Do I need Upper Control Arms? The answer: it depends.
Alejandro MorenoSo you got yourself a Toyota 4x4 and you want to modify the suspension for extra height. Maybe you want the rough and ready look of a lifted truck or maybe you're looking to increase the capabilities of your truck by adding height and bigger tires to clear obstacles more easily. As you're pricing out all the components you see that Upper Control Arms (UCAs) are recommended but they are kind of pricey and you're wondering if you really need them. Well we're going to break it down for you!
Reason 1: It will help bring caster back in spec.
Caster is important for vehicle stability and steering feel. As you lift your vehicle on stock upper control arms, caster is decreased, which adversely affects steering geometry. Lets look at what caster is and what it does for you.
The axis from the UBJ to the LBJ and its angle from vertical is caster.
If we draw a line from the UBJ to the LBJ and you extend that line all the way to the ground it SHOULD land somewhere in front of the contact patch. Then, if you measure the distance from that little point to the center of the contact patch, you should get a measurement called "trail". Like the casters on a shopping cart, trail automatically straightens out your wheel. A truck with very low caster will not self correct to center on the highway and is very tiring to drive.
As you increase the lift of your truck, you also decrease the caster.
Typically you will see lift kits spec'd out to 3in max, the reason for this is reduced caster. As you can see in the diagram above, the axis that the upper control arm pivots about is angled upwards towards the front of the vehicle. This is for anti-dive (another topic for another day), but this angle results in the upper ball joint moving forward as you lift the vehicle. As that ball joint moves forward it is reducing caster. Upgraded UCAs will move that upper ball joint rearward compared to stock, helping to keep caster in line with the stock suspension geometry.
Reason 2: Reduce rubbing between tire and UCA
When you increase tire diameter and put new after market wheels on you change a lot of geometry at once. A lot of times the bigger tires are also wider and they stick out more. While a lot of this stuff is pretty well documented, there are many tire manufacturers that have different dimensions of the same width tire. New wheels often come with a more aggressive offset which pushes the wheel out. All this stuff is hard to keep track of and often times when you finally put it all together and slap your shiny new wheel and tire combo you realize your tires are rubbing against your factory UCA!!
- Wheel spacers would move the wheel out, increasing clearance, but wheel spacers are seen by some to be dangerous due to the increased forces they can put on the studs and the hubs. Many national tire chains won't work on vehicles with wheel spacers.
- Wheels with increased offsets would also move the wheel out, but new wheels are expensive and may not be available with the offset you need.
- Upper control arms are designed with more clearance between the ball joint and tire in mind. You also get the benefit of getting a new ball joint and bushings designed for the increased forces seen with larger tires.
Reason 3: Eliminate Rubbing Between UCA and Coilover
Upper Control Arm Rubs On Springs - Reddit r/ToyotaTacoma
When you install a quality lift kit, it usually extends the length of the shock for increased travel. While this does have many benefits, including greater stroke for higher performance on and off-road, it pushes the stock control arm beyond its limits and sometimes it touches the coilover at full droop.
Do I need UCA's? It depends.
If your lift is on the milder side, 0-2in, rubbing on the coil-over is less likely. A smaller lift is also not changing the stock suspension geometry as much, so your steering may not be effected enough to warrant the added cost. So on a mild lift, you may get away with stock control arms. You can always add UCAs to your lift later if you want improved handling characteristics.
But if you get a 3in kit, you should DEFINITELY get UCA's. Typically the lift kit manufacturer will tell you if you need it but if you are getting a 3in lift kit, go ahead and budget for some UCA's.
