toe link replacement. Only a camber adjuster.

Yes I agree its a grey area and a lot of it reverts back to how the MFG references the piece in question in their literature. Honda calls it a toe-control arm.

 

Let me add - the grey area is regarding whether or not you can replace the toe control arm with adjustable length arm. And considering that it is already adjustable via the inner pickup point - I don't really see the point of the discussion.

 

Well, using that logic, we wouldn't need camber-adding arms, cuz the pickup points are adjustable, right? It doesn't matter, if BrianGT asked for clarification, and the EFs have similar geometry and in both cases aftermarket arms were deemed illegal, then you can't replace them. I've never had any intention of replacing them, so I have no dog in this fight. Just pointing out a possible loophole in the rules.

Besides, we some really stiff springs and good shocks, you can work around the bumpsteer for autox.

As long as we're on the subject of suspensions, I was wondering what ppl were going to do in terms of bushings for STR? Those Mugen bushings are $$$$$$$$$$$$$$, although there is at least one set that I would definitely add to the car.

James Yom

 

Powerflex sells a set for the S that is around $600 for the whole car.

www.powerflexusa.com