Now that we were sure our tires would point to where they were being told, we switched attention to our Progress re-valveable Competition Series (CS-1) coilovers. In response to our inquiry about a more trackworthy set-up, Progress informed us that it already had an off-the-shelf solution. Progress supplies the suspensions for the tCs driven in the Toyota Pro/Celebrity race at the Long Beach Grand Prix. This is a support race run at the seaside event, where some celebrities and pro racecar drivers bash it up for a few laps and wow the crowd in the name of charity. With inexperienced drivers at the helm, Progress couldn't dial up an edgy calibration. In fact, the spring and shock rates used for the 'celebrity' suspension look reasonable enough for a weekend warrior street car.
Due to the rampant copying of performance parts by offshore mills, Progress requested that we keep the exact numbers of its suspension calibrations secret, just in case some East Asian clone factory got the itch to actually make something good. So, unfortunately, we will not share the numbers, just the differences between the two calibrations.
The Pro/Celebrity suspension uses a front spring rate that's 30 percent higher than the street suspension and a rear spring rate 45 percent stiffer, putting the bias of front-to-rear stiffness a little less prone to understeer without making the car like a typical lighting quick rotation (and easy for the inexperienced to spin) front-wheel drive race car.
To handle the extra rebound energy from the stiffer springs, Progress revalved our dampers to Pro/Celebrity specs. The front dampers now have 35 percent more high-speed rebound damping, but 45 percent less low-speed rebound damping. Nearly 50 percent more compression damping was added across the velocity range. In the rear, 40 percent more high-speed rebound was added, as well as 30 percent more low-speed rebound damping. Rear compression damping is nearly the same.
After installing the new springs and recalibrated dampers, Joey at Progress aligned and corner-balanced our suspension. The rear camber was reduced from over three degrees negative to 1.7 degrees. Our front tires were in the vicinity of zero degrees of camber. Since the front suspension is not adjustable, Progress added a camber bolt to one of the two spindle bolts so we could dial in some negative camber. We normally frown on camber bolts because they are notorious for slippage. The smaller bolt used usually stretches and allows the spindle to move. The tC has huge strut-to-spindle bolts, so the smaller-than-stock-diameter camber bolts are still bigger than most bolts. We set the front suspension at two degrees of negative camber, while the front and rear toe settings were set to zero. This is a substantial improvement and will contribute greatly to increasing front grip and reducing understeer.
The rear ride height was found to be disproportionally lower than the front, so it was raised to reduce the chances of it bottoming out under roll. At this time, the corner weights were also set for a 50 percent cross weight. Corner weighting is weighing the car at each wheel and adjusting the spring perches until the diagonal cross weight percentage is equal or 50 percent. This assures that the car will have equal understeer/oversteer balance in both right and left turns.
To round out our set-up changes, we replaced our balding Kumho MX tires with some maximum-grip summer tires from Bridgestone. The 225/45/17 Potenza RE-01R tires are among the stickiest non-R-comps available in America. It might be overkill for a car in this price bracket, but it's a far cheaper and simpler option than a limited-slip diff to control excess front wheelspin engendered by the massive torque from our supercharged engine.