TECHNICAL HELP WRITE-UPS & FAQS

**APPLICABLE VEHICLE MODEL YEARS:

   -LEXUS IS: ALL MODEL YEARS

   -LEXUS GS: ALL MODEL YEARS

   -LEXUS LS400: ALL MODEL YEARS

   -LEXUS SC430: ALL MODEL YEARS

   -LEXUS RC: ALL MODEL YEARS

-> BEFORE WE BEGIN, PLEASE NOTE: 

   THE DETAILS DISCUSSED IN THIS ARTICLE APPLIES ONLY TO THE VEHICLES LISTED ABOVE.  SOME SUSPENSION CONFIGURATIONS ARE NOT COMPATIBLE WITH ROLL-CENTER ADJUSTMENT SPACERS, SUCH AS THE JZA80 CHASSIS (LEXUS SC300/400 & MKIV TOYOTA SUPRA) WHICH FEATURES A LOWER BALLJOINT WITH ITS STUD MATING DIRECTLY TO THE WHEEL SPINDLE INSTEAD OF THE LOWER CONTROL ARM.

-> ROLL-CENTER ADJUSTERS, WHAT ARE THEY?

   ROLL-CENTER ADJUSTERS ARE SPECIAL SPACERS FOR THE FRONT-END SUSPENSION THAT ARE DESIGNED TO ENHANCE STEERING AND HANDLING AS WELL AS CORRECT THE GEOMETRY SHIFT THAT OCCURS FROM LOWERING THE VEHICLE RIDE HEIGHT THROUGH THE USE OF COILOVERS OR LOWERING SPRINGS.  FOR AWD VEHICLES THAT HAVE BEEN LOWERED, ROLL-CENTER ADJUSTERS CAN HELP IN CORRECTING AXLE GEOMETRY AS A MEASURE TO HELP STOP AXLE JOINT FAILURE (OR AT LEAST PROLONG AXLE JOINT LIFE AS MUCH AS POSSIBLE AS IT ALL DEPENDS ON HOW MUCH DROP IS BEING RUN.  AWD VEHICLES SHOULD NEVER BE SUPER SLAMMED, AS THEY HAVE TIGHT OPERATIONAL LIMITS WITH RESPECT TO AXLE GEOMETRY WITH A MUCH SMALLER RANGE FOR HEIGHT LOWERING COMPARED TO RWD VEHICLES.

-> HOW DO ROLL-CENTER ADJUSTMENT SPACERS WORK?

   Roll-Center Adjustment Spacers (or RCAs for short) work by increasing the distance between the lower balljoint's pivot center point and the front wheel axes.  This basically "moves" the entire front end closer to the ground which, in effect, lowers the front end center of gravity.  The suspension geometry remains largely unchanged with the exception of the upper control arms and their angle of inclination relative to the front end instant centers (these are the lower control arm pivot axes around which the front end moves when the suspension moves).  The vehicle roll-center position can be approximated by drawing a basic representation of the vehicle front end frame with a straight line that intersects both instant center points.  Next, draw a line from the upper balljoint center of motion through the upper arm pivot center and project it out toward the line intersecting the vehicle instant centers.  Do the same for the other side, then find the point where the two lines intersect, THAT point is the vehicle roll-center.  When the RCAs are installed, the distance between the center of gravity and the roll-center is decreased.  The result is improved handling and stability.  The drawback is a potential camber shift and toe-in shift which will need to be evaluated and adjusted accordingly.

>>>Determining The Best RCA Size!  How Is Your Vehicle Setup?<<<  

   >IF YOU ARE ALREADY LOWERED ON COILOVERS: AFTER INSTALLING THE RCA SPACERS, USE A RULER OR TAPE MEASURE TO MEASUE THE DISTANCE FROM THE CENTER OF THE LOWER ARM PIVOT/MOUNTING BOLT TO THE GROUND. THEN, ADD THE LENGTH OF THE RCA SPACER TO THAT MEASUREMENT (MM -> INCHES: DIVIDE MM BY 25.4). REPEAT THIS STEP FOR THE OTHER SIDE. NEXT, ADJUST THE RIDE HEIGHT OF EACH OF YOUR FRONT COILOVERS UNTIL THE HEIGHT MEASURES THE VALUE YOU CALCULATED IN THE PREVIOUS STEP. THIS LAST STEP PROVIDES THE GEOMETRY CORRECTION NOW THAT THE RCA SPACERS ARE INSTALLED.

   >IF YOU ARE RUNNING STOCK SUSPENSION: NO ADJUSTMENTS ARE NECESSARY. AFTER INSTALLING THE RCA SPACERS, YOU WILL NOTICE THE RIDE HEIGHT IS NOW LOWER BY A DISTANCE EQUAL TO THE LENGTH OF THE RCA SPACERS. TO LOWER THE REAR END, I SUGGEST EITHER LOWERING SPRINGS (USE THE REAR END ONES ONLY) OR COILOVERS.

   >IF YOU ARE USING LOWERING SPRINGS: I WOULD SUGGEST REPLACING THE FRONT SPRINGS WITH YOUR ORIGINAL OE SPRINGS. THAT IS, UNLESS YOU ARE SIMPLY AIMING FOR EVEN MORE DROP IN THE FRONT; HOWEVER, BE AWARE THAT THE SUSPENSION GEOMETRY WILL NOT BE FULLY CORRECTED AND THINGS LIKE BUMP STEER AND CROWNING WILL STILL BE AN ISSUE.