UPPER CONTROL ARM REPLACEMENT
I'm jumping the gun with this post because the upper control arms are supposed to be installed tomorrow (Friday). Because of a delay in the shipment of the Light Racing Chubbies, it might even be delayed until Monday. Jason Demello and Chris are tired of seeing me ghosting the shop. Still and all, I wanted to share my thought process on the build-up page and will share photos when they're finally bolted into place.
---or---Did I drink the cool-aid?
There is certainly a lot of controversy about whether or not after market Upper Control Arms (UCA’s) are necessary. I've been told by people smarter than I am that THEY ARE and by others equally smarter that THEY ARE NOT. My sense is that if you keep everything else stock – primarily the tires, you never need to swap out the UCA’s. Let me tell you why I went with the people who said that they're necessary:
BIGGER TIRES, HEAVIER WHEELS -- LET'S TALK TIRES
When I swapped out the stock alloys for Walker Evans Beadlock Wheels with the wide rings and the 256/17 Bridgestone H/T’s for 305/17 Nitto Terra Grappler A/T’s I roughly DOUBLED the weight of the tires and wheels. So I exceeded design specifications by at least 100%. The Nitto T/G’s are also roughly 50% wider than the stock Bridgestones. My sense is that once you go down the slippery slope of mods, everything that you do changes everything else. The question is the extent to which those mods are radical enough that they will tend to cause other engineering on the FJ to fail.
I leave it to you, my fellow FJ drivers, to determine if my decision was cost-effective or foolhardy.
The FJ Cruiser uses a high-mounted, double-wishbone front suspension and stabilizer bar, and a 4-link rear suspension with lateral rod with coil springs and stabilizer bar. The upper control arms are an important part of your FJ’s suspension system. The control arms manage the motion of the wheels in relation to your FJ’s body. Too much movement and wear and tear occurs to the rest of your suspension system including your tires due to the inadequate (now under-engineered due do mods) stock control arms.
SCRUB AND SINGLE AXIS INCLINATION
In this is double-A suspension, the wheel spindles are supported by an upper and lower 'A' shaped arm. In this type, the lower arm carries most of the load. If you look head-on at this type of system, what you'll find is that it's a very parallelogram system that allows the spindles to travel vertically up and down. When they do this, they also have a slight side-to-side motion caused by the arc that the wishbones describe around their pivot points. This side-to-side motion is known as scrub.
Unless the links are infinitely long the scrub motion is always present to some degree. Scrub radius is the distance between where the Steering Axis Inclination (SAI) intersects the ground and the center of the tire.
This distance must be
exactly the same from side to side or the vehicle will pull strongly at all speeds. While included angle problems will affect the scrub radius, it is not the only thing that will affect it. Different after-market wheels or tires from side to side will cause differences in scrub radius as well as a tire that is low on air. Positive scrub radius is when the tire contact patch is outside of the SAI pivot, while negative scrub radius is when the contact patch is inboard of the SAI pivot.
OE Scrub radius is designed at the factory and is not adjustable. After market UCA's do have an effect on scrub radius and that impact is more profound on a WIDER TIRE/WHEEL.
STEER ANGLE
There are two other types of motion of the wheel relative to the body when the suspension articulates. The first and most important is a toe angle (steer angle). The second and least important, but the one, which produces most pub talk is the camber angle, or lean angle. Steer and camber are the ones, which wear tires.
As with camber, toe will change depending on vehicle speed. As aerodynamic forces change the riding height, the toe setting may change due to the geometry of the steering linkage in relation to the geometry of the suspension. Modern allignment processes address this through SAI, thrust angle and reference the vehicle's centerline by putting instruments on all four wheels.
When you steer a car through a turn, the outside front wheel has to navigate a wider arc then the inside wheel. For this reason, the inside front wheel must steer at a sharper angle than the outside wheel. (and with oversize tires you'll find that one tire may scrape when the other doesn't - this is explains why that happens) The toe-out angles are accomplished by the angle of the steering arm. This arm allows the inside wheel to turn sharper than the outside wheel.
CAMBER
Camber is the angle of the wheel, measured in degrees, when viewed from the front of the vehicle. If the top of the wheel is leaning out from the center of the car, then the camber is positive. If it's leaning in, then the camber is negative. If the camber is out of adjustment, it will cause tire wear on one side of the tire's tread. If the camber is too far negative, for instance, then the tire will wear on the inside of the tread.
If the camber is different from side to side it can cause a pulling problem. The vehicle will pull to the side with the more positive camber.
CASTOR
When you turn the steering wheel, the front wheels respond by turning on a pivot attached to the suspension system. Caster is the angle of this steering pivot, measured in degrees, when viewed from the side of the vehicle. If the top of the pivot is leaning toward the rear of the car, then the caster is positive, if it is leaning toward the front, it is negative. If the caster is out of adjustment, it can cause problems in straight line tracking.
Caster has little affect on tire wear.
If the caster is different from side to side, the vehicle will pull to the side with the less positive caster. If the caster is equal but too negative, the steering will be light and the vehicle will wander and be difficult to keep in a straight line. If the caster is equal but too positive, the steering will be heavy and the steering wheel may kick when you hit a bump. After-market UCA's assist with keeping the vehicle on track while driving with larger tires and heavier wheels.
IN SUMMARY
Because I changed the design perameters of the wheels and tires SIGNIFICANTLY, I have added Donahoe Racing Upper Control Arms.
DR's UCA's are "machined aluminum arms that use a recessed uni-ball for inner fender well clearance and full articulation. It is protected by a billet o-ring dust cover that protects the uni-ball from debris ensuring a longer life. They also incorporate castor and camber adjusting rod ends for easy alignments without the need to take off the arms. The Teflon lined rod ends ensure great control and handling with minimal deflection."
Putting larger wheels on the FJ to increase ground clearance came with all its own problems, changes to the steering and suspension geometry and steering load. It's also a possibility that larger tires and steering load may cause other components to fail more quickly. By adding heavier tires and wheels I have added stress to A arms, track rods, knuckle and ball joints. Changing the UCA's should tend to reduce this and at the same time they'll help keep the vehicle going down the road closer to Toyota's design specifications than is possible with stock UCA's
Rep Points to you 
Tucson Unified Romping District (TURD)
Linear Mode
