1g DSM Front Lower Control Arms

[tstkl]

I thought I'd share some photos of some control arms I made for the 1g dsm I autocross. Haven't dialed in the alignment just yet but the car seems to drive on the street alright. They're 2 pounds lighter each, add quite a bit of caster and camber, and are quite a bit stiffer than the oem arms. I should be able to meet my class's rules requirements for wheel offset etc now while also meeting my desired alignment goals, not rubbing, and improving front grip. Caster is at ~6.25 degrees.

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[decathect]

Did you change roll center at all with these? That's something these cars really need in the front.

 

[tstkl]

The answer to your question is technically yes, however practically it is no. Significantly moving the roll center would require extended ball joints. This really doesn't have anything to do with the control arm as it is just a question of if you have a supplier who will manufacture the ball joint for you. I do not have the funds (although I do have the contacts) to have custom ball joints made in a quantity of 2. Because I have lengthened the control arm I have changed the angle of the control arm for the same ride height, however this will not have a significant effect on the roll center.

That being said, I believe there is a lot of misconception around roll center adjustment kits that should be mentioned. The main benefit of RCA kits is not the fact that they adjust your roll center. As you might have noticed, they are exclusively used on McPherson strut vehicles. This is because a common production car with McPherson struts will have roughly 0.25 degrees of camber gain per degree of body roll (or 0.75 degrees of camber loss relative to the road). For reference typical modern multilink rear suspensions have roughly 0.5 degrees of camber gain per degree of body roll and this number stays relatively constant throughout the entire travel of the suspension system. Conversely, the 0.25 degrees of camber gain per degree of body roll on McPherson suspensions erodes away into camber loss with body roll only after a few tenths of degrees of body roll or the corresponding amount of lowering required to the same change in angle of the lower control arm. This is because the upper pivot point of the hub is stationary and the lower control arm follows an arch. If the control arm is perfectly horizontal (from the pivot point on the chassis to the pivot point of the ball joint) you can imagine that the ball joint can only move perfectly vertically when the wheel is disturbed. However the strut is at an angle which means that the top of the hub will move slightly inwards towards the vehicle center line. This is what causes the car to gain camber as you lower the car. However, once the control arm is perpendicular to the strut, you can imagine that the hub would not change it's angle at all and would in fact only translate along the axis of the strut. This would correspond to 0 degrees of camber gain per degree of body roll. Anything beyond this would then become camber loss per body roll.

The reason why I said all of that was to say this: These control arms have drastically increased my caster, which significantly helps with dynamic camber. While it would be nice to have more camber gain versus body roll, I bought this car for 500 dollars and spent about 30 dollars making these control arms. Also roll center adjusters aren't legal for the class that I race in, which is the most important reason for anything anyways.