Stim.Tech Articles

Controlling A Bit Of Tire (Part 1)

March 13, 2017 Suspension 0 Comments

The renown phrase; “big tire, big power” typically holds true in racing. At some point however, you must make advancements in controlling and aligning those big tires and that big power. The guys over at Unit 2 Motorsports are always in the midst of taking multiple cars to higher and higher levels.


Recently we have been helping them develop some lightweight adjustable front control arm assemblies for the Honda RSX chassis. The goal is to not only shed weight in the suspension, but also remove compliance from the suspension mounting points and provide every possible alignment adjustment with ease.

I find it comical, myself, that most projects to improve a factory component for race use, start with the most unsightly items. For this project our ground zero was this hydro formed mild steel factory RSX control arm. It looks as though it was recovered from a ship wreck in a coastal seabed.

The first order of business was to get some baseline dimensions that would be used in laying out the prototype design. The tricky part was determining the plane angle of the ball joint receiver. To aid in deciphering this, prior to measurement, a specific length rod, with the exact ball joint taper dimensions was 3-d printed. With this piece located precisely in it’s home we could set the control arm up for measurement and easily attain the exact angle of the ball joint and its centre line distance, relative to the two control arm mounting points.

Our initial prototype design features two solid links. The rear most link is a weldment linking the lower hub ball joint and the rear subframe pick-up point. This weldment will be made from 4130 Chromoly steel.

The second link connects the front subframe pick-up point to the rear link. This link is simply turned from 6061 aluminum round bar, with opposing thread directions in each end. The front link connects to the rear via a slick construction formed from a thicker spec Chromoly sheet.

The rear section of the Chromoly Link utilizes a double threaded adjuster sleeve. The rod end, being reverse thread, mates to the stainless double thread adjuster. This adjuster then threads into the end snub of the rear link, which is a standard thread. What does this mean? Being a single adjustable link, this means that the adjustment of the rear link can be made without having to release the rod end from it’s pickup point.

Each rod end will be fitted with stainless cone inserts to fit perfectly within the factory subframe points. Ideally both of the inner rod ends would actuate off axis (rotating misaligned from the mounting axis) but we must conform to how the factory bushings were mounted.

The front link is similar to all turnbuckle style links. One end uses a standard thread, the opposite is reversed. This allows the link to be adjusted, again, without having to disassemble anything.

The conical inserts for this link place the rod end centered in the Chromoly sheet construction coming off of the rear link. The dimension of the opening for this rod end matches the outer diameter of the rear link tubing. This minimizes the bulk of this assembly.

With the prototype design completed for the first-offs, we whipped up some 3-d printed versions of the turned parts to play around with. The tapered ball joint receiver was used to verify no interference issues would occur between the control arm weldment and the hub.

Up next for this project will be to finish the turned lathe parts. Unit 2 can then put together fixtures for these arms and start constructing the first weldment sections.

Checkout Unit 2 Motorsports on Instagram, as well as their prized leadman.

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