Suspension changes for a fast autocross setup

[GT_Rich]

This may be a controversial post as there are many schools of thought regarding a fast car setup for autocross and road racing. After 2.5 years of trying to make the FFF suspension "work" I gave up and started making big changes. This videos explains and shows where my car is now.

I have 750 lb/in springs in the front, 425 lb/in in the rear. The front also has a 1.25" diameter front swaybar. Prior to adding anti-dive and anti-squat I needed an 1100 lb/in spring up front to keep the splitter off the ground.

I have roll center height adjustment from 1" to 7" off the ground, all using stock height (inexpensive) ball joints. The swaybar rate is adjustable from 620 to about 350 lb/in. Anti-dive is adjustable from 15 to 50 percent.

Basically, welding in this front upper control arm mount completely changed the car.

https://youtu.be/AAugELe3eS4?si=DgPxMqYM8zL1ZO1O

[Jphoenix]

Rich, I'm interested in your roll bar, you mentioned Speedway for the arms - and I may have missed it but what bar are you using and is it stiffer than the Miata bar from FFR? You have no rear roll bar because it's a 3 link - or you prefer no rear bar?

Interesting you can lower your front roll center by placing the suspension pickups in the lower holes. I may experiment with that, I think lowering the roll center will be good for long sweepers. I was looking at the solid LCA mounts FFR sells in lieu of the rubber bushings, you went with Delrin bushings in the LCA mounts?

[J R Jones]

Very thoughtful, very impressive results. Kudos.
BTW brake caliper mounting position (F&R) can influence dive/anti dive.
jim

[GT_Rich]

Swaybar:
https://www.kartek.com/parts/kartek-offroad-1-14-diameter-48-spline-solid-sway-bar-33-long-1-spline-length-per-side.html

Swaybar arms:
https://www.kartek.com/parts/speedway-engineering-grade-50-alloy-steel-offset-bent-inward-48-spline-sway-bar-arm-for-1-14-bars.html

Regarding these arms. They are laser cut and the finish on them is poor. If you don't grind them smooth and radius the outside of the bent areas, they will crack. Also, the pair I bought did not have the splines indexed the same so they weren't level on the car. The vendor ended up sending me a second pair.

Swaybar links:
https://www.kartek.com/parts/kartek-offroad-2-12-long-miniature-aluminum-sway-bar-end-links-for-12-thread-heim-joints.html

Swaybar rod ends and jam nuts:
(Summit Racing part numbers)
QA1-PCYML8T
QA1-JNL8S
QA1-PCYMR8T
QA1-JNR8S

Swaybar mounts:
(Summit Racing part number)
ENS-9-5113G


Moving the upper arm to lower holes will raise the to center. In my case, it's only lowering the roll center because I am moving the lower arm mount at the same time. It's the combination that matters. This will also create bump steer, so plan on a bump steer kit to sort that out.

The Delrin lower arm bushings are a perfect solution. Nearly as stiff as a spherical bearing with no maintenance and long life.

Also, this swaybar is significantly stiffer than a Miata bar. At this time I do not feel like a rear bar is needed.

[Jphoenix]

Great info Rich, thanks. Going to add this to my winter list, that's getting longer by the day.

[Jacob McCrea]

That's really cool Rich. Well done and thanks for sharing the knowledge.

[nskaats]

Great bit of knowledge to have! I've been looking at making brackets for the rear of mine for this same reason.