Front rotor temperature over 10 consecutive runs.
Now, merely mention changing brake bias to a bunch of car geeks, and there is always some smart ass who will call for a proportioning valve. Wrong. Although proportioning valves can be used to adjust the ratio of front and rear hydraulic pressure, the way they adjust pressure is by pinching off the line pressure going to the front or rear, depending on where you place the valve. In other words, you can only increase rear bias by pinching off pressure going to the front, which reduces total clamping force in the front, which is stupid since you're sacrificing a lot of braking torque for a little more balance. Proportioning valves should only be added to the rear brake circuit to add front bias-which isn't what we want.
Since increasing the line pressure or piston sizes can't be done without significant cost and headache, we're basically left with using larger rotors and better pads to control brake bias. We picked up Powerslot's bolt-on plus-size brake kit, which pairs the stock calipers with aluminum spacer brackets and larger 12.8-inch and 12.5-inch rotors in the front and rear, respectively. This 18.9 percent increase in overall radius in the front and 19.3 percent in the rear roughly equates to the same percentage increase in brake torque, assuming nothing else changes. (The effective radius is usually the centerline of the brake pad. Assuming this, the percentage increase in effective radius is just slightly less than the increase in overall radius.) And since braking torque increased more in the rear than the front, the bias has been shifted just slightly to the rear.
Powerslot offers a more aggressive set of Hawk pads with a higher coefficient of friction () for only the front calipers with their kit. Even though this would have provided better feel and been more tolerant to aggressive driving, using aggressive front pads with the stock rear pads would have thrown the brake bias toward the front, undoing any advantage we might have gained. Instead, we used EBC's Greenstuff pads, which are available for both the front and rear calipers. Assuming EBC uses the same front and rear pad material, we would at least have an equal increase in brake torque so no change in bias.
The new hardware weighs 18.7 pounds in front and 11.8 pounds in the rear. Five pounds heav
We were so proud of ourselves for working all this out and were just about to try different combinations of stock, Hawk, and EBC front pads with the EBC pads in the rear to see which setup had the best balance, when Scion's engineers pointed out that the tC has electronic brake force distribution control.
As it turns out, like many Toyota parts, the tC's braking system is shared among other Toyota platforms. Even more interesting is that it is more cost effective for Scion to use these Toyota parts with the extra bells and whistles instead of developing new, less complicated parts. This explains why the budget-priced tC has Electronic Brake-force Distribution (EBD) and Brake Assist (BA). EBD acts as an automatic proportioning valve and controls bias on the fly, sending stopping power where it's needed. BA automatically applies full braking power when a panic stop is sensed via rapid pedal movement, such as when the driver stabs the brakes. So if your front tires reach their ABS threshold first, the EBD system will apply more braking pressure in the rear until the rears are at the edge of locking up. So much for all our efforts at adding more rear bias. All we had to do was increase brake torque everywhere and let the car's electronics do the rest.